using System.Runtime.CompilerServices;
using System.Runtime.InteropServices;
using gaemstone.ECS;
using gaemstone.Utility;
using static flecs_hub.flecs;

namespace gaemstone.Flecs;

[Module, Path("/flecs/doc")]
public static class Doc
{
	[Tag] public struct Brief {  }
	[Tag] public struct Detail {  }
	[Tag] public struct Link {  }
	[Tag] public struct Color {  }

	[Relation, Component]
	public struct Description
	{
		internal unsafe void* Value;

		public override string? ToString()
			{ unsafe { return Marshal.PtrToStringUTF8((nint)Value); } }
		public static implicit operator string?(Description desc)
			=> desc.ToString();
	}
}

public static unsafe class DocExtensions
{
	private static EntityRef Set<T>(EntityRef entity, string? value)
	{
		var world      = entity.World;
		var descEntity = world.LookupByTypeOrThrow<Doc.Description>();
		var docEntity  = world.LookupByTypeOrThrow<T>();
		var id = Identifier.Pair(descEntity, docEntity);

		var has   = entity.Has(id);
		var alloc = GlobalHeapAllocator.Instance;
		if (value != null) {
			var ptr = ecs_get_mut_id(world, entity, id);
			ref var desc = ref Unsafe.AsRef<Doc.Description>(ptr);
			// FIXME: Why does freeing these cause crashes?
			// if (has) alloc.Free((nint)desc.Value); // Free previous value.
			desc.Value = (void*)(nint)alloc.AllocateCString(value);
		} else if (has) {
			// var @ref = ecs_ref_init_id(world, entity, id);
			// var ptr  = ecs_ref_get_id(world, &@ref, id);
			// var desc = Unsafe.AsRef<Doc.Description>(ptr);
			// alloc.Free((nint)desc.Value); // Free previous value.
			entity.Remove(id);
		}
		return entity;
	}

	public static string? GetDocName(this EntityRef entity, bool fallbackToEntityName = true)
		=> fallbackToEntityName || entity.Has<Doc.Description, Core.Name>()
			? ecs_doc_get_name(entity.World, entity).FlecsToString() : null;
	public static EntityRef SetDocName(this EntityRef entity, string? value)
		=> Set<Core.Name>(entity, value);

	public static string? GetDocBrief(this EntityRef entity)
		=> ecs_doc_get_brief(entity.World, entity).FlecsToString()!;
	public static EntityRef SetDocBrief(this EntityRef entity, string? value)
		=> Set<Doc.Brief>(entity, value);

	public static string? GetDocDetail(this EntityRef entity)
		=> ecs_doc_get_detail(entity.World, entity).FlecsToString()!;
	public static EntityRef SetDocDetail(this EntityRef entity, string? value)
		=> Set<Doc.Detail>(entity, value);

	public static string? GetDocLink(this EntityRef entity)
		=> ecs_doc_get_link(entity.World, entity).FlecsToString()!;
	public static EntityRef SetDocLink(this EntityRef entity, string? value)
		=> Set<Doc.Link>(entity, value);

	public static string? GetDocColor(this EntityRef entity)
		=> ecs_doc_get_color(entity.World, entity).FlecsToString()!;
	public static EntityRef SetDocColor(this EntityRef entity, string? value)
		=> Set<Doc.Color>(entity, value);
}