KeyboardIntercept.cs

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

namespace BejeweledBot
{
    /// <summary>
    /// Based on https://blogs.msdn.microsoft.com/toub/2006/05/03/low-level-keyboard-hook-in-c/
    /// </summary>
    class KeyboardIntercept
    {
        public EventHandler<KeyEventArgs> KeyIntercepted;

        private const int WH_KEYBOARD_LL = 13;
        private const int WM_KEYDOWN = 0x0100;
        private static LowLevelKeyboardProc _proc = HookCallback;
        private static IntPtr _hookID = IntPtr.Zero;

        public KeyboardIntercept()
        {
            instance = this;
        }

        public static void Hook()
        {
            _hookID = SetHook(_proc);
        }

        private static KeyboardIntercept Instance { get { return instance; } }
        private static KeyboardIntercept instance; 

        public static void Unhook()
        {
            UnhookWindowsHookEx(_hookID);
        }

        private static IntPtr SetHook(LowLevelKeyboardProc proc)
        {
            using (Process curProcess = Process.GetCurrentProcess())
            using (ProcessModule curModule = curProcess.MainModule)
            {
                return SetWindowsHookEx(WH_KEYBOARD_LL, proc,
                    GetModuleHandle(curModule.ModuleName), 0);
            }
        }

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

        private static IntPtr HookCallback(int nCode, IntPtr wParam, IntPtr lParam)
        {
            if (nCode >= 0 && wParam == (IntPtr)WM_KEYDOWN)
            {
                int vkCode = Marshal.ReadInt32(lParam);
                Instance.onKeyIntercepted((Keys)vkCode);
            }

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

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

        [DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = true)]
        [return: MarshalAs(UnmanagedType.Bool)]

        private static extern bool UnhookWindowsHookEx(IntPtr hhk);

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

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

        private void onKeyIntercepted(Keys key)
        {
            KeyIntercepted?.Invoke(this, new KeyEventArgs(key));
        }
    }
}