/* Copyright 2013-2014 Daikon Forge */

namespace DaikonForge.VoIP
{
	using System;
	using System.Collections;
	using System.Collections.Generic;

	/// <summary>
	/// Defines a simplified Generic List customized specifically for 
	/// game development - Implements object pooling, minimizes memory
	/// allocations during common operations, replaces common extension
	/// methods with bespoke implementations that do not allocate 
	/// iterators, etc.
	/// </summary>
	public class FastList<T> : IList<T>, IDisposable
	{
		#region Object pooling

		#region Static variables

		// NOTE: Switched to Queue<object> in an attempt to work around 
		// a bug in the version of Mono used by Unity on iOS - http://stackoverflow.com/q/16542915
		private static Queue<object> pool = new Queue<object>( 1024 );

		#endregion

		/// <summary>
		/// Releases all instances in the object pool.
		/// </summary>
		public static void ClearPool()
		{
			lock( pool )
			{
				pool.Clear();
				pool.TrimExcess();
			}
		}

		/// <summary>
		/// Returns a reference to a <see cref="dfList<T>"/> instance. If there are 
		/// available instances in the object pool, the first available instance will
		/// be returned. If there are no instances available, then a new instance
		/// will be created. Use the <see cref="Release"/> function to return the instance
		/// to the object pool.
		/// </summary>
		public static FastList<T> Obtain()
		{
			lock( pool )
			{
				if( pool.Count == 0 )
					return new FastList<T>();

				return (FastList<T>)pool.Dequeue();
			}
		}

		/// <summary>
		/// Returns a reference to a <see cref="dfList<T>"/> instance. If there are 
		/// available instances in the object pool, the first available instance will
		/// be returned. If there are no instances available, then a new instance
		/// will be created. Use the <see cref="Release"/> function to return the instance
		/// to the object pool.
		/// </summary>
		public static FastList<T> Obtain( int capacity )
		{
			var list = Obtain();

			list.EnsureCapacity( capacity );

			return list;
		}

		/// <summary>
		/// Releases the <see cref="FastList"/> back to the object pool
		/// </summary>
		public void Release()
		{
			Clear();

			lock( pool )
			{
				pool.Enqueue( this );
			}
		}

		#endregion

		#region Private instance fields

		private const int DEFAULT_CAPACITY = 128;

		private T[] items = new T[ DEFAULT_CAPACITY ];
		private int count = 0;

		private bool isElementTypeValueType = false;
		//private bool isElementTypePoolable = false;

		#endregion

		#region Constructor

		internal FastList()
		{
#if !UNITY_EDITOR && UNITY_METRO 
			isElementTypeValueType = typeof( T ).GetTypeInfo().IsValueType;
			isElementTypePoolable = typeof( IPoolable ).GetTypeInfo().IsAssignableFrom( typeof( T ).GetTypeInfo() );
#else
			isElementTypeValueType = typeof( T ).IsValueType;
			//isElementTypePoolable = typeof( IPoolable ).IsAssignableFrom( typeof( T ) );
#endif
		}

		internal FastList( IList<T> listToClone )
			: this()
		{
			AddRange( listToClone );
		}

		internal FastList( int capacity )
			: this()
		{
			EnsureCapacity( capacity );
		}

		#endregion

		#region Public properties

		/// <summary>
		/// Returns the number of items in the list
		/// </summary>
		public int Count
		{
			get { return this.count; }
		}

		/// <summary>
		/// Returns the number of items this list can hold without needing to 
		/// resize the internal array (for internal use only)
		/// </summary>
		internal int Capacity
		{
			get { return this.items.Length; }
		}

		/// <summary>
		/// Gets a value indicating whether the list is read-only. Inherited from IList&lt;&gt;
		/// </summary>
		public bool IsReadOnly
		{
			get { return false; }
		}

		/// <summary>
		/// Gets/Sets the item at the specified index
		/// </summary>
		public T this[ int index ]
		{
			get
			{
				if( index < 0 || index > this.count - 1 )
					throw new IndexOutOfRangeException();
				return this.items[ index ];
			}
			set
			{
				if( index < 0 || index > this.count - 1 )
					throw new IndexOutOfRangeException();
				this.items[ index ] = value;
			}
		}

		/// <summary>
		/// Allows direct access to the underlying <see cref="System.Array"/>
		/// containing this list's data. This array will most likely contain more 
		/// elements than the list reports via the <see cref="Count"/> property.
		/// This property is intended for internal use by the UI library and should
		/// not be accessed by other code.
		/// </summary>
		internal T[] Items
		{
			get { return this.items; }
		}

