content: /*
   * Copyright (C) 2018-2025 Lightbend Inc. <https://www.lightbend.com>
   */
  
  package jdocs.cluster;
  
  import static jdocs.cluster.TransformationMessages.BACKEND_REGISTRATION;
  
  import akka.actor.AbstractActor;
  import akka.cluster.Cluster;
  import akka.cluster.ClusterEvent.CurrentClusterState;
  import akka.cluster.ClusterEvent.MemberUp;
  import akka.cluster.Member;
  import akka.cluster.MemberStatus;
  import jdocs.cluster.TransformationMessages.TransformationJob;
  import jdocs.cluster.TransformationMessages.TransformationResult;
  
  // #backend
  public class TransformationBackend extends AbstractActor {
  
    Cluster cluster = Cluster.get(getContext().getSystem());
  
    // subscribe to cluster changes, MemberUp
    @Override
    public void preStart() {
      cluster.subscribe(getSelf(), MemberUp.class);
    }
  
    // re-subscribe when restart
    @Override
    public void postStop() {
      cluster.unsubscribe(getSelf());
    }
  
    @Override
    public Receive createReceive() {
      return receiveBuilder()
          .match(
              TransformationJob.class,
              job -> {
                getSender().tell(new TransformationResult(job.getText().toUpperCase()), getSelf());
              })
          .match(
              CurrentClusterState.class,
              state -> {
                for (Member member : state.getMembers()) {
                  if (member.status().equals(MemberStatus.up())) {
                    register(member);
                  }
                }
              })
          .match(
              MemberUp.class,
              mUp -> {
                register(mUp.member());
              })
          .build();
    }
  
    void register(Member member) {
      if (member.hasRole("frontend"))
        getContext()
            .actorSelection(member.address() + "/user/frontend")
            .tell(BACKEND_REGISTRATION, getSelf());
    }
  }
  // #backend
  