jellyfin/RSSDP/IEnumerableExtensions.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace Rssdp.Infrastructure
{
	internal static class IEnumerableExtensions
	{
		public static IEnumerable<T> SelectManyRecursive<T>(this IEnumerable<T> source, Func<T, IEnumerable<T>> selector)
		{
			if (source == null) throw new ArgumentNullException(nameof(source));
			if (selector == null) throw new ArgumentNullException(nameof(selector));

			return !source.Any() ? source :
					source.Concat(
							source
							.SelectMany(i => selector(i).EmptyIfNull())
							.SelectManyRecursive(selector)
					);
		}

		public static IEnumerable<T> EmptyIfNull<T>(this IEnumerable<T> source)
		{
			return source ?? Enumerable.Empty<T>();
		}
	}
}