using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using Chernobyl.Utility;

namespace Chernobyl.Collections.Generic.Event
{
    /// <summary>
    /// Adds or removes items from an <see cref="ICollection{T}" /> when dictated
    /// by events.
    /// </summary>
    /// <typeparam name="T">The type of item being added/removed to/from the
    /// <see cref="ICollection{T}"/>.</typeparam>
    public class AddRemove<T>
    {
        /// <summary>
        /// Initializes a new instance of the <see cref="AddRemove{T}" /> class.
        /// </summary>
        /// <param name="items">The instances that are to be added or removed from
        /// <see cref="Collection" />.</param>
        /// <param name="addImmediately">True if <paramref name="items"/> should
        /// be added to <see cref="Collection"/> immediately.</param>
        public AddRemove(IEnumerable<T> items, bool addImmediately)
            : this(items, null, addImmediately)
        {}

        /// <summary>
        /// Initializes a new instance of the <see cref="AddRemove{T}" /> class.
        /// </summary>
        /// <param name="items">The instances that are to be added or removed from
        /// <see cref="Collection" />.</param>
        /// <param name="collection">The <see cref="ICollection{T}" /> that is to
        /// to have the <see cref="Items" /> added to it or removed from it.</param>
        /// <param name="addImmediately">True if <paramref name="items"/> should
        /// be added to <paramref name="collection"/> cref="collection"/> immediately.</param>
        public AddRemove(IEnumerable<T> items, ICollection<T> collection, bool addImmediately)
        {
            Items = items;
            Collection = collection;

            if(addImmediately)
                Add(this, EventArgs.Empty);
        }

        /// <summary>
        /// An event handler that, when invoked, adds the <see cref="Items"/> to 
        /// <see cref="Collection"/>.
        /// </summary>
        /// <param name="sender">The sender of the event.</param>
        /// <param name="e">The <see cref="EventArgs"/> instance containing the 
        /// event data.</param>
        public void Add(object sender, EventArgs e)
        {
            if(Collection != null)
                Collection.AddRange(Items);

            _addLastInvoked = true;
        }

        /// <summary>
        /// An event handler that, when invoked, removes the <see cref="Items"/> 
        /// from <see cref="Collection"/>.
        /// </summary>
        /// <param name="sender">The sender of the event.</param>
        /// <param name="e">The <see cref="EventArgs"/> instance containing the 
        /// event data.</param>
        public void Remove(object sender, EventArgs e)
        {
            if (Collection != null)
                Collection.RemoveRange(Items);

            _addLastInvoked = false;
        }

        /// <summary>
        /// The instances that are to be added or removed from 
        /// <see cref="Collection"/>.
        /// </summary>
        public IEnumerable<T> Items
        {
            get { return _items; }
            private set
            {
                value.ThrowIfNull("value");
                _items = value;
            }
        }

        /// <summary>
        /// The <see cref="ICollection{T}"/> that is to to have the 
        /// <see cref="Items"/> added to it or removed from it. Setting this 
        /// property will cause the <see cref="Items"/> to be removed from the 
        /// old value of this property and added to the new value but only if the
        /// <see cref="Items"/> were added to the previous value by this type. 
        /// This value can be set to null, in which case, addition/removal is 
        /// disabled.
        /// </summary>
        public ICollection<T> Collection
        {
            get { return _collection; }
            set
            {
                ICollection<T> previousItems = _collection;
                _collection = value;

                if (_addLastInvoked)
                {
                    if (previousItems != null)
                        previousItems.RemoveRange(Items);

                    if (_collection != null)
                        _collection.AddRange(Items);   
                }
            }
        }

        /// <summary>
        /// True if <see cref="Add(object, EventArgs)"/> was the last method
        /// invoked, false if otherwise.
        /// </summary>
        bool _addLastInvoked;

        /// <summary>
        /// The backing field to <see cref="Items"/>.
        /// </summary>
        IEnumerable<T> _items;

        /// <summary>
        /// The backing field to <see cref="Collection"/>.
        /// </summary>
        ICollection<T> _collection;
    }
}