// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.
 
// Description: Class used to track the visual appearance of Windows and make sure any events
// are propogated to that new UI.
 
using System;
using System.Windows.Automation;
using MS.Win32;
 
namespace MS.Internal.Automation
{
    // Class used to track new UI appearing and make sure any events
    // are propogated to that new UI.
    internal class WindowVisualStateTracker : WinEventWrap
    {
        //------------------------------------------------------
        //
        //  Constructors
        //
        //------------------------------------------------------
 
        #region Constructors
 
        internal WindowVisualStateTracker()
            : base(new int[] { NativeMethods.EVENT_OBJECT_LOCATIONCHANGE })
        {
            // Intentionally not setting the callback for the base WinEventWrap since the WinEventProc override
            // in this class calls RaiseEventInThisClientOnly to actually raise the event to the client.
        }
 
        #endregion Constructors
 
 
        //------------------------------------------------------
        //
        //  Internal Methods
        //
        //------------------------------------------------------
 
        #region Internal Methods
 
        internal override void WinEventProc(int eventId, IntPtr hwnd, int idObject, int idChild, uint eventTime)
        {
            // ignore any event not pertaining directly to the window
            if (idObject != UnsafeNativeMethods.OBJID_WINDOW)
            {
                return;
            }
 
            // Ignore if this is a bogus hwnd (shouldn't happen)
            if (hwnd == IntPtr.Zero)
            {
                return;
            }
 
            OnStateChange(hwnd, idObject, idChild);
        }
 
        #endregion Internal Methods
 
 
        //------------------------------------------------------
        //
        //  Private Methods
        //
        //------------------------------------------------------
 
        #region Private Methods
 
        private void OnStateChange(IntPtr hwnd, int idObject, int idChild)
        {
            NativeMethods.HWND nativeHwnd = NativeMethods.HWND.Cast(hwnd);
 
            // Ignore windows that have been destroyed
            if (!SafeNativeMethods.IsWindow(nativeHwnd))
            {
                return;
            }
 
            AutomationElement rawEl = AutomationElement.FromHandle(hwnd);
 
            // Raise this event only for elements with the WindowPattern.
            object patternObject;
            if (!rawEl.TryGetCurrentPattern(WindowPattern.Pattern, out patternObject))
                return;
 
            Object windowVisualState = rawEl.GetPatternPropertyValue(WindowPattern.WindowVisualStateProperty, false);
 
            // if has no state value just return
            if (!(windowVisualState is WindowVisualState))
            {
                return;
            }
 
            WindowVisualState state = (WindowVisualState)windowVisualState;
 
            // Filter... avoid duplicate events
            if (hwnd == _lastHwnd && state == _lastState)
            {
                return;
            }
 
            AutomationPropertyChangedEventArgs e = new AutomationPropertyChangedEventArgs(
                                    WindowPattern.WindowVisualStateProperty,
                                    null, 
                                    state);
 
            ClientEventManager.RaiseEventInThisClientOnly(AutomationElement.AutomationPropertyChangedEvent, rawEl, e);
 
            // save the last hwnd/rect for filtering out duplicates
            _lastHwnd = hwnd;
            _lastState = state;
        }
 
        #endregion Private Methods
 
 
        //------------------------------------------------------
        //
        //  Private Fields
        //
        //------------------------------------------------------
 
        #region Private Fields
 
        private WindowVisualState _lastState;      // keep track of last visual state
        private IntPtr _lastHwnd;                  // and hwnd for dup checking
 
        #endregion Private Fields
    }
}