Robovoice/Robovoice.App/PttHotkey.cs

using System.Runtime.InteropServices;
using System.Windows.Forms;

namespace Robovoice.App;

internal sealed class PttHotkey : IDisposable
{
    private const int WH_KEYBOARD_LL = 13;
    private const int WM_KEYDOWN = 0x0100;
    private const int WM_KEYUP = 0x0101;
    private const int WM_SYSKEYDOWN = 0x0104;
    private const int WM_SYSKEYUP = 0x0105;

    private readonly LowLevelKeyboardProc _proc;
    private IntPtr _hook = IntPtr.Zero;
    private bool _isDown;
    private bool _disposed;

    public Keys Key { get; set; } = Keys.F8;

    public event EventHandler? Pressed;
    public event EventHandler? Released;

    public PttHotkey()
    {
        _proc = HookCallback;
    }

    public void Install()
    {
        ObjectDisposedException.ThrowIf(_disposed, this);
        if (_hook != IntPtr.Zero) return;

        IntPtr hModule = GetModuleHandle(null);
        _hook = SetWindowsHookEx(WH_KEYBOARD_LL, _proc, hModule, 0);
    }

    public void Uninstall()
    {
        if (_hook != IntPtr.Zero)
        {
            UnhookWindowsHookEx(_hook);
            _hook = IntPtr.Zero;
            _isDown = false;
        }
    }

    private IntPtr HookCallback(int nCode, IntPtr wParam, IntPtr lParam)
    {
        if (nCode >= 0)
        {
            int vkCode = Marshal.ReadInt32(lParam);
            Keys key = (Keys)vkCode;

            bool isDown = wParam == WM_KEYDOWN || wParam == WM_SYSKEYDOWN;
            bool isUp = wParam == WM_KEYUP || wParam == WM_SYSKEYUP;

            if (key == Key && isDown && !_isDown)
            {
                _isDown = true;
                Pressed?.Invoke(this, EventArgs.Empty);
            }
            else if (key == Key && isUp && _isDown)
            {
                _isDown = false;
                Released?.Invoke(this, EventArgs.Empty);
            }
        }

        return CallNextHookEx(_hook, nCode, wParam, lParam);
    }

    public void Dispose()
    {
        if (_disposed) return;
        Uninstall();
        _disposed = true;
    }

    private delegate IntPtr LowLevelKeyboardProc(int nCode, IntPtr wParam, IntPtr lParam);

    [DllImport("user32.dll", SetLastError = true)]
    private static extern IntPtr SetWindowsHookEx(int idHook, LowLevelKeyboardProc lpfn, IntPtr hMod, uint dwThreadId);

    [DllImport("user32.dll", SetLastError = true)]
    [return: MarshalAs(UnmanagedType.Bool)]
    private static extern bool UnhookWindowsHookEx(IntPtr hhk);

    [DllImport("user32.dll", SetLastError = true)]
    private static extern IntPtr CallNextHookEx(IntPtr hhk, int nCode, IntPtr wParam, IntPtr lParam);

    [DllImport("kernel32.dll", SetLastError = true, CharSet = CharSet.Unicode)]
    private static extern IntPtr GetModuleHandle(string? lpModuleName);
}