fixed resolver issue

Reviewed-on: #14

Cargo.lock

@@ -17,6 +17,21 @@ version = "0.2.21"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "683d7910e743518b0e34f1186f92494becacb047c7b6bf616c96772180fef923"
 
+[[package]]
+name = "anstream"
+version = "0.6.21"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "43d5b281e737544384e969a5ccad3f1cdd24b48086a0fc1b2a5262a26b8f4f4a"
+dependencies = [
+ "anstyle",
+ "anstyle-parse 0.2.7",
+ "anstyle-query",
+ "anstyle-wincon",
+ "colorchoice",
+ "is_terminal_polyfill",
+ "utf8parse",
+]
+
 [[package]]
 name = "anstream"
 version = "1.0.0"
@@ -24,7 +39,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "824a212faf96e9acacdbd09febd34438f8f711fb84e09a8916013cd7815ca28d"
 dependencies = [
  "anstyle",
- "anstyle-parse",
+ "anstyle-parse 1.0.0",
  "anstyle-query",
  "anstyle-wincon",
  "colorchoice",
@@ -38,6 +53,15 @@ version = "1.0.14"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "940b3a0ca603d1eade50a4846a2afffd5ef57a9feac2c0e2ec2e14f9ead76000"
 
+[[package]]
+name = "anstyle-parse"
+version = "0.2.7"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "4e7644824f0aa2c7b9384579234ef10eb7efb6a0deb83f9630a49594dd9c15c2"
+dependencies = [
+ "utf8parse",
+]
+
 [[package]]
 name = "anstyle-parse"
 version = "1.0.0"
@@ -179,7 +203,7 @@ version = "4.6.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "714a53001bf66416adb0e2ef5ac857140e7dc3a0c48fb28b2f10762fc4b5069f"
 dependencies = [
- "anstream",
+ "anstream 1.0.0",
  "anstyle",
  "clap_lex",
  "strsim",
@@ -223,6 +247,26 @@ dependencies = [
  "static_assertions",
 ]
 
+[[package]]
+name = "const-random"
+version = "0.1.18"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "87e00182fe74b066627d63b85fd550ac2998d4b0bd86bfed477a0ae4c7c71359"
+dependencies = [
+ "const-random-macro",
+]
+
+[[package]]
+name = "const-random-macro"
+version = "0.1.16"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f9d839f2a20b0aee515dc581a6172f2321f96cab76c1a38a4c584a194955390e"
+dependencies = [
+ "getrandom 0.2.17",
+ "once_cell",
+ "tiny-keccak",
+]
+
 [[package]]
 name = "convert_case"
 version = "0.10.0"
@@ -268,6 +312,12 @@ dependencies = [
  "winapi",
 ]
 
+[[package]]
+name = "crunchy"
+version = "0.2.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "460fbee9c2c2f33933d720630a6a0bac33ba7053db5344fac858d4b8952d77d5"
+
 [[package]]
 name = "crypto-common"
 version = "0.1.7"
@@ -390,6 +440,15 @@ dependencies = [
  "windows-sys",
 ]
 
+[[package]]
+name = "dlv-list"
+version = "0.5.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "442039f5147480ba31067cb00ada1adae6892028e40e45fc5de7b7df6dcc1b5f"
+dependencies = [
+ "const-random",
+]
+
 [[package]]
 name = "document-features"
 version = "0.2.12"
@@ -405,6 +464,38 @@ version = "1.15.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "48c757948c5ede0e46177b7add2e67155f70e33c07fea8284df6576da70b3719"
 
+[[package]]
+name = "encoding_rs"
+version = "0.8.35"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "75030f3c4f45dafd7586dd6780965a8c7e8e285a5ecb86713e63a79c5b2766f3"
+dependencies = [
+ "cfg-if",
+]
+
+[[package]]
+name = "env_filter"
+version = "1.0.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7a1c3cc8e57274ec99de65301228b537f1e4eedc1b8e0f9411c6caac8ae7308f"
+dependencies = [
+ "log",
+ "regex",
+]
+
+[[package]]
+name = "env_logger"
+version = "0.11.9"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b2daee4ea451f429a58296525ddf28b45a3b64f1acf6587e2067437bb11e218d"
+dependencies = [
+ "anstream 0.6.21",
+ "anstyle",
+ "env_filter",
+ "jiff",
+ "log",
+]
+
 [[package]]
 name = "equivalent"
 version = "1.0.2"
@@ -533,6 +624,12 @@ dependencies = [
  "wasip3",
 ]
 
+[[package]]
+name = "hashbrown"
+version = "0.14.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e5274423e17b7c9fc20b6e7e208532f9b19825d82dfd615708b70edd83df41f1"
+
 [[package]]
 name = "hashbrown"
 version = "0.15.5"
@@ -632,6 +729,41 @@ version = "1.0.17"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "92ecc6618181def0457392ccd0ee51198e065e016d1d527a7ac1b6dc7c1f09d2"
 
+[[package]]
+name = "java-properties"
+version = "2.0.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "37bf6f484471c451f2b51eabd9e66b3fa7274550c5ec4b6c3d6070840945117f"
+dependencies = [
+ "encoding_rs",
+ "lazy_static",
+ "regex",
+]
+
+[[package]]
+name = "jiff"
+version = "0.2.23"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1a3546dc96b6d42c5f24902af9e2538e82e39ad350b0c766eb3fbf2d8f3d8359"
+dependencies = [
+ "jiff-static",
+ "log",
+ "portable-atomic",
+ "portable-atomic-util",
+ "serde_core",
+]
+
+[[package]]
+name = "jiff-static"
+version = "0.2.23"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "2a8c8b344124222efd714b73bb41f8b5120b27a7cc1c75593a6ff768d9d05aa4"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 2.0.117",
+]
+
 [[package]]
 name = "js-sys"
 version = "0.3.91"
@@ -782,16 +914,23 @@ dependencies = [
 
 [[package]]
 name = "mould"
-version = "0.2.0"
+version = "0.5.1"
 dependencies = [
+ "anyhow",
  "clap",
  "crossterm",
  "dirs",
+ "env_logger",
+ "java-properties",
+ "log",
+ "quick-xml",
  "ratatui",
+ "rust-ini",
  "serde",
  "serde_json",
  "serde_yaml",
  "tempfile",
+ "thiserror 2.0.18",
  "toml",
  "tui-input",
 ]
@@ -881,6 +1020,16 @@ dependencies = [
  "num-traits",
 ]
 
+[[package]]
+name = "ordered-multimap"
+version = "0.7.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "49203cdcae0030493bad186b28da2fa25645fa276a51b6fec8010d281e02ef79"
+dependencies = [
+ "dlv-list",
+ "hashbrown 0.14.5",
+]
+
 [[package]]
 name = "parking_lot"
 version = "0.12.5"
@@ -1005,6 +1154,15 @@ version = "1.13.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "c33a9471896f1c69cecef8d20cbe2f7accd12527ce60845ff44c153bb2a21b49"
 
+[[package]]
+name = "portable-atomic-util"
+version = "0.2.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "091397be61a01d4be58e7841595bd4bfedb15f1cd54977d79b8271e94ed799a3"
+dependencies = [
+ "portable-atomic",
+]
+
 [[package]]
 name = "powerfmt"
 version = "0.2.0"
@@ -1030,6 +1188,16 @@ dependencies = [
  "unicode-ident",
 ]
 
+[[package]]
+name = "quick-xml"
+version = "0.39.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "958f21e8e7ceb5a1aa7fa87fab28e7c75976e0bfe7e23ff069e0a260f894067d"
+dependencies = [
+ "memchr",
+ "serde",
+]
+
 [[package]]
 name = "quote"
 version = "1.0.45"
@@ -1200,6 +1368,16 @@ version = "0.8.10"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "dc897dd8d9e8bd1ed8cdad82b5966c3e0ecae09fb1907d58efaa013543185d0a"
 
+[[package]]
+name = "rust-ini"
+version = "0.21.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "796e8d2b6696392a43bea58116b667fb4c29727dc5abd27d6acf338bb4f688c7"
+dependencies = [
+ "cfg-if",
+ "ordered-multimap",
+]
+
 [[package]]
 name = "rustc_version"
 version = "0.4.1"
@@ -1282,6 +1460,7 @@ version = "1.0.149"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "83fc039473c5595ace860d8c4fafa220ff474b3fc6bfdb4293327f1a37e94d86"
 dependencies = [
+ "indexmap",
  "itoa",
  "memchr",
  "serde",
@@ -1558,10 +1737,19 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "7694e1cfe791f8d31026952abf09c69ca6f6fa4e1a1229e18988f06a04a12dca"
 
 [[package]]
-name = "toml"
+name = "tiny-keccak"
-version = "1.0.6+spec-1.1.0"
+version = "2.0.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "399b1124a3c9e16766831c6bba21e50192572cdd98706ea114f9502509686ffc"
+checksum = "2c9d3793400a45f954c52e73d068316d76b6f4e36977e3fcebb13a2721e80237"
+dependencies = [
+ "crunchy",
+]
+
+[[package]]
+name = "toml"
+version = "1.0.7+spec-1.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "dd28d57d8a6f6e458bc0b8784f8fdcc4b99a437936056fa122cb234f18656a96"
 dependencies = [
  "indexmap",
  "serde_core",
@@ -1574,27 +1762,27 @@ dependencies = [
 
 [[package]]
 name = "toml_datetime"
-version = "1.0.0+spec-1.1.0"
+version = "1.0.1+spec-1.1.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "32c2555c699578a4f59f0cc68e5116c8d7cabbd45e1409b989d4be085b53f13e"
+checksum = "9b320e741db58cac564e26c607d3cc1fdc4a88fd36c879568c07856ed83ff3e9"
 dependencies = [
  "serde_core",
 ]
 
 [[package]]
 name = "toml_parser"
-version = "1.0.9+spec-1.1.0"
+version = "1.0.10+spec-1.1.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "702d4415e08923e7e1ef96cd5727c0dfed80b4d2fa25db9647fe5eb6f7c5a4c4"
+checksum = "7df25b4befd31c4816df190124375d5a20c6b6921e2cad937316de3fccd63420"
 dependencies = [
  "winnow",
 ]
 
 [[package]]
 name = "toml_writer"
-version = "1.0.6+spec-1.1.0"
+version = "1.0.7+spec-1.1.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "ab16f14aed21ee8bfd8ec22513f7287cd4a91aa92e44edfe2c17ddd004e92607"
+checksum = "f17aaa1c6e3dc22b1da4b6bba97d066e354c7945cac2f7852d4e4e7ca7a6b56d"
 
 [[package]]
 name = "tui-input"
@@ -1906,9 +2094,9 @@ dependencies = [
 
 [[package]]
 name = "winnow"
-version = "0.7.15"
+version = "1.0.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "df79d97927682d2fd8adb29682d1140b343be4ac0f08fd68b7765d9c059d3945"
+checksum = "a90e88e4667264a994d34e6d1ab2d26d398dcdca8b7f52bec8668957517fc7d8"
 
 [[package]]
 name = "wit-bindgen"

Cargo.toml

@@ -1,23 +1,48 @@
 [package]
-name = "mould"
-version = "0.2.0"
-edition = "2024"
 authors = ["Nils Pukropp <nils@narl.io>"]
+edition = "2024"
+name = "mould"
+version = "0.5.1"
 
 [[bin]]
 name = "mould"
 path = "src/main.rs"
 
 [dependencies]
-clap = { version = "4.6.0", features = ["derive"] }
+anyhow = "1.0.102"
 crossterm = "0.29.0"
 dirs = "6.0.0"
+env_logger = "0.11.9"
+java-properties = "2.0.0"
+log = "0.4.29"
 ratatui = "0.30.0"
-serde = { version = "1.0.228", features = ["derive"] }
+rust-ini = "0.21.3"
-serde_json = "1.0.149"
 serde_yaml = "0.9.34"
-toml = "1.0.6"
+thiserror = "2.0.18"
 tui-input = "0.15.0"
 
+[dependencies.serde]
+version = "1.0.228"
+features = ["derive"]
+
+[dependencies.serde_json]
+version = "1.0.149"
+features = ["preserve_order"]
+
+[dependencies.toml]
+version = "1.0.7"
+features = ["preserve_order"]
+
+[dependencies.clap]
+version = "4.6.0"
+features = ["derive"]
+
+[dependencies.quick-xml]
+version = "0.39.2"
+features = [
+    "serde",
+    "serialize",
+]
+
 [dev-dependencies]
 tempfile = "3.27.0"

LICENSE

@@ -1,6 +1,6 @@
 MIT License
 
-Copyright (c) 2026 The mould Contributors
+Copyright (c) 2026 Nils Pukropp <nils@narl.io>
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal

README.md

@@ -1,38 +1,59 @@
 # mould
 
-mould is a modern Terminal User Interface (TUI) tool designed for interactively generating and editing configuration files from templates. Whether you are setting up a `.env` file from an example, creating a `docker-compose.override.yml`, or editing nested `JSON`, `YAML`, or `TOML` configurations, mould provides a fast, Vim-inspired workflow to get your environment ready.
+`mould` is a modern Terminal User Interface (TUI) tool designed for interactively generating and editing configuration files from templates. Whether you are setting up a `.env` file from an example, creating a `docker-compose.override.yml`, or editing nested `JSON`, `YAML`, `TOML`, `XML`, `INI`, or `Properties` configurations, `mould` provides a fast, Vim-inspired workflow to get your environment ready.
 
 ## Features
 
-- **Universal Format Support**: Handle `.env`, `JSON`, `YAML`, and `TOML` seamlessly.
+- **Universal Format Support**: Read, edit, and write `.env`, `JSON`, `YAML`, `TOML`, `XML`, `INI`, and `Properties` files seamlessly.
-- **Hierarchical Flattening**: Edit nested data structures (JSON, YAML, TOML) in a flat, searchable list.
+- **Tree View Navigation**: Edit nested data structures in a beautiful, depth-colored tree view.
-- **Docker Compose Integration**: Automatically generate `docker-compose.override.yml` from `docker-compose.yml`.
+- **Smart Template Discovery**: Rule-based resolver automatically discovers relationships (e.g., `.env.example` vs `.env`, `config.template.properties` vs `config.properties`) and highlights missing keys.
-- **Vim-inspired Workflow**: Navigate with `j`/`k`, edit with `i`, and save with `:w`.
+- **Strict Type Preservation**: Intelligently preserves data types (integers, booleans, strings) during edit-save cycles, ensuring your configuration stays valid.
-- **Modern UI**: A polished, rounded interface featuring the Catppuccin Mocha palette.
+- **Add Missing Keys**: Instantly pull missing keys and their default values from your template into your active configuration with a single keystroke.
-- **Highly Configurable**: Customize keybindings and themes via a simple TOML configuration.
+- **Advanced Undo/Redo Engine**: Features a tree-based undo/redo history that ensures you never lose changes during complex branching edits. It properly tracks all modifications, including nested renames and item additions/deletions.
-- **Dynamic Alignment**: Automatically aligns keys and values for perfect vertical readability.
+- **Vim-inspired Workflow**: Navigate with `j`/`k`, `gg`/`G`, edit with `i`, search with `/`, and save with `:w`.
+- **Modern UI**: A polished, rounded interface featuring a semantic Catppuccin Mocha palette with support for terminal transparency.
+- **Highly Configurable**: Customize keybindings and semantic themes via a simple TOML user configuration.
+- **Neovim Integration**: Comes with a built-in Neovim plugin for seamless in-editor configuration management.
+
+---
 
 ## Installation
 
+### 1. CLI Application
+
 Ensure you have Rust and Cargo installed, then run:
 
 ```sh
+# Install directly from the local path
 cargo install --path .
 ```
 
 Alternatively, you can build from source:
 
 ```sh
-git clone <repository_url>
+git clone https://git.narl.io/nvrl/mould-rs
-cd mould
+cd mould-rs
 cargo build --release
+# The executable will be located in target/release/mould
 ```
 
-The binary will be installed as `mould`.
+### 2. Neovim Plugin
+
+If you want to use `mould` directly inside Neovim, the repository includes a built-in Lua plugin that opens `mould` in a floating terminal buffer and synchronizes the file upon exit.
+
+**Using `mini.deps`:**
+```lua
+add({
+	source = 'https://git.narl.io/nvrl/mould-rs',
+	checkout = 'main',
+})
+```
+
+---
 
 ## Usage
 
-Provide an input template file to start editing:
+Provide an input template file to start editing. `mould` is smart enough to figure out if it's looking at a template or an active file, and will search for its counterpart to provide live diffing.
 
 ```sh
 mould .env.example
@@ -40,41 +61,154 @@ mould docker-compose.yml
 mould config.template.json -o config.json
 ```
 
+If you just run `mould` in a directory, it will automatically look for common template patterns like `.env.example` or `docker-compose.yml`.
+
+### Inside Neovim
+
+Open any configuration file in Neovim and run `:Mould`. It will launch a floating window targeting your active buffer.
+
 ### Keybindings (Default)
 
 - **Normal Mode**
   - `j` / `Down`: Move selection down
   - `k` / `Up`: Move selection up
-  - `i`: Edit the value of the currently selected key (Enter Insert Mode)
+  - `gg`: Jump to the top
-  - `:w` or `Enter`: Save the current configuration to the output file
+  - `G`: Jump to the bottom
+  - `i`: Edit value (cursor at start). If selected is a group, enters rename mode.
+  - `a`: Edit value (cursor at end)
+  - `s` / `S`: Substitute value (clear and edit)
+  - `r`: Rename the current key or group. (Cannot rename array indices).
+  - `o`: Append a new item (as a sibling or array element). Enters rename mode for non-array items.
+  - `O`: Prepend a new item (as a sibling or array element). Enters rename mode for non-array items.
+  - `alt+o`: Append a new group/object as a child. Enters rename mode for the new group.
+  - `alt+O`: Prepend a new group/object as a child. Enters rename mode for the new group.
+  - `t`: Toggle the selected item between a group/object and a standard variable.
+  - `dd`: Delete the currently selected variable or group (removes all nested children).
+  - `u`: Undo the last change
+  - `U`: Redo the reverted change
+  - `a`: Add missing value from template to active config
+  - `/`: Search for configuration keys
+  - `n` / `N`: Jump to next / previous search match
+  - `:w` or `Enter`: Save the current configuration
   - `:q` or `q`: Quit the application
   - `:wq`: Save and quit
   - `Esc`: Clear current command prompt
 
-- **Insert Mode**
+- **Insert / Rename Modes**
-  - Type your value for the selected key.
+  - Type your value/key string.
   - Arrow keys: Navigate within the input field
-  - `Enter` / `Esc`: Commit the value and return to Normal Mode
+  - `Enter`: Commit the value/key and return to Normal Mode. If renaming, checks for key collisions.
+  - `Esc`: Cancel edits and return to Normal Mode. Reverts changes to the current field.
+
+---
 
 ## Configuration
 
-mould can be configured using a `config.toml` file located in your user configuration directory (e.g., `~/.config/mould/config.toml` on Linux/macOS).
+`mould` can be configured using a `config.toml` file located in your user configuration directory:
+- **Linux/macOS**: `~/.config/mould/config.toml`
+- **Windows**: `%AppData%\mould\config.toml`
 
 Example configuration:
 
 ```toml
+[theme]
+transparent = false
+bg_normal = "#1e1e2e"
+bg_highlight = "#89b4fa"
+bg_active = "#a6e3a1"
+bg_search = "#cba6f7"
+fg_normal = "#cdd6f4"
+fg_dimmed = "#6c7086"
+fg_highlight = "#1e1e2e"
+fg_warning = "#f38ba8"
+fg_modified = "#fab387"
+fg_accent = "#b4befe"
+border_normal = "#45475a"
+border_active = "#a6e3a1"
+tree_depth_1 = "#b4befe"
+tree_depth_2 = "#cba6f7"
+tree_depth_3 = "#89b4fa"
+tree_depth_4 = "#fab387"
+
 [keybinds]
 down = "j"
 up = "k"
 edit = "i"
+edit_append = "a"
+edit_substitute = "s"
 save = ":w"
 quit = ":q"
 normal_mode = "Esc"
-
+search = "/"
-[theme]
+next_match = "n"
-name = "catppuccin_mocha"
+previous_match = "N"
+jump_top = "gg"
+jump_bottom = "G"
+append_item = "o"
+prepend_item = "O"
+delete_item = "dd"
+undo = "u"
+redo = "U"
+rename = "r"
+append_group = "alt+o"
+prepend_group = "alt+O"
+toggle_group = "t"
 ```
 
