Using AvalonEdit (WPF Text Editor)

// Copyright (c) AlphaSierraPapa for the SharpDevelop Team (for details please see \doc\copyright.txt)
// This code is distributed under the GNU LGPL (for details please see \doc\license.txt)

using System;
using System.Collections.Generic;
using System.Diagnostics;

namespace ICSharpCode.AvalonEdit.Utils
{
	/// <summary>
	/// Double-ended queue.
	/// </summary>
	[System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Naming", "CA1710:IdentifiersShouldHaveCorrectSuffix")]
	[Serializable]
	public sealed class Deque<T> : ICollection<T>
	{
		T[] arr = Empty<T>.Array;
		int size, head, tail;
		
		/// <inheritdoc/>
		public int Count {
			get { return size; }
		}
		
		/// <inheritdoc/>
		public void Clear()
		{
			arr = Empty<T>.Array;
			size = 0;
			head = 0;
			tail = 0;
		}
		
		/// <summary>
		/// Gets/Sets an element inside the deque.
		/// </summary>
		public T this[int index] {
			get {
				ThrowUtil.CheckInRangeInclusive(index, "index", 0, size - 1);
				return arr[(head + index) % arr.Length];
			}
			set {
				ThrowUtil.CheckInRangeInclusive(index, "index", 0, size - 1);
				arr[(head + index) % arr.Length] = value;
			}
		}
		
		/// <summary>
		/// Adds an element to the end of the deque.
		/// </summary>
		[System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Naming", "CA1702:CompoundWordsShouldBeCasedCorrectly", MessageId = "PushBack")]
		public void PushBack(T item)
		{
			if (size == arr.Length)
				SetCapacity(Math.Max(4, arr.Length * 2));
			arr[tail++] = item;
			if (tail == arr.Length) tail = 0;
			size++;
		}
		
		/// <summary>
		/// Pops an element from the end of the deque.
		/// </summary>
		public T PopBack()
		{
			if (size == 0)
				throw new InvalidOperationException();
			if (tail == 0)
				tail = arr.Length - 1;
			else
				tail--;
			T val = arr[tail];
			arr[tail] = default(T); // allow GC to collect the element
			size--;
			return val;
		}
		
		/// <summary>
		/// Adds an element to the front of the deque.
		/// </summary>
		public void PushFront(T item)
		{
			if (size == arr.Length)
				SetCapacity(Math.Max(4, arr.Length * 2));
			if (head == 0)
				head = arr.Length - 1;
			else
				head--;
			arr[head] = item;
			size++;
		}
		
		/// <summary>
		/// Pops an element from the end of the deque.
		/// </summary>
		public T PopFront()
		{
			if (size == 0)
				throw new InvalidOperationException();
			T val = arr[head];
			arr[head] = default(T); // allow GC to collect the element
			head++;
			if (head == arr.Length) head = 0;
			size--;
			return val;
		}
		
		void SetCapacity(int capacity)
		{
			T[] newArr = new T[capacity];
			CopyTo(newArr, 0);
			head = 0;
			tail = (size == capacity) ? 0 : size;
			arr = newArr;
		}
		
		/// <inheritdoc/>
		public IEnumerator<T> GetEnumerator()
		{
			if (head < tail) {
				for (int i = head; i < tail; i++)
					yield return arr[i];
			} else {
				for (int i = head; i < arr.Length; i++)
					yield return arr[i];
				for (int i = 0; i < tail; i++)
					yield return arr[i];
			}
		}
		
		System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator()
		{
			return this.GetEnumerator();
		}
		
		bool ICollection<T>.IsReadOnly {
			get { return false; }
		}
		
		void ICollection<T>.Add(T item)
		{
			PushBack(item);
		}
		
		/// <inheritdoc/>
		public bool Contains(T item)
		{
			EqualityComparer<T> comparer = EqualityComparer<T>.Default;
			foreach (T element in this)
				if (comparer.Equals(item, element))
					return true;
			return false;
		}
		
		/// <inheritdoc/>
		public void CopyTo(T[] array, int arrayIndex)
		{
			if (array == null)
				throw new ArgumentNullException("array");
			if (head < tail) {
				Array.Copy(arr, head, array, arrayIndex, tail - head);
			} else {
				int num1 = arr.Length - head;
				Array.Copy(arr, head, array, arrayIndex, num1);
				Array.Copy(arr, 0, array, arrayIndex + num1, tail);
			}
		}
		
		bool ICollection<T>.Remove(T item)
		{
			throw new NotSupportedException();
		}
	}
}