/*
 * Copyright (c) 2006-2016, openmetaverse.co
 * All rights reserved.
 *
 * - Redistribution and use in source and binary forms, with or without
 *   modification, are permitted provided that the following conditions are met:
 *
 * - Redistributions of source code must retain the above copyright notice, this
 *   list of conditions and the following disclaimer.
 * - Neither the name of the openmetaverse.co nor the names
 *   of its contributors may be used to endorse or promote products derived from
 *   this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */

namespace OpenMetaverse
{
    public class CircularQueue<T>
    {
        public readonly T[] Items;

        private readonly int _capacity;
        private readonly object _syncRoot;

        public int First { get; private set; }
        public int Next { get; private set; }

        public CircularQueue(int capacity)
        {
            _capacity = capacity;
            Items = new T[capacity];
            _syncRoot = new object();
        }

        /// <summary>
        /// Copy constructor
        /// </summary>
        /// <param name="queue">Circular queue to copy</param>
        public CircularQueue(CircularQueue<T> queue)
        {
            lock (queue._syncRoot)
            {
                _capacity = queue._capacity;
                Items = new T[_capacity];
                _syncRoot = new object();

                for (var i = 0; i < _capacity; i++)
                    Items[i] = queue.Items[i];

                First = queue.First;
                Next = queue.Next;
            }
        }

        public void Clear()
        {
            lock (_syncRoot)
            {
                // Explicitly remove references to help garbage collection
                for (var i = 0; i < _capacity; i++)
                    Items[i] = default(T);

                First = Next;
            }
        }

        public void Enqueue(T value)
        {
            lock (_syncRoot)
            {
                Items[Next] = value;
                Next = (Next + 1) % _capacity;
                if (Next == First) First = (First + 1) % _capacity;
            }
        }

        public T Dequeue()
        {
            lock (_syncRoot)
            {
                var value = Items[First];
                Items[First] = default(T);

                if (First != Next)
                    First = (First + 1) % _capacity;

                return value;
            }
        }

        public T DequeueLast()
        {
            lock (_syncRoot)
            {
                // If the next element is right behind the first element (queue is full),
                // back up the first element by one
                var firstTest = First - 1;
                if (firstTest < 0) firstTest = _capacity - 1;

                if (firstTest == Next)
                {
                    --Next;
                    if (Next < 0) Next = _capacity - 1;

                    --First;
                    if (First < 0) First = _capacity - 1;
                }
                else if (First != Next)
                {
                    --Next;
                    if (Next < 0) Next = _capacity - 1;
                }

                var value = Items[Next];
                Items[Next] = default(T);

                return value;
            }
        }
    }
}