<#@ 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" #>
// 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
    {
<#
var os = new[]
{
    new { type = "int", res = "double", sum = "long" },
    new { type = "long", res = "double", sum = "long" },
    new { type = "float", res = "float", sum = "double" },
    new { type = "double", res = "double", sum = "double" },
    new { type = "decimal", res = "decimal", sum = "decimal" },
    new { type = "int?", res = "double?", sum = "long" },
    new { type = "long?", res = "double?", sum = "long" },
    new { type = "float?", res = "float?", sum = "double" },
    new { type = "double?", res = "double?", sum = "double" },
    new { type = "decimal?", res = "decimal?", sum = "decimal" },
};

foreach (var o in os)
{
    var isNullable = o.type.EndsWith("?");
    var t = o.type.TrimEnd('?');

    string res = "";

    if (t == "int" || t == "long")
        res = "(double)sum / count";
    else if (t == "double" || t == "decimal")
        res = "sum / count";
    else if (t == "float")
        res = "(float)(sum / count)";
#>
        public static ValueTask<<#=o.res#>> AverageAsync(this IAsyncEnumerable<<#=o.type#>> source, CancellationToken cancellationToken = default)
        {
            if (source == null)
                throw Error.ArgumentNull(nameof(source));

            return Core(source, cancellationToken);

            static async ValueTask<<#=o.res#>> Core(IAsyncEnumerable<<#=o.type#>> _source, CancellationToken _cancellationToken)
            {
<#
if (isNullable)
{
#>
                var e = _source.GetConfiguredAsyncEnumerator(_cancellationToken, false);

                try // REVIEW: Can use `await using` if we get pattern bind (HAS_AWAIT_USING_PATTERN_BIND)
                {
                    while (await e.MoveNextAsync())
                    {
                        var v = e.Current;
                        if (v.HasValue)
                        {
                            <#=o.sum#> sum = v.GetValueOrDefault();
                            long count = 1;
                            checked
                            {
                                while (await e.MoveNextAsync())
                                {
                                    v = e.Current;
                                    if (v.HasValue)
                                    {
                                        sum += v.GetValueOrDefault();
                                        ++count;
                                    }
                                }
                            }

                            return <#=res#>;
                        }
                    }
                }
                finally
                {
                    await e.DisposeAsync();
                }

                return null;
<#
}
else
{
#>
                var e = _source.GetConfiguredAsyncEnumerator(_cancellationToken, false);

                try // REVIEW: Can use `await using` if we get pattern bind (HAS_AWAIT_USING_PATTERN_BIND)
                {
                    if (!await e.MoveNextAsync())
                    {
                        throw Error.NoElements();
                    }

                    <#=o.sum#> sum = e.Current;
                    long count = 1;
                    checked
                    {
                        while (await e.MoveNextAsync())
                        {
                            sum += e.Current;
                            ++count;
                        }
                    }

                    return <#=res#>;
                }
                finally
                {
                    await e.DisposeAsync();
                }
<#
}
#>
            }
        }

        public static ValueTask<<#=o.res#>> AverageAsync<TSource>(this IAsyncEnumerable<TSource> source, Func<TSource, <#=o.type#>> selector, CancellationToken cancellationToken = default)
        {
            if (source == null)
                throw Error.ArgumentNull(nameof(source));
            if (selector == null)
                throw Error.ArgumentNull(nameof(selector));

            return Core(source, selector, cancellationToken);

            static async ValueTask<<#=o.res#>> Core(IAsyncEnumerable<TSource> _source, Func<TSource, <#=o.type#>> _selector, CancellationToken _cancellationToken)
            {
<#
if (isNullable)
{
#>
                var e = _source.GetConfiguredAsyncEnumerator(_cancellationToken, false);

                try // REVIEW: Can use `await using` if we get pattern bind (HAS_AWAIT_USING_PATTERN_BIND)
                {
                    while (await e.MoveNextAsync())
                    {
                        var v = _selector(e.Current);
                        if (v.HasValue)
                        {
                            <#=o.sum#> sum = v.GetValueOrDefault();
                            long count = 1;
                            checked
                            {
                                while (await e.MoveNextAsync())
                                {
                                    v = _selector(e.Current);
                                    if (v.HasValue)
                                    {
                                        sum += v.GetValueOrDefault();
                                        ++count;
                                    }
                                }
                            }

                            return <#=res#>;
                        }
                    }
                }
                finally
                {
                    await e.DisposeAsync();
                }

                return null;
<#
}
else
{
#>
                var e = _source.GetConfiguredAsyncEnumerator(_cancellationToken, false);

                try // REVIEW: Can use `await using` if we get pattern bind (HAS_AWAIT_USING_PATTERN_BIND)
                {
                    if (!await e.MoveNextAsync())
                    {
                        throw Error.NoElements();
                    }

