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

namespace gaemstone.ECS;

public unsafe class Query<TContext>
	: IDisposable
{
	public World<TContext> World { get; }
	public ecs_query_t* Handle { get; }
	public Filter<TContext> Filter { get; }

	public Variable? ThisVar => Filter.ThisVar;

	public Query(World<TContext> world, QueryDesc desc)
	{
		using var alloc = TempAllocator.Use();
		var flecsDesc = desc.ToFlecs(alloc);
		World  = world;
		Handle = ecs_query_init(world, &flecsDesc);
		Filter = new(world, ecs_query_get_filter(Handle));
	}

	public void Dispose()
		=> ecs_query_fini(this);

	public QueryIterator<TContext> Iter()
		=> new(ecs_query_iter(World, this));

	public override string ToString()
		=> ecs_query_str(Handle).FlecsToStringAndFree()!;

	public static implicit operator ecs_query_t*(Query<TContext> query) => query.Handle;
}

public unsafe class QueryIterator<TContext>
	: Iterator<TContext>
{
	internal QueryIterator(ecs_iter_t value)
		: base(value) {  }
	public override bool Next()
		=> ecs_query_next(Handle);
}

public class QueryDesc : FilterDesc
{
	public QueryDesc(params Term[] terms) : base(terms) {  }
	public QueryDesc(string expression) : base(expression) {  }

	public new unsafe ecs_query_desc_t ToFlecs(IAllocator alloc)
	{
		var desc = new ecs_query_desc_t {
			filter = base.ToFlecs(alloc),
			// TODO: Implement more Query features.
		};
		return desc;
	}
}