namespace Nancy.Diagnostics

{

    using System.Collections;

    using System.Collections.Concurrent;

    using System.Collections.Generic;



    /// <summary>

    /// Provides a thread safe, limited size, collection of objects

    /// If the collection is full the oldest item gets removed.

    /// </summary>

    /// <typeparam name="T">Type to store</typeparam>

    public class ConcurrentLimitedCollection<T> : IEnumerable<T>

    {

        private readonly int maxSize;



        private ConcurrentQueue<T> internalStore;



        /// <summary>

        /// Gets the current size for the collection.

        /// </summary>

        /// <value> Current size of the collection.</value>

        public int CurrentSize

        {

            get

            {

                return this.internalStore.Count;

            }

        }



        /// <summary>

        /// Initializes a new instance of the <see cref="ConcurrentLimitedCollection{T}"/> class, with

        /// the provided <paramref name="maxSize"/>.

        /// </summary>

        /// <param name="maxSize">The maximum size for the collection.</param>

        public ConcurrentLimitedCollection(int maxSize)

        {

            this.maxSize = maxSize;

            this.internalStore = new ConcurrentQueue<T>();

        }



        /// <summary>

        /// Returns an enumerator that iterates through the collection.

        /// </summary>

        /// <returns>

        /// A <see cref="T:System.Collections.Generic.IEnumerator`1"/> that can be used to iterate through the collection.

        /// </returns>

        /// <filterpriority>1</filterpriority>

        public IEnumerator<T> GetEnumerator()

        {

            return this.internalStore.GetEnumerator();

        }



        /// <summary>

        /// Returns an enumerator that iterates through a collection.

        /// </summary>

        /// <returns>

        /// An <see cref="T:System.Collections.IEnumerator"/> object that can be used to iterate through the collection.

        /// </returns>

        /// <filterpriority>2</filterpriority>

        IEnumerator IEnumerable.GetEnumerator()

        {

            return this.GetEnumerator();

        }



        /// <summary>

        /// Adds an item to the collection.

        /// If the collection is full, the oldest item is removed and the new item

        /// is added to the end of the collection.

        /// </summary>

        /// <param name="item">Item to add</param>

        public void Add(T item)

        {

            if (this.internalStore.Count == this.maxSize)

            {

                T temp;

                this.internalStore.TryDequeue(out temp);

            }



            this.internalStore.Enqueue(item);

        }



        /// <summary>

        /// Clear the collection

        /// </summary>

        public void Clear()

        {

            this.internalStore = new ConcurrentQueue<T>();

        }

    }

}