//! Core traits defining the System Abstraction Layer (SAL).
//!
//! This module provides a set of hardware-agnostic interfaces that the
//! `BenchmarkOrchestrator` uses to interact with the underlying system.
//! These traits allow `ember-tune` to support diverse hardware by abstracting
//! away platform-specific details.

use miette::Diagnostic;
use std::sync::Arc;
use std::path::PathBuf;
use crate::sys::SyscallRunner;
use anyhow::Result;
use thiserror::Error;

/// Context holding OS abstractions (filesystem base and syscall runner).
///
/// This is injected into SAL implementations to allow for a mocked "virtual"
/// environment during testing, preventing `cargo test` from mutating the host system.
#[derive(Clone)]
pub struct EnvironmentCtx {
    pub sysfs_base: PathBuf,
    pub runner: Arc<dyn SyscallRunner>,
}

impl EnvironmentCtx {
    /// Creates a production-ready context pointing to the real filesystem root.
    pub fn production() -> Self {
        Self {
            sysfs_base: PathBuf::from("/"),
            runner: Arc::new(crate::sys::RealSyscallRunner),
        }
    }
}

/// Errors that can occur during the pre-flight system audit.
#[derive(Error, Diagnostic, Debug, Clone)]
pub enum AuditError {
    /// The user does not have root privileges (`uid=0`).
    #[error("Missing root privileges.")]
    #[diagnostic(code(ember_tune::root_required), severity(error))]
    #[help("ember-tune requires direct hardware access (MSRs, sysfs). Please run with 'sudo'.")]
    RootRequired,

    /// A required kernel parameter is missing from the boot command line.
    #[error("Missing kernel parameter: {0}")]
    #[diagnostic(code(ember_tune::missing_kernel_param), severity(error))]
    #[help("Add '{0}' to your GRUB_CMDLINE_LINUX_DEFAULT in /etc/default/grub, then run 'sudo update-grub' and reboot.")]
    MissingKernelParam(String),

    /// The system is running on battery power.
    #[error("System is running on battery: {0}")]
    #[diagnostic(code(ember_tune::ac_power_missing), severity(error))]
    #[help("Thermal benchmarking requires a stable AC power source to ensure consistent PL limits. Please plug in your charger.")]
    AcPowerMissing(String),

    /// The Linux kernel version is known to be incompatible.
    #[error("Incompatible kernel version: {0}")]
    #[diagnostic(code(ember_tune::kernel_incompatible), severity(error))]
    #[help("Your kernel version '{0}' may not support the required RAPL or SMM interfaces. Please upgrade to a recent LTS kernel (6.1+).")]
    KernelIncompatible(String),

    /// A required kernel module or CLI tool is not available.
    #[error("Required tool missing: {0}")]
    #[diagnostic(code(ember_tune::tool_missing), severity(error))]
    #[help("The utility '{0}' is required for this SAL. Please install it using your package manager (e.g., 'sudo apt install {0}').")]
    ToolMissing(String),
}

/// A single, verifiable step in the pre-flight audit process.
pub struct AuditStep {
    /// Human-readable description of the check.
    pub description: String,
    /// The outcome of the check.
    pub outcome: Result<(), AuditError>,
}

/// Evaluates immutable system states before the benchmark begins.
pub trait PreflightAuditor: Send + Sync {
    /// Returns an iterator of [AuditStep] results.
    /// This allows the UI to show a live checklist of system verification steps.
    fn audit(&self) -> Box<dyn Iterator<Item = AuditStep> + '_>;
}

impl<T: PreflightAuditor + ?Sized> PreflightAuditor for Arc<T> {
    fn audit(&self) -> Box<dyn Iterator<Item = AuditStep> + '_> {
        (**self).audit()
    }
}

/// Manages system services that conflict with the benchmark.
///
/// # Invariants
/// The `Drop` trait is *not* used for guaranteed cleanup. The orchestrator must
/// explicitly call `restore()` to ensure hardware state is reset.
pub trait EnvironmentGuard: Send + Sync {
    /// Stops any conflicting system daemons (e.g., `tlp`, `thermald`).
    ///
    /// # Errors
    /// Returns an error if the `systemctl` command fails.
    fn suppress(&self) -> Result<()>;

    /// Restarts any services that were stopped by `suppress`.
    ///
    /// # Errors
    /// Returns an error if the `systemctl` command fails.
    fn restore(&self) -> Result<()>;
}

impl<T: EnvironmentGuard + ?Sized> EnvironmentGuard for Arc<T> {
    fn suppress(&self) -> Result<()> {
        (**self).suppress()
    }
    fn restore(&self) -> Result<()> {
        (**self).restore()
    }
}

