// Copyright 1998-2014 Epic Games, Inc. All Rights Reserved.

using System;
using System.Collections;
using System.Collections.Generic;
using System.Threading;

namespace Tools.DotNETCommon.ThreadSafeQueue
{
	/// <summary>
	/// A thread-safe reader-writer-locked wrapper to the stock .NET Queue container.
	/// </summary>
	/// <typeparam name="TValue">The type of the classes that will be queued in this container.</typeparam>
	/// <remarks>All operations are exception checked, so it will return default values rather than crash when used improperly.</remarks>
	public class ThreadSafeQueue<TValue>
	{
		/// <summary>The key to protecting the contained queue properly</summary>
		private ReaderWriterLock AccessLock = new ReaderWriterLock();

		/// <summary>The protected queue</summary>
		private Queue<TValue> ProtectedQueue = new Queue<TValue>();

		/// <summary>
		/// Default constructor.
		/// </summary>
		public ThreadSafeQueue()
		{
		}	

		/// <summary>
		/// Completely empties the queue.
		/// </summary>
		public void Clear()
		{
			// Modifies the collection, use a writer lock
			AccessLock.AcquireWriterLock( Timeout.Infinite );
			try
			{
				ProtectedQueue.Clear();
			}
			finally
			{
				AccessLock.ReleaseWriterLock();
			}
		}

		/// <summary>
		/// Queue up a new element.
		/// </summary>
		/// <param name="V">A new element to queue.</param>
		public void Enqueue( TValue V )
		{
			// Modifies the collection, use a writer lock
			AccessLock.AcquireWriterLock( Timeout.Infinite );
			try
			{
				ProtectedQueue.Enqueue( V );
			}
			finally
			{
				AccessLock.ReleaseWriterLock();
			}
		}

		/// <summary>
		/// Dequeue an existing element.
		/// </summary>
		/// <returns>A previously queued element.</returns>
		public TValue Dequeue()
		{
			// Modifies the collection, use a writer lock
			AccessLock.AcquireWriterLock( Timeout.Infinite );
			TValue V = default( TValue );
			try
			{
				V = ProtectedQueue.Dequeue();
			}
			finally
			{
				AccessLock.ReleaseWriterLock();
			}

			return V;
		}

		/// <summary>
		/// Return all elements of the queue as an array.
		/// </summary>
		/// <returns>An array of all elements in the queue.</returns>
		public TValue[] ToArray()
		{
			// Does not modify the collection, use a reader lock
			AccessLock.AcquireReaderLock( Timeout.Infinite );
			TValue[] ReturnValues;
			try
			{
				ReturnValues = ProtectedQueue.ToArray();
			}
			finally
			{
				AccessLock.ReleaseReaderLock();
			}
			return ReturnValues;
		}

		/// <summary>
		/// Return the number of elements in the queue.
		/// </summary>
		/// <returns>A count of elements in the queue.</returns>
		public int Count
		{
			get
			{
				// Does not modify the collection, use a reader lock
				AccessLock.AcquireReaderLock( Timeout.Infinite );
				int ReturnValue = 0;
				try
				{
					ReturnValue = ProtectedQueue.Count;
				}
				finally
				{
					AccessLock.ReleaseReaderLock();
				}

				return ReturnValue;
			}
		}
	}
}