import Carbon.HIToolbox
import Foundation

final class HotkeyManager {
  private var hotkey: EventHotKeyRef?
  private var handler: EventHandlerRef?
  private var action: (() -> Void)?

  init() {
    var type = EventTypeSpec(
      eventClass: OSType(kEventClassKeyboard),
      eventKind: UInt32(kEventHotKeyPressed)
    )
    InstallEventHandler(
      GetApplicationEventTarget(),
      { _, event, context in
        guard let event, let context else { return noErr }
        var identifier = EventHotKeyID()
        let status = GetEventParameter(
          event,
          EventParamName(kEventParamDirectObject),
          EventParamType(typeEventHotKeyID),
          nil,
          MemoryLayout<EventHotKeyID>.size,
          nil,
          &identifier
        )
        guard status == noErr, identifier.id == 1 else { return status }
        let manager = Unmanaged<HotkeyManager>.fromOpaque(context).takeUnretainedValue()
        DispatchQueue.main.async { manager.action?() }
        return noErr
      },
      1,
      &type,
      Unmanaged.passUnretained(self).toOpaque(),
      &handler
    )
  }

  deinit {
    unregister()
    if let handler { RemoveEventHandler(handler) }
  }

  @discardableResult
  func register(_ shortcut: HotkeyShortcut, action: @escaping () -> Void) -> Bool {
    let identifier = EventHotKeyID(signature: Self.signature, id: 1)
    var candidate: EventHotKeyRef?
    let status = RegisterEventHotKey(
      shortcut.keyCode,
      shortcut.modifiers,
      identifier,
      GetApplicationEventTarget(),
      0,
      &candidate
    )
    guard status == noErr, let candidate else { return false }
    unregister()
    hotkey = candidate
    self.action = action
    return true
  }

  private func unregister() {
    if let hotkey { UnregisterEventHotKey(hotkey) }
    hotkey = nil
  }

  private static let signature: OSType = 0x5452_5549  // TRUI
}