text: ﻿// Licensed to the .NET Foundation under one or more agreements.
  // The .NET Foundation licenses this file to you under the MIT 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>
          /// Invokes a specified action after the source async-enumerable sequence terminates gracefully or exceptionally.
          /// </summary>
          /// <typeparam name="TSource">The type of the elements in the source sequence.</typeparam>
          /// <param name="source">Source sequence.</param>
          /// <param name="finallyAction">Action to invoke after the source async-enumerable sequence terminates.</param>
          /// <returns>Source sequence with the action-invoking termination behavior applied.</returns>
          /// <exception cref="ArgumentNullException"><paramref name="source"/> or <paramref name="finallyAction"/> is null.</exception>
          public static IAsyncEnumerable<TSource> Finally<TSource>(this IAsyncEnumerable<TSource> source, Action finallyAction)
          {
              if (source == null)
                  throw Error.ArgumentNull(nameof(source));
              if (finallyAction == null)
                  throw Error.ArgumentNull(nameof(finallyAction));
  
              return Core(source, finallyAction);
  
              static async IAsyncEnumerable<TSource> Core(IAsyncEnumerable<TSource> source, Action finallyAction, [System.Runtime.CompilerServices.EnumeratorCancellation] CancellationToken cancellationToken = default)
              {
                  try
                  {
                      await foreach (var item in source.WithCancellation(cancellationToken).ConfigureAwait(false))
                      {
                          yield return item;
                      }
                  }
                  finally
                  {
                      finallyAction();
                  }
              }
          }
  
          /// <summary>
          /// Invokes a specified asynchronous action after the source async-enumerable sequence terminates gracefully or exceptionally.
          /// </summary>
          /// <typeparam name="TSource">The type of the elements in the source sequence.</typeparam>
          /// <param name="source">Source sequence.</param>
          /// <param name="finallyAction">Action to invoke and await asynchronously after the source async-enumerable sequence terminates.</param>
          /// <returns>Source sequence with the action-invoking termination behavior applied.</returns>
          /// <exception cref="ArgumentNullException"><paramref name="source"/> or <paramref name="finallyAction"/> is null.</exception>
          public static IAsyncEnumerable<TSource> Finally<TSource>(this IAsyncEnumerable<TSource> source, Func<Task> finallyAction)
          {
              if (source == null)
                  throw Error.ArgumentNull(nameof(source));
              if (finallyAction == null)
                  throw Error.ArgumentNull(nameof(finallyAction));
  
              return Core(source, finallyAction);
  
              static async IAsyncEnumerable<TSource> Core(IAsyncEnumerable<TSource> source, Func<Task> finallyAction, [System.Runtime.CompilerServices.EnumeratorCancellation] CancellationToken cancellationToken = default)
              {
                  try
                  {
                      await foreach (var item in source.WithCancellation(cancellationToken).ConfigureAwait(false))
                      {
                          yield return item;
                      }
                  }
                  finally
                  {
                      // REVIEW: No cancellation support for finally action.
  
                      await finallyAction().ConfigureAwait(false);
                  }
              }
          }
      }
  }
  