                    <#=o.sum#> sum = _selector(e.Current);
                    long count = 1;
                    checked
                    {
                        while (await e.MoveNextAsync())
                        {
                            sum += _selector(e.Current);
                            ++count;
                        }
                    }

                    return <#=res#>;
                }
                finally
                {
                    await e.DisposeAsync();
                }
<#
}
#>
            }
        }

        public static ValueTask<<#=o.res#>> AverageAsync<TSource>(this IAsyncEnumerable<TSource> source, Func<TSource, ValueTask<<#=o.type#>>> selector, CancellationToken cancellationToken = default)
        {
            if (source == null)
                throw Error.ArgumentNull(nameof(source));
            if (selector == null)
                throw Error.ArgumentNull(nameof(selector));

            return Core(source, selector, cancellationToken);

            static async ValueTask<<#=o.res#>> Core(IAsyncEnumerable<TSource> _source, Func<TSource, ValueTask<<#=o.type#>>> _selector, CancellationToken _cancellationToken)
            {
<#
if (isNullable)
{
#>
                var e = _source.GetConfiguredAsyncEnumerator(_cancellationToken, false);

                try // REVIEW: Can use `await using` if we get pattern bind (HAS_AWAIT_USING_PATTERN_BIND)
                {
                    while (await e.MoveNextAsync())
                    {
                        var v = await _selector(e.Current).ConfigureAwait(false);
                        if (v.HasValue)
                        {
                            <#=o.sum#> sum = v.GetValueOrDefault();
                            long count = 1;
                            checked
                            {
                                while (await e.MoveNextAsync())
                                {
                                    v = await _selector(e.Current).ConfigureAwait(false);
                                    if (v.HasValue)
                                    {
                                        sum += v.GetValueOrDefault();
                                        ++count;
                                    }
                                }
                            }

                            return <#=res#>;
                        }
                    }
                }
                finally
                {
                    await e.DisposeAsync();
                }

                return null;
<#
}
else
{
#>
                var e = _source.GetConfiguredAsyncEnumerator(_cancellationToken, false);

                try // REVIEW: Can use `await using` if we get pattern bind (HAS_AWAIT_USING_PATTERN_BIND)
                {
                    if (!await e.MoveNextAsync())
                    {
                        throw Error.NoElements();
                    }

                    <#=o.sum#> sum = await _selector(e.Current).ConfigureAwait(false);
                    long count = 1;
                    checked
                    {
                        while (await e.MoveNextAsync())
                        {
                            sum += await _selector(e.Current).ConfigureAwait(false);
                            ++count;
                        }
                    }

                    return <#=res#>;
                }
                finally
                {
                    await e.DisposeAsync();
                }
<#
}
#>
            }
        }

#if !NO_DEEP_CANCELLATION
        public static ValueTask<<#=o.res#>> AverageAsync<TSource>(this IAsyncEnumerable<TSource> source, Func<TSource, CancellationToken, ValueTask<<#=o.type#>>> selector, CancellationToken cancellationToken = default)
        {
            if (source == null)
                throw Error.ArgumentNull(nameof(source));
            if (selector == null)
                throw Error.ArgumentNull(nameof(selector));

            return Core(source, selector, cancellationToken);

            static async ValueTask<<#=o.res#>> Core(IAsyncEnumerable<TSource> _source, Func<TSource, CancellationToken, ValueTask<<#=o.type#>>> _selector, CancellationToken _cancellationToken)
            {
<#
if (isNullable)
{
#>
                var e = _source.GetConfiguredAsyncEnumerator(_cancellationToken, false);

                try // REVIEW: Can use `await using` if we get pattern bind (HAS_AWAIT_USING_PATTERN_BIND)
                {
                    while (await e.MoveNextAsync())
                    {
                        var v = await _selector(e.Current, _cancellationToken).ConfigureAwait(false);
                        if (v.HasValue)
                        {
                            <#=o.sum#> sum = v.GetValueOrDefault();
                            long count = 1;
                            checked
                            {
                                while (await e.MoveNextAsync())
                                {
                                    v = await _selector(e.Current, _cancellationToken).ConfigureAwait(false);
                                    if (v.HasValue)
                                    {
                                        sum += v.GetValueOrDefault();
                                        ++count;
                                    }
                                }
                            }

                            return <#=res#>;
                        }
                    }
                }
                finally
                {
                    await e.DisposeAsync();
                }

                return null;
<#
}
else
{
#>
                var e = _source.GetConfiguredAsyncEnumerator(_cancellationToken, false);

                try // REVIEW: Can use `await using` if we get pattern bind (HAS_AWAIT_USING_PATTERN_BIND)
                {
                    if (!await e.MoveNextAsync())
                    {
                        throw Error.NoElements();
                    }

                    <#=o.sum#> sum = await _selector(e.Current, _cancellationToken).ConfigureAwait(false);
                    long count = 1;
                    checked
                    {
                        while (await e.MoveNextAsync())
                        {
                            sum += await _selector(e.Current, _cancellationToken).ConfigureAwait(false);
                            ++count;
                        }
                    }

                    return <#=res#>;
                }
                finally
                {
                    await e.DisposeAsync();
                }
<#
}
#>
            }
        }
#endif

<#
}
#>
    }
}