SystemTrayMenu/Helpers/KeyboardHook.cs

// <copyright file="KeyboardHook.cs" company="PlaceholderCompany">
// Copyright (c) PlaceholderCompany. All rights reserved.
// </copyright>

namespace SystemTrayMenu.Helpers
{
    using System;
    using System.Windows;
    using System.Windows.Input;
    using System.Windows.Interop;

    // TODO: Move this whole class into mainMenu to spare creating additional Win32 window handles by using Menu's Window directly.
    internal class KeyboardHook : IDisposable
    {
        private readonly HwndSourceHook hook;
        private readonly HwndSource hwnd;
        private readonly Window window = new();
        private int currentId;

        public KeyboardHook()
        {
            hwnd = HwndSource.FromHwnd(new WindowInteropHelper(window).EnsureHandle());
            hook = new HwndSourceHook(WndProc);
            hwnd.AddHook(hook);
        }

        /// <summary>
        /// A hot key has been pressed.
        /// </summary>
        internal event Action<Key, ModifierKeys>? KeyPressed;

        public void Dispose()
        {
            // On regular App.Dispose the handle was already invalidated
            if (hwnd.Handle != IntPtr.Zero)
            {
                // unregister all the registered hot keys.
                for (int i = currentId; i > 0; i--)
                {
                    GlobalHotkeys.UnregisterHotkey(hwnd.Handle, i);
                }

                hwnd.RemoveHook(hook);
            }

            hwnd.Dispose();
        }

        internal void RegisterHotKey(ModifierKeys modifiers, Key key) => currentId = GlobalHotkeys.RegisterHotkeyLocal(hwnd.Handle, currentId + 1, modifiers, key);

        internal void RegisterHotKey(string hotKeyString) => currentId = GlobalHotkeys.RegisterHotkeyLocal(hwnd.Handle, currentId + 1, hotKeyString);

        private IntPtr WndProc(IntPtr hwnd, int msg, IntPtr wParam, IntPtr lParam, ref bool handled)
        {
            const int WmHotkey = 0x0312;

            // check if we got a hot key pressed.
            if (msg == WmHotkey)
            {
                // get the keys.
                ModifierKeys modifiers = (ModifierKeys)((int)lParam & 0xFFFF);
                int virtualKeyCode = ((int)lParam >> 16) & 0xFFFF;
                Key key = KeyInterop.KeyFromVirtualKey(virtualKeyCode);

                // invoke the event to notify the parent.
                KeyPressed?.Invoke(key, modifiers);
            }

            handled = false;
            return IntPtr.Zero;
        }
    }
}