openquell/observers/player_observer.go

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 check  for  player collisions.
type PlayerObserver struct {
	Entities map[ecs.Entity]int
}

// 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 NewPlayerObserver(world *ecs.World) {
	observer := &PlayerObserver{}
	observer.Entities = make(map[ecs.Entity]int)

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

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

		event.EntityRemoved,
	)

	world.SetListener(&listen)
}

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

func (observer *PlayerObserver) AddEntity(entity ecs.Entity) {
	observer.Entities[entity] = 1
}

func (observer *PlayerObserver) RemoveEntity(entity ecs.Entity) {
	delete(observer.Entities, entity)
}

func (observer *PlayerObserver) RemoveEntities() {
	observer.Entities = make(map[ecs.Entity]int)
}