reactive/Ix.NET/Source/System.Linq.Async/System/Linq/Operators/SkipWhile.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.Collections.Generic;
using System.Diagnostics;
using System.Threading;
using System.Threading.Tasks;

namespace System.Linq
{
    public static partial class AsyncEnumerable
    {
        public static IAsyncEnumerable<TSource> SkipWhile<TSource>(this IAsyncEnumerable<TSource> source, Func<TSource, bool> predicate)
        {
            if (source == null)
                throw Error.ArgumentNull(nameof(source));
            if (predicate == null)
                throw Error.ArgumentNull(nameof(predicate));

            return Create(Core);

            async IAsyncEnumerator<TSource> Core(CancellationToken cancellationToken)
            {
                await using (var e = source.GetConfiguredAsyncEnumerator(cancellationToken, false))
                {
                    while (await e.MoveNextAsync())
                    {
                        var element = e.Current;

                        if (!predicate(element))
                        {
                            yield return element;

                            while (await e.MoveNextAsync())
                            {
                                yield return e.Current;
                            }

                            yield break;
                        }
                    }
                }
            }
        }

        public static IAsyncEnumerable<TSource> SkipWhile<TSource>(this IAsyncEnumerable<TSource> source, Func<TSource, int, bool> predicate)
        {
            if (source == null)
                throw Error.ArgumentNull(nameof(source));
            if (predicate == null)
                throw Error.ArgumentNull(nameof(predicate));

            return Create(Core);

            async IAsyncEnumerator<TSource> Core(CancellationToken cancellationToken)
            {
                await using (var e = source.GetConfiguredAsyncEnumerator(cancellationToken, false))
                {
                    var index = -1;

                    while (await e.MoveNextAsync())
                    {
                        checked
                        {
                            index++;
                        }

                        var element = e.Current;

                        if (!predicate(element, index))
                        {
                            yield return element;

                            while (await e.MoveNextAsync())
                            {
                                yield return e.Current;
                            }

                            yield break;
                        }
                    }
                }
            }
        }

        internal static IAsyncEnumerable<TSource> SkipWhileAwaitCore<TSource>(this IAsyncEnumerable<TSource> source, Func<TSource, ValueTask<bool>> predicate)
        {
            if (source == null)
                throw Error.ArgumentNull(nameof(source));
            if (predicate == null)
                throw Error.ArgumentNull(nameof(predicate));

            return Create(Core);

            async IAsyncEnumerator<TSource> Core(CancellationToken cancellationToken)
            {
                await using (var e = source.GetConfiguredAsyncEnumerator(cancellationToken, false))
                {
                    while (await e.MoveNextAsync())
                    {
                        var element = e.Current;

                        if (!await predicate(element).ConfigureAwait(false))
                        {
                            yield return element;

                            while (await e.MoveNextAsync())
                            {
                                yield return e.Current;
                            }

                            yield break;
                        }
                    }
                }
            }
        }

#if !NO_DEEP_CANCELLATION
        internal static IAsyncEnumerable<TSource> SkipWhileAwaitWithCancellationCore<TSource>(this IAsyncEnumerable<TSource> source, Func<TSource, CancellationToken, ValueTask<bool>> predicate)
        {
            if (source == null)
                throw Error.ArgumentNull(nameof(source));
            if (predicate == null)
                throw Error.ArgumentNull(nameof(predicate));

            return Create(Core);

            async IAsyncEnumerator<TSource> Core(CancellationToken cancellationToken)
            {
                await using (var e = source.GetConfiguredAsyncEnumerator(cancellationToken, false))
                {
                    while (await e.MoveNextAsync())
                    {
                        var element = e.Current;

                        if (!await predicate(element, cancellationToken).ConfigureAwait(false))
                        {
                            yield return element;

                            while (await e.MoveNextAsync())
                            {
                                yield return e.Current;
                            }

                            yield break;
                        }
                    }
                }
            }
        }
#endif

        internal static IAsyncEnumerable<TSource> SkipWhileAwaitCore<TSource>(this IAsyncEnumerable<TSource> source, Func<TSource, int, ValueTask<bool>> predicate)
        {
            if (source == null)
                throw Error.ArgumentNull(nameof(source));
            if (predicate == null)
                throw Error.ArgumentNull(nameof(predicate));

            return Create(Core);

            async IAsyncEnumerator<TSource> Core(CancellationToken cancellationToken)
            {
                await using (var e = source.GetConfiguredAsyncEnumerator(cancellationToken, false))
                {
                    var index = -1;

                    while (await e.MoveNextAsync())
                    {
                        checked
                        {
                            index++;
                        }

                        var element = e.Current;

                        if (!await predicate(element, index).ConfigureAwait(false))
                        {
                            yield return element;

                            while (await e.MoveNextAsync())
                            {
                                yield return e.Current;
                            }

                            yield break;
                        }
                    }
                }
            }
        }

#if !NO_DEEP_CANCELLATION
        internal static IAsyncEnumerable<TSource> SkipWhileAwaitWithCancellationCore<TSource>(this IAsyncEnumerable<TSource> source, Func<TSource, int, CancellationToken, ValueTask<bool>> predicate)
        {
            if (source == null)
                throw Error.ArgumentNull(nameof(source));
            if (predicate == null)
                throw Error.ArgumentNull(nameof(predicate));

            return Create(Core);

            async IAsyncEnumerator<TSource> Core(CancellationToken cancellationToken)
            {
                await using (var e = source.GetConfiguredAsyncEnumerator(cancellationToken, false))
                {
                    var index = -1;

                    while (await e.MoveNextAsync())
                    {
                        checked
                        {
                            index++;
                        }

                        var element = e.Current;

                        if (!await predicate(element, index, cancellationToken).ConfigureAwait(false))
                        {
                            yield return element;

                            while (await e.MoveNextAsync())
                            {
                                yield return e.Current;
                            }

                            yield break;
                        }
                    }
                }
            }
        }
#endif
    }
}