using System;
using System.Runtime.InteropServices;
using System.Collections;

namespace HSI_SEVENOCEAN_EF1_CsTest
{
  class User32Api
  {
    private static readonly Hashtable ProcessWnd = null;

    public delegate bool Wndenumproc(IntPtr hwnd, uint lParam);

    static User32Api()
    {
      if (ProcessWnd == null)
      {
        ProcessWnd = new Hashtable();
      }
    }

    [DllImport("user32.dll", EntryPoint = "EnumWindows", SetLastError = true)]
    public static extern bool EnumWindows(Wndenumproc lpEnumFunc, uint lParam);

    [DllImport("user32.dll", EntryPoint = "GetParent", SetLastError = true)]
    public static extern IntPtr GetParent(IntPtr hWnd);

    [DllImport("user32.dll", EntryPoint = "GetWindowThreadProcessId")]
    public static extern uint GetWindowThreadProcessId(IntPtr hWnd, ref uint lpdwProcessId);

    [DllImport("user32.dll", EntryPoint = "IsWindow")]
    public static extern bool IsWindow(IntPtr hWnd);

    [DllImport("kernel32.dll", EntryPoint = "SetLastError")]
    public static extern void SetLastError(uint dwErrCode);

    public static IntPtr GetCurrentWindowHandle()
    {
      IntPtr ptrWnd = IntPtr.Zero;
      uint uiPid = (uint)System.Diagnostics.Process.GetCurrentProcess().Id;  // 当前进程 ID
      object objWnd = ProcessWnd[uiPid];

      if (objWnd != null)
      {
        ptrWnd = (IntPtr)objWnd;
        if (ptrWnd != IntPtr.Zero && IsWindow(ptrWnd))  // 从缓存中获取句柄
        {
          return ptrWnd;
        }
        else
        {
          ptrWnd = IntPtr.Zero;
        }
      }

      bool bResult = EnumWindows(new Wndenumproc(EnumWindowsProc), uiPid);
      // 枚举窗口返回 false 并且没有错误号时表明获取成功
      if (!bResult && Marshal.GetLastWin32Error() == 0)
      {
        objWnd = ProcessWnd[uiPid];
        if (objWnd != null)
        {
          ptrWnd = (IntPtr)objWnd;
        }
      }

      return ptrWnd;
    }

    private static bool EnumWindowsProc(IntPtr hwnd, uint lParam)
    {
      uint uiPid = 0;

      if (GetParent(hwnd) == IntPtr.Zero)
      {
        GetWindowThreadProcessId(hwnd, ref uiPid);
        if (uiPid == lParam)    // 找到进程对应的主窗口句柄
        {
          ProcessWnd[uiPid] = hwnd;   // 把句柄缓存起来
          SetLastError(0);    // 设置无错误
          return false;   // 返回 false 以终止枚举窗口
        }
      }

      return true;
    }

  }
}