namespace Theater_ECS.Internal.Containers;

using System;
using System.Collections;

class PagedSparseSet
{
	public const uint32 PageSize = 4096;

	private List<List<Entity>> _sparse = new .()~ DeleteContainerAndItems!(_);
	private List<Entity> _packed = new .() ~ delete _;
	private UList _packedEntities ~ delete _;

	private function void(void* data) _deallocationFunction = null;

	public this(int_cosize size)
	{
		_packedEntities = new .(size);
	}

	public bool Contains(Entity e)
	{
		return _sparse[e.Index/PageSize][e.Index % PageSize] != Entity.Null;
	}

	public void Add(Entity e, void* toAdd)
	{
		EnsureLoadedPage(e.Index/PageSize);
		_packed.Add(e);
		_packedEntities.Add(toAdd);
		_sparse[e.Index/PageSize][e.Index % PageSize] = (.)_packed.Count-1;
	}

	public bool Remove(Entity e, bool cleanup = false)
	{
		EnsurePage(e.Index/PageSize);
		if(_sparse[e.Index/PageSize] == null)
			return false;

		if(_deallocationFunction != null && !cleanup)
			_deallocationFunction(_packedEntities[(.)(_sparse[e.Index/PageSize][e.Index % PageSize].Index)]);

		let toRm = _packed[_sparse[e.Index/PageSize][e.Index % PageSize].Index];
		let b = _packed.Back;
		_packed[_sparse[e.Index/PageSize][e.Index % PageSize].Index] = b;
		_packed.Back = toRm;

		_sparse[b.Index/PageSize][b.Index % PageSize] = Entity(e.Index, b.Version);
		_sparse[e.Index/PageSize][e.Index % PageSize] = Entity.Null;

		_packed.PopBack();
		return true;
	}

	[Inline, Unchecked]
	public void* Get(Entity e)
	{
		return _packedEntities[(.)(_sparse[e.Index/PageSize][e.Index % PageSize].Index)];
	}

	public Span<Entity> GetAll()
	{
		return _packed;
	}

	public int_cosize Count() => (.)_packed.Count;

	///Ensure that a page exist and is loaded
	public void EnsureLoadedPage(uint32 page)
	{
		EnsurePage(page);
		if(_sparse[page] == null)
		{
			_sparse[page] = new List<Entity>(PageSize);
			_sparse[page].[Friend]Count = 4096;
			_sparse[page].SetAll(Entity.Null);

		}
	}

	///Ensure that a page exists, it might be null though
	private void EnsurePage(uint32 page)
	{
		while(_sparse.Count < page+1)
			_sparse.Add(null);
	}
}