using System.Reflection;

namespace Connected.Entities
{
	internal static class QueryableMethods
	{
		static QueryableMethods()
		{
			var queryableMethodGroups = typeof(Queryable)
				.GetMethods(BindingFlags.Public | BindingFlags.Static | BindingFlags.DeclaredOnly)
				.GroupBy(mi => mi.Name)
				.ToDictionary(e => e.Key, l => l.ToList());

			SingleWithoutPredicate = GetMethod(nameof(Queryable.Single), 1, types => new[] { typeof(IQueryable<>).MakeGenericType(types[0]) });
			SingleOrDefaultWithoutPredicate = GetMethod(nameof(Queryable.SingleOrDefault), 1, types => new[] { typeof(IQueryable<>).MakeGenericType(types[0]) });

			MethodInfo GetMethod(string name, int genericParameterCount, Func<Type[], Type[]> parameterGenerator)
			{
				return queryableMethodGroups[name].Single(mi => ((genericParameterCount == 0 && !mi.IsGenericMethod)
								|| (mi.IsGenericMethod && mi.GetGenericArguments().Length == genericParameterCount))
								&& mi.GetParameters().Select(e => e.ParameterType).SequenceEqual(parameterGenerator(mi.IsGenericMethod ? mi.GetGenericArguments() : Array.Empty<Type>())));
			}
		}

		public static MethodInfo SingleWithoutPredicate { get; }
		public static MethodInfo SingleOrDefaultWithoutPredicate { get; }

	}
}