		#endregion

		#region Public methods

		/// <summary>
		/// Adds a new item to the end of the list. Provided only for call-level 
		/// compatability with code that treats this collection as a Queue.
		/// </summary>
		public void Enqueue( T item )
		{
			lock( items )
			{
				this.Add( item );
			}
		}

		/// <summary>
		/// Returns the first item in the collection and removes it from the list. 
		/// Provided only for call-level compatability with code that treats this 
		/// collection as a Queue.
		/// </summary>
		public T Dequeue()
		{
			lock( items )
			{
				if( this.count == 0 )
					throw new IndexOutOfRangeException();

				var item = this.items[ 0 ];

				this.RemoveAt( 0 );

				return item;
			}
		}

		/// <summary>
		/// Returns the last item in the collection and removes it frm the list.
		/// Provided only for call-level compatibility with code that treats this
		/// collection as a Stack.
		/// </summary>
		/// <returns></returns>
		public T Pop()
		{
			lock( items )
			{
				if( this.count == 0 )
					throw new IndexOutOfRangeException();

				var item = this.items[ this.count - 1 ];

				this.count -= 1;

				return item;
			}
		}

		/// <summary>
		/// Returns a shallow copy of this <see cref="dfList<T>"/> instance 
		/// </summary>
		/// <returns></returns>
		public FastList<T> Clone()
		{
			var clone = Obtain( this.count );

			Array.Copy( this.items, 0, clone.items, 0, this.count );

			clone.count = this.count;

			return clone;
		}

		/// <summary>
		/// Reverses the order of the elements in the list
		/// </summary>
		public void Reverse()
		{
			Array.Reverse( this.items, 0, this.count );
		}

		/// <summary>
		/// Sorts the elements in the entire <see cref="FastList" /> using the default comparer.
		/// </summary>
		public void Sort()
		{
			Array.Sort( this.items, 0, this.count, null );
		}

		/// <summary>
		/// Sorts the elements in the entire <see cref="FastList" /> using the specified comparer.
		/// </summary>
		public void Sort( IComparer<T> comparer )
		{
			Array.Sort( this.items, 0, this.count, comparer );
		}

		/// <summary>
		/// Sorts the elements in the entire <see cref="System.Collections.Generic.List" /> using the specified <see cref="System.Comparison" />.
		/// </summary>
		/// <param name="comparison">The <see cref="System.Comparison" /> to use when comparing elements.</param>
		public void Sort( Comparison<T> comparison )
		{
			if( comparison == null )
			{
				throw new ArgumentNullException( "comparison" );
			}
			if( this.count > 0 )
			{
				using( var comparer = FunctorComparer.Obtain( comparison ) )
				{
					Array.Sort<T>( this.items, 0, this.count, comparer );
				}
			}
		}

		/// <summary>
		/// Ensures that the <see cref="FastList" /> has enough capacity to store <paramref name="Size"/> elements
		/// </summary>
		/// <param name="Size"></param>
		public void EnsureCapacity( int Size )
		{
			if( items.Length < Size )
			{
				var newSize = ( Size / DEFAULT_CAPACITY ) * DEFAULT_CAPACITY + DEFAULT_CAPACITY;
				Array.Resize<T>( ref this.items, newSize );
			}
		}

		public void ForceCount( int count )
		{
			this.count = count;
		}

		/// <summary>
		/// Adds the elements of the specified collection to the end of the <see cref="FastList"/>
		/// </summary>
		public void AddRange( FastList<T> list )
		{
			var listCount = list.count;

			EnsureCapacity( this.count + listCount );
			Array.Copy( list.items, 0, this.items, this.count, listCount );
			this.count += listCount;
		}

		/// <summary>
		/// Adds the elements of the specified collection to the end of the <see cref="FastList"/>
		/// </summary>
		public void AddRange( IList<T> list )
		{
			var listCount = list.Count;

			EnsureCapacity( this.count + listCount );

			for( int i = 0; i < listCount; i++ )
			{
				this.items[ count++ ] = list[ i ];
			}
		}

		/// <summary>
		/// Adds the elements of the specified collection to the end of the <see cref="FastList"/>
		/// </summary>
		public void AddRange( T[] list )
		{
			var listLength = list.Length;

			EnsureCapacity( this.count + listLength );
			Array.Copy( list, 0, this.items, this.count, listLength );
			this.count += listLength;
		}

