namespace System.Collections
{
    using System.Threading;

    /// <summary>
    /// Same as Queue except Dequeue function blocks until there is an object to return.
    /// Note: This class does not need to be synchronized
    /// </summary>
    public class BlockingQueue : Queue
    {
        private bool open;

        /// <summary>
        /// Create new BlockingQueue.
        /// </summary>
        /// <param name="col">The System.Collections.ICollection to copy elements from</param>
        public BlockingQueue(ICollection col)
            : base(col)
        {
            open = true;
        }

        /// <summary>
        /// Create new BlockingQueue.
        /// </summary>
        /// <param name="capacity">The initial number of elements that the queue can contain</param>
        /// <param name="growFactor">The factor by which the capacity of the queue is expanded</param>
        public BlockingQueue(int capacity, float growFactor)
            : base(capacity, growFactor)
        {
            open = true;
        }

        /// <summary>
        /// Create new BlockingQueue.
        /// </summary>
        /// <param name="capacity">The initial number of elements that the queue can contain</param>
        public BlockingQueue(int capacity)
            : base(capacity)
        {
            open = true;
        }

        /// <summary>
        /// Create new BlockingQueue.
        /// </summary>
        public BlockingQueue()
            : base()
        {
            open = true;
        }

        /// <summary>
        /// BlockingQueue Destructor (Close queue, resume any waiting thread).
        /// </summary>
        ~BlockingQueue()
        {
            Close();
        }

        /// <summary>
        /// Remove all objects from the Queue.
        /// </summary>
        public override void Clear()
        {
            lock (base.SyncRoot)
            {
                base.Clear();
            }
        }

        /// <summary>
        /// Remove all objects from the Queue, resume all dequeue threads.
        /// </summary>
        public void Close()
        {
            lock (base.SyncRoot)
            {
                open = false;
                base.Clear();
                Monitor.PulseAll(base.SyncRoot); // resume any waiting threads
            }
        }

        /// <summary>
        /// Removes and returns the object at the beginning of the Queue.
        /// </summary>
        /// <returns>Object in queue.</returns>
        public override object Dequeue()
        {
            return Dequeue(Timeout.Infinite);
        }

        /// <summary>
        /// Removes and returns the object at the beginning of the Queue.
        /// </summary>
        /// <param name="timeout">time to wait before returning</param>
        /// <returns>Object in queue.</returns>
        public object Dequeue(TimeSpan timeout)
        {
            return Dequeue(timeout.Milliseconds);
        }

        /// <summary>
        /// Removes and returns the object at the beginning of the Queue.
        /// </summary>
        /// <param name="timeout">time to wait before returning (in milliseconds)</param>
        /// <returns>Object in queue.</returns>
        public object Dequeue(int timeout)
        {
            lock (base.SyncRoot)
            {
                while (open && (base.Count == 0))
                {
                    if (!Monitor.Wait(base.SyncRoot, timeout))
                        throw new InvalidOperationException("Timeout");
                }
                if (open)
                    return base.Dequeue();
                else
                    throw new InvalidOperationException("Queue Closed");
            }
        }

        /// <summary>
        /// Adds an object to the end of the Queue.
        /// </summary>
        /// <param name="obj">Object to put in queue</param>
        public override void Enqueue(object obj)
        {
            lock (base.SyncRoot)
            {
                base.Enqueue(obj);
                Monitor.Pulse(base.SyncRoot);
            }
        }

        /// <summary>
        /// Open Queue.
        /// </summary>
        public void Open()
        {
            lock (base.SyncRoot)
            {
                open = true;
            }
        }

        /// <summary>
        /// Gets flag indicating if queue has been closed.
        /// </summary>
        public bool Closed
        {
            get { return !open; }
        }
    }
}