package observers

import (
	"github.com/mlange-42/arche/ecs"
	"github.com/mlange-42/arche/ecs/event"
	"github.com/mlange-42/arche/generic"
	"github.com/mlange-42/arche/listener"
)

// will be added as  an ecs.Resource to the world so we  can use it in
// CollisionSystem to dynamically make it appear or disappear
type ParticleObserver struct {
	// we only have one particle so far, if we use multiple ones, turn
	// this in to a map, see player_observer.go for an example
	Entity ecs.Entity
}

// Create a  new resource of  type PlayerObserver which will  hold all
// player  entities.   We   also  add  a  Listener   which  looks  for
// EntityRemoved events and  if a player gets removed,  we also remove
// it from the Entity map in our observer.
func NewParticleObserver(world *ecs.World) {
	observer := &ParticleObserver{}

	resmanger := generic.NewResource[ParticleObserver](world)
	resmanger.Add(observer)

	listen := listener.NewCallback(
		func(world *ecs.World, event ecs.EntityEvent) {
			observerID := ecs.ResourceID[ParticleObserver](world)
			observer := world.Resources().Get(observerID).(*ParticleObserver)
			observer.RemoveEntity(event.Entity)
		},

		event.EntityRemoved,
	)

	world.SetListener(&listen)
}

func GetParticleObserver(world *ecs.World) *ParticleObserver {
	observerID := ecs.ResourceID[ParticleObserver](world)
	observer := world.Resources().Get(observerID).(*ParticleObserver)
	return observer
}

func (observer *ParticleObserver) AddEntity(entity ecs.Entity) {
	observer.Entity = entity
}

func (observer *ParticleObserver) RemoveEntity(entity ecs.Entity) {
	observer.Entity = ecs.Entity{}
}