import AppKit
import Carbon

@MainActor
public final class GlobalShortcut {
    public private(set) var shortcut: KeyboardShortcut?
    public private(set) var isRegistered = false

    private static let storageKey = "globalActivationShortcut"
    private let defaults: UserDefaults
    private let action: @MainActor () -> Void
    private let native = NativeHotKey()

    public init(defaults: UserDefaults = .standard, action: @escaping @MainActor () -> Void) {
        self.defaults = defaults
        self.action = action
        shortcut = KeyboardShortcut(storedValue: defaults.object(forKey: Self.storageKey))
        native.owner = self
    }

    deinit {
        native.disposeOnMainThread()
    }

    public func start() throws {
        guard !isRegistered else { return }
        if let saved = defaults.object(forKey: Self.storageKey) {
            guard let restored = KeyboardShortcut(storedValue: saved) else {
                throw ShortcutError.invalidSavedShortcut
            }
            try activate(restored)
            shortcut = restored
        }
    }

    public func setShortcut(_ candidate: KeyboardShortcut?) throws {
        if candidate == shortcut, isRegistered { return }
        if let candidate {
            try activate(candidate)
            defaults.set(candidate.storedValue, forKey: Self.storageKey)
        } else {
            try native.unregister()
            isRegistered = false
            defaults.removeObject(forKey: Self.storageKey)
        }
        shortcut = candidate
    }

    public func suspend() {
        do {
            try native.unregister()
            isRegistered = false
        } catch {
            NSLog("Conjure could not suspend its shortcut: %@", error.localizedDescription)
        }
    }

    public func stop() {
        native.dispose()
        isRegistered = false
    }

    fileprivate func activateFromEvent() {
        action()
    }

    private func activate(_ candidate: KeyboardShortcut) throws {
        try Self.rejectSystemConflict(candidate)
        try native.register(candidate)
        isRegistered = true
    }

    private static func rejectSystemConflict(_ candidate: KeyboardShortcut) throws {
        var copied: Unmanaged<CFArray>?
        let status = CopySymbolicHotKeys(&copied)
        let result = copied?.takeRetainedValue()
        guard status == noErr, let result else {
            throw ShortcutError.native(operation: "read macOS keyboard shortcuts", status: status)
        }
        let hotKeys = result as NSArray
        for case let record as NSDictionary in hotKeys {
            guard let enabled = record[kHISymbolicHotKeyEnabled] as? NSNumber, enabled.boolValue,
                  let code = record[kHISymbolicHotKeyCode] as? NSNumber,
                  let modifiers = record[kHISymbolicHotKeyModifiers] as? NSNumber else { continue }
            let relevantModifiers = UInt32(cmdKey | optionKey | controlKey | shiftKey)
            if code.uint16Value == candidate.keyCode,
               modifiers.uint32Value & relevantModifiers == candidate.carbonModifiers {
                throw ShortcutError.systemConflict(candidate.displayName)
            }
        }
    }
}

private enum ShortcutError: LocalizedError {
    case invalidSavedShortcut
    case systemConflict(String)
    case native(operation: String, status: OSStatus)

    var errorDescription: String? {
        switch self {
        case .invalidSavedShortcut:
            return "The saved activation shortcut is invalid. Choose a new shortcut or clear it in Conjure Settings."
        case .systemConflict(let shortcut):
            return "\(shortcut) is already an enabled macOS shortcut. Free it in System Settings → Keyboard → Keyboard Shortcuts (check Spotlight and Input Sources), or choose another shortcut. Conjure will not change your system settings."
        case .native(let operation, let status):
            if status == eventHotKeyExistsErr {
                return "That shortcut is already registered by another app. Change or disable the other app’s shortcut, or choose another one. For Command-Space, also check Spotlight and Input Sources in System Settings → Keyboard → Keyboard Shortcuts."
            }
            return "Conjure could not \(operation) (macOS error \(status)). Choose another shortcut or try again."
        }
    }
}

