gaemstone/src/gaemstone/ECS/Entity.cs

using System;
using static flecs_hub.flecs;

namespace gaemstone.ECS;

[AttributeUsage(AttributeTargets.Struct)]
public class EntityAttribute : Attribute, ICreateEntityAttribute
{
	/// <summary> If specified, uses this path instead of the default name. </summary>
	public string[]? Path { get; }

	/// <summary> If true, the path will be absolute instead of relative. </summary>
	public bool Global { get; init; }

	public EntityAttribute() {  }
	public EntityAttribute(params string[] path)
	{
		if (path.Length == 0) throw new ArgumentException(
			"Path must not be empty", nameof(path));
		Path = path;
	}
}

public readonly struct Entity
	: IEquatable<Entity>
{
	public static readonly Entity None = default;

	public readonly ecs_entity_t Value;
	public uint ID => (uint)Value.Data;

	public bool IsSome => Value.Data != 0;
	public bool IsNone => Value.Data == 0;

	public Entity(ecs_entity_t value) => Value = value;

	public bool Equals(Entity other) => Value.Data == other.Value.Data;
	public override bool Equals(object? obj) => (obj is Entity other) && Equals(other);
	public override int GetHashCode() => Value.Data.GetHashCode();
	public override string? ToString() => $"Entity(0x{Value.Data.Data:X})";

	public static bool operator ==(Entity left, Entity right) =>  left.Equals(right);
	public static bool operator !=(Entity left, Entity right) => !left.Equals(right);

	public static implicit operator ecs_entity_t(Entity e) => e.Value;
	public static implicit operator Identifier(Entity e) => new(e.Value.Data);
	public static implicit operator ecs_id_t(Entity e) => e.Value.Data;
}