import Carbon.HIToolbox
import Foundation

/// Thin wrapper around the Carbon RegisterEventHotKey API to register
/// system-wide keyboard shortcuts without requiring Accessibility/Input
/// Monitoring permission.
final class HotKeyManager {
    static let shared = HotKeyManager()

    private var hotKeyRefs: [UInt32: EventHotKeyRef] = [:]
    private var handlers: [UInt32: () -> Void] = [:]
    private var eventHandlerRef: EventHandlerRef?

    private static let signature: FourCharCode = {
        var result: FourCharCode = 0
        for byte in "SNAP".utf8 {
            result = (result << 8) + FourCharCode(byte)
        }
        return result
    }()

    private init() {
        installEventHandler()
    }

    private func installEventHandler() {
        var eventType = EventTypeSpec(
            eventClass: OSType(kEventClassKeyboard),
            eventKind: UInt32(kEventHotKeyPressed)
        )

        let callback: EventHandlerUPP = { _, event, userData in
            guard let event, let userData else { return noErr }
            var hotKeyID = EventHotKeyID()
            GetEventParameter(
                event,
                EventParamName(kEventParamDirectObject),
                EventParamType(typeEventHotKeyID),
                nil,
                MemoryLayout<EventHotKeyID>.size,
                nil,
                &hotKeyID
            )
            let manager = Unmanaged<HotKeyManager>.fromOpaque(userData).takeUnretainedValue()
            manager.handlers[hotKeyID.id]?()
            return noErr
        }

        InstallEventHandler(
            GetEventDispatcherTarget(),
            callback,
            1,
            &eventType,
            Unmanaged.passUnretained(self).toOpaque(),
            &eventHandlerRef
        )
    }

    @discardableResult
    func register(id: UInt32, keyCode: UInt32, modifiers: UInt32, handler: @escaping () -> Void) -> Bool {
        unregister(id: id)

        var hotKeyRef: EventHotKeyRef?
        let hotKeyID = EventHotKeyID(signature: Self.signature, id: id)
        let status = RegisterEventHotKey(
            keyCode,
            modifiers,
            hotKeyID,
            GetEventDispatcherTarget(),
            0,
            &hotKeyRef
        )

        guard status == noErr, let hotKeyRef else { return false }
        hotKeyRefs[id] = hotKeyRef
        handlers[id] = handler
        return true
    }

    func unregister(id: UInt32) {
        if let ref = hotKeyRefs.removeValue(forKey: id) {
            UnregisterEventHotKey(ref)
        }
        handlers.removeValue(forKey: id)
    }
}