Fold.sbntxt

namespace SuperLinq.Async;

#nullable enable

public static partial class AsyncSuperEnumerable
{
	{{~ for $i in 1..16 ~}}
	/// <summary>
	/// Returns the result of applying a function to a sequence of {{$i}} element{{if $i != 1}}s{{end}}.
	/// </summary>
	/// <remarks>
	/// This operator uses immediate execution and buffers as many items of the source sequence as necessary.
	/// </remarks>
	/// <typeparam name="T">Type of element in the source sequence</typeparam>
	/// <typeparam name="TResult">Type of the result</typeparam>
	/// <param name="source">The sequence of items to fold.</param>
	/// <param name="folder">Function to apply to the elements in the sequence.</param>
	/// <returns>The folded value returned by <paramref name="folder"/>.</returns>
	/// <exception cref="global::System.ArgumentNullException"><paramref name="source"/> or <paramref name="folder"/> is null.</exception>
	/// <exception cref="global::System.InvalidOperationException">
	/// <paramref name="source"/> does not contain exactly {{$i}} element{{if $i != 1}}s{{end}}.
	/// </exception>
	public static global::System.Threading.Tasks.ValueTask<TResult> Fold<T, TResult>(
		this global::System.Collections.Generic.IAsyncEnumerable<T> source, 
		global::System.Func<{{~ for $j in 1..$i ~}}T, {{ end ~}}TResult> folder
	)
	{
		ArgumentNullException.ThrowIfNull(source);
		ArgumentNullException.ThrowIfNull(folder);

		return Core(source, folder);

		static async global::System.Threading.Tasks.ValueTask<TResult> Core(
			global::System.Collections.Generic.IAsyncEnumerable<T> source, 
			global::System.Func<{{~ for $j in 1..$i ~}}T, {{ end ~}}TResult> folder
		)
		{
			var elements = await source.AssertCount({{$i}}).ToListAsync().ConfigureAwait(false);

			return folder(
				{{~ for $j in 1..$i ~}}
				elements[{{$j-1}}]{{ if !for.last }},{{ end }}
				{{~ end ~}}
			);
		}
	}

	{{~ end ~}}
}