// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT 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
    {
#if INCLUDE_SYSTEM_LINQ_ASYNCENUMERABLE_DUPLICATES
        // https://learn.microsoft.com/en-us/dotnet/api/system.linq.asyncenumerable.groupjoin?view=net-9.0-pp#system-linq-asyncenumerable-groupjoin-4(system-collections-generic-iasyncenumerable((-0))-system-collections-generic-iasyncenumerable((-1))-system-func((-0-2))-system-func((-1-2))-system-func((-0-system-collections-generic-ienumerable((-1))-3))-system-collections-generic-iequalitycomparer((-2)))
        // The method above covers the next two overloads because it supplies a default null value for comparer.

        /// <summary>
        /// Correlates the elements of two async-enumerable sequences based on equality of keys and groups the results. The default equality comparer is used to compare keys.
        /// </summary>
        /// <typeparam name="TOuter">The type of the elements of the first async-enumerable sequence.</typeparam>
        /// <typeparam name="TInner">The type of the elements of the second async-enumerable sequence.</typeparam>
        /// <typeparam name="TKey">The type of the keys returned by the key selector functions.</typeparam>
        /// <typeparam name="TResult">The type of the result elements.</typeparam>
        /// <param name="outer">The first async-enumerable sequence to join.</param>
        /// <param name="inner">The async-enumerable sequence to join to the first sequence.</param>
        /// <param name="outerKeySelector">A function to extract the join key from each element of the first sequence.</param>
        /// <param name="innerKeySelector">A function to extract the join key from each element of the second sequence.</param>
        /// <param name="resultSelector">A function to create a result element from an element from the first sequence and a collection of matching elements from the second sequence.</param>
        /// <returns>An async-enumerable sequence that contains elements of type TResult that are obtained by performing a grouped join on two sequences.</returns>
        /// <exception cref="ArgumentNullException"><paramref name="outer"/> or <paramref name="inner"/> or <paramref name="outerKeySelector"/> or <paramref name="innerKeySelector"/> or <paramref name="resultSelector"/> is null.</exception>
        public static IAsyncEnumerable<TResult> GroupJoin<TOuter, TInner, TKey, TResult>(this IAsyncEnumerable<TOuter> outer, IAsyncEnumerable<TInner> inner, Func<TOuter, TKey> outerKeySelector, Func<TInner, TKey> innerKeySelector, Func<TOuter, IAsyncEnumerable<TInner>, TResult> resultSelector) =>
            GroupJoin(outer, inner, outerKeySelector, innerKeySelector, resultSelector, comparer: null);

        /// <summary>
        /// Correlates the elements of two async-enumerable sequences based on equality of keys and groups the results. The specified equality comparer is used to compare keys.
        /// </summary>
        /// <typeparam name="TOuter">The type of the elements of the first async-enumerable sequence.</typeparam>
        /// <typeparam name="TInner">The type of the elements of the second async-enumerable sequence.</typeparam>
        /// <typeparam name="TKey">The type of the keys returned by the key selector functions.</typeparam>
        /// <typeparam name="TResult">The type of the result elements.</typeparam>
        /// <param name="outer">The first async-enumerable sequence to join.</param>
        /// <param name="inner">The async-enumerable sequence to join to the first async-enumerable sequence.</param>
        /// <param name="outerKeySelector">A function to extract the join key from each element of the first sequence.</param>
        /// <param name="innerKeySelector">A function to extract the join key from each element of the second sequence.</param>
        /// <param name="resultSelector">A function to create a result element from an element from the first sequence and a collection of matching elements from the second sequence.</param>
        /// <param name="comparer">An equality comparer to hash and compare keys.</param>
        /// <returns>An async-enumerable sequence that contains elements of type TResult that are obtained by performing a grouped join on two sequences.</returns>
        /// <exception cref="ArgumentNullException"><paramref name="outer"/> or <paramref name="inner"/> or <paramref name="outerKeySelector"/> or <paramref name="innerKeySelector"/> or <paramref name="resultSelector"/> is null.</exception>
        public static IAsyncEnumerable<TResult> GroupJoin<TOuter, TInner, TKey, TResult>(this IAsyncEnumerable<TOuter> outer, IAsyncEnumerable<TInner> inner, Func<TOuter, TKey> outerKeySelector, Func<TInner, TKey> innerKeySelector, Func<TOuter, IAsyncEnumerable<TInner>, TResult> resultSelector, IEqualityComparer<TKey>? comparer)
        {
            if (outer == null)
                throw Error.ArgumentNull(nameof(outer));
            if (inner == null)
                throw Error.ArgumentNull(nameof(inner));
            if (outerKeySelector == null)
                throw Error.ArgumentNull(nameof(outerKeySelector));
            if (innerKeySelector == null)
                throw Error.ArgumentNull(nameof(innerKeySelector));
            if (resultSelector == null)
                throw Error.ArgumentNull(nameof(resultSelector));