		/// <summary>
		/// Determines the index of a specific item in the collection
		/// </summary>
		public int IndexOf( T item )
		{
			return Array.IndexOf<T>( this.items, item, 0, this.count );
		}

		/// <summary>
		/// Inserts an item to the collection at the specified index
		/// </summary>
		/// <param name="index"></param>
		/// <param name="item"></param>
		public void Insert( int index, T item )
		{
			EnsureCapacity( this.count + 1 );

			if( index < this.count )
			{
				Array.Copy( this.items, index, this.items, index + 1, this.count - index );
			}

			this.items[ index ] = item;
			this.count += 1;
		}

		/// <summary>
		/// Inserts an array of items at the specified index
		/// </summary>
		public void InsertRange( int index, T[] array )
		{
			if( array == null )
				throw new ArgumentNullException( "items" );

			if( index < 0 || index > this.count )
				throw new ArgumentOutOfRangeException( "index" );

			EnsureCapacity( this.count + array.Length );

			if( index < this.count )
			{
				Array.Copy( this.items, index, this.items, index + array.Length, this.count - index );
			}

			array.CopyTo( this.items, index );

			this.count += array.Length;
		}

		/// <summary>
		/// Inserts a collection of items at the specified index
		/// </summary>
		public void InsertRange( int index, FastList<T> list )
		{
			if( list == null )
				throw new ArgumentNullException( "items" );

			if( index < 0 || index > this.count )
				throw new ArgumentOutOfRangeException( "index" );

			EnsureCapacity( this.count + list.count );

			if( index < this.count )
			{
				Array.Copy( this.items, index, this.items, index + list.count, this.count - index );
			}

			Array.Copy( list.items, 0, this.items, index, list.count );

			this.count += list.count;
		}

		/// <summary>
		/// Removes all items matching the predicate condition from the list
		/// </summary>
		public void RemoveAll( Predicate<T> predicate )
		{
			var index = 0;
			while( index < this.count )
			{
				if( predicate( items[ index ] ) )
				{
					RemoveAt( index );
				}
				else
				{
					index += 1;
				}
			}
		}

		/// <summary>
		/// Removes the item at the specified index
		/// </summary>
		public void RemoveAt( int index )
		{
			if( index >= this.count )
			{
				throw new ArgumentOutOfRangeException();
			}

			this.count -= 1;

			if( index < this.count )
			{
				Array.Copy( this.items, index + 1, this.items, index, this.count - index );
			}

			this.items[ this.count ] = default( T );
		}

		/// <summary>
		/// Removes <paramref name="length"/> items from the collection at the specified index
		/// </summary>
		public void RemoveRange( int index, int length )
		{
			if( index < 0 || length < 0 || this.count - index < length )
			{
				throw new ArgumentOutOfRangeException();
			}

			if( count > 0 )
			{
				this.count -= length;
				if( index < this.count )
				{
					Array.Copy( this.items, index + length, this.items, index, this.count - index );
				}

				Array.Clear( this.items, this.count, length );
			}
		}

		/// <summary>
		/// Adds an item to the collection
		/// </summary>
		public void Add( T item )
		{
			EnsureCapacity( this.count + 1 );
			this.items[ this.count++ ] = item;
		}

		/// <summary>
		/// Adds two items to the collection
		/// </summary>
		public void Add( T item0, T item1 )
		{
			EnsureCapacity( this.count + 2 );
			this.items[ this.count++ ] = item0;
			this.items[ this.count++ ] = item1;
		}

		/// <summary>
		/// Adds three items to the collection
		/// </summary>
		public void Add( T item0, T item1, T item2 )
		{
			EnsureCapacity( this.count + 3 );
			this.items[ this.count++ ] = item0;
			this.items[ this.count++ ] = item1;
			this.items[ this.count++ ] = item2;
		}

		/// <summary>
		/// Adds four items to the collection
		/// </summary>
		public void Add( T item0, T item1, T item2, T item3 )
		{
			EnsureCapacity( this.count + 3 );
			this.items[ this.count++ ] = item0;
			this.items[ this.count++ ] = item1;
			this.items[ this.count++ ] = item2;
			this.items[ this.count++ ] = item3;
		}

		/// <summary>
		/// Removes all items from the collection
		/// </summary>
		public void Clear()
		{
			if( !isElementTypeValueType )
			{
				Array.Clear( this.items, 0, this.items.Length );
			}

			this.count = 0;
		}

		/// <summary>
		/// Resizes the internal buffer to exactly match the number of elements in the collection
		/// </summary>
		public void TrimExcess()
		{
			Array.Resize( ref this.items, this.count );
		}

