﻿using System;
using System.Diagnostics;
using System.Runtime.InteropServices;

namespace UsageStats
{

    // http://blogs.msdn.com/toub/archive/2006/05/03/589423.aspx
    
    public class InterceptKeys : IDisposable
    {
        private const int WH_KEYBOARD_LL = 13;
        private const int WM_KEYDOWN = 0x0100;
        private static readonly LowLevelKeyboardProc _proc = HookCallback;
        private static IntPtr _hookID = IntPtr.Zero;

        public InterceptKeys()
        {
            _hookID = SetHook(_proc);
        }

        #region IDisposable Members

        public void Dispose()
        {
            bool result = UnhookWindowsHookEx(_hookID);
            if (!result)
                Trace.WriteLine("Could not unhook keyboard interception.");
        }

        #endregion

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

        private static IntPtr HookCallback(
            int nCode, IntPtr wParam, IntPtr lParam)
        {
            if (nCode >= 0 && wParam == (IntPtr) WM_KEYDOWN)
            {
                int vkCode = Marshal.ReadInt32(lParam);
                // Console.Write((char) 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);

        #region Nested type: LowLevelKeyboardProc

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

        #endregion
    }
}