// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the Apache 2.0 License.
// See the LICENSE file in the project root for more information. 

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

namespace System.Linq
{
    public static partial class AsyncEnumerableEx
    {
        /// <summary>
        /// Ignores all elements in an observable sequence leaving only the termination messages.
        /// </summary>
        /// <typeparam name="TSource">The type of the elements in the source sequence.</typeparam>
        /// <param name="source">Source sequence.</param>
        /// <returns>An empty observable sequence that signals termination, successful or exceptional, of the source sequence.</returns>
        /// <exception cref="ArgumentNullException"><paramref name="source"/> is null.</exception>
        public static IAsyncEnumerable<TSource> IgnoreElements<TSource>(this IAsyncEnumerable<TSource> source)
        {
            if (source == null)
                throw Error.ArgumentNull(nameof(source));

            return AsyncEnumerable.Create(Core);

            async IAsyncEnumerator<TSource> Core(CancellationToken cancellationToken)
            {
                await foreach (var _ in source.WithCancellation(cancellationToken).ConfigureAwait(false))
                {
                }

                yield break;
            }
        }
    }
}