		/// <summary>
		/// Determines whether the collection contains the specified value
		/// </summary>
		public bool Contains( T item )
		{
			if( item == null )
			{
				for( int i = 0; i < this.count; i++ )
				{
					if( this.items[ i ] == null )
					{
						return true;
					}
				}
				return false;
			}

			EqualityComparer<T> comparer = EqualityComparer<T>.Default;

			for( int j = 0; j < this.count; j++ )
			{
				if( comparer.Equals( this.items[ j ], item ) )
				{
					return true;
				}
			}

			return false;
		}

		/// <summary>
		/// Copies the elements of the collection to a <see cref="System.Array"/> instance
		/// </summary>
		/// <param name="array"></param>
		public void CopyTo( T[] array )
		{
			CopyTo( array, 0 );
		}

		/// <summary>
		/// Copies the elements of the collection to an <see cref="System.Array"/> starting at the specified index
		/// </summary>
		public void CopyTo( T[] array, int arrayIndex )
		{
			Array.Copy( this.items, 0, array, arrayIndex, this.count );
		}

		/// <summary>
		/// Copies the elements of the collection to an <see cref="System.Array"/>
		/// </summary>
		/// <param name="sourceIndex">The starting position in the collection</param>
		/// <param name="dest">The destination array</param>
		/// <param name="destIndex">The position in the array to start copying to</param>
		/// <param name="length">How many elements to copy</param>
		public void CopyTo( int sourceIndex, T[] dest, int destIndex, int length )
		{
			if( sourceIndex + length > this.count )
				throw new IndexOutOfRangeException( "sourceIndex" );

			if( dest == null )
				throw new ArgumentNullException( "dest" );

			if( destIndex + length > dest.Length )
				throw new IndexOutOfRangeException( "destIndex" );

			Array.Copy( this.items, sourceIndex, dest, destIndex, length );
		}

		/// <summary>
		/// Removes the first occurrence of a specific object from the collection
		/// </summary>
		public bool Remove( T item )
		{
			var index = IndexOf( item );
			if( index == -1 )
				return false;

			RemoveAt( index );

			return true;
		}

		/// <summary>
		/// Returns a List&lt;T&gt; collection containing all elements of this collection
		/// </summary>
		/// <returns></returns>
		public List<T> ToList()
		{
			var list = new List<T>( this.count );
			list.AddRange( this.ToArray() );
			return list;
		}

		/// <summary>
		/// For internal use only.
		/// </summary>
		// @private
		internal T[] ToTempArray()
		{
			var result = TempArray<T>.Obtain( this.count );
			Array.Copy( items, 0, result, 0, this.count );
			return result;
		}

		/// <summary>
		/// Returns an array containing all elements of this collection
		/// </summary>
		public T[] ToArray()
		{
			var array = new T[ this.count ];

			Array.Copy( this.items, 0, array, 0, this.count );

			return array;
		}

		/// <summary>
		/// Returns a subset of the collection's items as an array
		/// </summary>
		public T[] ToArray( int index, int length )
		{
			var array = new T[ this.count ];

			if( this.count > 0 )
			{
				CopyTo( index, array, 0, length );
			}

			return array;
		}

		/// <summary>
		/// Returns a subset of the collection's items as another dfList
		/// </summary>
		public FastList<T> GetRange( int index, int length )
		{
			var range = Obtain( length );
			CopyTo( 0, range.items, index, length );
			return range;
		}

		#endregion

		#region LINQ replacement methods (avoids allocating enumerators)

		/// <summary>
		/// Returns whether any items in the collection match the condition 
		/// defined by the predicate.
		/// </summary>
		/// <param name="predicate">A function to test each element for a condition.</param>
		/// <returns>true if any elements in the source sequence pass the test in the specified
		/// predicate; otherwise, false.</returns>
		public bool Any( Func<T, bool> predicate )
		{
			for( int i = 0; i < this.count; i++ )
			{
				if( predicate( this.items[ i ] ) )
					return true;
			}

			return false;
		}

		/// <summary>
		/// Returns the first element in the list. Throws an exception if the list is empty.
		/// </summary>
		/// <returns></returns>
		public T First()
		{
			if( this.count == 0 )
			{
				throw new IndexOutOfRangeException();
			}

