Connected.Framework/Connected.Interop/Enumerables.cs

using System.Reflection;

namespace Connected.Interop
{
	public static class Enumerables
	{
		public static Type? FindEnumerable(this Type type)
		{
			if (type is null || type == typeof(string))
				return default;

			if (type.IsArray)
			{
				var elementType = type.GetElementType();

				if (elementType is not null)
					return typeof(IEnumerable<>).MakeGenericType(elementType);
				else
					return default;
			}

			var typeInfo = type.GetTypeInfo();

			if (typeInfo.IsGenericType)
			{
				foreach (var arg in typeInfo.GenericTypeArguments)
				{
					var en = typeof(IEnumerable<>).MakeGenericType(arg);

					if (en.GetTypeInfo().IsAssignableFrom(typeInfo))
						return en;
				}
			}

			foreach (var itf in typeInfo.ImplementedInterfaces)
			{
				var en = itf.FindEnumerable();

				if (en is not null)
					return en;
			}

			if (typeInfo.BaseType is not null && typeInfo.BaseType != typeof(object))
				return typeInfo.BaseType.FindEnumerable();

			return default;
		}

		public static bool IsEnumerable(this Type type)
		{
			return type.FindEnumerable() is not null;
		}

		public static Type GetEnumerableType(this Type elementType)
		{
			return typeof(IEnumerable<>).MakeGenericType(elementType);
		}

		public static Type? GetEnumerableElementType(this Type? enumerableType)
		{
			if (enumerableType is null)
				return default;

			var en = enumerableType.FindEnumerable();

			if (en is null)
				return enumerableType;

			return en.GetTypeInfo().GenericTypeArguments[0];
		}
	}
}