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

namespace JD.Collections
{
    /// <summary>
    /// A Keyed collection that you can listen to through the CollectionChanged event. Differs from keyed collection in the fact the items are not stored in a list and in the collection.
    /// </summary>
    public abstract class ObservableKeyedCollection<TKey, TItem> : IObservableKeyedCollection<TKey, TItem>
    {
        #region Variables

        private readonly InnerCollection m_collection;
        private int m_updateLevel;

        #endregion

        #region Constructor

        /// <summary>
        /// Ctor
        /// </summary>
        protected ObservableKeyedCollection()
            : this(null)
        {
        }

        /// <summary>
        /// Override default key Comparer
        /// </summary>
        /// <param name="comparer"></param>
        protected ObservableKeyedCollection(IEqualityComparer<TKey> comparer)
        {
            m_collection = new InnerCollection(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 TItem this[TKey key]
        {
            get
            {
                TItem value;
                m_collection.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)
        {
            TItem value;
            if (m_collection.TryGetValue(key, out value))
            {
                return RemoveItem(value);
            }

            return false;
        }

        /// <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(TItem value);

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

        /// <summary>
        /// Adds the item in the list.
        /// </summary>
        /// <param name="item"></param>
        public void Add(TItem item)
        {
            Throw.IfNull(item, "item");

            InsertItem(item);
            RegisterItem(item);
            OnCollectionChanged(new CollectionChangedEventArgs<TItem>(CollectionChangeAction.ItemAdded, item));
        }

        protected virtual void InsertItem(TItem item)
        {
            m_collection.Add(item);
        }

        public bool Remove(TItem item)
        {
            return RemoveItem(item);
        }

        protected virtual bool RemoveItem(TItem item)
        {
            bool removed = m_collection.Remove(item);

            if (removed)
            {
                UnregisterItem(item);
                OnCollectionChanged(new CollectionChangedEventArgs<TItem>(CollectionChangeAction.ItemRemoved, item));
            }

            return removed;
        }

        /// <summary>
        /// Clears the list.
        /// </summary>
        public virtual void Clear()
        {
            if (Count == 0)
            {
                return;
            }

            OnCollectionChanged(new CollectionChangedEventArgs<TItem>(CollectionChangeAction.Clearing, default(TItem)));
            m_collection.Clear();
            OnCollectionChanged(new CollectionChangedEventArgs<TItem>(CollectionChangeAction.Cleared, default(TItem)));
        }

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

        public void CopyTo(TItem[] array, int arrayIndex)
        {
            Enumerable.AsEnumerable(this).CopyTo(array, arrayIndex);
        }

        public bool TryGetValue(TKey key, out TItem value)
        {
            return m_collection.TryGetValue(key, out value);
        }

        public int Count
        {
            get
            {
                return m_collection.Count;
            }
        }

        public bool IsReadOnly
        {
            get { throw new NotImplementedException(); }
        }

        #endregion

        #region ObservableCollectionTemplate

        /// <summary>
        /// REMARK : This code is copy pasted from ObservableCollectionTemplate
        /// 
        /// Any modification should be applied to other observable collection.
        /// </summary>

        /// <summary>
        /// Whether this set is updating.
        /// </summary>
        public bool IsUpdating
        {
            get
            {
                return m_updateLevel > 0;
            }
        }

        /// <summary>
        /// Suspends all events for this set.
        /// </summary>
        public void BeginUpdate()
        {
            ++m_updateLevel;
        }

        /// <summary>
        /// Resumes events for this set.
        /// </summary>
        /// <returns></returns>
        public bool EndUpdate()
        {
            if (--m_updateLevel == 0)
            {
                OnCollectionChanged(new CollectionChangedEventArgs<TItem>(CollectionChangeAction.EndUpdated, default(TItem)));
                return true;
            }

            return false;
        }

        /// <summary>
        /// Register an item in the list (for example, can bind to its events)
        /// </summary>
        /// <param name="item"></param>
        protected virtual void RegisterItem(TItem item)
        {
            IObservableItem observableItem = item as IObservableItem;

            if (observableItem != null)
            {
                observableItem.Changed += internal_itemChanged;
            }
        }

        /// <summary>
        /// Unregister an item from the list (for example, unbind from its events).
        /// </summary>
        /// <param name="item"></param>
        protected virtual void UnregisterItem(TItem item)
        {
            IObservableItem observableItem = item as IObservableItem;

            if (observableItem != null)
            {
                observableItem.Changed -= internal_itemChanged;
            }
        }

        #region Handlers

        private void internal_itemChanged(object sender, EventArgs e)
        {
            if (sender is TItem)
            {
                OnCollectionChanged(new CollectionChangedEventArgs<TItem>(CollectionChangeAction.ItemChanged, (TItem)sender));
            }
            else
            {
                System.Diagnostics.Debug.Assert(false, "Bad implementation of the IObservableItem interface. The object should be the sender of the event args");
                OnCollectionChanged(new CollectionChangedEventArgs<TItem>(CollectionChangeAction.ItemChanged, default(TItem)));
            }
        }

        #endregion

        #region Events

        /// <summary>
        /// Triggered when the collection changes.
        /// </summary>
        public event EventHandler<CollectionChangedEventArgs<TItem>> CollectionChanged;

        /// <summary>
        /// Triggers the <see cref="CollectionChanged"/> event.
        /// </summary>
        /// <param name="e">Event Args.</param>
        protected virtual void OnCollectionChanged(CollectionChangedEventArgs<TItem> e)
        {
            CollectionChanged?.Invoke(this, e);
        }

        #endregion

        #endregion

        #region Implementation of IEnumerable

        public virtual IEnumerator<TItem> GetEnumerator()
        {
            return m_collection.GetEnumerator();
        }

        IEnumerator IEnumerable.GetEnumerator()
        {
            return GetEnumerator();
        }

        #endregion

        #region Nested

        private class InnerCollection : KeyedCollection<TKey, TItem>
        {
            private readonly ObservableKeyedCollection<TKey, TItem> m_owner;

            public InnerCollection(ObservableKeyedCollection<TKey, TItem> owner, IEqualityComparer<TKey> comparer)
                : base(comparer)
            {
                m_owner = owner;
            }

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

        #endregion
    }
}