// Carbon is main-thread-only. This separate lifetime lets a nonisolated Swift
// deinit enqueue teardown without capturing a dying owner or dangling C context.
private final class NativeHotKey: @unchecked Sendable {
    @MainActor weak var owner: GlobalShortcut?
    @MainActor private var handler: EventHandlerRef?
    @MainActor private var hotKey: EventHotKeyRef?
    @MainActor private var identifier: UInt32 = 0
    @MainActor private var isPressed = false
    @MainActor private static var nextIdentifier: UInt32 = 0
    private static let signature: OSType = 0x434E4A52 // CNJR

    @MainActor init() {}

    @MainActor
    func register(_ shortcut: KeyboardShortcut) throws {
        precondition(Thread.isMainThread)
        try installHandler()
        Self.nextIdentifier &+= 1
        if Self.nextIdentifier == 0 { Self.nextIdentifier = 1 }
        let next = Self.nextIdentifier
        var replacement: EventHotKeyRef?
        let status = RegisterEventHotKey(
            UInt32(shortcut.keyCode), shortcut.carbonModifiers,
            EventHotKeyID(signature: Self.signature, id: next),
            GetApplicationEventTarget(), UInt32(kEventHotKeyExclusive), &replacement
        )
        guard status == noErr, let replacement else {
            throw ShortcutError.native(operation: "register the activation shortcut", status: status)
        }
        do {
            try unregister()
        } catch {
            UnregisterEventHotKey(replacement)
            throw error
        }
        hotKey = replacement
        identifier = next
        isPressed = false
    }

    @MainActor
    func unregister() throws {
        precondition(Thread.isMainThread)
        guard let hotKey else { return }
        let status = UnregisterEventHotKey(hotKey)
        guard status == noErr else {
            throw ShortcutError.native(operation: "release the previous activation shortcut", status: status)
        }
        self.hotKey = nil
        identifier = 0
        isPressed = false
    }

    @MainActor
    func dispose() {
        precondition(Thread.isMainThread)
        if let hotKey { UnregisterEventHotKey(hotKey) }
        hotKey = nil
        identifier = 0
        isPressed = false
        if let handler { RemoveEventHandler(handler) }
        handler = nil
    }

    func disposeOnMainThread() {
        if Thread.isMainThread {
            MainActor.assumeIsolated { dispose() }
        } else {
            DispatchQueue.main.async { self.dispose() }
        }
    }

    @MainActor
    private func installHandler() throws {
        guard handler == nil else { return }
        var types = [
            EventTypeSpec(eventClass: OSType(kEventClassKeyboard), eventKind: UInt32(kEventHotKeyPressed)),
            EventTypeSpec(eventClass: OSType(kEventClassKeyboard), eventKind: UInt32(kEventHotKeyReleased)),
        ]
        let status = InstallEventHandler(
            GetApplicationEventTarget(), { _, event, context in
                guard let event, let context else { return OSStatus(eventNotHandledErr) }
                return MainActor.assumeIsolated {
                    Unmanaged<NativeHotKey>.fromOpaque(context).takeUnretainedValue().receive(event)
                }
            }, types.count, &types, Unmanaged.passUnretained(self).toOpaque(), &handler
        )
        guard status == noErr else {
            throw ShortcutError.native(operation: "install the activation shortcut handler", status: status)
        }
    }

    @MainActor
    private func receive(_ event: EventRef) -> OSStatus {
        precondition(Thread.isMainThread)
        var keyID = EventHotKeyID()
        let status = GetEventParameter(
            event, EventParamName(kEventParamDirectObject), EventParamType(typeEventHotKeyID),
            nil, MemoryLayout<EventHotKeyID>.size, nil, &keyID
        )
        guard status == noErr, keyID.signature == Self.signature,
              hotKey != nil, keyID.id == identifier else { return OSStatus(eventNotHandledErr) }
        switch GetEventKind(event) {
        case UInt32(kEventHotKeyPressed):
            guard !isPressed else { return noErr }
            isPressed = true
            owner?.activateFromEvent()
        case UInt32(kEventHotKeyReleased):
            isPressed = false
        default:
            return OSStatus(eventNotHandledErr)
        }
        return noErr
    }
}