using System;
using System.Collections.ObjectModel;
using System.Collections.Specialized;
using System.Windows.Threading;

namespace Common.Infrastructure.Extensions
{
	/// <summary>
	/// Purpose of this class is to allow changes to the collection to be handled via <see cref="DispatcherObject"/>s.
	/// This is required in multi-threaded environments.
	/// </summary>
	/// <remarks>
	/// Ripped character for character from here: 
	/// http://geekswithblogs.net/NewThingsILearned/archive/2008/01/16/have-worker-thread-update-observablecollection-that-is-bound-to-a.aspx
	/// </remarks>
	/// <typeparam name="T"></typeparam>
	public class ObservableCollectionEx<T> : ObservableCollection<T>
	{
		// Override the event so this class can access it
		public override event NotifyCollectionChangedEventHandler CollectionChanged;

		protected override void OnCollectionChanged(NotifyCollectionChangedEventArgs e)
		{
			// Be nice - use BlockReentrancy like MSDN said
			using (BlockReentrancy())
			{
				NotifyCollectionChangedEventHandler eventHandler = CollectionChanged;
				if (eventHandler == null)
					return;

				Delegate[] delegates = eventHandler.GetInvocationList();
				// Walk thru invocation list
				foreach (NotifyCollectionChangedEventHandler handler in delegates)
				{
					DispatcherObject dispatcherObject = handler.Target as DispatcherObject;
					// If the subscriber is a DispatcherObject and different thread
					if (dispatcherObject != null && dispatcherObject.CheckAccess() == false)
					{
						// Invoke handler in the target dispatcher's thread
						dispatcherObject.Dispatcher.Invoke(DispatcherPriority.DataBind, handler, this, e);
					}
					else // Execute handler as is
						handler(this, e);
				}
			}
		}
	}

}