jmonkey-test/src/main/scala/wow/doge/mygame/events/EventBus.scala

package wow.doge.mygame.events

// import akka.event.ActorEventBus
// import akka.event.ManagedActorClassification
// import akka.event.ActorClassifier
import akka.actor.typed.ActorRef
// import akka.actor.ActorSystem
// import akka.event.EventBus
// import akka.util.Subclassification
// import java.util.concurrent.atomic.AtomicReference
import akka.actor.typed.Behavior
import akka.actor.typed.scaladsl.Behaviors
import scala.reflect.ClassTag
import akka.event.EventStream

// private[events] final case class ClassificationMessage(ref: ActorRef, id: Int)

// class ActorBusImpl(val system: ActorSystem, val busSize: Int)
//     extends ActorEventBus
//     with ActorClassifier
//     with ManagedActorClassification {
//   type Event = ClassificationMessage

//   // is used for extracting the classifier from the incoming events
//   override protected def classify(event: Event): ActorRef = event.ref

//   // determines the initial size of the index data structure
//   // used internally (i.e. the expected number of different classifiers)
//   override protected def mapSize: Int = busSize
// }

// class StartsWithSubclassification extends Subclassification[String] {
//   override def isEqual(x: String, y: String): Boolean =
//     x == y

//   override def isSubclass(x: String, y: String): Boolean =
//     x.startsWith(y)
// }

// import akka.event.SubchannelClassification

// final case class MsgEnvelope(topic: String, payload: Any)
// import akka.actor.typed.scaladsl.adapter._

// /**
//   * Publishes the payload of the MsgEnvelope when the topic of the
//   * MsgEnvelope starts with the String specified when subscribing.
//   */
// class SubchannelBusImpl extends EventBus with SubchannelClassification {
//   type Event = Any
//   type Classifier = Class[_]
//   type Subscriber = ActorRef

//   // Subclassification is an object providing `isEqual` and `isSubclass`
//   // to be consumed by the other methods of this classifier
// //   override protected val subclassification: Subclassification[Classifier] =
// //     new StartsWithSubclassification

//   private val initiallySubscribedOrUnsubscriber =
//     new AtomicReference[Either[Set[ActorRef], ActorRef]](Left(Set.empty))

//   override protected implicit val subclassification
//       : Subclassification[Classifier] = new Subclassification[Class[_]] {
//     def isEqual(x: Class[_], y: Class[_]) = x == y
//     def isSubclass(x: Class[_], y: Class[_]) = y.isAssignableFrom(x)
//   }

//   // is used for extracting the classifier from the incoming events
//   override protected def classify(event: Event): Classifier = event.getClass()

//   // will be invoked for each event for all subscribers which registered
//   // themselves for the event’s classifier
//   override protected def publish(event: Event, subscriber: Subscriber): Unit = {
//     // subscriber ! event.payload
//     subscriber ! event
//   }
// }

object EventBus {
  sealed trait Command[A]
  final case class Publish[A, E <: A](event: E, publisher: ActorRef[_])
      extends Command[A]

  /**
    * Subscribe a typed actor to listen for types or subtypes of E
    * by sending this command to the [[akka.actor.typed.ActorSystem.eventStream]].
    *
    * ==Simple example==
    * {{{
    *   sealed trait A
    *   case object A1 extends A
    *   //listen for all As
    *   def subscribe(actorSystem: ActorSystem[_], actorRef: ActorRef[A]) =
    *     actorSystem.eventStream ! EventStream.Subscribe(actorRef)
    *   //listen for A1s only
    *   def subscribe(actorSystem: ActorSystem[_], actorRef: ActorRef[A]) =
    *     actorSystem.eventStream ! EventStream.Subscribe[A1](actorRef)
    * }}}
    */
  final case class Subscribe[A, E <: A](subscriber: ActorRef[E])(implicit
      classTag: ClassTag[E]
  ) extends Command[A] {

    def topic: Class[_] = classTag.runtimeClass
  }

  /**
    * Unsubscribe an actor ref from the event stream
    * by sending this command to the [[akka.actor.typed.ActorSystem.eventStream]].
    */
  final case class Unsubscribe[A, E <: A](subscriber: ActorRef[E])
      extends Command[A]

  def apply[A](): Behavior[EventBus.Command[A]] =
    Behaviors.setup { ctx =>
      val eventStream = new EventStream(ctx.system.classicSystem)
      new EventBus().eventStreamBehavior(eventStream)
    }

}

class EventBus[B] {
  import akka.actor.typed.scaladsl.adapter._

  private def eventStreamBehavior(
      eventStream: akka.event.EventStream
  ): Behavior[EventBus.Command[B]] =
    Behaviors.receiveMessage {
      case EventBus.Publish(event, publisher) =>
        eventStream.publish(event)
        Behaviors.same
      case s @ EventBus.Subscribe(subscriber) =>
        eventStream.subscribe(subscriber.toClassic, s.topic)
        Behaviors.same
      case EventBus.Unsubscribe(subscriber) =>
        eventStream.unsubscribe(subscriber.toClassic)
        Behaviors.same
    }
}