FakeKey.swift

//
//  FakeKeyEvents.swift
//  CutBox
//
//  Created by Jason Milkins on 26/3/18.
//  Copyright © 2019-2020 ocodo. All rights reserved.
//

import Foundation
import Carbon

class FakeKey {

    static let shared = FakeKey()

    private let keyCodeRange = 0x00...0x7E

    func send(fakeKey key: String, useCommandFlag: Bool) {
        let keyCode = stringToKeyCode(key)
        send(fakeKey: numericCast(keyCode), useCommandFlag: useCommandFlag)
    }

    private func transformKeyCode(_ keyCode: Int) -> String {
        guard keyCodeRange.contains(keyCode)
            else { fatalError("Cannot transform \(keyCode) - out of range") }

        let inputSource = unsafeBitCast(
            TISGetInputSourceProperty(
                TISCopyCurrentASCIICapableKeyboardLayoutInputSource().takeUnretainedValue(),
                kTISPropertyUnicodeKeyLayoutData
        ), to: CFData.self)

        var deadKeyState: UInt32 = 0
        var char = UniChar()
        var length = 0

        CoreServices.UCKeyTranslate(unsafeBitCast(CFDataGetBytePtr(inputSource),
                                                  to: UnsafePointer<CoreServices.UCKeyboardLayout>.self),
                                    UInt16(keyCode),
                                    UInt16(CoreServices.kUCKeyActionDisplay),
                                    UInt32(0),
                                    UInt32(LMGetKbdType()),
                                    OptionBits(CoreServices.kUCKeyTranslateNoDeadKeysBit),

                                    &deadKeyState,
                                    1,
                                    &length,
                                    &char)

        return NSString(characters: &char, length: length).uppercased
    }

    private func keyCodeTranslationTable() -> [String: Int] {
        var table = [String: Int]()
        for code in keyCodeRange {
            table[transformKeyCode(code)] = code
        }
        return table
    }

    private func stringToKeyCode(_ key: String) -> Int {
        guard key.count == 1 else { fatalError("Only single char strings can be used") }

        let translationTable = keyCodeTranslationTable()

        guard let keyCode = translationTable[key]
            else { fatalError("Unable to get keyCode for: \(key)") }

        return keyCode
    }

    private func send(fakeKey keyCode: CGKeyCode, useCommandFlag: Bool) {
        let sourceRef = CGEventSource(stateID: .combinedSessionState)

        if sourceRef == nil {
            NSLog("No event source")
            return
        }

        let keyDownEvent = CGEvent(
            keyboardEventSource: sourceRef,
            virtualKey: keyCode,
            keyDown: true
        )

        if useCommandFlag {
            keyDownEvent?.flags = .maskCommand
        }

        let keyUpEvent = CGEvent(
            keyboardEventSource: sourceRef,
            virtualKey: keyCode,
            keyDown: false
        )

        keyDownEvent?.post(tap: .cghidEventTap)
        keyUpEvent?.post(tap: .cghidEventTap)
    }

}