            return Core(outer, inner, outerKeySelector, innerKeySelector, resultSelector, comparer);

            static async IAsyncEnumerable<TResult> Core(IAsyncEnumerable<TOuter> outer, IAsyncEnumerable<TInner> inner, Func<TOuter, TKey> outerKeySelector, Func<TInner, TKey> innerKeySelector, Func<TOuter, IAsyncEnumerable<TInner>, TResult> resultSelector, IEqualityComparer<TKey>? comparer, [System.Runtime.CompilerServices.EnumeratorCancellation] CancellationToken cancellationToken = default)
            {
                await using var e = outer.GetConfiguredAsyncEnumerator(cancellationToken, false);

                if (await e.MoveNextAsync())
                {
                    var lookup = await Internal.Lookup<TKey, TInner>.CreateForJoinAsync(inner, innerKeySelector, comparer, cancellationToken).ConfigureAwait(false);

                    do
                    {
                        var item = e.Current;
                        var outerKey = outerKeySelector(item);
                        yield return resultSelector(item, lookup[outerKey].ToAsyncEnumerable());
                    }
                    while (await e.MoveNextAsync());
                }
            }
        }
#endif // INCLUDE_SYSTEM_LINQ_ASYNCENUMERABLE_DUPLICATES

        [GenerateAsyncOverload]
        [Obsolete("Use GroupJoin. IAsyncEnumerable LINQ is now in System.Linq.AsyncEnumerable, and the GroupJoinAwait functionality now exists as an overload of GroupJoin. You will need to modify your callback to take an additional CancellationToken argument.")]
        private static IAsyncEnumerable<TResult> GroupJoinAwaitCore<TOuter, TInner, TKey, TResult>(this IAsyncEnumerable<TOuter> outer, IAsyncEnumerable<TInner> inner, Func<TOuter, ValueTask<TKey>> outerKeySelector, Func<TInner, ValueTask<TKey>> innerKeySelector, Func<TOuter, IAsyncEnumerable<TInner>, ValueTask<TResult>> resultSelector) =>
            GroupJoinAwaitCore<TOuter, TInner, TKey, TResult>(outer, inner, outerKeySelector, innerKeySelector, resultSelector, comparer: null);

        [GenerateAsyncOverload]
        [Obsolete("Use GroupJoin. IAsyncEnumerable LINQ is now in System.Linq.AsyncEnumerable, and the GroupJoinAwait functionality now exists as an overload of GroupJoin. You will need to modify your callback to take an additional CancellationToken argument. You will need to modify your callback to take an additional CancellationToken argument.")]
        private static IAsyncEnumerable<TResult> GroupJoinAwaitCore<TOuter, TInner, TKey, TResult>(this IAsyncEnumerable<TOuter> outer, IAsyncEnumerable<TInner> inner, Func<TOuter, ValueTask<TKey>> outerKeySelector, Func<TInner, ValueTask<TKey>> innerKeySelector, Func<TOuter, IAsyncEnumerable<TInner>, ValueTask<TResult>> resultSelector, IEqualityComparer<TKey>? comparer)
        {
            if (outer == null)
                throw Error.ArgumentNull(nameof(outer));
            if (inner == null)
                throw Error.ArgumentNull(nameof(inner));
            if (outerKeySelector == null)
                throw Error.ArgumentNull(nameof(outerKeySelector));
            if (innerKeySelector == null)
                throw Error.ArgumentNull(nameof(innerKeySelector));
            if (resultSelector == null)
                throw Error.ArgumentNull(nameof(resultSelector));

            return Core(outer, inner, outerKeySelector, innerKeySelector, resultSelector, comparer);

            static async IAsyncEnumerable<TResult> Core(IAsyncEnumerable<TOuter> outer, IAsyncEnumerable<TInner> inner, Func<TOuter, ValueTask<TKey>> outerKeySelector, Func<TInner, ValueTask<TKey>> innerKeySelector, Func<TOuter, IAsyncEnumerable<TInner>, ValueTask<TResult>> resultSelector, IEqualityComparer<TKey>? comparer, [System.Runtime.CompilerServices.EnumeratorCancellation] CancellationToken cancellationToken = default)
            {
                await using var e = outer.GetConfiguredAsyncEnumerator(cancellationToken, false);