+---
+
+## Development & Architecture
+
+`mould` is written in Rust and architected to decouple the file format parsing from the UI representation. This allows the TUI to render complex, nested configuration files in a unified tree-view.
+
+### Core Architectural Principles:
+
+-   **Separation of Concerns**: Clear boundaries between UI rendering, application state, input handling, and file format logic.
+-   **Unified Data Model**: All parsed configuration data is normalized into a single `Vec<ConfigItem>` structure, simplifying application logic across different file types.
+-   **Vim-inspired Modality**: The application operates in distinct modes (`Normal`, `Insert`, `InsertKey`, `Search`), each with specific keybinding behaviors, enabling efficient interaction.
+-   **Non-linear Undo/Redo**: A robust undo tree allows users to revert and re-apply changes across complex branching edit histories.
+
+### Key Components
+
+1.  **State Management & Undo Tree (`src/app.rs` & `src/undo.rs`)**
+    *   The central state is maintained in the `App` struct, which tracks the currently loaded configuration variables, application modes, and user input buffer.
+    *   It integrates an **UndoTree**, providing non-linear, branching history tracking for complex edits (additions, deletions, nested renaming). Each significant state change (`save_undo_state`) pushes a snapshot to this tree.
+
+2.  **Unified Data Model (`src/format/mod.rs`)**
+    *   Regardless of the underlying file format (JSON, YAML, .env, etc.), all data is translated into a flattened `Vec<ConfigItem>`.
+    *   A `ConfigItem` represents a single configuration entry. It contains:
+        *   `key`: The display key (e.g., `port` or `[0]`).
+        *   `path`: A `Vec<PathSegment>` (composed of `PathSegment::Key(String)` for object keys and `PathSegment::Index(usize)` for array indices) that defines its full hierarchical location.
+        *   `value`: `Option<String>` holding the actual value.
+        *   `is_group`: A boolean indicating if this item is a structural node (object or array).
+        *   `status`: (`ItemStatus::Present`, `MissingFromActive`, `Modified`) reflecting comparison with a template.
+        *   `value_type`: (`ValueType::String`, `Number`, `Bool`, `Null`) to ensure type preservation during writes.
+
+3.  **Format Handlers (`src/format/*`)**
+    *   Each file format has a dedicated handler (`EnvHandler`, `IniHandler`, `HierarchicalHandler`, `PropertiesHandler`) implementing the `FormatHandler` trait.
+    *   **`HierarchicalHandler`**: A generalized processor leveraging `serde_json::Value` as an intermediary layer to parse and write nested `JSON`, `YAML`, `TOML`, and even `XML` (via `quick-xml` transposition). This allows complex structures to be flattened for editing and then re-nested accurately.
+    *   These handlers are responsible for translating between the file's native format and the `Vec<ConfigItem>` internal representation.
+
+4.  **Template Resolver (`src/resolver.rs`)**
+    *   Automatically determines template-active file pairings without explicit user instruction.
+    *   Uses hardcoded exact rules (e.g., `compose.yml` -> `compose.override.yml`) and generic fallback rules to strip `.example` or `.template` suffixes to find target output files dynamically.
+
+5.  **Terminal UI & Event Loop (`src/ui.rs` & `src/runner.rs`)**
+    *   **UI Rendering (`src/ui.rs`)**: Powered by the `ratatui` library. Renders a flexible layout consisting of a styled hierarchical list, an active input field for editing, and a dynamic status bar.
+    *   **Event Runner (`src/runner.rs`)**: Powered by `crossterm`. It intercepts raw keyboard events, resolves multi-key sequences (like `dd` or `gg`), delegates character input to the `tui-input` backend during active editing, and dispatches actions to mutate the `App` state. It includes logic to prevent "one-key-behind" issues and manage complex keybindings like `alt+o`.
+
+6.  **Neovim Plugin (`lua/mould/init.lua`)**
+    *   Implements a Lua wrapper that calculates terminal geometries and launches the CLI `mould` binary inside an ephemeral, floating terminal buffer, ensuring automatic Neovim `checktime` synchronization upon `mould`'s exit.
+
+### Development Process Highlights:
+
+-   **Iterative Refinement**: Features like key renaming, group creation, and advanced undo/redo were developed iteratively, responding to user feedback and progressively enhancing the core data model and interaction logic.
+-   **Robust Error Handling**: Key functions (`commit_input`, `enter_insert_key`) include collision detection and validation to ensure data integrity during user modifications.
+-   **Modality-driven Design**: The introduction of `InsertKey` mode and careful handling of `InsertVariant` demonstrates a commitment to a precise, context-aware user experience, minimizing ambiguity during editing.
+-   **Debugging and Performance**: Issues like UI "hangs" were traced to subtle interactions in key event processing and input buffer management, leading to refactored key sequence logic for improved responsiveness.
+
+---
+
 ## License
 
 This project is licensed under the MIT License. See the [LICENSE](LICENSE) file for details.

config.example.toml

@@ -0,0 +1,52 @@
+# mould Configuration Example
+# Place this file at ~/.config/mould/config.toml (Linux/macOS)
+# or %AppData%\mould\config.toml (Windows)
+
+[theme]
+# If true, skip rendering the background block to let the terminal's transparency show.
+transparent = false
+
+# Colors are specified in hex format ("#RRGGBB").
+# Default values follow the Semantic Catppuccin Mocha palette.
+
+bg_normal = "#1e1e2e"
+bg_highlight = "#89b4fa"
+bg_active = "#a6e3a1"
+bg_search = "#cba6f7"
+fg_normal = "#cdd6f4"
+fg_dimmed = "#6c7086"
+fg_highlight = "#1e1e2e"
+fg_warning = "#f38ba8"
+fg_modified = "#fab387"
+fg_accent = "#b4befe"
+border_normal = "#45475a"
+border_active = "#a6e3a1"
+tree_depth_1 = "#b4befe"
+tree_depth_2 = "#cba6f7"
+tree_depth_3 = "#89b4fa"
+tree_depth_4 = "#fab387"
+
+[keybinds]
+# Keybindings for navigation and application control.
+down = "j"
+up = "k"
+edit = "i"
+edit_append = "a"
+edit_substitute = "s"
+save = ":w"
+quit = ":q"
+normal_mode = "Esc"
+search = "/"
+next_match = "n"
+previous_match = "N"
+jump_top = "gg"
+jump_bottom = "G"
+append_item = "o"
+prepend_item = "O"
+delete_item = "dd"
+undo = "u"
+redo = "U"
+rename = "r"
+append_group = "alt+o"
+prepend_group = "alt+O"
+toggle_group = "t"

lua/mould/init.lua

@@ -0,0 +1,92 @@
+local M = {}
+
+-- Helper function to get a set of files currently in a directory
+local function get_dir_files(dir)
+  local files = {}
+  if vim.fn.isdirectory(dir) == 1 then
+    for _, f in ipairs(vim.fn.readdir(dir)) do
+      files[f] = true
+    end
+  end
+  return files
+end
+
+local function open_floating_terminal(cmd, target_dir)
+  local buf = vim.api.nvim_create_buf(false, true)
+  local width = math.floor(vim.o.columns * 0.9)
+  local height = math.floor(vim.o.lines * 0.9)
+  local col = math.floor((vim.o.columns - width) / 2)
+  local row = math.floor((vim.o.lines - height) / 2)
+
+  local win_config = {
+    relative = "editor",
+    width = width,
+    height = height,
+    col = col,
+    row = row,
+    style = "minimal",
+    border = "rounded",
+  }
+
+  local win = vim.api.nvim_open_win(buf, true, win_config)
+  
+  -- Record the original buffer to reload it later
+  local original_buf = vim.api.nvim_get_current_buf()
+  local original_file = vim.api.nvim_buf_get_name(original_buf)
+
+  -- Snapshot the directory contents BEFORE the command runs
+  local files_before = get_dir_files(target_dir)
+
+  vim.fn.termopen(cmd, {
+    on_exit = function()
+      -- Close the floating window and delete the terminal buffer
+      vim.api.nvim_win_close(win, true)
+      vim.api.nvim_buf_delete(buf, { force = true })
+      
+      -- Reload the original file if it exists
+      if vim.fn.filereadable(original_file) == 1 then
+        vim.schedule(function()
+          vim.cmd("checktime " .. vim.fn.fnameescape(original_file))
+        end)
+      end
+
+      -- Snapshot the directory AFTER the command finishes
+      local files_after = get_dir_files(target_dir)
+      
+      -- Compare to find the newly created file
+      for f, _ in pairs(files_after) do
+        if not files_before[f] then
+          local new_filepath = target_dir .. "/" .. f
+          
+          -- Open the new file (wrapped in schedule to ensure it runs safely after term closes)
+          vim.schedule(function()
+            vim.cmd("edit " .. vim.fn.fnameescape(new_filepath))
+            -- Optional: Let the user know it worked
+            vim.notify("mould.nvim: Opened " .. f, vim.log.levels.INFO)
+          end)
+          
+          break -- Assuming only one file is generated; we can stop looking
+        end
+      end
+    end,
+  })
+
+  vim.cmd("startinsert")
+end
+
+function M.open()
+  local filepath = vim.api.nvim_buf_get_name(0)
+  if filepath == "" then
+    vim.notify("mould.nvim: Cannot open mould for an unnamed buffer.", vim.log.levels.ERROR)
+    return
+  end
+
+  -- Get the directory of the current file
+  local target_dir = vim.fn.fnamemodify(filepath, ":p:h")
+  local cmd = string.format("mould %s", vim.fn.shellescape(filepath))
+  
+  -- Pass the target directory to our terminal function
+  open_floating_terminal(cmd, target_dir)
+end
+
+return M

plugin/mould.lua

@@ -0,0 +1,8 @@
+if vim.g.loaded_mould == 1 then
+  return
+end
+vim.g.loaded_mould = 1
+
+vim.api.nvim_create_user_command("Mould", function()
+  require("mould").open()
+end, { desc = "Open mould for the current buffer" })

src/app.rs

@@ -1,23 +1,62 @@
-use crate::format::EnvVar;
+use crate::format::{ConfigItem, PathSegment};
 use tui_input::Input;
+use crate::undo::UndoTree;
 
+/// Represents the current operating mode of the application.
+/// 
+/// Modality allows the application to reuse the same keyboard events 
+/// for different contextual actions (navigation vs. text entry).
 pub enum Mode {
+    /// Standard navigation and command mode.
     Normal,
+    /// Active text entry mode for modifying values.
     Insert,
+    /// Active text entry mode for modifying keys.
+    InsertKey,
+    /// Active search mode for filtering keys.
+    Search,
 }
 
+/// Defines where the cursor starts when entering Insert mode.
+pub enum InsertVariant {
+    /// Cursor at the beginning of the text.
+    Start,
+    /// Cursor at the end of the text.
+    End,
+    /// Text is cleared before entry.
+    Substitute,
+}
+
+/// The core application state, holding all configuration variables and UI status.
+///
+/// This struct is the "Single Source of Truth" for the TUI. It manages 
+/// selection, filtering, history, and structural mutations.
 pub struct App {
-    pub vars: Vec<EnvVar>,
+    /// The flattened list of configuration variables being edited.
+    pub vars: Vec<ConfigItem>,
+    /// Index of the currently selected variable in the list.
     pub selected: usize,
+    /// The current interaction mode (Normal, Insert, etc.).
     pub mode: Mode,
+    /// Whether the main application loop should continue running.
     pub running: bool,
+    /// An optional message to display in the status bar.
     pub status_message: Option<String>,
+    /// The active text input buffer for the selected variable.
     pub input: Input,
+    /// The current search query for filtering keys.
+    pub search_query: String,
+    /// Undo history structured as a tree.
+    pub undo_tree: UndoTree,
 }
 
 impl App {
-    pub fn new(vars: Vec<EnvVar>) -> Self {
+    /// Initializes a new application instance with the provided variables.
-        let initial_input = vars.get(0).map(|v| v.value.clone()).unwrap_or_default();
+    ///
+    /// It automatically initializes the undo tree with the starting state.
+    pub fn new(vars: Vec<ConfigItem>) -> Self {
+        let initial_input = vars.first().and_then(|v| v.value.clone()).unwrap_or_default();
+        let undo_tree = UndoTree::new(vars.clone(), 0);
         Self {
             vars,
             selected: 0,
@@ -25,9 +64,26 @@ impl App {
             running: true,
             status_message: None,
             input: Input::new(initial_input),
+            search_query: String::new(),
+            undo_tree,
         }
     }
 
+    /// Returns the indices of variables that match the search query (case-insensitive).
+    pub fn matching_indices(&self) -> Vec<usize> {
+        if self.search_query.is_empty() {
+            return Vec::new();
+        }
+        let query = self.search_query.to_lowercase();
+        self.vars
+            .iter()
+            .enumerate()
+            .filter(|(_, v)| v.key.to_lowercase().contains(&query))
+            .map(|(i, _)| i)
+            .collect()
+    }
+
+    /// Moves the selection to the next variable in the list, wrapping around if necessary.
     pub fn next(&mut self) {
         if !self.vars.is_empty() {
             self.selected = (self.selected + 1) % self.vars.len();
@@ -35,6 +91,7 @@ impl App {
         }
     }
 
+    /// Moves the selection to the previous variable in the list, wrapping around if necessary.
     pub fn previous(&mut self) {
         if !self.vars.is_empty() {
             if self.selected == 0 {
@@ -46,30 +103,519 @@ impl App {
         }
     }
 
+    /// Jumps the selection to the top of the list.
+    pub fn jump_top(&mut self) {
+        if !self.vars.is_empty() {
+            self.selected = 0;
+            self.sync_input_with_selected();
+        }
+    }
+
+    /// Jumps the selection to the bottom of the list.
+    pub fn jump_bottom(&mut self) {
+        if !self.vars.is_empty() {
+            self.selected = self.vars.len() - 1;
+            self.sync_input_with_selected();
+        }
+    }
+
+    /// Jumps to the next variable that matches the search query.
+    pub fn jump_next_match(&mut self) {
+        let indices = self.matching_indices();
+        if indices.is_empty() {
+            return;
+        }
+
+        let next_match = indices
+            .iter()
+            .find(|&&i| i > self.selected)
+            .or_else(|| indices.first());
+
+        if let Some(&index) = next_match {
+            self.selected = index;
+            self.sync_input_with_selected();
+        }
+    }
+
+    /// Jumps to the previous variable that matches the search query.
+    pub fn jump_previous_match(&mut self) {
+        let indices = self.matching_indices();
+        if indices.is_empty() {
+            return;
+        }
+
+        let prev_match = indices
+            .iter()
+            .rev()
+            .find(|&&i| i < self.selected)
+            .or_else(|| indices.last());
+
+        if let Some(&index) = prev_match {
+            self.selected = index;
+            self.sync_input_with_selected();
+        }
+    }
+
+    /// Updates the input buffer to reflect the current state of the selected item.
+    ///
+    /// If in `InsertKey` mode, the buffer is synced with the item's `key`.
+    /// Otherwise, it is synced with the item's `value`.
     pub fn sync_input_with_selected(&mut self) {
         if let Some(var) = self.vars.get(self.selected) {
-            self.input = Input::new(var.value.clone());
+            let val = match self.mode {
+                Mode::InsertKey => var.key.clone(),
+                _ => var.value.clone().unwrap_or_default(),
+            };
+            self.input = Input::new(val);
         }
     }
 
-    pub fn commit_input(&mut self) {
+    /// Commits the current text in the input buffer back to the selected variable.
-        if let Some(var) = self.vars.get_mut(self.selected) {
+    /// 
-            var.value = self.input.value().to_string();
+    /// Returns true if commit was successful, false if there was an error 
+    /// (e.g., a key name collision or empty key).
+    pub fn commit_input(&mut self) -> bool {
+        match self.mode {
+            Mode::Insert => {
+                if let Some(var) = self.vars.get_mut(self.selected)
+                    && !var.is_group {
+                        var.value = Some(self.input.value().to_string());
+                        var.status = crate::format::ItemStatus::Modified;
+                    }
+                true
+            }
+            Mode::InsertKey => {
+                let new_key = self.input.value().trim().to_string();
+                if new_key.is_empty() {
+                    self.status_message = Some("Key cannot be empty".to_string());
+                    return false;
+                }
+                
+                let selected_var = self.vars[self.selected].clone();
+                if selected_var.key == new_key {
+                    return true;
+                }
+                
+                // Collision check: ensure siblings don't already have this key.
+                let parent_path = if selected_var.path.len() > 1 {
+                    &selected_var.path[..selected_var.path.len() - 1]
+                } else {
+                    &[]
+                };
+                
+                let exists = self.vars.iter().enumerate().any(|(i, v)| {
+                    i != self.selected 
+                    && v.path.len() == selected_var.path.len() 
+                    && v.path.starts_with(parent_path)
+                    && v.key == new_key
+                });
+                
+                if exists {
+                    self.status_message = Some(format!("Key already exists: {}", new_key));
+                    return false;
+                }
+                
+                // Update selected item's key and its full internal path.
+                let old_path = selected_var.path.clone();
+                let mut new_path = parent_path.to_vec();
+                new_path.push(PathSegment::Key(new_key.clone()));
+                
+                {
+                    let var = self.vars.get_mut(self.selected).unwrap();
+                    var.key = new_key;
+                    var.path = new_path.clone();
+                    var.status = crate::format::ItemStatus::Modified;
+                }
+                
+                // Recursively update paths of all children if the renamed item is a group.
+                if selected_var.is_group {
+                    for var in self.vars.iter_mut() {
+                        if var.path.starts_with(&old_path) && var.path.len() > old_path.len() {
+                            let mut p = new_path.clone();
+                            p.extend(var.path[old_path.len()..].iter().cloned());
+                            var.path = p;
+                            var.status = crate::format::ItemStatus::Modified;
+                        }
+                    }
+                }
+                true
+            }
+            _ => true,
         }
     }
 
-    pub fn enter_insert(&mut self) {
+    /// Transitions the application into `InsertKey` mode to modify item names.
+    ///
+    /// Renaming is blocked for array indices (e.g., `[0]`) as they are 
+    /// managed automatically by the application logic.
+    pub fn enter_insert_key(&mut self) {
+        if !self.vars.is_empty() {
+            if let Some(var) = self.vars.get(self.selected)
+                && matches!(var.path.last(), Some(PathSegment::Index(_))) {
+                    self.status_message = Some("Cannot rename array indices".to_string());
+                    return;
+                }
+            self.mode = Mode::InsertKey;
+            self.sync_input_with_selected();
+        }
+    }
+
+    /// Transitions the application into `Insert` mode to modify variable values.
+    ///
+    /// If the selected item is a group, it automatically routes to 
+    /// `enter_insert_key` instead.
+    pub fn enter_insert(&mut self, variant: InsertVariant) {
+        if let Some(var) = self.vars.get(self.selected) {
+            if var.is_group {
+                self.enter_insert_key();
+            } else {
+                if !matches!(variant, InsertVariant::Substitute) {
+                    self.sync_input_with_selected();
+                }
                 self.mode = Mode::Insert;
+                match variant {
+                    InsertVariant::Start => {
+                        use tui_input::InputRequest;
+                        self.input.handle(InputRequest::GoToStart);
+                    }
+                    InsertVariant::End => {
+                        use tui_input::InputRequest;
+                        self.input.handle(InputRequest::GoToEnd);
+                    }
+                    InsertVariant::Substitute => {
+                        self.input = Input::new(String::new());
+                    }
+                }
+            }
+        }
+    }
+
+    /// Commits the current input and transitions back to `Normal` mode.
+    pub fn enter_normal(&mut self) {
+        if self.commit_input() {
+            self.save_undo_state();
+            self.mode = Mode::Normal;
+        }
+    }
+
+    /// Aborts the current input and reverts to `Normal` mode without saving changes.
+    pub fn cancel_insert(&mut self) {
+        self.mode = Mode::Normal;
+        self.sync_input_with_selected();
         self.status_message = None;
     }
 
-    pub fn enter_normal(&mut self) {
+    /// Deletes the currently selected item and all its nested children.
-        self.commit_input();
+    ///
-        self.mode = Mode::Normal;
+    /// If the deleted item is part of an array, subsequent indices are 
+    /// automatically shifted and renamed to maintain a continuous sequence.
+    pub fn delete_selected(&mut self) {
+        if self.vars.is_empty() {
+            return;
         }
 
