reactive/Ix.NET/Source/System.Interactive.Async/Repeat.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<TResult> Repeat<TResult>(TResult element, int count)
        {
            if (count < 0)
                throw new ArgumentOutOfRangeException(nameof(count));

            return Enumerable.Repeat(element, count)
                             .ToAsyncEnumerable();
        }

        public static IAsyncEnumerable<TResult> Repeat<TResult>(TResult element)
        {
            return CreateEnumerable(
                () =>
                {
                    return CreateEnumerator(
                        ct => TaskExt.True,
                        () => element,
                        () => { }
                    );
                });
        }

        public static IAsyncEnumerable<TSource> Repeat<TSource>(this IAsyncEnumerable<TSource> source, int count)
        {
            if (source == null)
                throw new ArgumentNullException(nameof(source));
            if (count < 0)
                throw new ArgumentOutOfRangeException(nameof(count));

            return CreateEnumerable(
                () =>
                {
                    var e = default(IAsyncEnumerator<TSource>);
                    var a = new AssignableDisposable();
                    var n = count;
                    var current = default(TSource);

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

                    var f = default(Func<CancellationToken, Task<bool>>);
                    f = async ct =>
                        {
                            if (e == null)
                            {
                                if (n-- == 0)
                                {
                                    return false;
                                }

                                e = source.GetEnumerator();

                                a.Disposable = e;
                            }

                            if (await e.MoveNext(ct)
                                       .ConfigureAwait(false))
                            {
                                current = e.Current;
                                return true;
                            }
                            e = null;
                            return await f(ct)
                                       .ConfigureAwait(false);
                        };

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

        public static IAsyncEnumerable<TSource> Repeat<TSource>(this IAsyncEnumerable<TSource> source)
        {
            if (source == null)
                throw new ArgumentNullException(nameof(source));

            return CreateEnumerable(
                () =>
                {
                    var e = default(IAsyncEnumerator<TSource>);
                    var a = new AssignableDisposable();
                    var current = default(TSource);

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

                    var f = default(Func<CancellationToken, Task<bool>>);
                    f = async ct =>
                        {
                            if (e == null)
                            {
                                e = source.GetEnumerator();

                                a.Disposable = e;
                            }

                            if (await e.MoveNext(ct)
                                       .ConfigureAwait(false))
                            {
                                current = e.Current;
                                return true;
                            }
                            e = null;
                            return await f(ct)
                                       .ConfigureAwait(false);
                        };

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