virtual key codes to unicode characters

translatekeycodes.swift

    private static func keyCodeToString(keyCode: CGKeyCode, eventModifiers: Int) -> String? {
        let curKeyboard = TISCopyCurrentKeyboardInputSource().takeRetainedValue()
        let rawLayoutData = TISGetInputSourceProperty(curKeyboard, kTISPropertyUnicodeKeyLayoutData)
        let layoutData      = unsafeBitCast(rawLayoutData, to: CFData.self)
        let keyboardLayoutPtr = unsafeBitCast(CFDataGetBytePtr(layoutData), to: UnsafePointer<UCKeyboardLayout>.self)

        var deadKeyState: UInt32 = 0
        var actualStringLength = 0
        var unicodeString: [UniChar] = [0, 0, 0, 0]

        let status = UCKeyTranslate(keyboardLayoutPtr,
                                    keyCode,
                                    UInt16(kUCKeyActionDown),
                                    UInt32(eventModifiers >> 8), // from UCKeyTranslate doc
                                    UInt32(LMGetKbdType()),
                                    0,
                                    &deadKeyState,
                                    unicodeString.count,
                                    &actualStringLength,
                                    &unicodeString)

        if status != noErr {
            return nil
        }
        return NSString(characters: unicodeString, length: actualStringLength) as String
    }