reactive/Ix.NET/Source/System.Interactive.Async/Do.cs

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

namespace System.Linq
{
    public static partial class AsyncEnumerable
    {
        public static IAsyncEnumerable<TSource> Do<TSource>(this IAsyncEnumerable<TSource> source, Action<TSource> onNext)
        {
            if (source == null)
                throw new ArgumentNullException(nameof(source));
            if (onNext == null)
                throw new ArgumentNullException(nameof(onNext));

            return DoHelper(source, onNext, _ => { }, () => { });
        }

        public static IAsyncEnumerable<TSource> Do<TSource>(this IAsyncEnumerable<TSource> source, Action<TSource> onNext, Action onCompleted)
        {
            if (source == null)
                throw new ArgumentNullException(nameof(source));
            if (onNext == null)
                throw new ArgumentNullException(nameof(onNext));
            if (onCompleted == null)
                throw new ArgumentNullException(nameof(onCompleted));

            return DoHelper(source, onNext, _ => { }, onCompleted);
        }

        public static IAsyncEnumerable<TSource> Do<TSource>(this IAsyncEnumerable<TSource> source, Action<TSource> onNext, Action<Exception> onError)
        {
            if (source == null)
                throw new ArgumentNullException(nameof(source));
            if (onNext == null)
                throw new ArgumentNullException(nameof(onNext));
            if (onError == null)
                throw new ArgumentNullException(nameof(onError));

            return DoHelper(source, onNext, onError, () => { });
        }

        public static IAsyncEnumerable<TSource> Do<TSource>(this IAsyncEnumerable<TSource> source, Action<TSource> onNext, Action<Exception> onError, Action onCompleted)
        {
            if (source == null)
                throw new ArgumentNullException(nameof(source));
            if (onNext == null)
                throw new ArgumentNullException(nameof(onNext));
            if (onError == null)
                throw new ArgumentNullException(nameof(onError));
            if (onCompleted == null)
                throw new ArgumentNullException(nameof(onCompleted));

            return DoHelper(source, onNext, onError, onCompleted);
        }

        public static IAsyncEnumerable<TSource> Do<TSource>(this IAsyncEnumerable<TSource> source, IObserver<TSource> observer)
        {
            if (source == null)
                throw new ArgumentNullException(nameof(source));
            if (observer == null)
                throw new ArgumentNullException(nameof(observer));

            return DoHelper(source, observer.OnNext, observer.OnError, observer.OnCompleted);
        }

        private static IAsyncEnumerable<TSource> DoHelper<TSource>(this IAsyncEnumerable<TSource> source, Action<TSource> onNext, Action<Exception> onError, Action onCompleted)
        {
            return CreateEnumerable(
                () =>
                {
                    var e = source.GetEnumerator();

                    var cts = new CancellationTokenDisposable();
                    var d = Disposable.Create(cts, e);

                    var current = default(TSource);

                    var f = default(Func<CancellationToken, Task<bool>>);
                    f = async ct =>
                        {
                            try
                            {
                                var result = await e.MoveNext(ct)
                                                    .ConfigureAwait(false);
                                if (!result)
                                {
                                    onCompleted();
                                }
                                else
                                {
                                    current = e.Current;
                                    onNext(current);
                                }
                                return result;
                            }
                            catch (OperationCanceledException)
                            {
                                throw;
                            }
                            catch (Exception ex)
                            {
                                onError(ex);
                                throw;
                            }
                        };

                    return CreateEnumerator(
                        f,
                        () => current,
                        d.Dispose,
                        e
                    );
                });
        }
    }
}