/// Provides a read-only interface to system telemetry sensors.
pub trait SensorBus: Send + Sync {
    /// Returns the current package temperature in degrees Celsius.
    ///
    /// # Errors
    /// Returns an error if the underlying `hwmon` or `sysfs` node cannot be read.
    fn get_temp(&self) -> Result<f32>;

    /// Returns the current package power consumption in Watts.
    ///
    /// # Errors
    /// Returns an error if the underlying RAPL or power sensor cannot be read.
    fn get_power_w(&self) -> Result<f32>;

    /// Returns the current speed of all detected fans in RPM.
    ///
    /// # Errors
    /// Returns an error if the fan sensor nodes cannot be read.
    fn get_fan_rpms(&self) -> Result<Vec<u32>>;

    /// Returns the current average CPU frequency in MHz.
    ///
    /// # Errors
    /// Returns an error if `/proc/cpuinfo` or a `cpufreq` sysfs node cannot be read.
    fn get_freq_mhz(&self) -> Result<f32>;
}

impl<T: SensorBus + ?Sized> SensorBus for Arc<T> {
    fn get_temp(&self) -> Result<f32> {
        (**self).get_temp()
    }
    fn get_power_w(&self) -> Result<f32> {
        (**self).get_power_w()
    }
    fn get_fan_rpms(&self) -> Result<Vec<u32>> {
        (**self).get_fan_rpms()
    }
    fn get_freq_mhz(&self) -> Result<f32> {
        (**self).get_freq_mhz()
    }
}

/// Provides a write-only interface for hardware actuators.
pub trait ActuatorBus: Send + Sync {
    /// Sets the fan control mode (e.g., "auto" or "max").
    ///
    /// # Errors
    /// Returns an error if the fan control command or `sysfs` write fails.
    fn set_fan_mode(&self, mode: &str) -> Result<()>;

    /// Sets the sustained power limit (PL1) in Watts.
    ///
    /// # Errors
    /// Returns an error if the RAPL `sysfs` node cannot be written to.
    fn set_sustained_power_limit(&self, watts: f32) -> Result<()>;

    /// Sets the burst power limit (PL2) in Watts.
    ///
    /// # Errors
    /// Returns an error if the RAPL `sysfs` node cannot be written to.
    fn set_burst_power_limit(&self, watts: f32) -> Result<()>;
}

impl<T: ActuatorBus + ?Sized> ActuatorBus for Arc<T> {
    fn set_fan_mode(&self, mode: &str) -> Result<()> {
        (**self).set_fan_mode(mode)
    }
    fn set_sustained_power_limit(&self, watts: f32) -> Result<()> {
        (**self).set_sustained_power_limit(watts)
    }
    fn set_burst_power_limit(&self, watts: f32) -> Result<()> {
        (**self).set_burst_power_limit(watts)
    }
}

/// Represents the high-level safety status of the system.
#[derive(Debug, Clone, PartialEq, Eq)]
pub enum SafetyStatus {
    /// The system is operating within normal parameters.
    Nominal,
    /// A non-critical issue was detected and may have been auto-corrected.
    Warning(String),
    /// A potentially dangerous state was detected, but is not yet an emergency.
    Critical(String),
    /// A critical failure has occurred, requiring an immediate shutdown of the benchmark.
    EmergencyAbort(String),
}

/// A high-frequency monitor for catastrophic hardware states.
pub trait HardwareWatchdog: Send + Sync {
    /// Returns the current [SafetyStatus] of the system.
    ///
    /// # Errors
    /// This method can return an error if a sensor required for a safety check
    /// (e.g., the thermal sensor) fails to read. The orchestrator must treat
    /// this as an `EmergencyAbort` condition.
    fn get_safety_status(&self) -> Result<SafetyStatus>;
}

impl<T: HardwareWatchdog + ?Sized> HardwareWatchdog for Arc<T> {
    fn get_safety_status(&self) -> Result<SafetyStatus> {
        (**self).get_safety_status()
    }
}

/// Aggregate trait for a complete platform implementation.
///
/// This "super-trait" combines all SAL interfaces into a single object-safe
/// trait, simplifying dependency injection into the `BenchmarkOrchestrator`.
pub trait PlatformSal: PreflightAuditor + SensorBus + ActuatorBus + EnvironmentGuard + HardwareWatchdog {}

impl<T: PreflightAuditor + SensorBus + ActuatorBus + EnvironmentGuard + HardwareWatchdog + ?Sized> PlatformSal for T {}