gaemstone.ECS/src/gaemstone.ECS/Id.cs

using System;
using gaemstone.ECS.Utility;
using static flecs_hub.flecs;

namespace gaemstone.ECS;

public unsafe struct Id<TContext>
	: IEquatable<Id<TContext>>
{
	public readonly World<TContext> World;
	public readonly Id Value;

	public IdFlags Flags      => Value.Flags;
	public bool    IsPair     => Value.IsPair;
	public bool    IsWildcard => Value.IsWildcard;

	public bool IsValid => ecs_id_is_valid(World, this);
	public bool IsTag   => ecs_id_is_tag(World, this);
	public bool IsInUse => ecs_id_in_use(World, this);
	public int  Count   => ecs_count_id(World, this);

	private Id(World<TContext> world, Id id)
		{ World = world; Value = id; }

	public static Id<TContext> GetUnsafe(World<TContext> world, Id value)
		=> new(world, value);
	public static Id<TContext>? GetOrNull(World<TContext> world, Id value)
		=> ecs_id_is_valid(world, value) ? new(world, value) : null;
	public static Id<TContext> GetOrThrow(World<TContext> world, Id value)
		=> ecs_id_is_valid(world, value) ? new(world, value) : throw new InvalidOperationException($"The id {value} is not valid");

	public Entity<TContext>? AsEntity()
		=> !IsPair ? World.LookupAliveOrNull(new Entity(new() { Data = Value })) : null;
	public (Entity<TContext> Relation, Entity<TContext> Target)? AsPair()
		=> IsPair && (World.LookupAliveOrNull(Value.RelationUnsafe) is Entity<TContext> relation) &&
		             (World.LookupAliveOrNull(Value.TargetUnsafe  ) is Entity<TContext> target  )
			? (relation, target) : null;

	public bool Equals(Id<TContext> other)
	{
#if DEBUG
		// In DEBUG mode, we additionally check if the worlds the two compared
		// values are from the same world. This accounts for the world being a
		// stage, hence why it might not be the cheapest operation.
		if (World != other.World) throw new ArgumentException(
			"The specified values are not from the same world");
#endif
		return Value == other.Value;
	}
	public override bool Equals(object? obj)
		=> (obj is Id<TContext> other) && Equals(other);
	public override int GetHashCode()
		=> Value.GetHashCode();
	public override string? ToString()
		=> ecs_id_str(World, this).FlecsToStringAndFree()!;

	public static bool operator ==(Id<TContext> left, Id<TContext> right) =>  left.Equals(right);
	public static bool operator !=(Id<TContext> left, Id<TContext> right) => !left.Equals(right);

	public static implicit operator Id      (Id<TContext> id) => id.Value;
	public static implicit operator ecs_id_t(Id<TContext> id) => id.Value.Value;

	public static implicit operator Term(Id<TContext> id) => new(id.Value);
}

[Flags]
public enum IdFlags : ulong
{
	Pair     = 1ul << 63,
	Override = 1ul << 62,
	Toggle   = 1ul << 61,
	And      = 1ul << 60,
}