-    #[allow(dead_code)]
+        let selected_path = self.vars[self.selected].path.clone();
-    pub fn quit(&mut self) {
+        let is_group = self.vars[self.selected].is_group;
-        self.running = false;
+
+        // 1. Identify all items to remove (the item itself + all children)
+        let mut to_remove = Vec::new();
+        to_remove.push(self.selected);
+
+        if is_group {
+            for (i, var) in self.vars.iter().enumerate() {
+                if i == self.selected {
+                    continue;
+                }
+                if var.path.starts_with(&selected_path) {
+                    to_remove.push(i);
+                }
+            }
+        }
+
+        // 2. Perform removal (reverse order to preserve indices)
+        to_remove.sort_unstable_by(|a, b| b.cmp(a));
+        for i in to_remove {
+            self.vars.remove(i);
+        }
+
+        // 3. Re-index subsequent array items if applicable
+        if let Some(PathSegment::Index(removed_idx)) = selected_path.last() {
+            let base_path = &selected_path[..selected_path.len() - 1];
+            
+            for var in self.vars.iter_mut() {
+                if var.path.starts_with(base_path) && var.path.len() >= selected_path.len() {
+                    if let PathSegment::Index(i) = var.path[selected_path.len() - 1]
+                        && i > *removed_idx {
+                            let new_idx = i - 1;
+                            var.path[selected_path.len() - 1] = PathSegment::Index(new_idx);
+                            
+                            if var.path.len() == selected_path.len() {
+                                var.key = format!("[{}]", new_idx);
+                            }
+                        }
+                }
+            }
+        }
+
+        // 4. Adjust selection
+        if self.selected >= self.vars.len() && !self.vars.is_empty() {
+            self.selected = self.vars.len() - 1;
+        }
+        self.sync_input_with_selected();
+        self.save_undo_state();
+    }
+
+    /// Adds a new item relative to the selected item.
+    ///
+    /// - `after`: If true, adds below the selection; otherwise adds above.
+    /// - `is_group`: If true, creates a new structural node (object/array).
+    /// - `as_child`: If true, adds inside the selected group.
+    ///
+    /// The method automatically detects if the parent is an array and 
+    /// formats the new key accordingly (e.g., `[1]`).
+    pub fn add_item(&mut self, after: bool, is_group: bool, as_child: bool) {
+        if self.vars.is_empty() {
+            let new_key = if is_group { "NEW_GROUP".to_string() } else { "NEW_VAR".to_string() };
+            self.vars.push(ConfigItem {
+                key: new_key.clone(),
+                path: vec![PathSegment::Key(new_key)],
+                value: if is_group { None } else { Some("".to_string()) },
+                template_value: None,
+                default_value: None,
+                depth: 0,
+                is_group,
+                status: crate::format::ItemStatus::Modified,
+                value_type: if is_group { crate::format::ValueType::Null } else { crate::format::ValueType::String },
+            });
+            self.selected = 0;
+            self.sync_input_with_selected();
+            self.save_undo_state();
+            if is_group {
+                self.enter_insert_key();
+            } else {
+                self.enter_insert(InsertVariant::Start);
+            }
+            return;
+        }
+
+        let selected_item = self.vars[self.selected].clone();
+        
+        // 1. Determine new item properties (path, key, depth, position)
+        let mut new_path;
+        let new_depth;
+        let insert_pos;
+        let mut is_array_item = false;
+
+        if !as_child && let Some(PathSegment::Index(idx)) = selected_item.path.last() {
+            // ARRAY ITEM LOGIC (Adding sibling to an existing index)
+            is_array_item = true;
+            let base_path = selected_item.path[..selected_item.path.len() - 1].to_vec();
+            let new_idx = if after { idx + 1 } else { *idx };
+            insert_pos = if after { self.selected + 1 } else { self.selected };
+            
+            // Shift subsequent indices
+            for var in self.vars.iter_mut() {
+                if var.path.starts_with(&base_path) && var.path.len() > base_path.len()
+                    && let PathSegment::Index(i) = var.path[base_path.len()]
+                        && i >= new_idx {
+                            var.path[base_path.len()] = PathSegment::Index(i + 1);
+                            if var.path.len() == base_path.len() + 1 {
+                                var.key = format!("[{}]", i + 1);
+                            }
+                        }
+            }
+            
+            new_path = base_path;
+            new_path.push(PathSegment::Index(new_idx));
+            new_depth = selected_item.depth;
+        } else if as_child && selected_item.is_group {
+            // ADD AS CHILD OF GROUP
+            insert_pos = self.selected + 1;
+            new_path = selected_item.path.clone();
+            new_depth = selected_item.depth + 1;
+            
+            if self.is_array_group(&selected_item.path) {
+                is_array_item = true;
+                let new_idx = 0; // Prepend to array
+                new_path.push(PathSegment::Index(new_idx));
+                
+                // Shift existing children
+                for var in self.vars.iter_mut() {
+                    if var.path.starts_with(&selected_item.path) && var.path.len() > selected_item.path.len()
+                        && let PathSegment::Index(i) = var.path[selected_item.path.len()] {
+                            var.path[selected_item.path.len()] = PathSegment::Index(i + 1);
+                            if var.path.len() == selected_item.path.len() + 1 {
+                                var.key = format!("[{}]", i + 1);
+                            }
+                        }
+                }
+            }
+        } else {
+            // ADD AS SIBLING
+            let parent_path = if selected_item.path.len() > 1 {
+                selected_item.path[..selected_item.path.len() - 1].to_vec()
+            } else {
+                Vec::new()
+            };
+            
+            insert_pos = if after {
+                let mut p = self.selected + 1;
+                while p < self.vars.len() && self.vars[p].path.starts_with(&selected_item.path) {
+                    p += 1;
+                }
+                p
+            } else {
+                self.selected
+            };
+            
+            new_path = parent_path;
+            new_depth = selected_item.depth;
+            
+            if !new_path.is_empty() && self.is_array_group(&new_path) {
+                is_array_item = true;
+                if let Some(PathSegment::Index(idx)) = selected_item.path.last() {
+                    let new_idx = if after { idx + 1 } else { *idx };
+                    new_path.push(PathSegment::Index(new_idx));
+                } else {
+                    new_path.push(PathSegment::Index(0));
+                }
+            }
+        }
+
+        // 2. Generate a unique key for non-array items
+        let final_key = if is_array_item {
+            if let Some(PathSegment::Index(idx)) = new_path.last() {
+                format!("[{}]", idx)
+            } else {
+                "NEW_VAR".to_string()
+            }
+        } else {
+            let mut count = 1;
+            let mut candidate = if is_group { "NEW_GROUP".to_string() } else { "NEW_VAR".to_string() };
+            let parent_path_slice = new_path.as_slice();
+            
+            while self.vars.iter().any(|v| {
+                v.path.starts_with(parent_path_slice) 
+                && v.path.len() == parent_path_slice.len() + 1 
+                && v.key == candidate
+            }) {
+                candidate = if is_group { format!("NEW_GROUP_{}", count) } else { format!("NEW_VAR_{}", count) };
+                count += 1;
+            }
+            new_path.push(PathSegment::Key(candidate.clone()));
+            candidate
+        };
+
+        // 3. Insert new item
+        let new_item = ConfigItem {
+            key: final_key,
+            path: new_path,
+            value: if is_group { None } else { Some("".to_string()) },
+            template_value: None,
+            default_value: None,
+            depth: new_depth,
+            is_group,
+            status: crate::format::ItemStatus::Modified,
+            value_type: if is_group { crate::format::ValueType::Null } else { crate::format::ValueType::String },
+        };
+
+        self.vars.insert(insert_pos, new_item);
+        self.selected = insert_pos;
+        self.save_undo_state();
+        
+        if is_array_item {
+            self.sync_input_with_selected();
+            self.enter_insert(InsertVariant::Start);
+        } else {
+            self.enter_insert_key();
+        }
+        self.status_message = None;
+    }
+
+    /// Toggles the group status of the currently selected item.
+    ///
+    /// Changing a group to a variable clears its children (visually) 
+    /// and resets its value. Changing a variable to a group removes its value.
+    pub fn toggle_group_selected(&mut self) {
+        if let Some(var) = self.vars.get_mut(self.selected) {
+            if matches!(var.path.last(), Some(PathSegment::Index(_))) {
+                self.status_message = Some("Cannot toggle array items".to_string());
+                return;
+            }
+
+            var.is_group = !var.is_group;
+            if var.is_group {
+                var.value = None;
+                var.value_type = crate::format::ValueType::Null;
+            } else {
+                var.value = Some("".to_string());
+                var.value_type = crate::format::ValueType::String;
+            }
+            var.status = crate::format::ItemStatus::Modified;
+            self.sync_input_with_selected();
+        }
+    }
+
+    /// Returns true if the selected item is a structural node (group/object).
+    pub fn selected_is_group(&self) -> bool {
+        self.vars.get(self.selected).map(|v| v.is_group).unwrap_or(false)
+    }
+
+    /// Returns true if the provided path identifies a node that contains array elements.
+    pub fn is_array_group(&self, group_path: &[PathSegment]) -> bool {
+        self.vars.iter().any(|v| 
+            v.path.starts_with(group_path) 
+            && v.path.len() == group_path.len() + 1 
+            && matches!(v.path.last(), Some(PathSegment::Index(_)))
+        )
+    }
+
+    /// Returns true if the selected item is an indexed array element.
+    pub fn selected_is_array(&self) -> bool {
+        self.vars.get(self.selected)
+            .map(|v| !v.is_group && matches!(v.path.last(), Some(PathSegment::Index(_))))
+            .unwrap_or(false)
+    }
+
+    /// Returns true if the selected item exists in the template but not the active config.
+    pub fn selected_is_missing(&self) -> bool {
+        self.vars.get(self.selected)
+            .map(|v| v.status == crate::format::ItemStatus::MissingFromActive)
+            .unwrap_or(false)
+    }
+
+    /// Saves a snapshot of the current state to the undo history tree.
+    pub fn save_undo_state(&mut self) {
+        self.undo_tree.push(self.vars.clone(), self.selected);
+    }
+
+    /// Reverts the application state to the previous history point.
+    pub fn undo(&mut self) {
+        if let Some(action) = self.undo_tree.undo() {
+            self.vars = action.state.clone();
+            self.selected = action.selected;
+            if self.selected >= self.vars.len() && !self.vars.is_empty() {
+                self.selected = self.vars.len() - 1;
+            }
+            self.sync_input_with_selected();
+            self.status_message = Some("Undo applied".to_string());
+        } else {
+            self.status_message = Some("Nothing to undo".to_string());
+        }
+    }
+
+    /// Advances the application state to the next history point in the active branch.
+    pub fn redo(&mut self) {
+        if let Some(action) = self.undo_tree.redo() {
+            self.vars = action.state.clone();
+            self.selected = action.selected;
+            if self.selected >= self.vars.len() && !self.vars.is_empty() {
+                self.selected = self.vars.len() - 1;
+            }
+            self.sync_input_with_selected();
+            self.status_message = Some("Redo applied".to_string());
+        } else {
+            self.status_message = Some("Nothing to redo".to_string());
+        }
     }
 }

src/cli.rs

@@ -1,21 +1,34 @@
 use clap::Parser;
 use std::path::PathBuf;
 
+/// mould: A TUI tool to generate and edit configuration files (.env, json, yaml, toml)
 #[derive(Parser, Debug)]
-#[command(author, version, about = "mould: A TUI tool to generate and edit configuration files (.env, json, yaml, toml)")]
+#[command(
+    author,
+    version,
+    about = "mould: A TUI tool to generate and edit configuration files (.env, json, yaml, toml)",
+    long_about = "mould allows you to interactively edit and generate configuration files using templates. It supports various formats including .env, JSON, YAML, and TOML. It features a modern TUI with Vim-inspired keybindings and out-of-the-box support for theming.",
+    after_help = "EXAMPLES:\n  mould .env.example\n  mould docker-compose.yml\n  mould config.template.json -o config.json"
+)]
 pub struct Cli {
     /// The input template file (e.g., .env.example, config.json.template, docker-compose.yml)
-    pub input: PathBuf,
+    #[arg(required = false, value_name = "INPUT_FILE")]
+    pub input: Option<PathBuf>,
 
-    /// Optional output file. If not provided, it will be inferred (e.g., .env.example -> .env, docker-compose.yml -> docker-compose.override.yml)
+    /// Optional output file. If not provided, it will be inferred.
-    #[arg(short, long)]
+    #[arg(short, long, value_name = "OUTPUT_FILE")]
     pub output: Option<PathBuf>,
 
     /// Override the format detection (env, json, yaml, toml)
-    #[arg(short, long)]
+    #[arg(short, long, value_name = "FORMAT", value_parser = ["env", "json", "yaml", "toml"])]
     pub format: Option<String>,
+
+    /// Increase verbosity for logging (can be used multiple times)
+    #[arg(short, long, action = clap::ArgAction::Count)]
+    pub verbose: u8,
 }
 
+/// Parses and returns the command-line arguments.
 pub fn parse() -> Cli {
     Cli::parse()
 }

src/config.rs

@@ -1,23 +1,49 @@
+use ratatui::style::Color;
 use serde::{Deserialize, Serialize};
 use std::fs;
-use ratatui::style::Color;
 
+/// Configuration for the application's appearance.
 #[derive(Debug, Deserialize, Serialize, Clone)]
+#[serde(default)]
 pub struct ThemeConfig {
-    #[serde(default)]
+    /// If true, skip rendering the background block to let the terminal's transparency show.
     pub transparent: bool,
-    pub crust: String,
+    /// Default background.
-    pub surface0: String,
+    pub bg_normal: String,
-    pub surface1: String,
+    /// Background for selected items and standard UI elements.
-    pub text: String,
+    pub bg_highlight: String,
-    pub blue: String,
+    /// Active element background (e.g., insert mode).
-    pub green: String,
+    pub bg_active: String,
-    pub lavender: String,
+    /// Active element background (e.g., search mode).
-    pub mauve: String,
+    pub bg_search: String,
-    pub peach: String,
+    /// Standard text.
+    pub fg_normal: String,
+    /// Secondary/inactive text.
+    pub fg_dimmed: String,
+    /// Text on selected items.
+    pub fg_highlight: String,
+    /// Red/Alert color for missing items.
+    pub fg_warning: String,
+    /// Accent color for modified items.
+    pub fg_modified: String,
+    /// High-contrast accent for titles and active UI elements.
+    pub fg_accent: String,
+    /// Borders.
+    pub border_normal: String,
+    /// Active borders (e.g., input mode).
+    pub border_active: String,
+    /// Color for tree indentation depth 1.
+    pub tree_depth_1: String,
+    /// Color for tree indentation depth 2.
+    pub tree_depth_2: String,
+    /// Color for tree indentation depth 3.
+    pub tree_depth_3: String,
+    /// Color for tree indentation depth 4.
+    pub tree_depth_4: String,
 }
 
 impl ThemeConfig {
+    /// Internal helper to parse a hex color string ("#RRGGBB") into a TUI Color.
     fn parse_hex(hex: &str) -> Color {
         let hex = hex.trim_start_matches('#');
         if hex.len() == 6 {
@@ -30,57 +56,107 @@ impl ThemeConfig {
         }
     }
 
-    pub fn crust(&self) -> Color { Self::parse_hex(&self.crust) }
+    pub fn bg_normal(&self) -> Color { Self::parse_hex(&self.bg_normal) }
-    pub fn surface0(&self) -> Color { Self::parse_hex(&self.surface0) }
+    pub fn bg_highlight(&self) -> Color { Self::parse_hex(&self.bg_highlight) }
-    pub fn surface1(&self) -> Color { Self::parse_hex(&self.surface1) }
+    pub fn bg_active(&self) -> Color { Self::parse_hex(&self.bg_active) }
-    pub fn text(&self) -> Color { Self::parse_hex(&self.text) }
+    pub fn bg_search(&self) -> Color { Self::parse_hex(&self.bg_search) }
-    pub fn blue(&self) -> Color { Self::parse_hex(&self.blue) }
+    pub fn fg_normal(&self) -> Color { Self::parse_hex(&self.fg_normal) }
-    pub fn green(&self) -> Color { Self::parse_hex(&self.green) }
+    pub fn fg_dimmed(&self) -> Color { Self::parse_hex(&self.fg_dimmed) }
-    pub fn lavender(&self) -> Color { Self::parse_hex(&self.lavender) }
+    pub fn fg_highlight(&self) -> Color { Self::parse_hex(&self.fg_highlight) }
-    pub fn mauve(&self) -> Color { Self::parse_hex(&self.mauve) }
+    pub fn fg_warning(&self) -> Color { Self::parse_hex(&self.fg_warning) }
-    pub fn peach(&self) -> Color { Self::parse_hex(&self.peach) }
+    pub fn fg_modified(&self) -> Color { Self::parse_hex(&self.fg_modified) }
+    pub fn fg_accent(&self) -> Color { Self::parse_hex(&self.fg_accent) }
+    pub fn border_normal(&self) -> Color { Self::parse_hex(&self.border_normal) }
+    pub fn border_active(&self) -> Color { Self::parse_hex(&self.border_active) }
+    pub fn tree_depth_1(&self) -> Color { Self::parse_hex(&self.tree_depth_1) }
+    pub fn tree_depth_2(&self) -> Color { Self::parse_hex(&self.tree_depth_2) }
+    pub fn tree_depth_3(&self) -> Color { Self::parse_hex(&self.tree_depth_3) }
+    pub fn tree_depth_4(&self) -> Color { Self::parse_hex(&self.tree_depth_4) }
 }
 
 impl Default for ThemeConfig {
+    /// Default theme: Semantic Catppuccin Mocha.
     fn default() -> Self {
         Self {
             transparent: false,
-            crust: "#11111b".to_string(),
+            bg_normal: "#1e1e2e".to_string(), // base
-            surface0: "#313244".to_string(),
+            bg_highlight: "#89b4fa".to_string(), // blue
-            surface1: "#45475a".to_string(),
+            bg_active: "#a6e3a1".to_string(), // green
-            text: "#cdd6f4".to_string(),
+            bg_search: "#cba6f7".to_string(), // mauve
-            blue: "#89b4fa".to_string(),
+            fg_normal: "#cdd6f4".to_string(), // text
-            green: "#a6e3a1".to_string(),
+            fg_dimmed: "#6c7086".to_string(), // overlay0
-            lavender: "#b4befe".to_string(),
+            fg_highlight: "#1e1e2e".to_string(), // base (dark for contrast against highlights)
-            mauve: "#cba6f7".to_string(),
+            fg_warning: "#f38ba8".to_string(), // red
-            peach: "#fab387".to_string(),
+            fg_modified: "#fab387".to_string(), // peach
+            fg_accent: "#b4befe".to_string(), // lavender
+            border_normal: "#45475a".to_string(), // surface1
+            border_active: "#a6e3a1".to_string(), // green
+            tree_depth_1: "#b4befe".to_string(), // lavender
+            tree_depth_2: "#cba6f7".to_string(), // mauve
+            tree_depth_3: "#89b4fa".to_string(), // blue
+            tree_depth_4: "#fab387".to_string(), // peach
         }
     }
 }
 
+/// Custom keybindings for navigation and application control.
 #[derive(Debug, Deserialize, Serialize, Clone)]
+#[serde(default)]
 pub struct KeybindsConfig {
     pub down: String,
     pub up: String,
     pub edit: String,
+    pub edit_append: String,
+    pub edit_substitute: String,
     pub save: String,
     pub quit: String,
     pub normal_mode: String,
-}
+    pub search: String,
+    pub next_match: String,
+    pub previous_match: String,
+    pub jump_top: String,
+    pub jump_bottom: String,
+    pub append_item: String,
+    pub prepend_item: String,
+    pub delete_item: String,
+    pub undo: String,
+    pub redo: String,
+    pub rename: String,
+    pub append_group: String,
+    pub prepend_group: String,
+    pub toggle_group: String,
+    }
 
-impl Default for KeybindsConfig {
+    impl Default for KeybindsConfig {
     fn default() -> Self {
         Self {
             down: "j".to_string(),
             up: "k".to_string(),
             edit: "i".to_string(),
+            edit_append: "a".to_string(),
+            edit_substitute: "s".to_string(),
             save: ":w".to_string(),
             quit: ":q".to_string(),
             normal_mode: "Esc".to_string(),
+            search: "/".to_string(),
+            next_match: "n".to_string(),
+            previous_match: "N".to_string(),
+            jump_top: "gg".to_string(),
+            jump_bottom: "G".to_string(),
+            append_item: "o".to_string(),
+            prepend_item: "O".to_string(),
+            delete_item: "dd".to_string(),
+            undo: "u".to_string(),
+            redo: "U".to_string(),
+            rename: "r".to_string(),
+            append_group: "alt+o".to_string(),
+            prepend_group: "alt+O".to_string(),
+            toggle_group: "t".to_string(),
+        }
     }
     }
-}
 
