using System;
using System.Collections.Generic;
using Chernobyl.Collections.Generic.Event;
using Chernobyl.Event;

namespace Chernobyl.Creation.Collections
{
    /// <summary>
    /// An <see cref="IEnumerable{T}"/> that stores items created by an <see cref="IBuilder{T}"/>.
    /// </summary>
    public class Warehouse<T> : DecoratingEventEnumerable<T>
    {
        /// <summary>
        /// Initializes a new instance of the <see cref="Warehouse{T}"/> class.
        /// </summary>
        /// <param name="builder">Instance to listen to for item creation. Use
        /// <see cref="BuilderComposite{T}"/> for multiple <see cref="IBuilder{T}"/> instances.</param>
        public Warehouse(IBuilder<T> builder)
            : this(builder, new List<T>())
        {}

        /// <summary>
        /// Initializes a new instance of the <see cref="Warehouse{T}" /> class.
        /// </summary>
        /// <param name="builder">Instance to listen to for item creation. Use
        /// <see cref="BuilderComposite{T}"/> for multiple <see cref="IBuilder{T}"/> instances.</param>
        /// <param name="items">The <see cref="ICollection{T}"/> that is to be used to store items.</param>
        /// <exception cref="ArgumentNullException">Thrown if <paramref name="items"/> is null.</exception>
        public Warehouse(IBuilder<T> builder, ICollection<T> items)
            : base(items)
        {
            items.ThrowIfNull(nameof(items));
            builder.ThrowIfNull(nameof(builder));

            Items = items;
            builder.Created += OnItemCreated;
        }

        /// <summary>
        /// An event handler that can be assigned to any event which notifies
        /// client code of an items creation. When invoked this method will
        /// store the created item, if applicable, in this instance's internal
        /// collection so that it can be iterated over.
        /// </summary>
        /// <param name="sender">The sender of the event.</param>
        /// <param name="e">The argument that contains the event data.</param>
        public void OnItemCreated(object sender, CreationEventArgs<T> e)
        {
            if (e.Cancelled == false && e.Error == null)
            {
                Items.Add(e.CreatedInstance);
                ItemsAddedHandler?.Invoke(this, new ItemsEventArgs<T>(e.CreatedInstance));
            }
        }

        /// <summary>
        /// The <see cref="ICollection{T}" /> of items that have been built.
        /// </summary>
        protected ICollection<T> Items { get; }
    }

    /// <summary>
    /// Utility and extension methods for <see cref="Warehouse{T}"/>.
    /// </summary>
    public static class WarehouseExt
    {
        /// <summary>
        /// Creates a <see cref="Warehouse{T}"/> to store items produced by <paramref name="builder"/>.
        /// </summary>
        public static IEventEnumerable<T> Warehouse<T>(this IBuilder<T> builder) => new Warehouse<T>(builder);
    }
}