                if (await e.MoveNextAsync())
                {
                    var lookup = await Internal.LookupWithTask<TKey, TInner>.CreateForJoinAsync(inner, innerKeySelector, comparer, cancellationToken).ConfigureAwait(false);

                    do
                    {
                        var item = e.Current;
                        var outerKey = await outerKeySelector(item).ConfigureAwait(false);
                        yield return await resultSelector(item, lookup[outerKey].ToAsyncEnumerable()).ConfigureAwait(false);
                    }
                    while (await e.MoveNextAsync());
                }
            }
        }

#if !NO_DEEP_CANCELLATION
        [GenerateAsyncOverload]
        [Obsolete("Use GroupJoin. IAsyncEnumerable LINQ is now in System.Linq.AsyncEnumerable, and the GroupJoinAwaitWithCancellation functionality now exists as an overload of GroupJoin.")]
        private static IAsyncEnumerable<TResult> GroupJoinAwaitWithCancellationCore<TOuter, TInner, TKey, TResult>(this IAsyncEnumerable<TOuter> outer, IAsyncEnumerable<TInner> inner, Func<TOuter, CancellationToken, ValueTask<TKey>> outerKeySelector, Func<TInner, CancellationToken, ValueTask<TKey>> innerKeySelector, Func<TOuter, IAsyncEnumerable<TInner>, CancellationToken, ValueTask<TResult>> resultSelector) =>
            GroupJoinAwaitWithCancellationCore<TOuter, TInner, TKey, TResult>(outer, inner, outerKeySelector, innerKeySelector, resultSelector, comparer: null);

        [GenerateAsyncOverload]
        [Obsolete("Use GroupJoin. IAsyncEnumerable LINQ is now in System.Linq.AsyncEnumerable, and the GroupJoinAwaitWithCancellation functionality now exists as an overload of GroupJoin.")]
        private static IAsyncEnumerable<TResult> GroupJoinAwaitWithCancellationCore<TOuter, TInner, TKey, TResult>(this IAsyncEnumerable<TOuter> outer, IAsyncEnumerable<TInner> inner, Func<TOuter, CancellationToken, ValueTask<TKey>> outerKeySelector, Func<TInner, CancellationToken, ValueTask<TKey>> innerKeySelector, Func<TOuter, IAsyncEnumerable<TInner>, CancellationToken, ValueTask<TResult>> resultSelector, IEqualityComparer<TKey>? comparer)
        {
            if (outer == null)
                throw Error.ArgumentNull(nameof(outer));
            if (inner == null)
                throw Error.ArgumentNull(nameof(inner));
            if (outerKeySelector == null)
                throw Error.ArgumentNull(nameof(outerKeySelector));
            if (innerKeySelector == null)
                throw Error.ArgumentNull(nameof(innerKeySelector));
            if (resultSelector == null)
                throw Error.ArgumentNull(nameof(resultSelector));

            return Core(outer, inner, outerKeySelector, innerKeySelector, resultSelector, comparer);

            static async IAsyncEnumerable<TResult> Core(IAsyncEnumerable<TOuter> outer, IAsyncEnumerable<TInner> inner, Func<TOuter, CancellationToken, ValueTask<TKey>> outerKeySelector, Func<TInner, CancellationToken, ValueTask<TKey>> innerKeySelector, Func<TOuter, IAsyncEnumerable<TInner>, CancellationToken, ValueTask<TResult>> resultSelector, IEqualityComparer<TKey>? comparer, [System.Runtime.CompilerServices.EnumeratorCancellation] CancellationToken cancellationToken = default)
            {
                await using var e = outer.GetConfiguredAsyncEnumerator(cancellationToken, false);

                if (await e.MoveNextAsync())
                {
                    var lookup = await Internal.LookupWithTask<TKey, TInner>.CreateForJoinAsync(inner, innerKeySelector, comparer, cancellationToken).ConfigureAwait(false);

                    do
                    {
                        var item = e.Current;
                        var outerKey = await outerKeySelector(item, cancellationToken).ConfigureAwait(false);
                        yield return await resultSelector(item, lookup[outerKey].ToAsyncEnumerable(), cancellationToken).ConfigureAwait(false);
                    }
                    while (await e.MoveNextAsync());
                }
            }
        }
#endif
    }
}