using System;
using System.Collections.Generic;

namespace MoonTools.ECS
{
	public struct FilterSignature
	{
		private const int HASH_FACTOR = 97;

		public readonly HashSet<Type> Included;
		public readonly HashSet<Type> Excluded;

		public FilterSignature(HashSet<Type> included, HashSet<Type> excluded)
		{
			Included = included;
			Excluded = excluded;
		}

		public override bool Equals(object? obj)
		{
			return obj is FilterSignature signature && Equals(signature);
		}

		public bool Equals(FilterSignature other)
		{
			return Included.SetEquals(other.Included) && Excluded.SetEquals(other.Excluded);
		}

		private int GuidToInt(Guid guid)
		{
			return BitConverter.ToInt32(guid.ToByteArray());
		}

		public override int GetHashCode()
		{
			int result = 1;
			foreach (var type in Included)
			{
				result *= HASH_FACTOR + GuidToInt(type.GUID);
			}

			// FIXME: Is there a way to avoid collisions when this is the same set as included?
			foreach (var type in Excluded)
			{
				result *= HASH_FACTOR + GuidToInt(type.GUID);
			}

			return result;
		}
	}
}