namespace Applications.UI
{
    class CurrentProcess
    {
            private static Hashtable processWnd = null;

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

            static CurrentProcess()
            {
                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 IntPtr GetCurrentWindowHandle(Process process)
            {
                IntPtr ptrWnd = IntPtr.Zero;
                uint uiPid = (uint)process.Id;  // 程序 ID
                object objWnd = processWnd[uiPid];

                if (objWnd != null)
                {
                    ptrWnd = (IntPtr)objWnd;
                    if (ptrWnd != IntPtr.Zero && IsWindow(ptrWnd))  // 從快取中獲取控制代碼
                    {
                        return ptrWnd;
                    }
                    else
                    {
                        ptrWnd = IntPtr.Zero;
                    }
                }

                bool bResult = EnumWindows(new WNDENUMPROC(EnumWindowsProc), uiPid);
                // 列舉視窗返回 false 並且沒有錯誤號時表明獲取成功
                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)    // 找到程序對應的主視窗控制代碼
                    {
                        processWnd[uiPid] = hwnd;   // 把控制代碼快取起來
                        SetLastError(0);    // 設定無錯誤
                        return false;   // 返回 false 以終止列舉視窗
                    }
                }

                return true;
            }
        }
   
}