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

namespace gaemstone.ECS;

public unsafe partial class World
{
	private readonly Dictionary<Type, Entity> _lookupByType = new();

	public void AddLookupByType(Type type, Entity entity)
	{
		// If an existing lookup already exists with the same entity, don't throw an exception.
		if (_lookupByType.TryGetValue(type, out var existing) && (existing == entity)) return;
		_lookupByType.Add(type, entity);
	}
	public void RemoveLookupByType(Type type)
		{ if (!_lookupByType.Remove(type)) throw new InvalidOperationException(
			$"Lookup for {type} does not exist"); }


	public EntityRef? LookupByType<T>()
		=> LookupByType(typeof(T));
	public EntityRef? LookupByType(Type type)
		=> LookupAlive(_lookupByType.GetValueOrDefault(type));
	public EntityRef LookupByTypeOrThrow<T>()
		=> LookupByTypeOrThrow(typeof(T));
	public EntityRef LookupByTypeOrThrow(Type type)
		=> LookupByType(type) ?? throw new EntityNotFoundException(
			$"Entity of type {type} not found");

	public EntityRef? LookupAlive(Entity value)
		=> EntityRef.CreateOrNull(this, new(ecs_get_alive(this, value)));
	public EntityRef LookupAliveOrThrow(Entity entity)
		=> LookupAlive(entity) ?? throw new EntityNotFoundException(
			$"Entity {entity} is not alive");

	public EntityRef? LookupByPath(EntityPath path)
		=> LookupByPath(default, path);
	public EntityRef? LookupByPath(Entity parent, EntityPath path)
		=> EntityRef.CreateOrNull(this, EntityPath.Lookup(this, parent, path, false));
	public EntityRef LookupByPathOrThrow(EntityPath path)
		=> LookupByPathOrThrow(default, path);
	public EntityRef LookupByPathOrThrow(Entity parent, EntityPath path)
		=> new(this, EntityPath.Lookup(this, parent, path, true));

	public EntityRef? LookupBySymbol(string symbol)
	{
		using var alloc = TempAllocator.Use();
		var entity = ecs_lookup_symbol(this, alloc.AllocateCString(symbol), false);
		return EntityRef.CreateOrNull(this, new(entity));
	}
	public EntityRef LookupBySymbolOrThrow(string symbol)
		=> LookupBySymbol(symbol) ?? throw new EntityNotFoundException(
			$"Entity with symbol '{symbol}' not found");


	public class EntityNotFoundException : Exception
		{ public EntityNotFoundException(string message) : base(message) {  } }
}

public static class LookupExtensions
{
	public static EntityRef CreateLookup<T>(this EntityRef entity)
		=> entity.CreateLookup(typeof(T));
	public static EntityRef CreateLookup(this EntityRef entity, Type type)
		{ entity.World.AddLookupByType(type, entity); return entity; }
}