import SwiftUI
import WebKit

/// The Proton account, at the top of the shares page: why one would sign in,
/// or who is signed in and how watch-history sync is doing.
struct AccountCard: View {
    let onSignIn: () -> Void
    let onBrowse: () -> Void
    @Environment(AppModel.self) private var model
    @Environment(\.scheme) private var scheme

    var body: some View {
        if let state = model.account.state {
            Group {
                if case let .signedIn(username) = state {
                    VStack(alignment: .leading, spacing: 0) {
                        HStack(spacing: 16) {
                            Image(systemName: "person.crop.circle.fill").font(.system(size: 22)).foregroundStyle(scheme.primary)
                            VStack(alignment: .leading, spacing: 2) {
                                Text(username).textStyle(.bodyLarge, semibold: true).foregroundStyle(scheme.onSurface)
                                TimelineView(.periodic(from: .now, by: 30)) { context in
                                    Text(syncLine(model.account, now: context.date))
                                        .textStyle(.bodyMedium).foregroundStyle(scheme.onSurfaceVariant)
                                }
                            }
                            Spacer(minLength: 0)
                            Menu {
                                Button(action: model.syncNow) { Label("Sync now", systemImage: "arrow.triangle.2.circlepath") }
                                Button(action: model.signOut) { Label("Sign out", systemImage: "rectangle.portrait.and.arrow.right") }
                            } label: {
                                Image(systemName: "ellipsis").font(.system(size: 20)).frame(width: 48, height: 48)
                                    .foregroundStyle(scheme.onSurfaceVariant)
                            }
                            .accessibilityLabel("Account actions")
                        }
                        .padding(.leading, 16)
                        .padding(.trailing, 4)
                        .padding(.vertical, 8)
                        Button(action: onBrowse) { Label("Add from your Drive", systemImage: "folder") }
                            .buttonStyle(.tonal)
                            .padding(.horizontal, 16)
                            .padding(.bottom, 12)
                    }
                } else {
                    VStack(alignment: .leading, spacing: 8) {
                        Text("Proton account").textStyle(.titleMedium).foregroundStyle(scheme.onSurface)
                        Text("Optional. Signed in, watch history is kept in your own Drive so every device resumes where another left off, and folders of your Drive can join the library.")
                            .textStyle(.bodyMedium).foregroundStyle(scheme.onSurfaceVariant)
                        Button("Sign in", action: onSignIn).buttonStyle(.tonal)
                    }
                    .padding(16)
                    .frame(maxWidth: .infinity, alignment: .leading)
                }
            }
            .card()
            .padding(.horizontal, 16)
            .padding(.vertical, 8)
        }
    }
}

/// "Synced 3 min ago · 2 from other devices", or why it did not.
func syncLine(_ account: AccountUiState, now: Date) -> String {
    if let error = account.syncError { return "Watch history did not sync: \(error)" }
    guard let at = account.syncedAt else { return "Watch history syncs with your Drive" }
    let minutes = Int(max(now.timeIntervalSince(at), 0) / 60)
    let ago = minutes < 1 ? "just now" : minutes < 60 ? "\(minutes) min ago" : "\(minutes / 60) h ago"
    let applied = account.applied > 0 ? " · \(account.applied) from other devices" : ""
    return "Synced \(ago)\(applied)"
}

/// Security keys need WebAuthn, which the sign-in here does not speak. An
/// account with nothing else is refused before this form (`AccountStore::sign_in`).
private let securityKeyNote = "Security keys are not supported here — use the code from your authenticator app."

/// Signing in, one step at a time: address and password, then a second-factor
/// code or the mailbox password if the account has them, with Proton's CAPTCHA
/// over the top when it asks for one.
struct SignInSheet: View {
    let onDismiss: () -> Void
    @Environment(AppModel.self) private var model
    @Environment(\.scheme) private var scheme
    @State private var username = ""
    @State private var password = ""
    @State private var code = ""
    @State private var mailbox = ""