			return this.items[ 0 ];
		}

		/// <summary>
		/// Returns the first element of the collection, or a default value 
		/// if the collection contains no elements.
		/// </summary>
		public T FirstOrDefault()
		{
			if( this.count > 0 )
				return this.items[ 0 ];

			return default( T );
		}

		/// <summary>
		/// Returns the first element of the collection matching the condition defined by 
		/// <paramref name="predicate"/>, or the default value for the element type if the 
		/// collection contains no elements.
		/// </summary>
		public T FirstOrDefault( Func<T, bool> predicate )
		{
			for( int i = 0; i < this.count; i++ )
			{
				if( predicate( items[ i ] ) )
					return items[ i ];
			}

			return default( T );
		}

		/// <summary>
		/// Returns the last element in the list. Throws an exception if the list is empty.
		/// </summary>
		public T Last()
		{
			if( this.count == 0 )
			{
				throw new IndexOutOfRangeException();
			}

			return this.items[ this.count - 1 ];
		}

		/// <summary>
		/// Returns the last element of the collection, or a default value 
		/// if the collection contains no elements.
		/// </summary>
		public T LastOrDefault()
		{
			if( this.count == 0 )
			{
				return default( T );
			}

			return this.items[ this.count - 1 ];
		}

		/// <summary>
		/// Returns the last element of the collection matching the condition defined by 
		/// <paramref name="predicate"/>, or the default value for the element type if the 
		/// collection contains no elements.
		/// </summary>
		public T LastOrDefault( Func<T, bool> predicate )
		{
			var result = default( T );

			for( int i = 0; i < this.count; i++ )
			{
				if( predicate( items[ i ] ) )
				{
					result = items[ i ];
				}
			}

			return result;
		}

		/// <summary>
		/// Returns a <see cref="FastList"/> list containing all elements
		/// of the collection matching the condition specified by <paramref name="predicate"/>
		/// </summary>
		public FastList<T> Where( Func<T, bool> predicate )
		{
			var result = FastList<T>.Obtain( this.count );

			for( int i = 0; i < this.count; i++ )
			{
				if( predicate( items[ i ] ) )
				{
					result.Add( items[ i ] );
				}
			}

			return result;
		}

		/// <summary>
		/// Returns the count of elements in the list that satisfy the
		/// condition defined by <paramref name="predicate"/>
		/// </summary>
		public int Matching( Func<T, bool> predicate )
		{
			var matching = 0;

			for( int i = 0; i < this.count; i++ )
			{
				if( predicate( items[ i ] ) )
					matching += 1;
			}

			return matching;
		}

		/// <summary>
		/// Projects each element of a sequence into a new form defined by <paramref name="selector"/>
		/// </summary>
		public FastList<TResult> Select<TResult>( Func<T, TResult> selector )
		{
			var result = FastList<TResult>.Obtain( this.count );

			for( int i = 0; i < this.count; i++ )
			{
				result.Add( selector( items[ i ] ) );
			}

			return result;
		}

		/// <summary>
		/// Returns a concatenated list containing all elements both lists
		/// </summary>
		public FastList<T> Concat( FastList<T> list )
		{
			var result = FastList<T>.Obtain( this.count + list.count );

			result.AddRange( this );
			result.AddRange( list );

			return result;
		}

		/// <summary>
		/// Converts all elements of the list to the specified target type
		/// </summary>
		public FastList<TResult> Convert<TResult>()
		{
			var result = FastList<TResult>.Obtain( this.count );

			for( int i = 0; i < this.count; i++ )
			{
				result.Add( (TResult)System.Convert.ChangeType( this.items[ i ], typeof( TResult ) ) );
			}

			return result;
		}

		/// <summary>
		/// Performs an action on each element of the list
		/// </summary>
		/// <param name="action">The action to be performed on each element</param>
		public void ForEach( Action<T> action )
		{
			var index = 0;
			while( index < this.Count )
			{
				action( items[ index++ ] );
			}
		}

		#endregion

		#region IEnumerable<T> implementation

		// NOTE: The IEnumerable<T> implementation here is horribly broken on iOS, and until
		// I can figure out a way to implement typed enumerators that do work on iOS, please
		// use a for(;;) loop instead of foreach(). Note that this may also apply to using
		// LINQ queries, which may use foreach() or an GetEnumerator() internally.

