// 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.Threading;
using System.Threading.Tasks;

namespace System.Linq
{
    public static partial class AsyncEnumerable
    {
        /// <summary>
        /// Determines whether an async-enumerable sequence contains any elements.
        /// </summary>
        /// <typeparam name="TSource">The type of the elements in the source sequence.</typeparam>
        /// <param name="source">An async-enumerable sequence to check for non-emptiness.</param>
        /// <param name="cancellationToken">The optional cancellation token to be used for cancelling the sequence at any time.</param>
        /// <returns>An async-enumerable sequence containing a single element determining whether the source sequence contains any elements.</returns>
        /// <exception cref="ArgumentNullException"><paramref name="source"/> is null.</exception>
        /// <remarks>The return type of this operator differs from the corresponding operator on IEnumerable in order to retain asynchronous behavior.</remarks>
        public static ValueTask<bool> AnyAsync<TSource>(this IAsyncEnumerable<TSource> source, CancellationToken cancellationToken = default)
        {
            if (source == null)
                throw Error.ArgumentNull(nameof(source));

            return Core(source, cancellationToken);

            static async ValueTask<bool> Core(IAsyncEnumerable<TSource> source, CancellationToken cancellationToken)
            {
                await using var e = source.GetConfiguredAsyncEnumerator(cancellationToken, false);

                return await e.MoveNextAsync();
            }
        }

        /// <summary>
        /// Determines whether any element of an async-enumerable sequence satisfies a condition.
        /// </summary>
        /// <typeparam name="TSource">The type of the elements in the source sequence.</typeparam>
        /// <param name="source">An async-enumerable sequence whose elements to apply the predicate to.</param>
        /// <param name="predicate">A function to test each element for a condition.</param>
        /// <param name="cancellationToken">The optional cancellation token to be used for cancelling the sequence at any time.</param>
        /// <returns>An async-enumerable sequence containing a single element determining whether any elements in the source sequence pass the test in the specified predicate.</returns>
        /// <exception cref="ArgumentNullException"><paramref name="source"/> or <paramref name="predicate"/> is null.</exception>
        /// <remarks>The return type of this operator differs from the corresponding operator on IEnumerable in order to retain asynchronous behavior.</remarks>
        public static ValueTask<bool> AnyAsync<TSource>(this IAsyncEnumerable<TSource> source, Func<TSource, bool> predicate, CancellationToken cancellationToken = default)
        {
            if (source == null)
                throw Error.ArgumentNull(nameof(source));
            if (predicate == null)
                throw Error.ArgumentNull(nameof(predicate));

            return Core(source, predicate, cancellationToken);

            static async ValueTask<bool> Core(IAsyncEnumerable<TSource> source, Func<TSource, bool> predicate, CancellationToken cancellationToken)
            {
                await foreach (var item in source.WithCancellation(cancellationToken).ConfigureAwait(false))
                {
                    if (predicate(item))
                    {
                        return true;
                    }
                }

                return false;
            }
        }

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

            return Core(source, predicate, cancellationToken);

            static async ValueTask<bool> Core(IAsyncEnumerable<TSource> source, Func<TSource, ValueTask<bool>> predicate, CancellationToken cancellationToken)
            {
                await foreach (var item in source.WithCancellation(cancellationToken).ConfigureAwait(false))
                {
                    if (await predicate(item).ConfigureAwait(false))
                    {
                        return true;
                    }
                }

                return false;
            }
        }

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

            return Core(source, predicate, cancellationToken);

            static async ValueTask<bool> Core(IAsyncEnumerable<TSource> source, Func<TSource, CancellationToken, ValueTask<bool>> predicate, CancellationToken cancellationToken)
            {
                await foreach (var item in source.WithCancellation(cancellationToken).ConfigureAwait(false))
                {
                    if (await predicate(item, cancellationToken).ConfigureAwait(false))
                    {
                        return true;
                    }
                }

                return false;
            }
        }
#endif
    }
}