    var body: some View {
        let account = model.account
        DialogSheet("Sign in to Proton") {
            switch account.state {
            case .secondFactor:
                Field(label: "Code from your authenticator app", text: $code, keyboard: .numberPad, content: .oneTimeCode)
                Text(securityKeyNote).textStyle(.bodySmall)
            case .mailboxPassword:
                Text("This account has a separate mailbox password. It unlocks your files.").textStyle(.bodySmall)
                Field(label: "Mailbox password", text: $mailbox, secret: true, content: .password)
            default:
                Field(label: "Address", text: $username, keyboard: .emailAddress, content: .username)
                Field(label: "Password", text: $password, secret: true, content: .password)
            }
            if let error = account.error {
                Text(error).foregroundStyle(scheme.error)
            }
            if account.busy {
                ProgressView().tint(scheme.primary).padding(.top, 4)
            }
        } buttons: {
            Button("Cancel", action: dismiss).buttonStyle(.tonal)
            switch account.state {
            case .secondFactor:
                Button("Continue") { model.submitSecondFactor(code.trimmingCharacters(in: .whitespaces)) }
                    .buttonStyle(.accent)
                    .disabled(code.trimmingCharacters(in: .whitespaces).isEmpty || account.busy)
            case .mailboxPassword:
                Button("Unlock") { model.submitMailboxPassword(mailbox) }
                    .buttonStyle(.accent)
                    .disabled(mailbox.isEmpty || account.busy)
            default:
                Button("Sign in") { model.signIn(username.trimmingCharacters(in: .whitespaces), password) }
                    .buttonStyle(.accent)
                    .disabled(username.trimmingCharacters(in: .whitespaces).isEmpty || password.isEmpty || account.busy)
            }
        }
        .secureContent()
        .interactiveDismissDisabled(account.busy)
        .onChange(of: account.state) { _, state in
            if case .signedIn = state { onDismiss() }
        }
        .fullScreenCover(isPresented: Binding(
            get: { account.verificationUrl != nil },
            set: { if !$0 { model.dismissVerification() } }
        )) {
            if let url = account.verificationUrl {
                VerificationView(url: url, onToken: { token in
                    model.signIn(username.trimmingCharacters(in: .whitespaces), password, verificationToken: token)
                }, onDismiss: model.dismissVerification)
            }
        }
    }

    private func dismiss() {
        if model.account.state == .secondFactor || model.account.state == .mailboxPassword { model.cancelSignIn() }
        onDismiss()
    }
}

/// Proton's hosted CAPTCHA, which it puts in front of a sign-in it does not
/// recognise — a new network, a VPN exit.
///
/// In a web view rather than Safari because the page reports success by
/// posting a message to its host, not by redirecting. The page targets
/// `window.parent`, which for a top-level page is the page itself, so a
/// listener on its own window hears it.
private struct VerificationView: View {
    let url: String
    let onToken: (String) -> Void
    let onDismiss: () -> Void
    @Environment(\.scheme) private var scheme

    var body: some View {
        VStack(spacing: 0) {
            HStack {
                Text("Confirm you are human").textStyle(.titleMedium).foregroundStyle(scheme.onSurface).padding(.leading, 16)
                Spacer()
                IconButton("xmark", "Cancel", action: onDismiss)
            }
            .frame(height: 56)
            VerificationWebView(url: url, onToken: onToken)
        }
        .background(scheme.surfaceContainerHigh)
    }
}

/// Installed once per page, at start and again at finish in case the first ran
/// too early.
private let verificationBridge = """
if (!window.__pstrVerification) {
    window.__pstrVerification = true;
    window.addEventListener('message', function (event) {
        try {
            window.webkit.messageHandlers.pstrVerification.postMessage(
                typeof event.data === 'string' ? event.data : JSON.stringify(event.data));
        } catch (e) {}
    });
}
"""

/// Whether a page is Proton's own, over HTTPS.
func isProtonPage(scheme: String?, host: String?) -> Bool {
    guard scheme == "https", let host else { return false }
    return host == "proton.me" || host.hasSuffix(".proton.me")
}

private struct VerificationWebView: UIViewRepresentable {
    let url: String
    let onToken: (String) -> Void

    func makeCoordinator() -> Coordinator { Coordinator(onToken: onToken) }

    func makeUIView(context: Context) -> WKWebView {
        let configuration = WKWebViewConfiguration()
        configuration.websiteDataStore = .nonPersistent()
        let content = configuration.userContentController
        for time in [WKUserScriptInjectionTime.atDocumentStart, .atDocumentEnd] {
            content.addUserScript(WKUserScript(source: verificationBridge, injectionTime: time, forMainFrameOnly: true))
        }
        content.add(WeakHandler(context.coordinator), name: "pstrVerification")
        let view = WKWebView(frame: .zero, configuration: configuration)
        view.navigationDelegate = context.coordinator
        if let address = URL(string: url) { view.load(URLRequest(url: address)) }
        return view
    }

    func updateUIView(_: WKWebView, context _: Context) {}

    static func dismantleUIView(_ view: WKWebView, coordinator _: Coordinator) {
        view.configuration.userContentController.removeScriptMessageHandler(forName: "pstrVerification")
    }

    @MainActor
    final class Coordinator: NSObject, WKScriptMessageHandler, WKNavigationDelegate {
        let onToken: (String) -> Void
        private var answered = false

        init(onToken: @escaping (String) -> Void) {
            self.onToken = onToken
        }

        /// Every message the page posts lands here, most of them its own chatter.
        func userContentController(_: WKUserContentController, didReceive message: WKScriptMessage) {
            guard !answered, let text = message.body as? String, let token = verificationToken(message: text) else { return }
            answered = true
            onToken(token)
        }

        /// The bridge is reachable by whatever the frame shows, so the frame
        /// stays on Proton.
        func webView(_: WKWebView, decidePolicyFor action: WKNavigationAction) async -> WKNavigationActionPolicy {
            guard action.targetFrame?.isMainFrame ?? true else { return .allow }
            return isProtonPage(scheme: action.request.url?.scheme, host: action.request.url?.host) ? .allow : .cancel
        }
    }

