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

namespace Chernobyl.Collections.Generic
{
    /// <summary>
    /// A list that holds its items in <see cref="WeakReference{T}"/> instances.
    /// </summary>
    /// <typeparam name="T">The type to hold in the list</typeparam>
    public class WeakReferenceList<T> : IList<T> where T : class
    {
        /// <summary>
        /// Initializes a new instance of the <see cref="WeakReferenceList{T}"/> 
        /// class.
        /// </summary>
        public WeakReferenceList() : this(0)
        { }

        /// <summary>
        /// Initializes a new instance of the <see cref="WeakReferenceList{T}"/> 
        /// class.
        /// </summary>
        /// <param name="capacity">The capacity of the new list.</param>
        public WeakReferenceList(int capacity)
        {
            TheList = new List<WeakReference<T>>(capacity);
        }

        /// <summary>
        /// Removes all items that are no longer alive (see 
        /// <see cref="WeakReference.IsAlive"/>).
        /// </summary>
        public int Clean()
        {
            return TheList.RemoveAll((wr) => wr.IsAlive == false);
        }

        /// <summary>
        /// Determines the index of a specific item in the <see cref="IList{T}"/>.
        /// </summary>
        /// <param name="item">The object to locate in the 
        /// <see cref="IList{T}"/>.</param>
        /// <returns>
        /// The index of <paramref name="item"/> if found in the list; otherwise, 
        /// -1.
        /// </returns>
        public int IndexOf(T item)
        {
            return TheList.FindIndex((wr) => wr.Target == item);
        }

        /// <summary>
        /// Inserts an item to the <see cref="IList{T}"/> at the specified index.
        /// </summary>
        /// <param name="index">The zero-based index at which 
        /// <paramref name="item"/> should be inserted.</param>
        /// <param name="item">The object to insert into the 
        /// <see cref="IList{T}"/>.</param>
        /// <exception cref="ArgumentOutOfRangeException">
        /// <paramref name="index"/> is not a valid index in the 
        /// <see cref="IList{T}"/>.</exception>
        /// <exception cref="NotSupportedException">The <see cref="IList{T}"/> 
        /// is read-only.</exception>
        public void Insert(int index, T item)
        {
            TheList.Insert(index, new WeakReference<T>(item));
        }

        /// <summary>
        /// Removes the <see cref="IList{T}"/> item at the specified index.
        /// </summary>
        /// <param name="index">The zero-based index of the item to remove.</param>
        /// <exception cref="ArgumentOutOfRangeException">
        /// 	<paramref name="index"/> is not a valid index in the 
        /// 	<see cref="ICollection{T}"/>.</exception>
        /// <exception cref="NotSupportedException">The 
        /// <see cref="ICollection{T}"/> is read-only.</exception>
        public void RemoveAt(int index)
        {
            TheList.RemoveAt(index);
        }

        /// <summary>
        /// Gets or sets the item at the specified index.
        /// </summary>
        public T this[int index]
        {
            get { return TheList[index].Target; }
            set { TheList[index].Target = value; }
        }

        /// <summary>
        /// Adds an item to the <see cref="ICollection{T}"/>.
        /// </summary>
        /// <param name="item">The object to add to the 
        /// <see cref="ICollection{T}"/>.</param>
        /// <exception cref="NotSupportedException">The 
        /// <see cref="ICollection{T}"/> is read-only.</exception>
        public void Add(T item)
        {
            TheList.Add(new WeakReference<T>(item));
        }

        /// <summary>
        /// Removes all items from the <see cref="ICollection{T}"/>.
        /// </summary>
        /// <exception cref="NotSupportedException">The 
        /// <see cref="ICollection{T}"/> is read-only. </exception>
        public void Clear()
        {
            TheList.Clear();
        }

        /// <summary>
        /// Determines whether the <see cref="ICollection{T}"/> contains a 
        /// specific value.
        /// </summary>
        /// <param name="item">The object to locate in the 
        /// <see cref="ICollection{T}"/>.</param>
        /// <returns>
        /// true if <paramref name="item"/> is found in the 
        /// <see cref="ICollection{T}"/>; otherwise, false.
        /// </returns>
        public bool Contains(T item)
        {
            return TheList.Exists((wr) => wr.Target == item);
        }

