import Carbon
import AppKit

/// Manages global hotkey registration using Carbon RegisterEventHotKey.
final class HotKeyManager {
    typealias Handler = () -> Void

    private var hotKeyRef: EventHotKeyRef?
    private var eventHandler: EventHandlerRef?
    private let handler: Handler

    /// The signature used to identify our hotkey events.
    private static let hotKeySignature: FourCharCode = {
        let chars: [UInt8] = [0x4D, 0x43, 0x54, 0x48] // "MCTH"
        return FourCharCode(chars[0]) << 24 | FourCharCode(chars[1]) << 16 | FourCharCode(chars[2]) << 8 | FourCharCode(chars[3])
    }()

    private static let hotKeyID = EventHotKeyID(signature: hotKeySignature, id: 1)

    init(handler: @escaping Handler) {
        self.handler = handler
    }

    deinit {
        unregister()
    }

    /// Register the global hotkey. Default: Ctrl+Up Arrow.
    func register(keyCode: UInt32 = UInt32(kVK_UpArrow), modifiers: UInt32 = UInt32(controlKey)) {
        unregister()

        // Install Carbon event handler
        var eventType = EventTypeSpec(eventClass: OSType(kEventClassKeyboard), eventKind: UInt32(kEventHotKeyPressed))
        let selfPtr = Unmanaged.passUnretained(self).toOpaque()

        InstallEventHandler(
            GetApplicationEventTarget(),
            { (_, event, userData) -> OSStatus in
                guard let userData = userData else { return OSStatus(eventNotHandledErr) }
                let manager = Unmanaged<HotKeyManager>.fromOpaque(userData).takeUnretainedValue()
                var hotKeyID = EventHotKeyID()
                GetEventParameter(
                    event,
                    EventParamName(kEventParamDirectObject),
                    EventParamType(typeEventHotKeyID),
                    nil,
                    MemoryLayout<EventHotKeyID>.size,
                    nil,
                    &hotKeyID
                )
                if hotKeyID.signature == HotKeyManager.hotKeySignature {
                    DispatchQueue.main.async {
                        manager.handler()
                    }
                }
                return noErr
            },
            1,
            &eventType,
            selfPtr,
            &eventHandler
        )

        // Register the hotkey
        let hotKeyIDVar = Self.hotKeyID
        RegisterEventHotKey(
            keyCode,
            modifiers,
            hotKeyIDVar,
            GetApplicationEventTarget(),
            0,
            &hotKeyRef
        )
    }

    func unregister() {
        if let ref = hotKeyRef {
            UnregisterEventHotKey(ref)
            hotKeyRef = nil
        }
        if let handler = eventHandler {
            RemoveEventHandler(handler)
            eventHandler = nil
        }
    }
}