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

namespace Umbraco.Cms.Core.Composing
{

    /// <summary>
    /// Provides a base class for builder collections.
    /// </summary>
    /// <typeparam name="TItem">The type of the items.</typeparam>
    public abstract class BuilderCollectionBase<TItem> : IBuilderCollection<TItem>
    {
        private readonly LazyReadOnlyCollection<TItem> _items;

        /// Initializes a new instance of the <see cref="BuilderCollectionBase{TItem}"/> with items.
        /// </summary>
        /// <param name="items">The items.</param>
        public BuilderCollectionBase(Func<IEnumerable<TItem>> items) => _items = new LazyReadOnlyCollection<TItem>(items);

        /// <inheritdoc />
        public int Count => _items.Count;

        /// <summary>
        /// Gets an enumerator.
        /// </summary>
        public IEnumerator<TItem> GetEnumerator() => ((IEnumerable<TItem>)_items).GetEnumerator();

        /// <summary>
        /// Gets an enumerator.
        /// </summary>
        IEnumerator IEnumerable.GetEnumerator() => GetEnumerator();
    }
}