prole/prole-app/Sources/HotKeyManager.swift

import AppKit
import Carbon.HIToolbox

final class HotKeyManager {
    private var hotKeyRef: EventHotKeyRef?

    enum Key: UInt32 { case p = 35 /* US keyboard virtual keycode for P */ }

    struct Modifiers: OptionSet {
        let rawValue: UInt32
        static let command = Modifiers(rawValue: UInt32(cmdKey))
        static let option  = Modifiers(rawValue: UInt32(optionKey))
        static let shift   = Modifiers(rawValue: UInt32(shiftKey))
    }

    func registerGlobalHotKey(modifiers: Modifiers, key: Key, handler: @escaping () -> Void) {
        var eventSpec = EventTypeSpec(eventClass: OSType(kEventClassKeyboard), eventKind: UInt32(kEventHotKeyPressed))
        InstallEventHandler(GetApplicationEventTarget(), { (_, _, userData) -> OSStatus in
            let handler = Unmanaged<HotKeyHandlerWrapper>.fromOpaque(userData!).takeUnretainedValue()
            handler.handler()
            return noErr
        }, 1, &eventSpec, Unmanaged.passRetained(HotKeyHandlerWrapper(handler: handler)).toOpaque(), nil)

        let hotKeyID = EventHotKeyID(signature: OSType(UInt32(bitPattern: Int32(bitPattern: 0x50524F4C))), id: 1) // 'PROL'
        RegisterEventHotKey(UInt32(key.rawValue), modifiers.rawValue, hotKeyID, GetApplicationEventTarget(), 0, &hotKeyRef)
    }

    deinit { if let ref = hotKeyRef { UnregisterEventHotKey(ref) } }
}

private final class HotKeyHandlerWrapper {
    let handler: () -> Void
    init(handler: @escaping () -> Void) { self.handler = handler }
}