/*

   This Source Code Form is subject to the terms of the Mozilla Public

   License, v. 2.0. If a copy of the MPL was not distributed with this

   file, You can obtain one at http://mozilla.org/MPL/2.0/.

   Copyright (C) 2010 Michael Möller <mmoeller@openhardwaremonitor.org>

 */

 using System;

 using System.Runtime.InteropServices;

 using System.Windows.Forms;

 namespace OpenHardwareMonitor.GUI {

   public class ShowDesktop {

     private static ShowDesktop instance = new ShowDesktop();

     public delegate void ShowDesktopChangedEventHandler(bool showDesktop);

     private event ShowDesktopChangedEventHandler ShowDesktopChangedEvent;

     private System.Threading.Timer timer;

     private bool showDesktop = false;   

     private NativeWindow referenceWindow;

     private string referenceWindowCaption =

       "OpenHardwareMonitorShowDesktopReferenceWindow";

     private ShowDesktop() {

       // create a reference window to detect show desktop

       referenceWindow = new NativeWindow();

       CreateParams cp = new CreateParams();

       cp.ExStyle = GadgetWindow.WS_EX_TOOLWINDOW;

       cp.Caption = referenceWindowCaption;

       referenceWindow.CreateHandle(cp);

       NativeMethods.SetWindowPos(referenceWindow.Handle, 

         GadgetWindow.HWND_BOTTOM, 0, 0, 0, 0, GadgetWindow.SWP_NOMOVE | 

         GadgetWindow.SWP_NOSIZE | GadgetWindow.SWP_NOACTIVATE | 

         GadgetWindow.SWP_NOSENDCHANGING);

       // start a repeated timer to detect "Show Desktop" events 

       timer = new System.Threading.Timer(OnTimer, null,

         System.Threading.Timeout.Infinite, System.Threading.Timeout.Infinite);

     }

     private void StartTimer() {

       timer.Change(0, 200);

     }

     private void StopTimer() {

       timer.Change(System.Threading.Timeout.Infinite,

         System.Threading.Timeout.Infinite);

     }

     // the desktop worker window (if available) can hide the reference window

     private IntPtr GetDesktopWorkerWindow() {

       IntPtr shellWindow = NativeMethods.GetShellWindow();

       if (shellWindow == IntPtr.Zero)

         return IntPtr.Zero;

       int shellId;

       NativeMethods.GetWindowThreadProcessId(shellWindow, out shellId);

       IntPtr workerWindow = IntPtr.Zero;

       while ((workerWindow = NativeMethods.FindWindowEx(

           IntPtr.Zero, workerWindow, "WorkerW", null)) != IntPtr.Zero) {

         int workerId;

         NativeMethods.GetWindowThreadProcessId(workerWindow, out workerId);

         if (workerId == shellId) {

           IntPtr window = NativeMethods.FindWindowEx(

             workerWindow, IntPtr.Zero, "SHELLDLL_DefView", null);

           if (window != IntPtr.Zero) {

             IntPtr desktopWindow = NativeMethods.FindWindowEx(

               window, IntPtr.Zero, "SysListView32", null);

             if (desktopWindow != IntPtr.Zero)

               return workerWindow;

           }

         }

       }

       return IntPtr.Zero;

     }

     private void OnTimer(Object state) {

       bool showDesktopDetected;

       IntPtr workerWindow = GetDesktopWorkerWindow();

       if (workerWindow != IntPtr.Zero) {

         // search if the reference window is behind the worker window

         IntPtr reference = NativeMethods.FindWindowEx(

           IntPtr.Zero, workerWindow, null, referenceWindowCaption);

         showDesktopDetected = reference != IntPtr.Zero;

       } else {

         // if there is no worker window, then nothing can hide the reference

         showDesktopDetected = false;

       }

       if (showDesktop != showDesktopDetected) {

         showDesktop = showDesktopDetected;

         if (ShowDesktopChangedEvent != null) {

           ShowDesktopChangedEvent(showDesktop);

         }

       }

     }

     public static ShowDesktop Instance {

       get { return instance; }

     }

     // notify when the "show desktop" mode is changed

     public event ShowDesktopChangedEventHandler ShowDesktopChanged {

       add {

         // start the monitor timer when someone is listening

         if (ShowDesktopChangedEvent == null)           

           StartTimer();

         ShowDesktopChangedEvent += value;

       }

       remove {

         ShowDesktopChangedEvent -= value;

         // stop the monitor timer if nobody is interested

         if (ShowDesktopChangedEvent == null)

           StopTimer();

       }

     }

     private static class NativeMethods {

       private const string USER = "user32.dll";

       [DllImport(USER, CallingConvention = CallingConvention.Winapi)]

       public static extern bool SetWindowPos(IntPtr hWnd,

         IntPtr hWndInsertAfter, int X, int Y, int cx, int cy, uint uFlags);

       [DllImport(USER, CallingConvention = CallingConvention.Winapi)]

       public static extern IntPtr FindWindowEx(IntPtr hwndParent,

         IntPtr hwndChildAfter, string lpszClass, string lpszWindow);

       [DllImport(USER, CallingConvention = CallingConvention.Winapi)]

       public static extern IntPtr GetShellWindow();

       [DllImport(USER, CallingConvention = CallingConvention.Winapi)]

       public static extern int GetWindowThreadProcessId(IntPtr hWnd,

         out int processId);

     }  

   }

 }