        /// <summary>
        /// Copies the elements of the <see cref="ICollection{T}"/> to an 
        /// <see cref="Array"/>, starting at a particular <see cref="Array"/> 
        /// index.
        /// </summary>
        /// <param name="array">The one-dimensional <see cref="Array"/> that is 
        /// the destination of the elements copied from 
        /// <see cref="ICollection{T}"/>. The <see cref="Array"/> must have 
        /// zero-based indexing.</param>
        /// <param name="arrayIndex">The zero-based index in 
        /// <paramref name="array"/> at which copying begins.</param>
        /// <exception cref="ArgumentNullException">
        /// <paramref name="array"/> is null.</exception>
        /// <exception cref="ArgumentOutOfRangeException">
        /// <paramref name="arrayIndex"/> is less than 0.</exception>
        /// <exception cref="ArgumentException">
        /// <paramref name="array"/> is multidimensional or 
        /// <paramref name="arrayIndex"/> is equal to or greater than the length 
        /// of <paramref name="array"/>.-or-The number of elements in the source 
        /// <see cref="ICollection{T}"/> is greater than the available space from 
        /// <paramref name="arrayIndex"/> to the end of the destination 
        /// <paramref name="array"/>.-or-Type <typeparamref name="T"/> cannot be cast 
        /// automatically to the type of the destination <paramref name="array"/>.
        /// </exception>
        public void CopyTo(T[] array, int arrayIndex)
        {
            if (arrayIndex < 0)
                throw new ArgumentException("The index into the array cannot be less than zero.", "arrayIndex");
            if (arrayIndex >= array.Length)
                throw new ArgumentOutOfRangeException("The index into the array cannot exceed the arrays length", "arrayIndex");
            if (array.Length - arrayIndex < Count)
                throw new ArgumentOutOfRangeException("There is not enough room in the array to fit the requested contents of the list.");

            int currentListIndex = 0;
            for (int i = arrayIndex; i < array.Length; ++i)
            {
                array[i] = TheList[currentListIndex].Target;
                ++currentListIndex;
            }
        }

        /// <summary>
        /// Gets the number of elements contained in the 
        /// <see cref="ICollection{T}"/>.
        /// </summary>
        /// <value></value>
        /// <returns>The number of elements contained in the 
        /// <see cref="ICollection{T}"/>.</returns>
        public int Count
        {
            get
            {
                // clean out the list first to ensure we have an accurate count
                Clean();
                return TheList.Count;
            }
        }

        /// <summary>
        /// Gets a value indicating whether the <see cref="ICollection{T}"/> is 
        /// read-only.
        /// </summary>
        /// <value></value>
        /// <returns>true if the <see cref="ICollection{T}"/> is read-only; 
        /// otherwise, false.</returns>
        public bool IsReadOnly
        {
            get { return false; }
        }

        /// <summary>
        /// Removes the first occurrence of a specific object from the 
        /// <see cref="ICollection{T}"/>.
        /// </summary>
        /// <param name="item">The object to remove from the 
        /// <see cref="ICollection{T}"/>.</param>
        /// <returns>
        /// true if <paramref name="item"/> was successfully removed from the 
        /// <see cref="ICollection{T}"/>; otherwise, false. This method also 
        /// returns false if <paramref name="item"/> is not found in the original 
        /// <see cref="ICollection{T}"/>.
        /// </returns>
        /// <exception cref="T:System.NotSupportedException">The 
        /// <see cref="ICollection{T}"/> is read-only.</exception>
        public bool Remove(T item)
        {
            int count = TheList.Count;
            TheList.RemoveAll((wr) => wr.Target == item);

            // if the last count of the list is greater than the new count, then 
            // the item was removed.
            return count > TheList.Count;
        }

        /// <summary>
        /// Returns an enumerator that iterates through the collection.
        /// </summary>
        /// <returns>
        /// A <see cref="IEnumerator{T}"/> that can be used to 
        /// iterate through the collection.
        /// </returns>
        public IEnumerator<T> GetEnumerator()
        {
            return new WeakReferenceEnumerator<T>(TheList.GetEnumerator());
        }

        /// <summary>
        /// Returns an enumerator that iterates through a collection.
        /// </summary>
        /// <returns>
        /// An <see cref="IEnumerator{T}"/> object that can be used 
        /// to iterate through the collection.
        /// </returns>
        IEnumerator IEnumerable.GetEnumerator()
        {
            return new WeakReferenceEnumerator<T>(TheList.GetEnumerator());
        }

        /// <summary>
        /// Holds the item in the list.
        /// </summary>
        List<WeakReference<T>> TheList { get; set; }
    }
}