+/// Root configuration structure for mould.
 #[derive(Debug, Deserialize, Serialize, Default, Clone)]
 pub struct Config {
     #[serde(default)]
@@ -89,18 +165,18 @@ pub struct Config {
     pub keybinds: KeybindsConfig,
 }
 
+/// Loads the configuration from the user's home config directory (~/.config/mould/config.toml).
+/// Falls back to default settings if no configuration is found.
 pub fn load_config() -> Config {
     if let Some(mut config_dir) = dirs::config_dir() {
         config_dir.push("mould");
         config_dir.push("config.toml");
 
-        if config_dir.exists() {
+        if config_dir.exists()
-            if let Ok(content) = fs::read_to_string(config_dir) {
+            && let Ok(content) = fs::read_to_string(config_dir)
-                if let Ok(config) = toml::from_str(&content) {
+                && let Ok(config) = toml::from_str(&content) {
                     return config;
                 }
     }
-        }
-    }
     Config::default()
 }

src/error.rs

@@ -0,0 +1,14 @@
+use thiserror::Error;
+
+/// Custom error types for the mould application.
+#[derive(Error, Debug)]
+pub enum MouldError {
+    #[error("IO error: {0}")]
+    Io(#[from] std::io::Error),
+
+    #[error("File not found: {0}")]
+    FileNotFound(String),
+
+    #[error("Terminal error: {0}")]
+    Terminal(String),
+}

src/format/env.rs

@@ -1,27 +1,47 @@
-use super::{EnvVar, FormatHandler};
+//! Handler for flat `.env` (Environment) configuration files.
+//!
+//! This handler manages simple `KEY=VALUE` pairs. It does not support 
+//! native nesting or grouping, treating all entries as root-level variables.
+
+use super::{ConfigItem, FormatHandler, ItemStatus, ValueType, PathSegment};
 use std::fs;
-use std::io::{self, Write};
+use std::io::Write;
 use std::path::Path;
 
+/// A format handler for parsing and writing `.env` files.
 pub struct EnvHandler;
 
 impl FormatHandler for EnvHandler {
-    fn parse(&self, path: &Path) -> io::Result<Vec<EnvVar>> {
+    /// Parses an environment file into a flat list of `ConfigItem`s.
+    fn parse(&self, path: &Path) -> anyhow::Result<Vec<ConfigItem>> {
+        if !path.exists() {
+            return Ok(Vec::new());
+        }
+
         let content = fs::read_to_string(path)?;
         let mut vars = Vec::new();
 
         for line in content.lines() {
             let line = line.trim();
+            // Skip empty lines and comments.
             if line.is_empty() || line.starts_with('#') {
-                continue; // Skip comments and empty lines
+                continue;
             }
 
-            if let Some((key, val)) = line.split_once('=') {
+            if let Some((key, value)) = line.split_once('=') {
-                let parsed_val = val.trim().trim_matches('"').trim_matches('\'').to_string();
+                let key = key.trim().to_string();
-                vars.push(EnvVar {
+                let value = value.trim().to_string();
-                    key: key.trim().to_string(),
+                
-                    value: parsed_val.clone(),
+                vars.push(ConfigItem {
-                    default_value: parsed_val,
+                    key: key.clone(),
+                    path: vec![PathSegment::Key(key)],
+                    value: Some(value.clone()),
+                    template_value: Some(value.clone()),
+                    default_value: Some(value.clone()),
+                    depth: 0,
+                    is_group: false,
+                    status: ItemStatus::Present,
+                    value_type: ValueType::String,
                 });
             }
         }
@@ -29,41 +49,17 @@ impl FormatHandler for EnvHandler {
         Ok(vars)
     }
 
-    fn merge(&self, path: &Path, vars: &mut Vec<EnvVar>) -> io::Result<()> {
+    /// Writes the list of variables back to a flat `.env` file.
-        if !path.exists() {
+    fn write(&self, path: &Path, vars: &[ConfigItem]) -> anyhow::Result<()> {
-            return Ok(());
-        }
-
-        let content = fs::read_to_string(path)?;
-        for line in content.lines() {
-            let line = line.trim();
-            if line.is_empty() || line.starts_with('#') {
-                continue;
-            }
-
-            if let Some((key, val)) = line.split_once('=') {
-                let key = key.trim();
-                let parsed_val = val.trim().trim_matches('"').trim_matches('\'').to_string();
-
-                if let Some(var) = vars.iter_mut().find(|v| v.key == key) {
-                    var.value = parsed_val;
-                } else {
-                    vars.push(EnvVar {
-                        key: key.to_string(),
-                        value: parsed_val.clone(),
-                        default_value: String::new(),
-                    });
-                }
-            }
-        }
-
-        Ok(())
-    }
-
-    fn write(&self, path: &Path, vars: &[EnvVar]) -> io::Result<()> {
         let mut file = fs::File::create(path)?;
         for var in vars {
-            writeln!(file, "{}={}", var.key, var.value)?;
+            // .env files ignore structural groups.
+            if !var.is_group {
+                let val = var.value.as_deref()
+                    .or(var.template_value.as_deref())
+                    .unwrap_or("");
+                writeln!(file, "{}={}", var.key, val)?;
+            }
         }
         Ok(())
     }
@@ -72,65 +68,36 @@ impl FormatHandler for EnvHandler {
 #[cfg(test)]
 mod tests {
     use super::*;
-    use std::io::Write;
     use tempfile::NamedTempFile;
 
     #[test]
     fn test_parse_env_example() {
         let mut file = NamedTempFile::new().unwrap();
-        writeln!(
+        writeln!(file, "# Comment\nKEY1=value1\n  KEY2 = value2  ").unwrap();
-            file,
-            "# A comment\nKEY1=value1\nKEY2=\"value2\"\nKEY3='value3'\nEMPTY="
-        )
-        .unwrap();
         
         let handler = EnvHandler;
         let vars = handler.parse(file.path()).unwrap();
-        assert_eq!(vars.len(), 4);
+        
+        assert_eq!(vars.len(), 2);
         assert_eq!(vars[0].key, "KEY1");
-        assert_eq!(vars[0].value, "value1");
+        assert_eq!(vars[0].value.as_deref(), Some("value1"));
-        assert_eq!(vars[0].default_value, "value1");
         assert_eq!(vars[1].key, "KEY2");
-        assert_eq!(vars[1].value, "value2");
+        assert_eq!(vars[1].value.as_deref(), Some("value2"));
-        assert_eq!(vars[2].key, "KEY3");
-        assert_eq!(vars[2].value, "value3");
-        assert_eq!(vars[3].key, "EMPTY");
-        assert_eq!(vars[3].value, "");
-    }
-
-    #[test]
-    fn test_merge_env() {
-        let mut example_file = NamedTempFile::new().unwrap();
-        writeln!(example_file, "KEY1=default1\nKEY2=default2").unwrap();
-        let handler = EnvHandler;
-        let mut vars = handler.parse(example_file.path()).unwrap();
-
-        let mut env_file = NamedTempFile::new().unwrap();
-        writeln!(env_file, "KEY1=custom1\nKEY3=custom3").unwrap();
-
-        handler.merge(env_file.path(), &mut vars).unwrap();
-
-        assert_eq!(vars.len(), 3);
-        assert_eq!(vars[0].key, "KEY1");
-        assert_eq!(vars[0].value, "custom1");
-        assert_eq!(vars[0].default_value, "default1");
-
-        assert_eq!(vars[1].key, "KEY2");
-        assert_eq!(vars[1].value, "default2");
-        assert_eq!(vars[1].default_value, "default2");
-
-        assert_eq!(vars[2].key, "KEY3");
-        assert_eq!(vars[2].value, "custom3");
-        assert_eq!(vars[2].default_value, "");
     }
 
     #[test]
     fn test_write_env() {
         let file = NamedTempFile::new().unwrap();
-        let vars = vec![EnvVar {
+        let vars = vec![ConfigItem {
             key: "KEY1".to_string(),
-            value: "value1".to_string(),
+            path: vec![PathSegment::Key("KEY1".to_string())],
-            default_value: "def".to_string(),
+            value: Some("value1".to_string()),
+            template_value: None,
+            default_value: None,
+            depth: 0,
+            is_group: false,
+            status: ItemStatus::Present,
+            value_type: ValueType::String,
         }];
 
         let handler = EnvHandler;
@@ -139,4 +106,39 @@ mod tests {
         let content = fs::read_to_string(file.path()).unwrap();
         assert_eq!(content.trim(), "KEY1=value1");
     }
+
+    #[test]
+    fn test_merge_env() {
+        let template = NamedTempFile::new().unwrap();
+        writeln!(template.as_file(), "KEY1=template_val\nKEY2=default_val").unwrap();
+
+        let mut active_vars = vec![ConfigItem {
+            key: "KEY1".to_string(),
+            path: vec![PathSegment::Key("KEY1".to_string())],
+            value: Some("active_val".to_string()),
+            template_value: None,
+            default_value: None,
+            depth: 0,
+            is_group: false,
+            status: ItemStatus::Present,
+            value_type: ValueType::String,
+        }];
+
+        let handler = EnvHandler;
+        handler.merge(template.path(), &mut active_vars).unwrap();
+
+        assert_eq!(active_vars.len(), 2);
+        
+        // KEY1 should be marked modified
+        let key1 = active_vars.iter().find(|v| v.key == "KEY1").unwrap();
+        assert_eq!(key1.status, ItemStatus::Modified);
+        assert_eq!(key1.value.as_deref(), Some("active_val"));
+        assert_eq!(key1.template_value.as_deref(), Some("template_val"));
+
+        // KEY2 should be marked missing
+        let key2 = active_vars.iter().find(|v| v.key == "KEY2").unwrap();
+        assert_eq!(key2.status, ItemStatus::MissingFromActive);
+        assert_eq!(key2.value, None);
+        assert_eq!(key2.template_value.as_deref(), Some("default_val"));
+    }
 }

src/format/hierarchical.rs

@@ -1,217 +1,477 @@
-use super::{EnvVar, FormatHandler, FormatType};
+//! Provides a generalized handler for hierarchical configuration formats 
+//! (JSON, YAML, TOML, XML).
+//!
+//! This handler works by using `serde_json::Value` as an intermediary 
+//! representation. It "flattens" nested structures into a list of 
+//! `ConfigItem`s for the TUI, and "unflattens" them back into their 
+//! nested form when saving.
+
+use super::{ConfigItem, FormatHandler, FormatType, ItemStatus, ValueType, PathSegment};
 use serde_json::{Map, Value};
 use std::fs;
-use std::io;
 use std::path::Path;
 
+/// A format handler capable of processing nested configuration structures.
 pub struct HierarchicalHandler {
+    /// The specific file format this instance is configured to handle.
     format_type: FormatType,
 }
 
 impl HierarchicalHandler {
+    /// Creates a new hierarchical handler for the specified format.
     pub fn new(format_type: FormatType) -> Self {
         Self { format_type }
     }
 
-    fn read_value(&self, path: &Path) -> io::Result<Value> {
+    /// Reads a file and parses it into an intermediary `serde_json::Value`.
+    fn read_value(&self, path: &Path) -> anyhow::Result<Value> {
         let content = fs::read_to_string(path)?;
         let value = match self.format_type {
-            FormatType::Json => serde_json::from_str(&content).map_err(|e| io::Error::new(io::ErrorKind::InvalidData, e))?,
+            FormatType::Json => serde_json::from_str(&content)?,
-            FormatType::Yaml => serde_yaml::from_str(&content).map_err(|e| io::Error::new(io::ErrorKind::InvalidData, e))?,
+            FormatType::Yaml => serde_yaml::from_str(&content)?,
-            FormatType::Toml => toml::from_str(&content).map_err(|e| io::Error::new(io::ErrorKind::InvalidData, e))?,
+            FormatType::Toml => toml::from_str(&content)?,
+            FormatType::Xml => xml_to_json(&content)?,
             _ => unreachable!(),
         };
         Ok(value)
     }
 
-    fn write_value(&self, path: &Path, value: &Value) -> io::Result<()> {
+    /// Serializes a `serde_json::Value` and writes it to the specified path.
+    fn write_value(&self, path: &Path, value: &Value) -> anyhow::Result<()> {
         let content = match self.format_type {
-            FormatType::Json => serde_json::to_string_pretty(value).map_err(|e| io::Error::new(io::ErrorKind::InvalidData, e))?,
+            FormatType::Json => serde_json::to_string_pretty(value)?,
-            FormatType::Yaml => serde_yaml::to_string(value).map_err(|e| io::Error::new(io::ErrorKind::InvalidData, e))?,
+            FormatType::Yaml => serde_yaml::to_string(value)?,
             FormatType::Toml => {
-                // toml requires the root to be a table
+                // TOML requires the root to be a table (Object).
                 if value.is_object() {
-                    let toml_value: toml::Value = serde_json::from_value(value.clone()).map_err(|e| io::Error::new(io::ErrorKind::InvalidData, e))?;
+                    let toml_value: toml::Value = serde_json::from_value(value.clone())?;
-                    toml::to_string_pretty(&toml_value).map_err(|e| io::Error::new(io::ErrorKind::InvalidData, e))?
+                    toml::to_string_pretty(&toml_value)?
                 } else {
-                    return Err(io::Error::new(io::ErrorKind::InvalidData, "Root of TOML must be an object"));
+                    anyhow::bail!("Root of TOML must be an object");
                 }
             }
+            FormatType::Xml => json_to_xml(value),
             _ => unreachable!(),
         };
-        fs::write(path, content)
+        fs::write(path, content)?;
+        Ok(())
     }
 }
 
-fn flatten(value: &Value, prefix: &str, vars: &mut Vec<EnvVar>) {
+/// Converts an XML string into an intermediary `serde_json::Value`.
+/// 
+/// This implementation handles basic element nesting and text content. 
+/// Attributes are currently not supported.
+fn xml_to_json(content: &str) -> anyhow::Result<Value> {
+    use quick_xml::reader::Reader;
+    use quick_xml::events::Event;
+
+    let mut reader = Reader::from_str(content);
+    reader.config_mut().trim_text(true);
+    let mut buf = Vec::new();
+    
+    /// Recursively parses XML elements into a nested Map structure.
+    fn parse_recursive(reader: &mut Reader<&[u8]>) -> anyhow::Result<Value> {
+        let mut map = Map::new();
+        let mut text = String::new();
+        let mut buf = Vec::new();
+
+        loop {
+            match reader.read_event_into(&mut buf) {
+                Ok(Event::Start(e)) => {
+                    let name = String::from_utf8_lossy(e.name().as_ref()).to_string();
+                    let val = parse_recursive(reader)?;
+                    
+                    // If multiple elements have the same name, they are collected into an Array.
+                    if let Some(existing) = map.get_mut(&name) {
+                        if let Some(arr) = existing.as_array_mut() {
+                            arr.push(val);
+                        } else {
+                            let old = existing.take();
+                            *existing = Value::Array(vec![old, val]);
+                        }
+                    } else {
+                        map.insert(name, val);
+                    }
+                }
+                Ok(Event::End(_)) => break,
+                Ok(Event::Text(e)) => {
+                    text.push_str(&String::from_utf8_lossy(e.as_ref()));
+                }
+                Ok(Event::Eof) => break,
+                _ => {}
+            }
+            buf.clear();
+        }
+
+        if map.is_empty() {
+            if text.is_empty() {
+                Ok(Value::Null)
+            } else {
+                Ok(Value::String(text))
+            }
+        } else {
+            if !text.is_empty() {
+                // Special key used to store raw text content of an element that also has children.
+                map.insert("$text".to_string(), Value::String(text));
+            }
+            Ok(Value::Object(map))
+        }
+    }
+
+    // Move to the first start tag
+    loop {
+        match reader.read_event_into(&mut buf) {
+            Ok(Event::Start(e)) => {
+                let name = String::from_utf8_lossy(e.name().as_ref()).to_string();
+                let val = parse_recursive(&mut reader)?;
+                let mut root = Map::new();
+                root.insert(name, val);
+                return Ok(Value::Object(root));
+            }
+            Ok(Event::Eof) => break,
+            _ => {}
+        }
+        buf.clear();
+    }
+
+    Ok(Value::Object(Map::new()))
+}
+
+/// Converts a nested `serde_json::Value` back into an XML string.
+fn json_to_xml(value: &Value) -> String {
+    use quick_xml::Writer;
+    use quick_xml::events::{Event, BytesStart, BytesEnd, BytesText};
+
+    let mut writer = Writer::new_with_indent(Vec::new(), b' ', 4);
+    
+    /// Recursively writes JSON values as XML elements.
+    fn write_recursive(writer: &mut Writer<Vec<u8>>, value: &Value, key_name: Option<&str>) {
+        if let Some(k) = key_name
+            && k == "$text" {
+                if let Some(s) = value.as_str() {
+                    writer.write_event(Event::Text(BytesText::new(s))).unwrap();
+                }
+                return;
+            }
+        
         match value {
             Value::Object(map) => {
+                if let Some(k) = key_name {
+                    writer.write_event(Event::Start(BytesStart::new(k))).unwrap();
+                }
                 for (k, v) in map {
-                let new_prefix = if prefix.is_empty() {
+                    if let Some(arr) = v.as_array() {
-                    k.clone()
+                        for item in arr {
+                            write_recursive(writer, item, Some(k));
+                        }
                     } else {
-                    format!("{}.{}", prefix, k)
+                        write_recursive(writer, v, Some(k));
-                };
+                    }
-                flatten(v, &new_prefix, vars);
+                }
+                if let Some(k) = key_name {
+                    writer.write_event(Event::End(BytesEnd::new(k))).unwrap();
                 }
             }
             Value::Array(arr) => {
-            for (i, v) in arr.iter().enumerate() {
+                for v in arr {
-                let new_prefix = format!("{}[{}]", prefix, i);
+                    write_recursive(writer, v, key_name);
-                flatten(v, &new_prefix, vars);
                 }
             }
             Value::String(s) => {
-            vars.push(EnvVar {
+                if let Some(k) = key_name {
-                key: prefix.to_string(),
+                    writer.write_event(Event::Start(BytesStart::new(k))).unwrap();
-                value: s.clone(),
+                }
-                default_value: s.clone(),
+                writer.write_event(Event::Text(BytesText::new(s))).unwrap();
+                if let Some(k) = key_name {
+                    writer.write_event(Event::End(BytesEnd::new(k))).unwrap();
+                }
+            }
+            Value::Number(n) => {
+                if let Some(k) = key_name {
+                    writer.write_event(Event::Start(BytesStart::new(k))).unwrap();
+                }
+                writer.write_event(Event::Text(BytesText::new(&n.to_string()))).unwrap();
+                if let Some(k) = key_name {
+                    writer.write_event(Event::End(BytesEnd::new(k))).unwrap();
+                }
+            }
+            Value::Bool(b) => {
+                if let Some(k) = key_name {
+                    writer.write_event(Event::Start(BytesStart::new(k))).unwrap();
+                }
+                writer.write_event(Event::Text(BytesText::new(&b.to_string()))).unwrap();
+                if let Some(k) = key_name {
+                    writer.write_event(Event::End(BytesEnd::new(k))).unwrap();
+                }
+            }
+            Value::Null => {
+                if let Some(k) = key_name {
+                    writer.write_event(Event::Empty(BytesStart::new(k))).unwrap();
+                }
+            }
+        }
+    }
+
+    if value.is_object() {
+        for (k, v) in value.as_object().unwrap() {
+            if let Some(arr) = v.as_array() {
+                for item in arr {
+                    write_recursive(&mut writer, item, Some(k));
+                }
+            } else {
+                write_recursive(&mut writer, v, Some(k));
+            }
+        }
+    } else {
+        write_recursive(&mut writer, value, None);
+    }
+    
+    let mut out = String::from_utf8(writer.into_inner()).unwrap();
+    if !out.ends_with('\n') {
+        out.push('\n');
+    }
+    out
+}
+
+/// Recursively flattens a nested `serde_json::Value` into a list of `ConfigItem`s.
+///
+/// This function translates the structural hierarchy of the JSON into 
+/// linear entries with associated paths and depth levels for UI rendering.
+fn flatten(value: &Value, current_path: Vec<PathSegment>, key_name: Option<String>, depth: usize, vars: &mut Vec<ConfigItem>) {
+    let mut next_path = current_path.clone();
+    
+    if let Some(ref k) = key_name {
+        if !current_path.is_empty() {
+            // It's a key in an object, so append to path
+            next_path.push(PathSegment::Key(k.clone()));
+        } else {
+            // First element, maybe root
+            if !k.is_empty() {
+                next_path.push(PathSegment::Key(k.clone()));
+            }
+        }
+    }
+
+    let display_key = match next_path.last() {
+        Some(PathSegment::Key(k)) => k.clone(),
+        Some(PathSegment::Index(i)) => format!("[{}]", i),
+        None => "".to_string(),
+    };
+
+    match value {
+        Value::Object(map) => {
+            if !next_path.is_empty() {
+                vars.push(ConfigItem {
+                    key: display_key,
+                    path: next_path.clone(),
+                    value: None,
+                    template_value: None,
+                    default_value: None,
+                    depth,
+                    is_group: true,
+                    status: ItemStatus::Present,
+                    value_type: ValueType::Null,
+                });
+            }
+            let next_depth = if next_path.is_empty() { depth } else { depth + 1 };
+            for (k, v) in map {
+                flatten(v, next_path.clone(), Some(k.clone()), next_depth, vars);
+            }
+        }
+        Value::Array(arr) => {
+            if !next_path.is_empty() {
+                vars.push(ConfigItem {
+                    key: display_key,
+                    path: next_path.clone(),
+                    value: None,
+                    template_value: None,
+                    default_value: None,
+                    depth,
+                    is_group: true,
+                    status: ItemStatus::Present,
+                    value_type: ValueType::Null,
+                });
+            }
+            let next_depth = if next_path.is_empty() { depth } else { depth + 1 };
+            for (i, v) in arr.iter().enumerate() {
+                let mut arr_path = next_path.clone();
+                arr_path.push(PathSegment::Index(i));
+                flatten(v, arr_path, None, next_depth, vars);
+            }
+        }
+        Value::String(s) => {
+            vars.push(ConfigItem {
+                key: display_key,
+                path: next_path.clone(),
+                value: Some(s.clone()),
+                template_value: Some(s.clone()),
+                default_value: Some(s.clone()),
+                depth,
+                is_group: false,
+                status: ItemStatus::Present,
+                value_type: ValueType::String,
             });
         }
         Value::Number(n) => {
             let s = n.to_string();
-            vars.push(EnvVar {
+            vars.push(ConfigItem {
-                key: prefix.to_string(),
+                key: display_key,
-                value: s.clone(),
+                path: next_path.clone(),
-                default_value: s.clone(),
+                value: Some(s.clone()),
+                template_value: Some(s.clone()),
+                default_value: Some(s.clone()),
+                depth,
+                is_group: false,
+                status: ItemStatus::Present,
+                value_type: ValueType::Number,
             });
         }
         Value::Bool(b) => {
             let s = b.to_string();
-            vars.push(EnvVar {
+            vars.push(ConfigItem {
-                key: prefix.to_string(),
+                key: display_key,
-                value: s.clone(),
+                path: next_path.clone(),
-                default_value: s.clone(),
+                value: Some(s.clone()),
+                template_value: Some(s.clone()),
+                default_value: Some(s.clone()),
+                depth,
+                is_group: false,
+                status: ItemStatus::Present,
+                value_type: ValueType::Bool,
             });
         }
         Value::Null => {
-            vars.push(EnvVar {
+            vars.push(ConfigItem {
-                key: prefix.to_string(),
+                key: display_key,
-                value: "".to_string(),
+                path: next_path.clone(),
-                default_value: "".to_string(),
+                value: Some("".to_string()),
+                template_value: Some("".to_string()),
+                default_value: Some("".to_string()),
+                depth,
+                is_group: false,
+                status: ItemStatus::Present,
+                value_type: ValueType::Null,
             });
         }
     }
 }
 
