/*

  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);

    }  

  }

}