		/// <summary>
		/// Returns an IEnumerator instance that can be used to iterate through
		/// the elements in this list.
		/// </summary>
		public IEnumerator<T> GetEnumerator()
		{
			return PooledEnumerator.Obtain( this, null );
		}

		/// <summary>
		/// Returns an IEnumerator instance that can be used to iterate through
		/// the elements in this list.
		/// </summary>
		IEnumerator IEnumerable.GetEnumerator()
		{
			return PooledEnumerator.Obtain( this, null );
		}

		#endregion

		#region IDisposable implementation

		/// <summary>
		/// Releases the memory used by this object and returns it to the object pool
		/// </summary>
		public void Dispose()
		{
			Release();
		}

		#endregion

		#region Nested classes

		/// <summary>
		/// This custom enumerator class implements object pooling in order
		/// to reduce the number and frequency of memory allocations. It is 
		/// primarily expected to be used by framework and library code which
		/// treats the associated collection as an IEnumerable&lt;T&gt; rather
		/// than as a <see cref="dfList"/>. For instance, LINQ contains 
		/// several extension methods which will treat the collection as 
		/// an IEnumerable&lt;T&gt; and will create, use, and Dispose() of 
		/// the enumerator while performing the query. Similarly, many 
		/// third-party libraries will use a foreach() loop over a collection 
		/// rather than using for() with numeric indices, and the object pooling 
		/// implemented by this class will help to mitigate the number of 
		/// allocations typically caused by using such code.
		/// </summary>
		private class PooledEnumerator : IEnumerator<T>, IEnumerable<T>
		{

			#region Static variables

			private static Queue<PooledEnumerator> pool = new Queue<PooledEnumerator>();

			#endregion

			#region Private variables

			private FastList<T> list;
			private Func<T, bool> predicate;
			private int currentIndex;
			private T currentValue;
			private bool isValid = false;

			#endregion

			#region Pooling

			public static PooledEnumerator Obtain( FastList<T> list, Func<T, bool> predicate )
			{
				var enumerator = ( pool.Count > 0 ) ? pool.Dequeue() : new PooledEnumerator();
				enumerator.ResetInternal( list, predicate );

				return enumerator;
			}

			public void Release()
			{
				if( this.isValid )
				{
					this.isValid = false;
					pool.Enqueue( this );
				}
			}

			#endregion

			#region IEnumerator<T> Members

			public T Current
			{
				get
				{
					if( !this.isValid )
						throw new InvalidOperationException( "The enumerator is no longer valid" );

					return this.currentValue;
				}
			}

			#endregion

			#region Private utility methods

			private void ResetInternal( FastList<T> list, Func<T, bool> predicate )
			{
				this.isValid = true;
				this.list = list;
				this.predicate = predicate;
				this.currentIndex = 0;
				this.currentValue = default( T );
			}

			#endregion

			#region IDisposable Members

			public void Dispose()
			{
				Release();
			}

			#endregion

			#region IEnumerator Members

			object IEnumerator.Current
			{
				get
				{
					return this.Current;
				}
			}

			public bool MoveNext()
			{
				if( !this.isValid )
					throw new InvalidOperationException( "The enumerator is no longer valid" );

				while( this.currentIndex < this.list.Count )
				{
					var valueAtIndex = this.list[ currentIndex++ ];
					if( predicate != null )
					{
						if( !predicate( valueAtIndex ) )
							continue;
					}

					this.currentValue = valueAtIndex;
					return true;
				}

				Release();

				this.currentValue = default( T );
				return false;
			}

			public void Reset()
			{
				throw new NotImplementedException();
			}

			#endregion

			#region IEnumerable Members

			public IEnumerator<T> GetEnumerator()
			{
				return this;
			}

			IEnumerator IEnumerable.GetEnumerator()
			{
				return this;
			}

			#endregion
		}

		private class FunctorComparer : IComparer<T>, IDisposable
		{
			#region Static variables

			private static Queue<FunctorComparer> pool = new Queue<FunctorComparer>();

			#endregion

			#region Private instance variables

			private Comparison<T> comparison;

			#endregion

			#region Object pooling

			public static FunctorComparer Obtain( Comparison<T> comparison )
			{
				var comparer = ( pool.Count > 0 ) ? pool.Dequeue() : new FunctorComparer();
				comparer.comparison = comparison;
				return comparer;
			}

			public void Release()
			{
				this.comparison = null;

				if( !pool.Contains( this ) )
				{
					pool.Enqueue( this );
				}
			}

			#endregion

			#region IComparer<T> implementation

			public int Compare( T x, T y )
			{
				return this.comparison( x, y );
			}

			#endregion

			#region IDisposable implementation

			public void Dispose()
			{
				this.Release();
			}

			#endregion
		}

		#endregion
	}
}