// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
 
using System.Collections.Generic;
using System.Runtime.CompilerServices;
using System.Threading;
using System.Threading.Tasks;
 
namespace System.Linq
{
    public static partial class AsyncEnumerable
    {
        /// <summary>Determines whether a sequence contains any elements.</summary>
        /// <typeparam name="TSource">The type of the elements of source.</typeparam>
        /// <param name="source">The <see cref="IAsyncEnumerable{T}"/> to check for emptiness.</param>
        /// <param name="cancellationToken">The <see cref="CancellationToken"/> to monitor for cancellation requests. The default is <see cref="CancellationToken.None"/>.</param>
        /// <returns>true if the source sequence contains any elements; otherwise, false.</returns>
        /// <exception cref="ArgumentNullException"><paramref name="source"/> is <see langword="null"/>.</exception>
        public static ValueTask<bool> AnyAsync<TSource>(
            this IAsyncEnumerable<TSource> source,
            CancellationToken cancellationToken = default)
        {
            ThrowHelper.ThrowIfNull(source);
 
            return Impl(source, cancellationToken);
 
            static async ValueTask<bool> Impl(
                IAsyncEnumerable<TSource> source,
                CancellationToken cancellationToken)
            {
                IAsyncEnumerator<TSource> enumerator = source.GetAsyncEnumerator(cancellationToken);
                try
                {
                    return await enumerator.MoveNextAsync().ConfigureAwait(false);
                }
                finally
                {
                    await enumerator.DisposeAsync().ConfigureAwait(false);
                }
            }
        }
 
        /// <summary>Determines whether any element of a sequence satisfies a condition.</summary>
        /// <typeparam name="TSource"></typeparam>
        /// <param name="source">An <see cref="IAsyncEnumerable{T}"/> 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 <see cref="CancellationToken"/> to monitor for cancellation requests. The default is <see cref="CancellationToken.None"/>.</param>
        /// <returns>
        /// true if the source sequence is not empty and at least one of its elements passes
        /// the test in the specified predicate; otherwise, false.
        /// </returns>
        /// <exception cref="ArgumentNullException"><paramref name="source"/> is <see langword="null"/>.</exception>
        /// <exception cref="ArgumentNullException"><paramref name="predicate"/> is <see langword="null"/>.</exception>
        public static ValueTask<bool> AnyAsync<TSource>(
            this IAsyncEnumerable<TSource> source,
            Func<TSource, bool> predicate,
            CancellationToken cancellationToken = default)
        {
            ThrowHelper.ThrowIfNull(source);
            ThrowHelper.ThrowIfNull(predicate);
 
            return Impl(source.WithCancellation(cancellationToken).ConfigureAwait(false), predicate);
 
            static async ValueTask<bool> Impl(
                ConfiguredCancelableAsyncEnumerable<TSource> source,
                Func<TSource, bool> predicate)
            {
                await foreach (TSource element in source)
                {
                    if (predicate(element))
                    {
                        return true;
                    }
                }
 
                return false;
            }
        }
 
        /// <summary>Determines whether any element of a sequence satisfies a condition.</summary>
        /// <typeparam name="TSource"></typeparam>
        /// <param name="source">An <see cref="IAsyncEnumerable{T}"/> 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 <see cref="CancellationToken"/> to monitor for cancellation requests. The default is <see cref="CancellationToken.None"/>.</param>
        /// <returns>
        /// true if the source sequence is not empty and at least one of its elements passes
        /// the test in the specified predicate; otherwise, false.
        /// </returns>
        /// <exception cref="ArgumentNullException"><paramref name="source"/> is <see langword="null"/>.</exception>
        /// <exception cref="ArgumentNullException"><paramref name="predicate"/> is <see langword="null"/>.</exception>
        public static ValueTask<bool> AnyAsync<TSource>(
            this IAsyncEnumerable<TSource> source,
            Func<TSource, CancellationToken, ValueTask<bool>> predicate,
            CancellationToken cancellationToken = default)
        {
            ThrowHelper.ThrowIfNull(source);
            ThrowHelper.ThrowIfNull(predicate);
 
            return Impl(source, predicate, cancellationToken);
 
            static async ValueTask<bool> Impl(
                IAsyncEnumerable<TSource> source,
                Func<TSource, CancellationToken, ValueTask<bool>> predicate,
                CancellationToken cancellationToken)
            {
                await foreach (TSource element in source.WithCancellation(cancellationToken).ConfigureAwait(false))
                {
                    if (await predicate(element, cancellationToken).ConfigureAwait(false))
                    {
                        return true;
                    }
                }
 
                return false;
            }
        }
    }
}