// 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. 

<#@ template debug="false" hostspecific="false" language="C#" #>
<#@ assembly name="System.Core" #>
<#@ import namespace="System.Linq" #>
<#@ import namespace="System.Text" #>
<#@ import namespace="System.Collections.Generic" #>
<#@ output extension=".cs" #>
<#
int maxCombine = 4;
#>
using System.Threading;
using System.Threading.Tasks;

namespace System.Linq
{
    public static partial class AsyncEnumerable
    {
<#
for (var i = 2; i <= maxCombine; i++)
{
    Func<int, string> getInputType = j => j == 1 ? "TSource" : "TMiddle" + (j - 1);
    Func<int, string> getOutputType = j => j == i ? "TResult" : "TMiddle" + j;
    Func<int, string> getSelectorType = j => "Func<" + getInputType(j) + ", " + getOutputType(j) + ">";

    var types = string.Join(", ", Enumerable.Range(1, i - 1).Select(j => "TMiddle" + j));
    var allSelectors = string.Join(", ", Enumerable.Range(1, i).Select(j => getSelectorType(j) + " selector" + j));

    var applyAll = Enumerable.Range(1, i).Reverse().Aggregate("", (s, j) => s + "_selector" + j + "(") + "x" + new string(')', i);
#>
        private sealed class CombinedSelectors<#=i#><TSource, <#=types#>, TResult> : ICombinedSelectors<TSource, TResult>
        {
<#
for (var j = 1; j <= i; j++)
{
    var type = getSelectorType(j);
#>
            private readonly <#=type#> _selector<#=j#>;
<#
}
#>

            public CombinedSelectors<#=i#>(<#=allSelectors#>)
            {
<#
for (var j = 1; j <= i; j++)
{
#>
                _selector<#=j#> = selector<#=j#>;
<#
}
#>
            }

            public ICombinedSelectors<TSource, TNewResult> Combine<TNewResult>(Func<TResult, TNewResult> selector) =>
<#
if (i == maxCombine)
{
#>
                new CombinedSelectors2<TSource, TResult, TNewResult>(this.Invoke, selector);
<#
}
else
{
#>
                new CombinedSelectors<#=i + 1#><TSource, <#=types#>, TResult, TNewResult>(
<#
for (var j = 1; j <= i; j++)
{
#>
                    _selector<#=j#>,
<#
}
#>
                    selector
                );
<#
}
#>

            public TResult Invoke(TSource x) => <#=applyAll#>;
        }

<#
}
#>
<#
for (var i = 2; i <= maxCombine; i++)
{
    Func<int, string> getInputType = j => j == 1 ? "TSource" : "TMiddle" + (j - 1);
    Func<int, string> getOutputType = j => "ValueTask<" + (j == i ? "TResult" : "TMiddle" + j) + ">";
    Func<int, string> getSelectorType = j => "Func<" + getInputType(j) + ", " + getOutputType(j) + ">";

    var types = string.Join(", ", Enumerable.Range(1, i - 1).Select(j => "TMiddle" + j));
    var allSelectors = string.Join(", ", Enumerable.Range(1, i).Select(j => getSelectorType(j) + " selector" + j));

    var applyAll = Enumerable.Range(1, i).Reverse().Aggregate("", (s, j) => s + "await _selector" + j + "(") + "x" + string.Join("", Enumerable.Repeat(").ConfigureAwait(false)", i));
#>
        private sealed class CombinedAsyncSelectors<#=i#><TSource, <#=types#>, TResult> : ICombinedAsyncSelectors<TSource, TResult>
        {
<#
for (var j = 1; j <= i; j++)
{
    var type = getSelectorType(j);
#>
            private readonly <#=type#> _selector<#=j#>;
<#
}
#>

            public CombinedAsyncSelectors<#=i#>(<#=allSelectors#>)
            {
<#
for (var j = 1; j <= i; j++)
{
#>
                _selector<#=j#> = selector<#=j#>;
<#
}
#>
            }

            public ICombinedAsyncSelectors<TSource, TNewResult> Combine<TNewResult>(Func<TResult, ValueTask<TNewResult>> selector) =>
<#
if (i == maxCombine)
{
#>
                new CombinedAsyncSelectors2<TSource, TResult, TNewResult>(this.Invoke, selector);
<#
}
else
{
#>
                new CombinedAsyncSelectors<#=i + 1#><TSource, <#=types#>, TResult, TNewResult>(
<#
for (var j = 1; j <= i; j++)
{
#>
                    _selector<#=j#>,
<#
}
#>
                    selector
                );
<#
}
#>

            public async ValueTask<TResult> Invoke(TSource x) => <#=applyAll#>;
        }

<#
}
#>
#if !NO_DEEP_CANCELLATION
<#
for (var i = 2; i <= maxCombine; i++)
{
    Func<int, string> getInputType = j => j == 1 ? "TSource" : "TMiddle" + (j - 1);
    Func<int, string> getOutputType = j => "ValueTask<" + (j == i ? "TResult" : "TMiddle" + j) + ">";
    Func<int, string> getSelectorType = j => "Func<" + getInputType(j) + ", CancellationToken, " + getOutputType(j) + ">";

    var types = string.Join(", ", Enumerable.Range(1, i - 1).Select(j => "TMiddle" + j));
    var allSelectors = string.Join(", ", Enumerable.Range(1, i).Select(j => getSelectorType(j) + " selector" + j));

    var applyAll = Enumerable.Range(1, i).Reverse().Aggregate("", (s, j) => s + "await _selector" + j + "(") + "x" + string.Join("", Enumerable.Repeat(", ct).ConfigureAwait(false)", i));
#>
        private sealed class CombinedAsyncSelectorsWithCancellation<#=i#><TSource, <#=types#>, TResult> : ICombinedAsyncSelectorsWithCancellation<TSource, TResult>
        {
<#
for (var j = 1; j <= i; j++)
{
    var type = getSelectorType(j);
#>
            private readonly <#=type#> _selector<#=j#>;
<#
}
#>

            public CombinedAsyncSelectorsWithCancellation<#=i#>(<#=allSelectors#>)
            {
<#
for (var j = 1; j <= i; j++)
{
#>
                _selector<#=j#> = selector<#=j#>;
<#
}
#>
            }

            public ICombinedAsyncSelectorsWithCancellation<TSource, TNewResult> Combine<TNewResult>(Func<TResult, CancellationToken, ValueTask<TNewResult>> selector) =>
<#
if (i == maxCombine)
{
#>
                new CombinedAsyncSelectorsWithCancellation2<TSource, TResult, TNewResult>(this.Invoke, selector);
<#
}
else
{
#>
                new CombinedAsyncSelectorsWithCancellation<#=i + 1#><TSource, <#=types#>, TResult, TNewResult>(
<#
for (var j = 1; j <= i; j++)
{
#>
                    _selector<#=j#>,
<#
}
#>
                    selector
                );
<#
}
#>

            public async ValueTask<TResult> Invoke(TSource x, CancellationToken ct) => <#=applyAll#>;
        }

<#
}
#>
#endif
    }
}