using System;
using System.Runtime.InteropServices;
using static flecs_hub.flecs;

namespace gaemstone.ECS.Utility;

public unsafe readonly struct ReferenceHandle
	: IDisposable
{
	public static int NumActiveHandles { get; private set; }


	private readonly nint _value;

	public object? Target => (_value != default)
		? ((GCHandle)_value).Target : null;

	private ReferenceHandle(nint value)
		=> _value = value;

	public static ReferenceHandle Alloc(object? target)
	{
		if (target == null) return default;
		NumActiveHandles++;
		return new((nint)GCHandle.Alloc(target));
	}

	public ReferenceHandle Clone()
		=> Alloc(Target);

	public void Dispose()
	{
		if (_value == default) return;
		NumActiveHandles--;
		((GCHandle)_value).Free();
	}


	[UnmanagedCallersOnly]
	internal static void Construct(void* ptr, int count, ecs_type_info_t* _)
		=> new Span<ReferenceHandle>(ptr, count).Clear();

	[UnmanagedCallersOnly]
	internal static void Destruct(void* ptr, int count, ecs_type_info_t* _)
	{
		var span = new Span<ReferenceHandle>(ptr, count);
		foreach (var handle in span) handle.Dispose();
		span.Clear();
	}

	[UnmanagedCallersOnly]
	internal static void Move(void* dstPtr, void* srcPtr, int count, ecs_type_info_t* _)
	{
		var dst = new Span<ReferenceHandle>(dstPtr, count);
		var src = new Span<ReferenceHandle>(srcPtr, count);
		foreach (var handle in dst) handle.Dispose();
		src.CopyTo(dst);
		src.Clear();
	}

	[UnmanagedCallersOnly]
	internal static void Copy(void* dstPtr, void* srcPtr, int count, ecs_type_info_t* _)
	{
		var dst = new Span<ReferenceHandle>(dstPtr, count);
		var src = new Span<ReferenceHandle>(srcPtr, count);
		for (var i = 0; i < count; i++) {
			dst[i].Dispose();
			dst[i] = src[i].Clone();
		}
	}
}