/* Copyright (c) 2010 Michael Lidgren

Permission is hereby granted, free of charge, to any person obtaining a copy of this software
and associated documentation files (the "Software"), to deal in the Software without
restriction, including without limitation the rights to use, copy, modify, merge, publish,
distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom
the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or
substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE
USE OR OTHER DEALINGS IN THE SOFTWARE.

*/
using System;
using System.Diagnostics;

namespace Lidgren.Network
{
	/// <summary>
	/// Thread safe (blocking) queue with TryDequeue() and EnqueueFirst()
	/// </summary>
	[DebuggerDisplay("Count={Count} Capacity={Capacity}")]
	public sealed class NetQueue<T>
	{
		// Example:
		// m_capacity = 8
		// m_size = 6
		// m_head = 4
		//
		// [0] item
		// [1] item (tail = ((head + size - 1) % capacity)
		// [2] 
		// [3] 
		// [4] item (head)
		// [5] item
		// [6] item 
		// [7] item
		//
		private T[] m_items;
		private readonly object m_lock;
		private int m_size;
		private int m_head;

		public int Count { get { return m_size; } }

		public int Capacity { get { return m_items.Length; } }

		public NetQueue(int initialCapacity)
		{
			m_lock = new object();
			m_items = new T[initialCapacity];
		}

		/// <summary>
		/// Places an item last/tail of the queue
		/// </summary>
		public void Enqueue(T item)
		{
#if DEBUG
			if (typeof(T) == typeof(NetSending))
			{
				NetSending om = item as NetSending;
				if (om != null)
					if (om.MessageType == NetMessageType.Error)
						throw new NetException("Enqueuing NetSending with MessageType.Error!");
			}
#endif
			lock (m_lock)
			{
				if (m_size == m_items.Length)
					SetCapacity(m_items.Length + 8);
							
				int slot = (m_head + m_size) % m_items.Length;
				m_items[slot] = item;
				m_size++;
			}
		}

		/// <summary>
		/// Places an item first, at the head of the queue
		/// </summary>
		public void EnqueueFirst(T item)
		{
			lock (m_lock)
			{
				if (m_size >= m_items.Length)
					SetCapacity(m_items.Length + 8);
			
				m_head--;
				if (m_head < 0)
					m_head = m_items.Length - 1;
				m_items[m_head] = item;
				m_size++;
			}
		}

		// must be called from within a lock(m_lock) !
		private void SetCapacity(int newCapacity)
		{
			if (m_size == 0)
			{
				if (m_size == 0)
				{
					m_items = new T[newCapacity];
					m_head = 0;
					return;
				}
			}

			T[] newItems = new T[newCapacity];

			if (m_head + m_size - 1 < m_items.Length)
			{
				Array.Copy(m_items, m_head, newItems, 0, m_size);
			}
			else
			{
				Array.Copy(m_items, m_head, newItems, 0, m_items.Length - m_head);
				Array.Copy(m_items, 0, newItems, m_items.Length - m_head, (m_size - (m_items.Length - m_head)));
			}

			m_items = newItems;
			m_head = 0;

		}

		/// <summary>
		/// Gets an item from the head of the queue, or returns default(T) if empty
		/// </summary>
		public bool TryDequeue(out T item)
		{
			if (m_size == 0)
			{
				item = default(T);
				return false;
			}

			lock (m_lock)
			{
				if (m_size == 0)
				{
					item = default(T);
					return false;
				}

				item = m_items[m_head];
				m_items[m_head] = default(T);

				m_head = (m_head + 1) % m_items.Length;
				m_size--;

				return true;
			}
		}

		public T TryPeek(int offset)
		{
			if (m_size == 0)
				return default(T);

			lock (m_lock)
			{
				if (m_size == 0)
					return default(T);
				return m_items[(m_head + offset) % m_items.Length];
			}
		}

		public bool Contains(T item)
		{
			lock (m_lock)
			{
				int ptr = m_head;
				for (int i = 0; i < m_size; i++)
				{
					if (m_items[ptr] == null)
					{
						if (item == null)
							return true;
					}
					else
					{
						if (m_items[ptr].Equals(item))
							return true;
					}
					ptr = (ptr + 1) % m_items.Length;
				}
			}
			return false;
		}

		public T[] ToArray()
		{
			lock (m_lock)
			{
				T[] retval = new T[m_size];
				int ptr = m_head;
				for (int i = 0; i < m_size; i++)
				{
					retval[i] = m_items[ptr++];
					if (ptr >= m_items.Length)
						ptr = 0;
				}
				return retval;
			}
		}

		public void Clear()
		{
			lock (m_lock)
			{
				for (int i = 0; i < m_items.Length; i++)
					m_items[i] = default(T);
				m_head = 0;
				m_size = 0;
			}
		}
	}
}