-// Removed unused update_leaf and update_leaf_value functions
-
 impl FormatHandler for HierarchicalHandler {
-    fn parse(&self, path: &Path) -> io::Result<Vec<EnvVar>> {
+    fn parse(&self, path: &Path) -> anyhow::Result<Vec<ConfigItem>> {
         let value = self.read_value(path)?;
         let mut vars = Vec::new();
-        flatten(&value, "", &mut vars);
+        flatten(&value, Vec::new(), Some("".to_string()), 0, &mut vars);
         Ok(vars)
     }
 
-    fn merge(&self, path: &Path, vars: &mut Vec<EnvVar>) -> io::Result<()> {
+    fn write(&self, path: &Path, vars: &[ConfigItem]) -> anyhow::Result<()> {
-        if !path.exists() {
-            return Ok(());
-        }
-        let existing_value = self.read_value(path)?;
-        let mut existing_vars = Vec::new();
-        flatten(&existing_value, "", &mut existing_vars);
-
-        for var in vars.iter_mut() {
-            if let Some(existing) = existing_vars.iter().find(|v| v.key == var.key) {
-                var.value = existing.value.clone();
-            }
-        }
-        Ok(())
-    }
-
-    fn write(&self, path: &Path, vars: &[EnvVar]) -> io::Result<()> {
-        // For writing hierarchical formats, we ideally want to preserve the original structure.
-        // But we don't have it here. We should parse the template again to get the structure!
-        // Oh wait, `write` is called with only `vars`.
-        // If we want to construct the tree from scratch, it's very difficult to guess array vs object
-        // and data types without the original template.
-        // Let's change the trait or just keep a copy of the template?
-        // Actually, if we require the user to have the template, we can just parse the template, update the leaves, and write.
-        // We'll write a reconstruction algorithm that just creates objects based on keys.
         let mut root = Value::Object(Map::new());
         for var in vars {
-            insert_into_value(&mut root, &var.key, &var.value);
+            if !var.is_group {
+                let val = var.value.as_deref()
+                    .or(var.template_value.as_deref())
+                    .unwrap_or("");
+                insert_into_value(&mut root, &var.path, val, var.value_type);
+            }
         }
         self.write_value(path, &root)
     }
 }
 
-fn insert_into_value(root: &mut Value, path: &str, new_val_str: &str) {
+/// Reconstructs a nested `serde_json::Value` from a hierarchical path and a leaf value.
-    let mut parts = path.split('.');
+/// 
-    let last_part = match parts.next_back() {
+/// This is the core "unflattening" logic used when saving modified configuration.
-        Some(p) => p,
+fn insert_into_value(root: &mut Value, path: &[PathSegment], new_val_str: &str, value_type: ValueType) {
-        None => return,
+    if path.is_empty() {
-    };
+        return;
+    }
 
     let mut current = root;
-    for part in parts {
+    
-        let (key, idx) = parse_array_key(part);
+    // Traverse all but the last segment to build the intermediate structure.
+    for i in 0..path.len() - 1 {
+        let segment = &path[i];
+        let next_segment = &path[i + 1];
+
+        match segment {
+            PathSegment::Key(key) => {
                 if !current.is_object() {
                     *current = Value::Object(Map::new());
                 }
                 let map = current.as_object_mut().unwrap();
                 
-        let next_node = map.entry(key.to_string()).or_insert_with(|| {
+                let next_node = map.entry(key.clone()).or_insert_with(|| {
-            if idx.is_some() {
+                    match next_segment {
-                Value::Array(Vec::new())
+                        PathSegment::Index(_) => Value::Array(Vec::new()),
-            } else {
+                        PathSegment::Key(_) => Value::Object(Map::new()),
-                Value::Object(Map::new())
                     }
                 });
-
-        if let Some(i) = idx {
-            if !next_node.is_array() {
-                *next_node = Value::Array(Vec::new());
-            }
-            let arr = next_node.as_array_mut().unwrap();
-            while arr.len() <= i {
-                arr.push(Value::Object(Map::new()));
-            }
-            current = &mut arr[i];
-        } else {
                 current = next_node;
             }
+            PathSegment::Index(idx) => {
+                if !current.is_array() {
+                    *current = Value::Array(Vec::new());
+                }
+                let arr = current.as_array_mut().unwrap();
+                while arr.len() <= *idx {
+                    match next_segment {
+                        PathSegment::Index(_) => arr.push(Value::Array(Vec::new())),
+                        PathSegment::Key(_) => arr.push(Value::Object(Map::new())),
+                    }
+                }
+                current = &mut arr[*idx];
+            }
+        }
     }
 
-    let (final_key, final_idx) = parse_array_key(last_part);
+    // Insert the actual leaf value at the end of the path.
-    if !current.is_object() {
+    let final_segment = &path[path.len() - 1];
-        *current = Value::Object(Map::new());
-    }
-    let map = current.as_object_mut().unwrap();
     
-    // Attempt basic type inference
+    // Attempt to preserve the original data type during insertion.
-    let final_val = if let Ok(n) = new_val_str.parse::<i64>() {
+    let final_val = match value_type {
+        ValueType::Number => {
+            if let Ok(n) = new_val_str.parse::<i64>() {
                 Value::Number(n.into())
-    } else if let Ok(b) = new_val_str.parse::<bool>() {
+            } else if let Ok(f) = new_val_str.parse::<f64>() {
+                if let Some(n) = serde_json::Number::from_f64(f) {
+                    Value::Number(n)
+                } else {
+                    Value::String(new_val_str.to_string())
+                }
+            } else {
+                Value::String(new_val_str.to_string())
+            }
+        }
+        ValueType::Bool => {
+            if let Ok(b) = new_val_str.parse::<bool>() {
                 Value::Bool(b)
             } else {
                 Value::String(new_val_str.to_string())
+            }
+        }
+        ValueType::Null if new_val_str.is_empty() => Value::Null,
+        _ => Value::String(new_val_str.to_string()),
     };
 
-    if let Some(i) = final_idx {
+    match final_segment {
-        let next_node = map.entry(final_key.to_string()).or_insert_with(|| Value::Array(Vec::new()));
+        PathSegment::Key(key) => {
-        if !next_node.is_array() {
+            if !current.is_object() {
-            *next_node = Value::Array(Vec::new());
+                *current = Value::Object(Map::new());
             }
-        let arr = next_node.as_array_mut().unwrap();
+            let map = current.as_object_mut().unwrap();
-        while arr.len() <= i {
+            map.insert(key.clone(), final_val);
+        }
+        PathSegment::Index(idx) => {
+            if !current.is_array() {
+                *current = Value::Array(Vec::new());
+            }
+            let arr = current.as_array_mut().unwrap();
+            while arr.len() <= *idx {
                 arr.push(Value::Null);
             }
-        arr[i] = final_val;
+            arr[*idx] = final_val;
-    } else {
-        map.insert(final_key.to_string(), final_val);
         }
-}
-
-fn parse_array_key(part: &str) -> (&str, Option<usize>) {
-    if part.ends_with(']') && part.contains('[') {
-        let start_idx = part.find('[').unwrap();
-        let key = &part[..start_idx];
-        let idx = part[start_idx+1..part.len()-1].parse::<usize>().ok();
-        (key, idx)
-    } else {
-        (part, None)
     }
 }
 
@@ -220,7 +480,7 @@ mod tests {
     use super::*;
 
     #[test]
-    fn test_flatten_unflatten() {
+    fn test_json_flatten_unflatten() {
         let mut vars = Vec::new();
         let json = serde_json::json!({
             "services": {
@@ -233,17 +493,155 @@ mod tests {
             }
         });
 
-        flatten(&json, "", &mut vars);
+        flatten(&json, Vec::new(), Some("".to_string()), 0, &mut vars);
-        assert_eq!(vars.len(), 2);
+        assert_eq!(vars.len(), 6);
 
         let mut root = Value::Object(Map::new());
         for var in vars {
-            insert_into_value(&mut root, &var.key, &var.value);
+            if !var.is_group {
+                insert_into_value(&mut root, &var.path, var.value.as_deref().unwrap_or(""), var.value_type);
+            }
         }
 
-        // When unflattening, it parses bool back
         let unflattened_json = serde_json::to_string(&root).unwrap();
         assert!(unflattened_json.contains("\"8080:80\""));
         assert!(unflattened_json.contains("true"));
     }
+
+    #[test]
+    fn test_type_preservation() {
+        let mut vars = Vec::new();
+        let json = serde_json::json!({
+            "port_num": 8080,
+            "port_str": "8080",
+            "is_enabled": true,
+            "is_enabled_str": "true",
+            "float_num": 42.42,
+            "float_str": "42.42"
+        });
+
+        flatten(&json, Vec::new(), Some("".to_string()), 0, &mut vars);
+        
+        let mut root = Value::Object(Map::new());
+        for var in vars {
+            if !var.is_group {
+                insert_into_value(&mut root, &var.path, var.value.as_deref().unwrap_or(""), var.value_type);
+            }
+        }
+
+        let unflattened = root.as_object().unwrap();
+        
+        assert!(unflattened["port_num"].is_number(), "port_num should be a number");
+        assert_eq!(unflattened["port_num"].as_i64(), Some(8080));
+        
+        assert!(unflattened["port_str"].is_string(), "port_str should be a string");
+        assert_eq!(unflattened["port_str"].as_str(), Some("8080"));
+        
+        assert!(unflattened["is_enabled"].is_boolean(), "is_enabled should be a boolean");
+        assert_eq!(unflattened["is_enabled"].as_bool(), Some(true));
+        
+        assert!(unflattened["is_enabled_str"].is_string(), "is_enabled_str should be a string");
+        assert_eq!(unflattened["is_enabled_str"].as_str(), Some("true"));
+        
+        assert!(unflattened["float_num"].is_number(), "float_num should be a number");
+        assert_eq!(unflattened["float_num"].as_f64(), Some(42.42));
+        
+        assert!(unflattened["float_str"].is_string(), "float_str should be a string");
+        assert_eq!(unflattened["float_str"].as_str(), Some("42.42"));
+    }
+
+    #[test]
+    fn test_yaml_flatten_unflatten() {
+        let yaml_str = "
+server:
+  port: 8080
+  port_str: \"8080\"
+  enabled: true
+";
+        let yaml_val: Value = serde_yaml::from_str(yaml_str).unwrap();
+        let mut vars = Vec::new();
+        flatten(&yaml_val, Vec::new(), Some("".to_string()), 0, &mut vars);
+        
+        let mut root = Value::Object(Map::new());
+        for var in vars {
+            if !var.is_group {
+                insert_into_value(&mut root, &var.path, var.value.as_deref().unwrap_or(""), var.value_type);
+            }
+        }
+        
+        let unflattened_yaml = serde_yaml::to_string(&root).unwrap();
+        assert!(unflattened_yaml.contains("port: 8080"));
+        assert!(unflattened_yaml.contains("port_str: '8080'") || unflattened_yaml.contains("port_str: \"8080\""));
+        assert!(unflattened_yaml.contains("enabled: true"));
+    }
+
+    #[test]
+    fn test_toml_flatten_unflatten() {
+        let toml_str = "
+[server]
+port = 8080
+port_str = \"8080\"
+enabled = true
+";
+        let toml_val: toml::Value = toml::from_str(toml_str).unwrap();
+        let json_val: Value = serde_json::to_value(toml_val).unwrap();
+
+        let mut vars = Vec::new();
+        flatten(&json_val, Vec::new(), Some("".to_string()), 0, &mut vars);
+        
+        let mut root = Value::Object(Map::new());
+        for var in vars {
+            if !var.is_group {
+                insert_into_value(&mut root, &var.path, var.value.as_deref().unwrap_or(""), var.value_type);
+            }
+        }
+        
+        let toml_root: toml::Value = serde_json::from_value(root).unwrap();
+        let unflattened_toml = toml::to_string(&toml_root).unwrap();
+        
+        assert!(unflattened_toml.contains("port = 8080"));
+        assert!(unflattened_toml.contains("port_str = \"8080\""));
+        assert!(unflattened_toml.contains("enabled = true"));
+    }
+
+    #[test]
+    fn test_group_rename_write() {
+        let mut vars = Vec::new();
+        let json = serde_json::json!({
+            "old_group": {
+                "key": "val"
+            }
+        });
+
+        flatten(&json, Vec::new(), Some("".to_string()), 0, &mut vars);
+        assert_eq!(vars.len(), 2);
+        assert_eq!(vars[0].key, "old_group");
+        assert_eq!(vars[0].is_group, true);
+        assert_eq!(vars[1].key, "key");
+        assert_eq!(vars[1].path_string(), "old_group.key");
+
+        // Manually simulate a rename of "old_group" to "new_group"
+        let old_path = vars[0].path.clone();
+        let new_key = "new_group".to_string();
+        let mut new_path = vec![PathSegment::Key(new_key.clone())];
+        
+        vars[0].key = new_key;
+        vars[0].path = new_path.clone();
+        
+        // Update child path
+        vars[1].path = vec![PathSegment::Key("new_group".to_string()), PathSegment::Key("key".to_string())];
+        
+        let handler = HierarchicalHandler::new(FormatType::Json);
+        let mut root = Value::Object(Map::new());
+        for var in &vars {
+            if !var.is_group {
+                insert_into_value(&mut root, &var.path, var.value.as_deref().unwrap_or(""), var.value_type);
+            }
+        }
+        
+        let out = serde_json::to_string(&root).unwrap();
+        assert!(out.contains("\"new_group\""));
+        assert!(out.contains("\"key\":\"val\""));
+        assert!(!out.contains("\"old_group\""));
+    }
 }

src/format/ini.rs

@@ -0,0 +1,125 @@
+use super::{ConfigItem, FormatHandler, ItemStatus, ValueType, PathSegment};
+use ini::Ini;
+use std::path::Path;
+
+pub struct IniHandler;
+
+impl FormatHandler for IniHandler {
+    fn parse(&self, path: &Path) -> anyhow::Result<Vec<ConfigItem>> {
+        let conf = Ini::load_from_file(path)?;
+        let mut vars = Vec::new();
+
+        for (section, prop) in &conf {
+            let section_name = section.unwrap_or_default();
+            
+            if !section_name.is_empty() {
+                vars.push(ConfigItem {
+                    key: section_name.to_string(),
+                    path: vec![PathSegment::Key(section_name.to_string())],
+                    value: None,
+                    template_value: None,
+                    default_value: None,
+                    depth: 0,
+                    is_group: true,
+                    status: ItemStatus::Present,
+                    value_type: ValueType::Null,
+                });
+            }
+
+            for (key, value) in prop {
+                let path = if section_name.is_empty() {
+                    vec![PathSegment::Key(key.to_string())]
+                } else {
+                    vec![PathSegment::Key(section_name.to_string()), PathSegment::Key(key.to_string())]
+                };
+
+                vars.push(ConfigItem {
+                    key: key.to_string(),
+                    path,
+                    value: Some(value.to_string()),
+                    template_value: Some(value.to_string()),
+                    default_value: Some(value.to_string()),
+                    depth: if section_name.is_empty() { 0 } else { 1 },
+                    is_group: false,
+                    status: ItemStatus::Present,
+                    value_type: ValueType::String,
+                });
+            }
+        }
+
+        Ok(vars)
+    }
+
+    fn write(&self, path: &Path, vars: &[ConfigItem]) -> anyhow::Result<()> {
+        let mut conf = Ini::new();
+        for var in vars {
+            if !var.is_group {
+                let val = var.value.as_deref()
+                    .or(var.template_value.as_deref())
+                    .unwrap_or("");
+                
+                if var.path.len() == 2 {
+                    if let (PathSegment::Key(section), PathSegment::Key(key)) = (&var.path[0], &var.path[1]) {
+                        conf.with_section(Some(section)).set(key, val);
+                    }
+                } else if var.path.len() == 1
+                    && let PathSegment::Key(key) = &var.path[0] {
+                        conf.with_section(None::<String>).set(key, val);
+                    }
+            }
+        }
+        conf.write_to_file(path)?;
+        Ok(())
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use tempfile::NamedTempFile;
+    use std::io::Write;
+
+    #[test]
+    fn test_section_rename_write() {
+        let handler = IniHandler;
+        let mut vars = vec![
+            ConfigItem {
+                key: "server".to_string(),
+                path: vec![PathSegment::Key("server".to_string())],
+                value: None,
+                template_value: None,
+                default_value: None,
+                depth: 0,
+                is_group: true,
+                status: ItemStatus::Present,
+                value_type: ValueType::Null,
+            },
+            ConfigItem {
+                key: "port".to_string(),
+                path: vec![PathSegment::Key("server".to_string()), PathSegment::Key("port".to_string())],
+                value: Some("8080".to_string()),
+                template_value: Some("8080".to_string()),
+                default_value: Some("8080".to_string()),
+                depth: 1,
+                is_group: false,
+                status: ItemStatus::Present,
+                value_type: ValueType::String,
+            }
+        ];
+
+        // Rename "server" to "srv"
+        vars[0].key = "srv".to_string();
+        vars[0].path = vec![PathSegment::Key("srv".to_string())];
+        
+        // Update child path
+        vars[1].path = vec![PathSegment::Key("srv".to_string()), PathSegment::Key("port".to_string())];
+        
+        let file = NamedTempFile::new().unwrap();
+        handler.write(file.path(), &vars).unwrap();
+        
+        let content = std::fs::read_to_string(file.path()).unwrap();
+        assert!(content.contains("[srv]"));
+        assert!(content.contains("port=8080"));
+        assert!(!content.contains("[server]"));
+    }
+}

src/format/mod.rs

@@ -1,30 +1,173 @@
+//! This module defines the unified data model used by `mould` to represent 
+//! configuration data across all supported file formats.
+//!
+//! By normalizing heterogeneous structures (like nested YAML or flat .env) 
+//! into a standard tree-like representation, the TUI logic remains 
+//! independent of the underlying file format.
+
 use std::path::Path;
-use std::io;
 
 pub mod env;
 pub mod hierarchical;
+pub mod ini;
+pub mod properties;
 