    /// `WKUserContentController` holds its handlers strongly.
    @MainActor
    private final class WeakHandler: NSObject, WKScriptMessageHandler {
        weak var target: WKScriptMessageHandler?

        init(_ target: WKScriptMessageHandler) {
            self.target = target
        }

        func userContentController(_ controller: WKUserContentController, didReceive message: WKScriptMessage) {
            target?.userContentController(controller, didReceive: message)
        }
    }
}

/// Walk the account's Drive and add a folder of it to the library.
///
/// Full screen, because a Drive is deep. Listings are asked for here rather
/// than through the model: they are this view's alone, and gone when it closes.
struct DriveBrowser: View {
    @Environment(AppModel.self) private var model
    @Environment(\.scheme) private var scheme
    @Environment(\.dismiss) private var dismiss
    @State private var trail: [(name: String, place: DrivePlaceRecord)] = []
    @State private var places: [DrivePlaceRecord]?
    @State private var entries: [DriveEntryRecord]?
    @State private var error: String?

    var body: some View {
        let current = trail.last?.place
        VStack(spacing: 0) {
            HStack(spacing: 0) {
                IconButton(trail.isEmpty ? "xmark" : "chevron.backward", trail.isEmpty ? "Close" : "Up a folder", tint: scheme.onSurface) {
                    if trail.isEmpty { dismiss() } else { trail.removeLast() }
                }
                Text(trail.last?.name ?? "Your Drive").textStyle(.titleLarge).foregroundStyle(scheme.onSurface).lineLimit(1)
                Spacer()
            }
            .frame(height: 56)
            Group {
                let loading = error == nil && (current == nil ? places == nil : entries == nil)
                if let error {
                    EmptyState("Could not list this", error)
                } else if loading {
                    ProgressView().tint(scheme.primary).frame(maxWidth: .infinity, maxHeight: .infinity)
                } else if current == nil {
                    ScrollView {
                        LazyVStack(spacing: 0) {
                            ForEach(places ?? [], id: \.linkId) { place in
                                DriveRow(icon: place.kind.icon, name: place.name, detail: nil) {
                                    trail.append((place.name, place))
                                }
                            }
                        }
                        .padding(.vertical, 8)
                    }
                } else if (entries ?? []).isEmpty {
                    EmptyState("Empty folder", "Nothing to add from here.")
                } else {
                    ScrollView {
                        LazyVStack(spacing: 0) {
                            ForEach(entries ?? [], id: \.linkId) { entry in
                                DriveRow(
                                    icon: entry.isFolder ? "folder.fill" : entry.isVideo ? "film" : "doc",
                                    name: entry.name,
                                    detail: entry.size.map(formatBytes),
                                    open: entry.isFolder ? {
                                        trail.append((entry.name, DrivePlaceRecord(kind: .myFiles, name: entry.name, volumeId: entry.volumeId, linkId: entry.linkId)))
                                    } : nil
                                )
                            }
                        }
                        .padding(.vertical, 8)
                    }
                }
            }
            .frame(maxHeight: .infinity)
            // A folder already in the library is refused by the engine, with a
            // message saying so.
            if let folder = current, let name = trail.last?.name {
                HStack {
                    Spacer()
                    Button("Add this folder") {
                        model.addAccountFolder(name: name, volumeId: folder.volumeId, linkId: folder.linkId)
                        dismiss()
                    }
                    .buttonStyle(.accent)
                }
                .padding(16)
            }
        }
        .background(scheme.background)
        .environment(\.colorScheme, scheme.colorScheme)
        .task(id: current?.linkId) {
            error = nil
            do {
                if let current {
                    entries = nil
                    entries = try await NativeRuntime.engine().driveFolder(volumeId: current.volumeId, linkId: current.linkId)
                } else if places == nil {
                    places = try await NativeRuntime.engine().drivePlaces()
                }
            } catch {
                self.error = errorMessage(error)
            }
        }
    }
}

private extension PlaceType {
    var icon: String {
        switch self {
        case .myFiles: "externaldrive"
        case .device: "desktopcomputer"
        case .sharedWithMe: "folder.badge.person.crop"
        }
    }
}

private struct DriveRow: View {
    let icon: String
    let name: String
    let detail: String?
    var open: (() -> Void)?
    @Environment(\.scheme) private var scheme

    var body: some View {
        Button { open?() } label: {
            HStack(spacing: 16) {
                Image(systemName: icon).font(.system(size: 20))
                    .foregroundStyle(open != nil ? scheme.primary : scheme.onSurfaceVariant).frame(width: 24)
                VStack(alignment: .leading, spacing: 2) {
                    Text(name).textStyle(.bodyLarge).foregroundStyle(scheme.onSurface).lineLimit(2)
                    if let detail { Text(detail).textStyle(.bodyMedium).foregroundStyle(scheme.onSurfaceVariant) }
                }
                Spacer(minLength: 0)
            }
            .padding(.horizontal, 16)
            .padding(.vertical, 12)
            .contentShape(Rectangle())
        }
        .buttonStyle(.plain)
        .disabled(open == nil)
    }
}