// 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.Runtime.CompilerServices;

namespace System.Threading.Tasks
{
    public static class AsyncEnumerableExtensions
    {
#if !BCL_HAS_CONFIGUREAWAIT // https://github.com/dotnet/coreclr/pull/21939

        /// <summary>Configures how awaits on the tasks returned from an async iteration will be performed.</summary>
        /// <typeparam name="T">The type of the objects being iterated.</typeparam>
        /// <param name="source">The source enumerable being iterated.</param>
        /// <param name="continueOnCapturedContext">Whether to capture and marshal back to the current context.</param>
        /// <returns>The configured enumerable.</returns>
        public static ConfiguredCancelableAsyncEnumerable<T> ConfigureAwait<T>(
            this IAsyncEnumerable<T> source, bool continueOnCapturedContext) =>
            new ConfiguredCancelableAsyncEnumerable<T>(source, continueOnCapturedContext, cancellationToken: default);

        /// <summary>Sets the <see cref="CancellationToken"/> to be passed to <see cref="IAsyncEnumerable{T}.GetAsyncEnumerator(CancellationToken)"/> when iterating.</summary>
        /// <typeparam name="T">The type of the objects being iterated.</typeparam>
        /// <param name="source">The source enumerable being iterated.</param>
        /// <param name="cancellationToken">The <see cref="CancellationToken"/> to use.</param>
        /// <returns>The configured enumerable.</returns>
        public static ConfiguredCancelableAsyncEnumerable<T> WithCancellation<T>(
            this IAsyncEnumerable<T> source, CancellationToken cancellationToken) =>
            new ConfiguredCancelableAsyncEnumerable<T>(source, continueOnCapturedContext: true, cancellationToken);

#endif

        public static ConfiguredCancelableAsyncEnumerable<T>.Enumerator ConfigureAwait<T>(this IAsyncEnumerator<T> enumerator, bool continueOnCapturedContext)
        {
            if (enumerator == null)
                throw Error.ArgumentNull(nameof(enumerator));

            return new ConfiguredCancelableAsyncEnumerable<T>.Enumerator(enumerator, continueOnCapturedContext);
        }
    }
}