-#[derive(Debug, Clone)]
+/// Represents the status of a configuration item relative to a template.
-pub struct EnvVar {
+#[derive(Debug, Clone, PartialEq, Eq)]
-    pub key: String,
+pub enum ItemStatus {
-    pub value: String,
+    /// Item exists in the active configuration and matches the template (or no template exists).
-    pub default_value: String,
+    Present,
+    /// Item exists in the template but is missing from the active configuration.
+    MissingFromActive,
+    /// Item has been changed by the user during the current session.
+    Modified,
 }
 
+/// Hints about the original data type to ensure correct serialization during writes.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum ValueType {
+    /// Standard text.
+    String,
+    /// Numeric values (integers or floats).
+    Number,
+    /// True/False values.
+    Bool,
+    /// Representing an explicit null or empty value.
+    Null,
+}
+
+/// A single segment in a hierarchical configuration path.
+///
+/// For example, `services[0].image` would be represented as:
+/// `[Key("services"), Index(0), Key("image")]`
+#[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
+pub enum PathSegment {
+    /// A named key in an object/map.
+    Key(String),
+    /// A numeric index in an array/list.
+    Index(usize),
+}
+
+impl std::fmt::Display for PathSegment {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            PathSegment::Key(k) => write!(f, "{}", k),
+            PathSegment::Index(i) => write!(f, "[{}]", i),
+        }
+    }
+}
+
+/// The unified representation of a single configuration entry.
+///
+/// This model is used for UI rendering and internal manipulation. 
+/// Format-specific handlers are responsible for translating their native 
+/// data into this structure.
+#[derive(Debug, Clone)]
+pub struct ConfigItem {
+    /// The short display name of the key (e.g., `port`).
+    pub key: String,
+    /// The full hierarchical path defining this item's location in the config tree.
+    pub path: Vec<PathSegment>,
+    /// The active value of the configuration entry.
+    pub value: Option<String>,
+    /// The value found in the template file (if any).
+    pub template_value: Option<String>,
+    /// A fallback value to use if the item is missing.
+    pub default_value: Option<String>,
+    /// Visual depth in the tree (used for indentation in the TUI).
+    pub depth: usize,
+    /// True if this item represents a structural node (object or array) rather than a leaf value.
+    pub is_group: bool,
+    /// Comparison status relative to the template.
+    pub status: ItemStatus,
+    /// Metadata about the original data type.
+    pub value_type: ValueType,
+}
+
+impl ConfigItem {
+    /// Returns a human-readable string representation of the full path (e.g., `server.port`).
+    pub fn path_string(&self) -> String {
+        let mut s = String::new();
+        for (i, segment) in self.path.iter().enumerate() {
+            match segment {
+                PathSegment::Key(k) => {
+                    if i > 0 {
+                        s.push('.');
+                    }
+                    s.push_str(k);
+                }
+                PathSegment::Index(idx) => {
+                    s.push_str(&format!("[{}]", idx));
+                }
+            }
+        }
+        s
+    }
+}
+
+/// Supported configuration file formats.
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
 pub enum FormatType {
     Env,
     Json,
     Yaml,
     Toml,
+    Xml,
+    Ini,
+    Properties,
 }
 
+/// Defines the interface for parsing, merging, and writing configuration files.
+///
+/// Implementing this trait allows `mould` to support new file formats.
 pub trait FormatHandler {
-    fn parse(&self, path: &Path) -> io::Result<Vec<EnvVar>>;
+    /// Parses a file into the unified `Vec<ConfigItem>` representation.
-    fn merge(&self, path: &Path, vars: &mut Vec<EnvVar>) -> io::Result<()>;
+    fn parse(&self, path: &Path) -> anyhow::Result<Vec<ConfigItem>>;
-    fn write(&self, path: &Path, vars: &[EnvVar]) -> io::Result<()>;
+
+    /// Merges an active configuration with a template file.
+    ///
+    /// This identifies missing keys, marks modifications, and syncs default values.
+    fn merge(&self, path: &Path, vars: &mut Vec<ConfigItem>) -> anyhow::Result<()> {
+        if !path.exists() {
+            return Ok(());
+        }
+
+        let template_vars = self.parse(path).unwrap_or_default();
+
+        for var in vars.iter_mut() {
+            if let Some(template_var) = template_vars.iter().find(|v| v.path == var.path) {
+                var.template_value = template_var.value.clone();
+                var.default_value = template_var.value.clone();
+                
+                if var.value != template_var.value {
+                    var.status = ItemStatus::Modified;
+                } else {
+                    var.status = ItemStatus::Present;
+                }
+            } else {
+                // Exists in active, but not in template
+                var.status = ItemStatus::Present;
+            }
+        }
+        
+        // Add items from template that are missing in active
+        for template_var in template_vars {
+            if !vars.iter().any(|v| v.path == template_var.path) {
+                let mut new_item = template_var.clone();
+                new_item.status = ItemStatus::MissingFromActive;
+                new_item.value = None;
+                vars.push(new_item);
+            }
+        }
+
+        Ok(())
+    }
+
+    /// Writes the unified representation back to the original file format.
+    fn write(&self, path: &Path, vars: &[ConfigItem]) -> anyhow::Result<()>;
 }
 
+/// Automatically detects the configuration format based on file extension or an explicit override.
 pub fn detect_format(path: &Path, override_format: Option<String>) -> FormatType {
     if let Some(fmt) = override_format {
         match fmt.to_lowercase().as_str() {
@@ -32,27 +175,34 @@ pub fn detect_format(path: &Path, override_format: Option<String>) -> FormatType
             "json" => return FormatType::Json,
             "yaml" | "yml" => return FormatType::Yaml,
             "toml" => return FormatType::Toml,
+            "xml" => return FormatType::Xml,
+            "ini" => return FormatType::Ini,
+            "properties" => return FormatType::Properties,
             _ => {}
         }
     }
 
-    let file_name = path.file_name().unwrap_or_default().to_string_lossy();
+    let ext = path.extension().and_then(|s| s.to_str()).unwrap_or_default();
-    if file_name.ends_with(".json") {
+    match ext {
-        FormatType::Json
+        "json" => FormatType::Json,
-    } else if file_name.ends_with(".yaml") || file_name.ends_with(".yml") {
+        "yaml" | "yml" => FormatType::Yaml,
-        FormatType::Yaml
+        "toml" => FormatType::Toml,
-    } else if file_name.ends_with(".toml") {
+        "xml" => FormatType::Xml,
-        FormatType::Toml
+        "ini" => FormatType::Ini,
-    } else {
+        "properties" => FormatType::Properties,
-        FormatType::Env
+        _ => FormatType::Env,
     }
 }
 
+/// Factory function to return the appropriate handler implementation for a given format.
 pub fn get_handler(format: FormatType) -> Box<dyn FormatHandler> {
     match format {
         FormatType::Env => Box::new(env::EnvHandler),
         FormatType::Json => Box::new(hierarchical::HierarchicalHandler::new(FormatType::Json)),
         FormatType::Yaml => Box::new(hierarchical::HierarchicalHandler::new(FormatType::Yaml)),
         FormatType::Toml => Box::new(hierarchical::HierarchicalHandler::new(FormatType::Toml)),
+        FormatType::Xml => Box::new(hierarchical::HierarchicalHandler::new(FormatType::Xml)),
+        FormatType::Ini => Box::new(ini::IniHandler),
+        FormatType::Properties => Box::new(properties::PropertiesHandler),
     }
 }

src/format/properties.rs

@@ -0,0 +1,133 @@
+use super::{ConfigItem, FormatHandler, ItemStatus, ValueType, PathSegment};
+use java_properties::{LineContent, PropertiesIter, PropertiesWriter};
+use std::fs::File;
+use std::io::{BufReader, BufWriter};
+use std::path::Path;
+
+pub struct PropertiesHandler;
+
+impl FormatHandler for PropertiesHandler {
+    fn parse(&self, path: &Path) -> anyhow::Result<Vec<ConfigItem>> {
+        let file = File::open(path)?;
+        let reader = BufReader::new(file);
+        let iter = PropertiesIter::new(reader);
+
+        let mut vars = Vec::new();
+        let mut groups = std::collections::HashSet::new();
+
+        for line_result in iter {
+            let line = line_result?;
+            
+            if let LineContent::KVPair(path, value) = line.consume_content() {
+                // Add groups based on dot notation
+                let parts: Vec<&str> = path.split('.').collect();
+                let mut current_path = Vec::new();
+                
+                for (i, part) in parts.iter().enumerate().take(parts.len().saturating_sub(1)) {
+                    current_path.push(PathSegment::Key(part.to_string()));
+                    
+                    if groups.insert(current_path.clone()) {
+                        vars.push(ConfigItem {
+                            key: part.to_string(),
+                            path: current_path.clone(),
+                            value: None,
+                            template_value: None,
+                            default_value: None,
+                            depth: i,
+                            is_group: true,
+                            status: ItemStatus::Present,
+                            value_type: ValueType::Null,
+                        });
+                    }
+                }
+
+                let mut final_path = current_path.clone();
+                let last_key = parts.last().unwrap_or(&"").to_string();
+                final_path.push(PathSegment::Key(last_key.clone()));
+
+                vars.push(ConfigItem {
+                    key: last_key,
+                    path: final_path,
+                    value: Some(value.clone()),
+                    template_value: Some(value.clone()),
+                    default_value: Some(value.clone()),
+                    depth: parts.len().saturating_sub(1),
+                    is_group: false,
+                    status: ItemStatus::Present,
+                    value_type: ValueType::String,
+                });
+            }
+        }
+
+
+        Ok(vars)
+    }
+
+    fn write(&self, path: &Path, vars: &[ConfigItem]) -> anyhow::Result<()> {
+        let file = File::create(path)?;
+        let writer = BufWriter::new(file);
+        let mut prop_writer = PropertiesWriter::new(writer);
+        
+        for var in vars {
+            if !var.is_group {
+                let val = var.value.as_deref()
+                    .or(var.template_value.as_deref())
+                    .unwrap_or("");
+                prop_writer.write(&var.path_string(), val)?;
+            }
+        }
+
+        prop_writer.finish()?;
+        Ok(())
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use tempfile::NamedTempFile;
+    use std::io::Write;
+
+    #[test]
+    fn test_group_rename_write() {
+        let handler = PropertiesHandler;
+        let mut vars = vec![
+            ConfigItem {
+                key: "server".to_string(),
+                path: vec![PathSegment::Key("server".to_string())],
+                value: None,
+                template_value: None,
+                default_value: None,
+                depth: 0,
+                is_group: true,
+                status: ItemStatus::Present,
+                value_type: ValueType::Null,
+            },
+            ConfigItem {
+                key: "port".to_string(),
+                path: vec![PathSegment::Key("server".to_string()), PathSegment::Key("port".to_string())],
+                value: Some("8080".to_string()),
+                template_value: Some("8080".to_string()),
+                default_value: Some("8080".to_string()),
+                depth: 1,
+                is_group: false,
+                status: ItemStatus::Present,
+                value_type: ValueType::String,
+            }
+        ];
+
+        // Rename "server" to "srv"
+        vars[0].key = "srv".to_string();
+        vars[0].path = vec![PathSegment::Key("srv".to_string())];
+        
+        // Update child path
+        vars[1].path = vec![PathSegment::Key("srv".to_string()), PathSegment::Key("port".to_string())];
+        
+        let file = NamedTempFile::new().unwrap();
+        handler.write(file.path(), &vars).unwrap();
+        
+        let content = std::fs::read_to_string(file.path()).unwrap();
+        assert!(content.contains("srv.port=8080"));
+        assert!(!content.contains("server.port=8080"));
+    }
+}

src/main.rs

@@ -1,104 +1,149 @@
 mod app;
 mod cli;
 mod config;
+mod error;
 mod format;
 mod runner;
 mod ui;
+mod resolver;
+mod undo;
 
 use app::App;
 use config::load_config;
+use error::MouldError;
 use format::{detect_format, get_handler};
+use log::{error, info, warn};
 use runner::AppRunner;
-use std::error::Error;
 use std::io;
-use std::path::{Path, PathBuf};
 
 use crossterm::{
     event::{DisableMouseCapture, EnableMouseCapture},
     execute,
-    terminal::{disable_raw_mode, enable_raw_mode, EnterAlternateScreen, LeaveAlternateScreen},
+    terminal::{EnterAlternateScreen, LeaveAlternateScreen, disable_raw_mode, enable_raw_mode},
 };
-use ratatui::{backend::CrosstermBackend, Terminal};
+use ratatui::{Terminal, backend::CrosstermBackend};
 
-fn determine_output_path(input: &Path) -> PathBuf {
+fn main() -> anyhow::Result<()> {
-    let file_name = input.file_name().unwrap_or_default().to_string_lossy();
-    if file_name == ".env.example" {
-        return input.with_file_name(".env");
-    }
-    if file_name == "docker-compose.yml" {
-        return input.with_file_name("docker-compose.override.yml");
-    }
-    if file_name == "docker-compose.yaml" {
-        return input.with_file_name("docker-compose.override.yaml");
-    }
-    if file_name.ends_with(".example.json") {
-        return input.with_file_name(file_name.replace(".example.json", ".json"));
-    }
-    if file_name.ends_with(".template.json") {
-        return input.with_file_name(file_name.replace(".template.json", ".json"));
-    }
-    input.with_extension(format!(
-        "{}.out",
-        input.extension().unwrap_or_default().to_string_lossy()
-    ))
-}
-
-fn main() -> Result<(), Box<dyn Error>> {
     let args = cli::parse();
 
-    let input_path = args.input;
+    // Initialize logger with verbosity from CLI
-    if !input_path.exists() {
+    let log_level = match args.verbose {
-        println!("Input file does not exist: {}", input_path.display());
+        0 => log::LevelFilter::Warn,
-        return Ok(());
+        1 => log::LevelFilter::Info,
+        _ => log::LevelFilter::Debug,
+    };
+    env_logger::Builder::new()
+        .filter_level(log_level)
+        .format_timestamp(None)
+        .init();
+
+    let input_path = match args.input {
+        Some(path) => {
+            if !path.exists() {
+                error!("Input file not found: {}", path.display());
+                return Err(MouldError::FileNotFound(path.display().to_string()).into());
             }
+            path
+        }
+        None => match resolver::find_input_file() {
+            Some(path) => {
+                info!("Discovered template: {}", path.display());
+                path
+            }
+            None => {
+                error!("No template file provided and none discovered in current directory.");
+                println!("Usage: mould <INPUT_FILE>");
+                println!("Supported defaults: .env.example, compose.yml, docker-compose.yml, etc.");
+                return Err(MouldError::FileNotFound("None".to_string()).into());
+            }
+        },
+    };
+
+    info!("Input: {}", input_path.display());
 
     let format_type = detect_format(&input_path, args.format);
     let handler = get_handler(format_type);
 
+    // Smart Comparison Logic
+    let (active_path, template_path) = resolver::resolve_paths(&input_path);
+
     let output_path = args
         .output
-        .unwrap_or_else(|| determine_output_path(&input_path));
+        .unwrap_or_else(|| active_path.clone().unwrap_or_else(|| resolver::determine_output_path(&input_path)));
 
-    let mut vars = handler.parse(&input_path).unwrap_or_else(|err| {
+    info!("Output: {}", output_path.display());
-        println!("Error parsing input file: {}", err);
-        vec![]
-    });
 
+    // 1. Load active config if it exists
+    let mut vars = if let Some(active) = &active_path {
+        handler.parse(active).unwrap_or_default()
+    } else {
+        Vec::new()
+    };
+
+    // 2. Load template config and merge
+    if let Some(template) = &template_path {
+        info!("Comparing with template: {}", template.display());
+        let template_vars = handler.parse(template).unwrap_or_default();
         if vars.is_empty() {
-        println!(
+             vars = template_vars;
-            "No variables found in {} or file could not be parsed.",
+             // If we only have template, everything is missing from active initially
-            input_path.display()
+             for v in vars.iter_mut() {
-        );
+                 v.status = crate::format::ItemStatus::MissingFromActive;
-        return Ok(());
+                 v.value = None;
+             }
+        } else {
+             // Merge template into active
+             handler.merge(template, &mut vars).unwrap_or_default();
+        }
+    } else if vars.is_empty() {
+        // Fallback if no template and active is empty
+         vars = handler.parse(&input_path)?;
     }
 
-    if let Err(e) = handler.merge(&output_path, &mut vars) {
+    if vars.is_empty() {
-        println!("Warning: Could not merge existing output file: {}", e);
+        warn!("No variables found.");
     }
 
     let config = load_config();
     let mut app = App::new(vars);
 
-    enable_raw_mode()?;
+    // Terminal lifecycle
+    enable_raw_mode()
+        .map_err(|e| MouldError::Terminal(format!("Failed to enable raw mode: {}", e)))?;
     let mut stdout = io::stdout();
-    execute!(stdout, EnterAlternateScreen, EnableMouseCapture)?;
+    execute!(stdout, EnterAlternateScreen, EnableMouseCapture)
+        .map_err(|e| MouldError::Terminal(format!("Failed to enter alternate screen: {}", e)))?;
     let backend = CrosstermBackend::new(stdout);
-    let mut terminal = Terminal::new(backend)?;
+    let mut terminal = Terminal::new(backend)
+        .map_err(|e| MouldError::Terminal(format!("Failed to create terminal backend: {}", e)))?;
 
-    let mut runner = AppRunner::new(&mut terminal, &mut app, &config, &output_path, handler.as_ref());
+    let mut runner = AppRunner::new(
+        &mut terminal,
+        &mut app,
+        &config,
+        &output_path,
+        handler.as_ref(),
+    );
     let res = runner.run();
 
-    disable_raw_mode()?;
+    // Restoration
+    disable_raw_mode().ok();
     execute!(
         terminal.backend_mut(),
         LeaveAlternateScreen,
         DisableMouseCapture
-    )?;
+    )
-    terminal.show_cursor()?;
+    .ok();
-
+    terminal.show_cursor().ok();
-    if let Err(err) = res {
-        println!("{:?}", err);
-    }
 
