using System.Collections.Generic;
using JD.Collections.Interfaces;
using JD.Kernel.StaticHelpers;

namespace JD.Collections
{
    /// <summary>
    /// A Keyed collection that you can listen to through the CollectionChanged event.
    /// </summary>
    public abstract class ObservableKeyedList<TKey, TValue> : ObservableList<TValue>, IObservableKeyedList<TKey, TValue>
    {
        #region Variables

        private readonly KeyedCollection m_dictionary;

        #endregion

        #region Constructor

        /// <summary>
        /// Ctor
        /// </summary>
        protected ObservableKeyedList()
        {
            m_dictionary = new KeyedCollection(this);
        }

        /// <summary>
        /// Override default key Comparer
        /// </summary>
        /// <param name="comparer"></param>
        protected ObservableKeyedList(IEqualityComparer<TKey> comparer)
        {
            m_dictionary = new KeyedCollection(this, comparer);
        }

        #endregion

        #region Methods

        /// <summary>
        /// Get value from key.
        /// </summary>
        /// <param name="key"></param>
        /// <returns></returns>
        /// <remarks>Does not throw when the key is not contained.</remarks>
        public virtual TValue this[TKey key]
        {
            get
            {
                if (Equals(key, null))
                {
                    return default(TValue);
                }

                TValue value;
                m_dictionary.TryGetValue(key, out value);
                return value;
            }
        }

        /// <summary>
        /// Removes the item with the given <paramref name="key"/>.
        /// </summary>
        /// <param name="key"></param>
        /// <returns></returns>
        public bool Remove(TKey key)
        {
            TValue value;
            if (!m_dictionary.TryGetValue(key, out value))
            {
                return false;
            }

            return Remove(value);
        }

        /// <summary>
        /// When implemented in a derived class, extracts the key from the specified element.
        /// </summary>
        /// <param name="value"></param>
        /// <returns></returns>
        protected abstract TKey GetKeyForItem(TValue value);

        /// <summary>
        /// Whether the keyed collection contains the key.
        /// </summary>
        /// <param name="key"></param>
        /// <returns></returns>
        public virtual bool ContainsKey(TKey key)
        {
            if (Equals(key, null))
            {
                return false;
            }

            return m_dictionary.ContainsKey(key);
        }

        /// <summary>
        /// True if it contains the item.
        /// </summary>
        /// <param name="item"></param>
        /// <returns></returns>
        public override bool Contains(TValue item)
        {
            return !Equals(item, null) && ContainsKey(GetKeyForItem(item));
        }

        /// <summary>
        /// Overridden.
        /// </summary>
        /// <param name="index"></param>
        /// <param name="item"></param>
        protected override void InsertItem(int index, TValue item)
        {
            Throw.IfNull(item, "Cannot add a null item");
            m_dictionary.Add(item);
            base.InsertItem(index, item);
        }

        /// <summary>
        /// Overridden.
        /// </summary>
        /// <param name="index"></param>
        protected override void RemoveItem(int index)
        {
            m_dictionary.Remove(GetKeyForItem(base[index]));
            base.RemoveItem(index);
        }

        /// <summary>
        /// Overridden.
        /// </summary>
        /// <param name="index"></param>
        /// <param name="item"></param>
        protected override void SetItem(int index, TValue item)
        {
            Throw.IfNull(item, "Cannot add a null item");
            TValue oldItem = base[index];
            if (!Equals(oldItem, item))
            {
                m_dictionary.Remove(oldItem);
                m_dictionary.Add(item);

                base.SetItem(index, item);
            }
        }

        /// <summary>
        /// Overridden.
        /// </summary>
        protected override void ClearItems()
        {
            if (Count == 0)
            {
                return;
            }

            m_dictionary.Clear();
            base.ClearItems();
        }

        /// <summary>
        /// TryGetValue.
        /// </summary>
        public bool TryGetValue(TKey key, out TValue result)
        {
            return m_dictionary.TryGetValue(key, out result);
        }

        public override int IndexOf(TValue item)
        {
            // Contains is optimized O(1).
            if (!Contains(item))
            {
                return -1;
            }

            return base.IndexOf(item);
        }

        #endregion

        #region Nested

        private class KeyedCollection : KeyedCollection<TKey, TValue>
        {
            private readonly ObservableKeyedList<TKey, TValue> m_owner;

            public KeyedCollection(ObservableKeyedList<TKey, TValue> owner)
            {
                m_owner = owner;
            }

            public KeyedCollection(ObservableKeyedList<TKey, TValue> owner, IEqualityComparer<TKey> comparer)
                : base(comparer)
            {
                m_owner = owner;
            }

            protected override TKey GetKeyForItem(TValue value)
            {
                return m_owner.GetKeyForItem(value);
            }
        }

        #endregion
    }
}