import AppKit
import Combine

/// Application delegate that bootstraps the notch overlay system.
@MainActor
class AppDelegate: NSObject, NSApplicationDelegate {

    private var cancellables = Set<AnyCancellable>()

    func applicationDidFinishLaunching(_ notification: Notification) {
        NotchSettings.registerDefaults()
        NSApp.setActivationPolicy(.accessory)

        // Sync the launch-at-login toggle with the actual system state
        // in case the user toggled it from System Settings.
        UserDefaults.standard.set(LaunchAtLoginHelper.isEnabled, forKey: NotchSettings.Keys.launchAtLogin)

        ScreenManager.shared.start()
        observeDisplayPreference()
        observeSizePreferences()
        observeFontSizeChanges()
        observeTerminalThemeChanges()
    }

    func applicationWillTerminate(_ notification: Notification) {
        ScreenManager.shared.stop()
    }

    // MARK: - Preference observers

    /// Only rebuild windows when the display-count preference changes.
    private func observeDisplayPreference() {
        UserDefaults.standard.publisher(for: \.showOnAllDisplays)
            .removeDuplicates()
            .dropFirst()
            .sink { _ in
                ScreenManager.shared.rebuildWindows()
            }
            .store(in: &cancellables)
    }

    /// Reposition (not rebuild) when any sizing preference changes.
    private func observeSizePreferences() {
        NotificationCenter.default.publisher(for: UserDefaults.didChangeNotification)
            .debounce(for: .milliseconds(300), scheduler: RunLoop.main)
            .sink { _ in
                ScreenManager.shared.repositionWindows()
            }
            .store(in: &cancellables)
    }

    /// Live-update terminal font size across all sessions.
    private func observeFontSizeChanges() {
        UserDefaults.standard.publisher(for: \.terminalFontSize)
            .removeDuplicates()
            .sink { newSize in
                guard newSize > 0 else { return }
                TerminalManager.shared.updateAllFontSizes(CGFloat(newSize))
            }
            .store(in: &cancellables)
    }

    /// Live-update terminal colors across all sessions.
    private func observeTerminalThemeChanges() {
        UserDefaults.standard.publisher(for: \.terminalTheme)
            .removeDuplicates()
            .sink { newTheme in
                TerminalManager.shared.updateAllThemes(TerminalTheme.resolve(newTheme))
            }
            .store(in: &cancellables)
    }
}

// MARK: - KVO key paths

private extension UserDefaults {
    @objc var terminalFontSize: Double {
        double(forKey: NotchSettings.Keys.terminalFontSize)
    }

    @objc var terminalTheme: String {
        string(forKey: NotchSettings.Keys.terminalTheme) ?? NotchSettings.Defaults.terminalTheme
    }

    @objc var showOnAllDisplays: Bool {
        bool(forKey: NotchSettings.Keys.showOnAllDisplays)
    }
}