+    match res {
+        Ok(_) => {
+            info!("Successfully finished mould session.");
             Ok(())
+        }
+        Err(e) => {
+            error!("Application error during run: {}", e);
+            Err(e.into())
+        }
+    }
 }

src/resolver.rs

@@ -0,0 +1,294 @@
+//! Automatically resolves relationships between template and active configuration files.
+//!
+//! The resolver allows `mould` to be run without explicit output arguments
+//! by intelligently guessing the counterpart of a given input file based
+//! on common naming conventions.
+
+use std::path::{Path, PathBuf};
+
+pub struct Rule {
+    pub template_suffix: &'static str,
+    pub active_suffix: &'static str,
+    pub is_exact_match: bool,
+}
+
+pub const RULES: &[Rule] = &[
+    // Exact matches
+    Rule {
+        template_suffix: "compose.yml",
+        active_suffix: "compose.override.yml",
+        is_exact_match: true,
+    },
+    Rule {
+        template_suffix: "compose.yaml",
+        active_suffix: "compose.override.yaml",
+        is_exact_match: true,
+    },
+    Rule {
+        template_suffix: "docker-compose.yml",
+        active_suffix: "docker-compose.override.yml",
+        is_exact_match: true,
+    },
+    Rule {
+        template_suffix: "docker-compose.yaml",
+        active_suffix: "docker-compose.override.yaml",
+        is_exact_match: true,
+    },
+    // Pattern matches
+    Rule {
+        template_suffix: ".env.example",
+        active_suffix: ".env",
+        is_exact_match: false,
+    },
+    Rule {
+        template_suffix: ".env.template",
+        active_suffix: ".env",
+        is_exact_match: false,
+    },
+    Rule {
+        template_suffix: ".example.json",
+        active_suffix: ".json",
+        is_exact_match: false,
+    },
+    Rule {
+        template_suffix: ".template.json",
+        active_suffix: ".json",
+        is_exact_match: false,
+    },
+    Rule {
+        template_suffix: ".example.yml",
+        active_suffix: ".yml",
+        is_exact_match: false,
+    },
+    Rule {
+        template_suffix: ".template.yml",
+        active_suffix: ".yml",
+        is_exact_match: false,
+    },
+    Rule {
+        template_suffix: ".example.yaml",
+        active_suffix: ".yaml",
+        is_exact_match: false,
+    },
+    Rule {
+        template_suffix: ".template.yaml",
+        active_suffix: ".yaml",
+        is_exact_match: false,
+    },
+    Rule {
+        template_suffix: ".example.toml",
+        active_suffix: ".toml",
+        is_exact_match: false,
+    },
+    Rule {
+        template_suffix: ".template.toml",
+        active_suffix: ".toml",
+        is_exact_match: false,
+    },
+    Rule {
+        template_suffix: ".example.xml",
+        active_suffix: ".xml",
+        is_exact_match: false,
+    },
+    Rule {
+        template_suffix: ".template.xml",
+        active_suffix: ".xml",
+        is_exact_match: false,
+    },
+    Rule {
+        template_suffix: ".example.ini",
+        active_suffix: ".ini",
+        is_exact_match: false,
+    },
+    Rule {
+        template_suffix: ".template.ini",
+        active_suffix: ".ini",
+        is_exact_match: false,
+    },
+    Rule {
+        template_suffix: ".example.properties",
+        active_suffix: ".properties",
+        is_exact_match: false,
+    },
+    Rule {
+        template_suffix: ".template.properties",
+        active_suffix: ".properties",
+        is_exact_match: false,
+    },
+];
+
+pub const DEFAULT_CANDIDATES: &[&str] = &[
+    ".env.example",
+    "compose.yml",
+    "docker-compose.yml",
+    ".env.template",
+    "compose.yaml",
+    "docker-compose.yaml",
+];
+
+/// Helper to automatically determine the output file path based on common naming conventions.
+pub fn determine_output_path(input: &Path) -> PathBuf {
+    let file_name = input.file_name().unwrap_or_default().to_string_lossy();
+
+    for rule in RULES {
+        if rule.is_exact_match {
+            if file_name == rule.template_suffix {
+                return input.with_file_name(rule.active_suffix);
+            }
+        } else if file_name == rule.template_suffix {
+            return input.with_file_name(rule.active_suffix);
+        } else if let Some(base) = file_name.strip_suffix(rule.template_suffix) {
+            return input.with_file_name(format!("{}{}", base, rule.active_suffix));
+        }
+    }
+
+    input.with_extension(format!(
+        "{}.out",
+        input.extension().unwrap_or_default().to_string_lossy()
+    ))
+}
+
+/// Discovers common configuration template files in the current directory.
+pub fn find_input_file() -> Option<PathBuf> {
+    // Priority 1: Exact matches for well-known defaults
+    for &name in DEFAULT_CANDIDATES {
+        let path = PathBuf::from(name);
+        if path.exists() {
+            return Some(path);
+        }
+    }
+
+    // Priority 2: Pattern matches
+    if let Ok(entries) = std::fs::read_dir(".") {
+        let mut fallback = None;
+        for entry in entries.flatten() {
+            let name = entry.file_name();
+            let name_str = name.to_string_lossy();
+
+            for rule in RULES {
+                if !rule.is_exact_match && name_str.ends_with(rule.template_suffix) {
+                    if name_str.contains(".env") || name_str.contains("compose") {
+                        return Some(entry.path());
+                    }
+                    if fallback.is_none() {
+                        fallback = Some(entry.path());
+                    }
+                    break;
+                }
+            }
+        }
+        if let Some(path) = fallback {
+            return Some(path);
+        }
+    }
+
+    None
+}
+
+/// Resolves the active and template paths given an input path.
+/// Returns `(active_path, template_path)`.
+pub fn resolve_paths(input: &Path) -> (Option<PathBuf>, Option<PathBuf>) {
+    let file_name = input.file_name().unwrap_or_default().to_string_lossy();
+
+    // Check if the input matches any known template pattern
+    let mut is_template = false;
+    for rule in RULES {
+        if rule.is_exact_match {
+            if file_name == rule.template_suffix {
+                is_template = true;
+                break;
+            }
+        } else if file_name.ends_with(rule.template_suffix) {
+            is_template = true;
+            break;
+        }
+    }
+
+    // Fallback template detection
+    if !is_template && (file_name.contains(".example") || file_name.contains(".template")) {
+        is_template = true;
+    }
+
+    if is_template {
+        let expected_active = determine_output_path(input);
+        let active = if expected_active.exists() {
+            Some(expected_active)
+        } else {
+            None
+        };
+        (active, Some(input.to_path_buf()))
+    } else {
+        // Input is treated as the active config
+        let active = Some(input.to_path_buf());
+        let mut template = None;
+
+        // Try to reverse match rules to find a template
+        for rule in RULES {
+            if rule.is_exact_match {
+                if file_name == rule.active_suffix {
+                    let t = input.with_file_name(rule.template_suffix);
+                    if t.exists() {
+                        template = Some(t);
+                        break;
+                    }
+                }
+            } else if file_name.ends_with(rule.active_suffix) {
+                if file_name == rule.active_suffix {
+                    let t = input.with_file_name(rule.template_suffix);
+                    if t.exists() {
+                        template = Some(t);
+                        break;
+                    }
+                } else if let Some(base) = file_name.strip_suffix(rule.active_suffix) {
+                    let t = input.with_file_name(format!("{}{}", base, rule.template_suffix));
+                    if t.exists() {
+                        template = Some(t);
+                        break;
+                    }
+                }
+            }
+        }
+
+        // Fallback reverse detection
+        if template.is_none() {
+            let possible_templates = [
+                format!("{}.example", file_name),
+                format!("{}.template", file_name),
+            ];
+            for t in possible_templates {
+                let p = input.with_file_name(t);
+                if p.exists() {
+                    template = Some(p);
+                    break;
+                }
+            }
+        }
+
+        (active, template)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_determine_output_path() {
+        assert_eq!(
+            determine_output_path(Path::new(".env.example")),
+            PathBuf::from(".env")
+        );
+        assert_eq!(
+            determine_output_path(Path::new("compose.yml")),
+            PathBuf::from("compose.override.yml")
+        );
+        assert_eq!(
+            determine_output_path(Path::new("config.template.json")),
+            PathBuf::from("config.json")
+        );
+        assert_eq!(
+            determine_output_path(Path::new("config.example")),
+            PathBuf::from("config.example.out")
+        );
+    }
+}

src/runner.rs

@@ -1,26 +1,41 @@
-use crate::app::{App, Mode};
+//! Orchestrates the main application execution, terminal events, and TUI rendering.
+//!
+//! The `AppRunner` is responsible for the event loop, intercepting raw 
+//! keyboard input, and translating it into high-level application actions.
+
+use crate::app::{App, InsertVariant, Mode};
 use crate::config::Config;
 use crate::format::FormatHandler;
 use crossterm::event::{self, Event, KeyCode, KeyEvent};
-use ratatui::backend::Backend;
 use ratatui::Terminal;
+use ratatui::backend::Backend;
 use std::io;
 use std::path::Path;
 use tui_input::backend::crossterm::EventHandler;
 
+/// Manages the main application execution loop, event handling, and terminal interaction.
 pub struct AppRunner<'a, B: Backend> {
+    /// Reference to the terminal instance.
     terminal: &'a mut Terminal<B>,
+    /// Mutable reference to the application state.
     app: &'a mut App,
+    /// Loaded user configuration (keybinds, theme).
     config: &'a Config,
+    /// Path where the final configuration will be saved.
     output_path: &'a Path,
+    /// Handler for the specific file format (env, json, yaml, toml).
     handler: &'a dyn FormatHandler,
+    /// Buffer for storing active command entry (e.g., ":w").
     command_buffer: String,
+    /// Buffer for storing multi-key sequence of presses (e.g., "gg").
+    key_sequence: String,
 }
 
 impl<'a, B: Backend> AppRunner<'a, B>
 where
     io::Error: From<B::Error>,
 {
+    /// Creates a new runner instance with all required dependencies.
     pub fn new(
         terminal: &'a mut Terminal<B>,
         app: &'a mut App,
@@ -35,12 +50,18 @@ where
             output_path,
             handler,
             command_buffer: String::new(),
+            key_sequence: String::new(),
         }
     }
 
+    /// Starts the main application loop.
+    /// 
+    /// This loop continues until `self.app.running` is set to false. 
+    /// Each iteration draws the UI and waits for a keyboard event.
     pub fn run(&mut self) -> io::Result<()> {
         while self.app.running {
-            self.terminal.draw(|f| crate::ui::draw(f, self.app, self.config))?;
+            self.terminal
+                .draw(|f| crate::ui::draw(f, self.app, self.config))?;
 
             if let Event::Key(key) = event::read()? {
                 self.handle_key_event(key)?;
@@ -49,13 +70,20 @@ where
         Ok(())
     }
 
+    /// Primary dispatcher for all keyboard events.
+    ///
+    /// It delegates handling to specialized methods based on the 
+    /// current application mode.
     fn handle_key_event(&mut self, key: KeyEvent) -> io::Result<()> {
         match self.app.mode {
             Mode::Normal => self.handle_normal_mode(key),
             Mode::Insert => self.handle_insert_mode(key),
+            Mode::InsertKey => self.handle_insert_key_mode(key),
+            Mode::Search => self.handle_search_mode(key),
         }
     }
 
+    /// Handles keys in Normal mode, separating navigation from command entry.
     fn handle_normal_mode(&mut self, key: KeyEvent) -> io::Result<()> {
         if !self.command_buffer.is_empty() {
             self.handle_command_mode(key)
@@ -64,6 +92,7 @@ where
         }
     }
 
+    /// Logic for entering and executing ":" style commands.
     fn handle_command_mode(&mut self, key: KeyEvent) -> io::Result<()> {
         match key.code {
             KeyCode::Enter => {
@@ -90,35 +119,181 @@ where
         }
     }
 
+    /// Handles primary navigation and transitions to insert or command modes.
+    ///
+    /// This method manages multi-key sequences (like `gg`) and immediate 
+    /// actions (like `i`). It correctly re-evaluates sequences to prevent 
+    /// "one-key-behind" responsiveness bugs.
     fn handle_navigation_mode(&mut self, key: KeyEvent) -> io::Result<()> {
-        if let KeyCode::Char(c) = key.code {
+        let key_str = if let KeyCode::Char(c) = key.code {
-            let c_str = c.to_string();
+            let mut s = String::new();
-            if c_str == self.config.keybinds.down {
+            if key.modifiers.contains(event::KeyModifiers::ALT) {
-                self.app.next();
+                s.push_str("alt+");
-            } else if c_str == self.config.keybinds.up {
+            }
-                self.app.previous();
+            s.push(c);
-            } else if c_str == self.config.keybinds.edit {
+            s
-                self.app.enter_insert();
+        } else {
-            } else if c_str == ":" {
+            String::new()
+        };
+
+        if !key_str.is_empty() {
+            self.key_sequence.push_str(&key_str);
+
+            let mut match_result = self.find_binding();
+            if match_result.is_none() {
+                if self.is_prefix_binding() {
+                    // It's a prefix for a multi-key bind (like first 'g' in 'gg'), wait for more.
+                    return Ok(());
+                } else {
+                    // Not a match and not a prefix, restart the buffer with the current key.
+                    self.key_sequence.clear();
+                    self.key_sequence.push_str(&key_str);
+                    match_result = self.find_binding();
+                }
+            }
+
+            if let Some(action) = match_result {
+                self.key_sequence.clear();
+                match action {
+                    "down" => self.app.next(),
+                    "up" => self.app.previous(),
+                    "edit" => self.app.enter_insert(InsertVariant::Start),
+                    "edit_append" => self.app.enter_insert(InsertVariant::End),
+                    "edit_substitute" => self.app.enter_insert(InsertVariant::Substitute),
+                    "search" => {
+                        self.app.mode = Mode::Search;
+                        self.app.search_query.clear();
+                        self.app.status_message = Some(format!("{} ", self.config.keybinds.search));
+                    }
+                    "next_match" => self.app.jump_next_match(),
+                    "previous_match" => self.app.jump_previous_match(),
+                    "jump_top" => self.app.jump_top(),
+                    "jump_bottom" => self.app.jump_bottom(),
+                    "append_item" => self.app.add_item(true, false, false),
+                    "prepend_item" => self.app.add_item(false, false, false),
+                    "delete_item" => self.app.delete_selected(),
+                    "undo" => self.app.undo(),
+                    "redo" => self.app.redo(),
+                    "rename" => self.app.enter_insert_key(),
+                    "append_group" => self.app.add_item(true, true, true),
+                    "prepend_group" => self.app.add_item(false, true, true),
+                    "toggle_group" => {
+                        self.app.toggle_group_selected();
+                        self.app.save_undo_state();
+                    }
+                    "add_missing" => {
+                        self.add_missing_item();
+                    }
+                    "command" => {
                         self.command_buffer.push(':');
                         self.sync_command_status();
-            } else if c_str == "q" {
+                    }
-                self.app.running = false;
+                    "quit" => self.app.running = false,
+                    _ => {}
+                }
             }
         } else {
+            // Reset the sequence buffer if a non-character key (like Arrow Keys) is pressed.
+            self.key_sequence.clear();
             match key.code {
                 KeyCode::Down => self.app.next(),
                 KeyCode::Up => self.app.previous(),
                 KeyCode::Enter => self.save_file()?,
+                KeyCode::Esc => self.app.status_message = None,
                 _ => {}
             }
         }
         Ok(())
     }
 
+    /// Looks up the current `key_sequence` in the configured keybindings.
+    fn find_binding(&self) -> Option<&'static str> {
+        let binds = [
+            (&self.config.keybinds.down, "down"),
+            (&self.config.keybinds.up, "up"),
+            (&self.config.keybinds.edit, "edit"),
+            (&self.config.keybinds.edit_append, "edit_append"),
+            (&self.config.keybinds.edit_substitute, "edit_substitute"),
+            (&"S".to_string(), "edit_substitute"), // Semantic alias for Vim compatibility.
+            (&self.config.keybinds.search, "search"),
+            (&self.config.keybinds.next_match, "next_match"),
+            (&self.config.keybinds.previous_match, "previous_match"),
+            (&self.config.keybinds.jump_top, "jump_top"),
+            (&self.config.keybinds.jump_bottom, "jump_bottom"),
+            (&self.config.keybinds.append_item, "append_item"),
+            (&self.config.keybinds.prepend_item, "prepend_item"),
+            (&self.config.keybinds.delete_item, "delete_item"),
+            (&self.config.keybinds.undo, "undo"),
+            (&self.config.keybinds.redo, "redo"),
+            (&self.config.keybinds.rename, "rename"),
+            (&self.config.keybinds.append_group, "append_group"),
+            (&self.config.keybinds.prepend_group, "prepend_group"),
+            (&self.config.keybinds.toggle_group, "toggle_group"),
+            (&"a".to_string(), "add_missing"),
+            (&":".to_string(), "command"),
+            (&"q".to_string(), "quit"),
+        ];
+
+        for (bind, action) in binds.iter() {
+            if bind == &&self.key_sequence {
+                return Some(*action);
+            }
+        }
+        None
+    }
+
+    /// Returns true if the current `key_sequence` is a partial prefix of any configured bind.
+    fn is_prefix_binding(&self) -> bool {
+        let binds = [
+            &self.config.keybinds.down,
+            &self.config.keybinds.up,
+            &self.config.keybinds.edit,
+            &self.config.keybinds.edit_append,
+            &self.config.keybinds.edit_substitute,
+            &self.config.keybinds.search,
+            &self.config.keybinds.next_match,
+            &self.config.keybinds.previous_match,
+            &self.config.keybinds.jump_top,
+            &self.config.keybinds.jump_bottom,
+            &self.config.keybinds.append_item,
+            &self.config.keybinds.prepend_item,
+            &self.config.keybinds.delete_item,
+            &self.config.keybinds.undo,
+            &self.config.keybinds.redo,
+            &self.config.keybinds.rename,
+            &self.config.keybinds.append_group,
+            &self.config.keybinds.prepend_group,
+            &self.config.keybinds.toggle_group,
+        ];
+
+        for bind in binds.iter() {
+            if bind.starts_with(&self.key_sequence) && bind.as_str() != self.key_sequence {
+                return true;
+            }
+        }
+        false
+    }
+
+    /// Adds a missing item from the template to the active configuration.
+    fn add_missing_item(&mut self) {
+        if let Some(var) = self.app.vars.get_mut(self.app.selected)
+            && var.status == crate::format::ItemStatus::MissingFromActive {
+                var.status = crate::format::ItemStatus::Present;
+                if !var.is_group {
+                    var.value = var.template_value.clone();
+                }
+                self.app.sync_input_with_selected();
+                self.app.save_undo_state();
+            }
+    }
+
+    /// Delegates key events to the `tui_input` handler during active value editing.
     fn handle_insert_mode(&mut self, key: KeyEvent) -> io::Result<()> {
         match key.code {
-            KeyCode::Esc | KeyCode::Enter => {
+            KeyCode::Esc => {
+                self.app.cancel_insert();
+            }
+            KeyCode::Enter => {
                 self.app.enter_normal();
             }
             _ => {
@@ -128,6 +303,45 @@ where
         Ok(())
     }
 
+    /// Delegates key events to the `tui_input` handler during active key renaming.
+    fn handle_insert_key_mode(&mut self, key: KeyEvent) -> io::Result<()> {
+        match key.code {
+            KeyCode::Esc => {
+                self.app.cancel_insert();
+            }
+            KeyCode::Enter => {
+                self.app.enter_normal();
+            }
+            _ => {
+                self.app.input.handle_event(&Event::Key(key));
+            }
+        }
+        Ok(())
+    }
+
+    /// Handles search mode key events and live-updates search filtering.
+    fn handle_search_mode(&mut self, key: KeyEvent) -> io::Result<()> {
+        match key.code {
+            KeyCode::Enter | KeyCode::Esc => {
+                self.app.mode = Mode::Normal;
+                self.app.status_message = None;
+            }
+            KeyCode::Backspace => {
+                self.app.search_query.pop();
+                self.app.status_message = Some(format!("{}{}", self.config.keybinds.search, self.app.search_query));
+                self.app.jump_next_match();
+            }
+            KeyCode::Char(c) => {
+                self.app.search_query.push(c);
+                self.app.status_message = Some(format!("{}{}", self.config.keybinds.search, self.app.search_query));
+                self.app.jump_next_match();
+            }
+            _ => {}
+        }
+        Ok(())
+    }
+
+    /// Logic to map command strings (like ":w") to internal application actions.
     fn execute_command(&mut self, cmd: &str) -> io::Result<()> {
         if cmd == self.config.keybinds.save {
             self.save_file()
@@ -144,6 +358,7 @@ where
         }
     }
 
+    /// Attempts to write the current app state to the specified output file.
     fn save_file(&mut self) -> io::Result<()> {
         if self.handler.write(self.output_path, &self.app.vars).is_ok() {
             self.app.status_message = Some(format!("Saved to {}", self.output_path.display()));
@@ -153,6 +368,7 @@ where
         Ok(())
     }
 
+    /// Synchronizes the status bar display with the active command buffer.
     fn sync_command_status(&mut self) {
         if self.command_buffer.is_empty() {
             self.app.status_message = None;

src/ui.rs

@@ -1,176 +1,344 @@
+//! Renders the hierarchical Terminal User Interface (TUI).
+//!
+//! This module uses `ratatui` to compose the visual layout of the application, 
+//! providing a navigable tree-view of configuration items.
+
 use crate::app::{App, Mode};
 use crate::config::Config;
 use ratatui::{
+    Frame,
     layout::{Constraint, Direction, Layout},
     style::{Modifier, Style},
     text::{Line, Span},
     widgets::{Block, BorderType, Borders, List, ListItem, ListState, Paragraph},
-    Frame,
 };
 
+/// Renders the main application interface using ratatui.
+///
+/// The interface is composed of:
+/// 1. A hierarchical list of configuration items.
+/// 2. An active input field for editing values/keys.
+/// 3. A status bar showing the current mode and available keybinds.
 pub fn draw(f: &mut Frame, app: &mut App, config: &Config) {
     let theme = &config.theme;
     let size = f.area();
 
