gaemstone/src/gaemstone/ECS/Component.cs

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

namespace gaemstone.ECS;

[AttributeUsage(AttributeTargets.Class | AttributeTargets.Struct | AttributeTargets.Enum)]
public class ComponentAttribute : EntityAttribute
{
	public ComponentAttribute() {  }
	public ComponentAttribute(params string[] path) : base(path) {  }
}

public static class ComponentExtensions
{
	public unsafe static EntityRef CreateComponent<T>(this EntityRef entity)
		=> entity.CreateComponent(typeof(T));
	public unsafe static EntityRef CreateComponent(this EntityRef entity, Type type)
	{
		// TODO: Do some additional sanity checking for this type.

		var typeInfo = default(ecs_type_info_t);
		if (type.IsPrimitive) throw new ArgumentException(
			"Must not be primitive", nameof(type));
		var wrapper = TypeWrapper.For(type);
		if (type.IsValueType && !wrapper.IsUnmanaged) throw new Exception(
			"Struct component must satisfy the unmanaged constraint. " +
			"Consider making it a class if you need to store references.");
		typeInfo.size      = wrapper.Size;
		typeInfo.alignment = wrapper.Size;

		var desc = new ecs_component_desc_t { entity = entity, type = typeInfo };
		ecs_component_init(entity.Universe, &desc);
		return entity.CreateLookup(type);
	}
}