using System.Collections.Generic;
using System.Threading;
using System.Threading.Tasks;

namespace ZeroLevel.Services.Async
{
	/// <summary>
	/// Represents a thread-safe collection that allows asynchronous consuming.
	/// </summary>
	/// <typeparam name="T">The type of the items contained in the collection.</typeparam>
	public interface IAsyncCollection<T> 
		: IReadOnlyCollection<T>
	{
		/// <summary>
		/// Gets an amount of pending item requests.
		/// </summary>
		int AwaiterCount { get; }

		/// <summary>
		/// Adds an item to the collection.
		/// </summary>
		/// <param name="item">The item to add to the collection.</param>
		void Add(T item);

		/// <summary>
		/// Removes and returns an item from the collection in an asynchronous manner.
		/// </summary>
		ValueTask<T> TakeAsync(CancellationToken cancellationToken);
	}

	public static class AsyncCollectionExtensions
	{
		/// <summary>
		/// Removes and returns an item from the collection in an asynchronous manner.
		/// </summary>
		public static ValueTask<T> TakeAsync<T>(this IAsyncCollection<T> collection)
		{
			return collection.TakeAsync(CancellationToken.None);
		}
	}
}