-    // Background
+    // Render the main background.
     if !theme.transparent {
-        f.render_widget(Block::default().style(Style::default().bg(theme.crust())), size);
+        f.render_widget(
+            Block::default().style(Style::default().bg(theme.bg_normal())),
+            size,
+        );
     }
 
-    // Main layout with horizontal padding
+    // Define outer margins.
     let outer_layout = Layout::default()
         .direction(Direction::Horizontal)
         .constraints([
-            Constraint::Length(1), // Left padding
+            Constraint::Length(1),
-            Constraint::Min(0),    // Content
+            Constraint::Min(0),
-            Constraint::Length(1), // Right padding
+            Constraint::Length(1),
         ])
         .split(size);
 
+    // Split the center area vertically.
     let chunks = Layout::default()
         .direction(Direction::Vertical)
         .constraints([
-            Constraint::Length(1), // Top padding
+            Constraint::Length(1), // Top margin
-            Constraint::Min(3),    // List
+            Constraint::Min(3),    // Main tree list
-            Constraint::Length(3), // Input area
+            Constraint::Length(3), // Focused input area
-            Constraint::Length(1), // Bottom padding
+            Constraint::Length(1), // Spacer
             Constraint::Length(1), // Status bar
         ])
         .split(outer_layout[1]);
 
-    let max_key_len = app
+    // Construct the interactive hierarchical list.
-        .vars
+    let matching_indices = app.matching_indices();
-        .iter()
-        .map(|v| v.key.len())
-        .max()
-        .unwrap_or(20)
-        .min(40);
-
-    // List
     let items: Vec<ListItem> = app
         .vars
         .iter()
         .enumerate()
         .map(|(i, var)| {
             let is_selected = i == app.selected;
+            let is_match = matching_indices.contains(&i);
 
-            let val = if is_selected && matches!(app.mode, Mode::Insert) {
+            // Indentation and tree-branch markers.
-                app.input.value()
+            let indent = "  ".repeat(var.depth);
+            let prefix = if var.is_group { "+ " } else { "  " };
+
+            // Determine depth-based coloring for the key name.
+            let depth_color = if is_selected {
+                theme.bg_normal()
             } else {
-                &var.value
+                match var.depth % 4 {
+                    0 => theme.tree_depth_1(),
+                    1 => theme.tree_depth_2(),
+                    2 => theme.tree_depth_3(),
+                    3 => theme.tree_depth_4(),
+                    _ => theme.fg_normal(),
+                }
+            };
+
+            let text_color = if is_selected {
+                theme.fg_highlight()
+            } else {
+                match var.status {
+                    crate::format::ItemStatus::MissingFromActive if !var.is_group => theme.fg_dimmed(),
+                    crate::format::ItemStatus::Modified => theme.fg_modified(),
+                    _ => theme.fg_normal(),
+                }
             };
 
             let key_style = if is_selected {
-                Style::default().fg(theme.crust()).add_modifier(Modifier::BOLD)
+                Style::default()
+                    .fg(theme.fg_highlight())
+                    .add_modifier(Modifier::BOLD)
+            } else if is_match {
+                Style::default()
+                    .fg(theme.bg_search())
+                    .add_modifier(Modifier::UNDERLINED)
+            } else if var.status == crate::format::ItemStatus::MissingFromActive && !var.is_group {
+                Style::default()
+                    .fg(theme.fg_dimmed())
+                    .add_modifier(Modifier::DIM)
             } else {
-                Style::default().fg(theme.lavender())
+                Style::default().fg(depth_color)
+            };
+
+            let mut key_spans = vec![
+                Span::raw(indent),
+                Span::styled(prefix, Style::default().fg(theme.border_normal())),
+                Span::styled(&var.key, key_style),
+            ];
+
+            // Add semantic status labels (missing, modified).
+            match var.status {
+                crate::format::ItemStatus::MissingFromActive if !var.is_group => {
+                    let missing_style = if is_selected {
+                        Style::default().fg(theme.fg_highlight()).add_modifier(Modifier::BOLD)
+                    } else {
+                        Style::default().fg(theme.fg_warning()).add_modifier(Modifier::BOLD)
+                    };
+                    key_spans.push(Span::styled(" (missing)", missing_style));
+                }
+                crate::format::ItemStatus::MissingFromActive if var.is_group => {
+                    let missing_style = if is_selected {
+                        Style::default().fg(theme.fg_highlight()).add_modifier(Modifier::BOLD)
+                    } else {
+                        Style::default().fg(theme.fg_warning()).add_modifier(Modifier::BOLD)
+                    };
+                    key_spans.push(Span::styled(" (missing group)", missing_style));
+                }
+                crate::format::ItemStatus::Modified => {
+                    if !is_selected {
+                        key_spans.push(Span::styled(" (*)", Style::default().fg(theme.fg_modified())));
+                    }
+                }
+                _ => {}
+            }
+
+            let item_style = if is_selected {
+                Style::default().bg(theme.bg_highlight())
+            } else {
+                Style::default().fg(text_color)
+            };
+
+            if var.is_group {
+                ListItem::new(Line::from(key_spans)).style(item_style)
+            } else {
+                // Determine which value to display (live input vs. stored value).
+                let val = if is_selected && matches!(app.mode, Mode::Insert) {
+                    app.input.value()
+                } else {
+                    var.value.as_deref().unwrap_or("")
                 };
 
                 let value_style = if is_selected {
-                Style::default().fg(theme.crust())
+                    Style::default().fg(theme.fg_highlight())
                 } else {
-                Style::default().fg(theme.text())
+                    Style::default().fg(theme.fg_normal())
                 };
 
-            let line = Line::from(vec![
+                let mut val_spans = vec![
-                Span::styled(format!(" {:<width$} ", var.key, width = max_key_len), key_style),
+                    Span::raw(format!("{}    └─ ", "  ".repeat(var.depth))),
-                Span::styled("│ ", Style::default().fg(theme.surface1())),
+                    Span::styled(val, value_style),
-                Span::styled(format!(" {} ", val), value_style),
+                ];
-            ]);
 
-            let item_style = if is_selected {
+                // Show default value if it differs from current.
-                Style::default().bg(theme.blue())
+                if let Some(t_val) = &var.template_value
+                    && Some(t_val) != var.value.as_ref() {
+                        let t_style = if is_selected {
+                            Style::default().fg(theme.bg_normal()).add_modifier(Modifier::DIM)
                         } else {
-                Style::default().fg(theme.text())
+                            Style::default().fg(theme.fg_dimmed()).add_modifier(Modifier::ITALIC)
                         };
+                        val_spans.push(Span::styled(format!(" [Def: {}]", t_val), t_style));
+                    }
 
-            ListItem::new(line).style(item_style)
+                ListItem::new(vec![Line::from(key_spans), Line::from(val_spans)]).style(item_style)
+            }
         })
         .collect();
 
-    let list = List::new(items)
+    let list = List::new(items).block(
-        .block(
         Block::default()
             .borders(Borders::ALL)
             .border_type(BorderType::Rounded)
             .title(" Config Variables ")
-                .title_style(Style::default().fg(theme.mauve()).add_modifier(Modifier::BOLD))
+            .title_style(
-                .border_style(Style::default().fg(theme.surface1())),
+                Style::default()
+                    .fg(theme.fg_accent())
+                    .add_modifier(Modifier::BOLD),
+            )
+            .border_style(Style::default().fg(theme.border_normal())),
     );
 
     let mut state = ListState::default();
     state.select(Some(app.selected));
     f.render_stateful_widget(list, chunks[1], &mut state);
 
-    // Input Area
+    // Compose the focused input area details.
     let current_var = app.vars.get(app.selected);
-    let input_title = if let Some(var) = current_var {
+    let mut input_title = " Input ".to_string();
-        if var.default_value.is_empty() {
+    let mut extra_info = String::new();
-            format!(" Editing: {} ", var.key)
+
+    if let Some(var) = current_var {
+        if matches!(app.mode, Mode::InsertKey) {
+            input_title = format!(" Rename Key: {} ", var.path_string());
+        } else if var.is_group {
+            input_title = format!(" Group: {} ", var.path_string());
         } else {
-            format!(" Editing: {} (Default: {}) ", var.key, var.default_value)
+            input_title = format!(" Editing: {} ", var.path_string());
+            if let Some(t_val) = &var.template_value {
+                extra_info = format!("  [Template: {}]", t_val);
+            }
+        }
     }
-    } else {
-        " Input ".to_string()
-    };
 
     let input_border_color = match app.mode {
-        Mode::Insert => theme.green(),
+        Mode::Insert | Mode::InsertKey => theme.border_active(),
-        Mode::Normal => theme.surface1(),
+        _ => theme.border_normal(),
     };
 
     let input_text = app.input.value();
     let cursor_pos = app.input.visual_cursor();
 
-    let input = Paragraph::new(input_text)
+    let display_text = if let Some(var) = current_var {
-        .style(Style::default().fg(theme.text()))
+        if matches!(app.mode, Mode::InsertKey) {
+            input_text.to_string()
+        } else if var.is_group {
+            "<group>".to_string()
+        } else if matches!(app.mode, Mode::Normal) {
+            format!("{}{}", input_text, extra_info)
+        } else {
+            input_text.to_string()
+        }
+    } else {
+        input_text.to_string()
+    };
+
+    let input = Paragraph::new(display_text)
+        .style(Style::default().fg(theme.fg_normal()))
         .block(
             Block::default()
                 .borders(Borders::ALL)
                 .border_type(BorderType::Rounded)
                 .title(input_title)
-                .title_style(Style::default().fg(theme.peach()).add_modifier(Modifier::BOLD))
+                .title_style(
+                    Style::default()
+                        .fg(theme.fg_accent())
+                        .add_modifier(Modifier::BOLD),
+                )
                 .border_style(Style::default().fg(input_border_color)),
         );
     f.render_widget(input, chunks[2]);
 
-    if let Mode::Insert = app.mode {
+    // Position terminal cursor during active input.
+    if matches!(app.mode, Mode::Insert) || matches!(app.mode, Mode::InsertKey) {
         f.set_cursor_position(ratatui::layout::Position::new(
             chunks[2].x + 1 + cursor_pos as u16,
             chunks[2].y + 1,
         ));
     }
 
-    // Status bar
+    // Render the status bar with mode-specific help hints.
     let (mode_str, mode_style) = match app.mode {
         Mode::Normal => (
             " NORMAL ",
             Style::default()
-                .bg(theme.blue())
+                .bg(theme.bg_highlight())
-                .fg(theme.crust())
+                .fg(theme.bg_normal())
                 .add_modifier(Modifier::BOLD),
         ),
         Mode::Insert => (
             " INSERT ",
             Style::default()
-                .bg(theme.green())
+                .bg(theme.bg_active())
-                .fg(theme.crust())
+                .fg(theme.bg_normal())
+                .add_modifier(Modifier::BOLD),
+        ),
+        Mode::InsertKey => (
+            " RENAME ",
+            Style::default()
+                .bg(theme.bg_active())
+                .fg(theme.bg_normal())
+                .add_modifier(Modifier::BOLD),
+        ),
+        Mode::Search => (
+            " SEARCH ",
+            Style::default()
+                .bg(theme.bg_search())
+                .fg(theme.bg_normal())
                 .add_modifier(Modifier::BOLD),
         ),
     };
 
-    let status_msg = app.status_message.as_deref().unwrap_or_else(|| {
+    let status_msg = if let Some(msg) = &app.status_message {
+        msg.clone()
+    } else {
+        let kb = &config.keybinds;
         match app.mode {
-            Mode::Normal => " navigation | i: edit | :w: save | :q: quit ",
+            Mode::Normal => {
-            Mode::Insert => " Esc: back to normal | Enter: commit ",
+                let mut parts = vec![
+                    format!("{}/{} move", kb.down, kb.up),
+                    format!("{}/{} jump", kb.jump_top, kb.jump_bottom),
+                    format!("{} search", kb.search),
+                ];
+                if !app.selected_is_group() {
+                    parts.push(format!("{}/{}/{} edit", kb.edit, kb.edit_append, kb.edit_substitute));
                 }
-    });
+                parts.push(format!("{} rename", kb.rename));
+                parts.push(format!("{} toggle", kb.toggle_group));
+                if app.selected_is_missing() {
+                    parts.push(format!("{} add", "a"));
+                }
+                if app.selected_is_array() {
+                    parts.push(format!("{}/{} array", kb.append_item, kb.prepend_item));
+                } else {
+                    parts.push(format!("{}/{} add", kb.append_item, kb.prepend_item));
+                    parts.push(format!("{}/{} group", kb.append_group, kb.prepend_group));
+                }
+                parts.push(format!("{} del", kb.delete_item));
+                parts.push(format!("{} undo", kb.undo));
+                parts.push(format!("{} save", kb.save));
+                parts.push(format!("{} quit", kb.quit));
+                parts.join(" · ")
+            }
+            Mode::Insert => "Esc cancel · Enter commit".to_string(),
+            Mode::InsertKey => "Esc cancel · Enter rename".to_string(),
+            Mode::Search => "Esc normal · type to filter".to_string(),
+        }
+    };
 
     let status_line = Line::from(vec![
         Span::styled(mode_str, mode_style),
-        Span::styled(format!(" {} ", status_msg), Style::default().bg(theme.surface0()).fg(theme.text())),
+        Span::styled(
+            format!(" {} ", status_msg),
+            Style::default().bg(theme.border_normal()).fg(theme.fg_normal()),
+        ),
     ]);
 
-    let status = Paragraph::new(status_line).style(Style::default().bg(theme.surface0()));
+    let status = Paragraph::new(status_line).style(Style::default().bg(theme.border_normal()));
     f.render_widget(status, chunks[4]);
 }

src/undo.rs

@@ -0,0 +1,216 @@
+use crate::format::ConfigItem;
+use std::collections::HashMap;
+
+/// Represents a single snapshot of the application state for undo/redo purposes.
+pub struct EditAction {
+    /// The complete list of configuration items at the time of the action.
+    pub state: Vec<ConfigItem>,
+    /// The index of the item that was selected during this action.
+    pub selected: usize,
+}
+
+/// A node in the undo tree, representing a point in the application's history.
+pub struct UndoNode {
+    /// The state data captured at this history point.
+    pub action: EditAction,
+    /// ID of the parent node (previous state). Root node has None.
+    pub parent: Option<usize>,
+    /// IDs of all states that branched off from this one.
+    pub children: Vec<usize>,
+}
+
+/// A non-linear undo/redo system that tracks history as a branching tree.
+///
+/// Unlike a simple stack, an UndoTree allows users to undo several steps, 
+/// make a new change (creating a branch), and still navigate through 
+/// the most recent history path.
+pub struct UndoTree {
+    /// Map of node IDs to their respective history nodes.
+    nodes: HashMap<usize, UndoNode>,
+    /// The ID of the node representing the current application state.
+    current_node: usize,
+    /// Counter for assigning unique IDs to new nodes.
+    next_id: usize,
+    /// Tracks the most recently active branch for each node.
+    /// This allows the 'redo' operation to follow the path the user 
+    /// actually took when multiple branches exist.
+    latest_branch: HashMap<usize, usize>,
+}
+
+impl UndoTree {
+    /// Creates a new undo tree initialized with the starting application state.
+    pub fn new(initial_state: Vec<ConfigItem>, initial_selected: usize) -> Self {
+        let root_id = 0;
+        let root_node = UndoNode {
+            action: EditAction {
+                state: initial_state,
+                selected: initial_selected,
+            },
+            parent: None,
+            children: Vec::new(),
+        };
+
+        let mut nodes = HashMap::new();
+        nodes.insert(root_id, root_node);
+
+        Self {
+            nodes,
+            current_node: root_id,
+            next_id: 1,
+            latest_branch: HashMap::new(),
+        }
+    }
+
+    /// Pushes a new state onto the tree, branching off from the current node.
+    ///
+    /// This creates a new child node for the current position and updates
+    /// the branch tracking to ensure this new path is preferred during redo.
+    pub fn push(&mut self, state: Vec<ConfigItem>, selected: usize) {
+        let new_id = self.next_id;
+        self.next_id += 1;
+
+        let new_node = UndoNode {
+            action: EditAction { state, selected },
+            parent: Some(self.current_node),
+            children: Vec::new(),
+        };
+
+        // Add to nodes
+        self.nodes.insert(new_id, new_node);
+
+        // Update parent's children
+        if let Some(parent_node) = self.nodes.get_mut(&self.current_node) {
+            parent_node.children.push(new_id);
+        }
+
+        // Record this as the latest branch for the parent
+        self.latest_branch.insert(self.current_node, new_id);
+
+        // Move current pointer
+        self.current_node = new_id;
+    }
+
+    /// Moves the current pointer back to the parent node and returns the previous state.
+    /// Returns None if the current node is the root (no more history to undo).
+    pub fn undo(&mut self) -> Option<&EditAction> {
+        if let Some(current) = self.nodes.get(&self.current_node)
+            && let Some(parent_id) = current.parent {
+                self.current_node = parent_id;
+                return self.nodes.get(&parent_id).map(|n| &n.action);
+            }
+        None
+    }
+
+    /// Moves the current pointer forward to the latest child branch and returns the state.
+    ///
+    /// Redo follows the `latest_branch` map to decide which path to take 
+    /// if multiple branches exist. If no branch is recorded, it defaults to the 
+    /// most recently created child.
+    pub fn redo(&mut self) -> Option<&EditAction> {
+        if let Some(next_id) = self.latest_branch.get(&self.current_node).copied() {
+            self.current_node = next_id;
+            return self.nodes.get(&next_id).map(|n| &n.action);
+        } else {
+            // Fallback: if there is no recorded latest branch but there are children
+            let current_id = self.current_node;
+            if let Some(current) = self.nodes.get(&current_id)
+                && let Some(&first_child_id) = current.children.last() {
+                    self.current_node = first_child_id;
+                    self.latest_branch.insert(current_id, first_child_id);
+                    return self.nodes.get(&first_child_id).map(|n| &n.action);
+                }
+        }
+        None
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::format::{ItemStatus, ValueType};
+
+    fn dummy_item(key: &str) -> ConfigItem {
+        ConfigItem {
+            key: key.to_string(),
+            path: vec![],
+            value: Some(key.to_string()),
+            template_value: None,
+            default_value: None,
+            depth: 0,
+            is_group: false,
+            status: ItemStatus::Present,
+            value_type: ValueType::String,
+        }
+    }
+
+    #[test]
+    fn test_undo_redo_tree() {
+        let state1 = vec![dummy_item("A")];
+        let mut tree = UndoTree::new(state1.clone(), 0);
+
+        // Push state 2
+        let state2 = vec![dummy_item("B")];
+        tree.push(state2.clone(), 1);
+
+        // Push state 3
+        let state3 = vec![dummy_item("C")];
+        tree.push(state3.clone(), 2);
+
+        // Undo -> State 2
+        let action = tree.undo().unwrap();
+        assert_eq!(action.state[0].key, "B");
+        assert_eq!(action.selected, 1);
+
+        // Undo -> State 1
+        let action = tree.undo().unwrap();
+        assert_eq!(action.state[0].key, "A");
+        assert_eq!(action.selected, 0);
+
+        // Undo again -> None (already at root)
+        assert!(tree.undo().is_none());
+
+        // Redo -> State 2
+        let action = tree.redo().unwrap();
+        assert_eq!(action.state[0].key, "B");
+        assert_eq!(action.selected, 1);
+
+        // Redo -> State 3
+        let action = tree.redo().unwrap();
+        assert_eq!(action.state[0].key, "C");
+        assert_eq!(action.selected, 2);
+
+        // Branching: Undo twice to State 1
+        tree.undo();
+        tree.undo();
+        
+        // Push State 4 (from State 1)
+        let state4 = vec![dummy_item("D")];
+        tree.push(state4.clone(), 3);
+
+        // Undo -> State 1
+        let action = tree.undo().unwrap();
+        assert_eq!(action.state[0].key, "A");
+
+        // Redo -> State 4 (follows latest branch D, not old branch B)
+        let action = tree.redo().unwrap();
+        assert_eq!(action.state[0].key, "D");
+    }
+
+    #[test]
+    fn test_redo_fallback_fix() {
+        let state1 = vec![dummy_item("A")];
+        let mut tree = UndoTree::new(state1.clone(), 0);
+
+        let state2 = vec![dummy_item("B")];
+        tree.push(state2.clone(), 1);
+
+        tree.undo();
+        // Redo should move to state 2
+        let action = tree.redo().unwrap();
+        assert_eq!(action.state[0].key, "B");
+
+        // Calling redo again should NOT change the current node or returned action
+        // (since it's already at the latest child)
+        assert!(tree.redo().is_none());
+    }
+}