val config = ConfigFactory.load("application.conf")
    val man: ActorSystem[GreetStarter.Command] = ActorSystem(GreetStarter(), "greetDemo",config)
    man ! GreetStarter.RepeatedGreeting("Tiger",1.seconds)

  object GreetStarter {
    import Messages._
    def apply(): Behavior[SayHi] = {
      Behaviors.setup { ctx =>
        val props = DispatcherSelector.fromConfig("akka.actor.default-blocking-io-dispatcher")
        val helloActor = ctx.spawn(HelloActor(), "hello-actor",props)
        val greeter = ctx.spawn(Greeter(helloActor), "greeter")
        ctx.watch(greeter)
        ctx.watchWith(helloActor,StopWorker("something happend"))
        Behaviors.receiveMessage { who =>
          if (who.name == "stop") {
            ctx.stop(helloActor)
            ctx.stop(greeter)
            Behaviors.stopped
          } else {
            greeter ! who
            Behaviors.same
          }
        }
      }
    }
  }

import akka.actor.typed.Behavior
import akka.actor.typed.SpawnProtocol
import akka.actor.typed.scaladsl.Behaviors
import akka.actor.typed.scaladsl.LoggerOps
object HelloWorldMain {
  def apply(): Behavior[SpawnProtocol.Command] =
    Behaviors.setup { context =>
      // Start initial tasks
      // context.spawn(...)
      SpawnProtocol()
    }
}
object Main extends App {
implicit val system: ActorSystem[SpawnProtocol.Command] =
  ActorSystem(HelloWorldMain(), "hello")
// needed in implicit scope for ask (?)
import akka.actor.typed.scaladsl.AskPattern._
implicit val ec: ExecutionContext = system.executionContext
implicit val timeout: Timeout = Timeout(3.seconds)
val greeter: Future[ActorRef[HelloWorld.Greet]] =
  system.ask(SpawnProtocol.Spawn(behavior = HelloWorld(), name = "greeter", props = Props.empty, _))
val greetedBehavior = Behaviors.receive[HelloWorld.Greeted] { (context, message) =>
  context.log.info2("Greeting for {} from {}", message.whom, message.from)
  Behaviors.stopped
}
val greetedReplyTo: Future[ActorRef[HelloWorld.Greeted]] =
  system.ask(SpawnProtocol.Spawn(greetedBehavior, name = "", props = Props.empty, _))
for (greeterRef <- greeter; replyToRef <- greetedReplyTo) {
  greeterRef ! HelloWorld.Greet("Akka", replyToRef)
}
...
}

object SpawnProtocol {
...
  final case class Spawn[T](behavior: Behavior[T], name: String, props: Props, replyTo: ActorRef[ActorRef[T]])
      extends Command
...
  def apply(): Behavior[Command] =
    Behaviors.receive { (ctx, msg) =>
      msg match {
        case Spawn(bhvr, name, props, replyTo) =>
          val ref =
            if (name == null || name.equals(""))
              ctx.spawnAnonymous(bhvr, props)
            else {
              @tailrec def spawnWithUniqueName(c: Int): ActorRef[Any] = {
                val nameSuggestion = if (c == 0) name else s"$name-$c"
                ctx.child(nameSuggestion) match {
                  case Some(_) => spawnWithUniqueName(c + 1) // already taken, try next
                  case None    => ctx.spawn(bhvr, nameSuggestion, props)
                }
              }
              spawnWithUniqueName(0)
            }
          replyTo ! ref
          Behaviors.same
      }
    }
}

object HelloWorldBot {
  def apply(max: Int): Behavior[HelloWorld.Greeted] = {
    bot(0, max)
  }
  private def bot(greetingCounter: Int, max: Int): Behavior[HelloWorld.Greeted] =
    Behaviors.receive { (context, message) =>
      val n = greetingCounter + 1
      context.log.info2("Greeting {} for {}", n, message.whom)
      if (n == max) {
        Behaviors.stopped
      } else {
        message.from ! HelloWorld.Greet(message.whom, context.self)
        bot(n, max)
      }
    }
}

object MasterControlProgram {
  sealed trait Command
  final case class SpawnJob(name: String) extends Command
  case object GracefulShutdown extends Command
  // Predefined cleanup operation
  def cleanup(log: Logger): Unit = log.info("Cleaning up!")
  def apply(): Behavior[Command] = {
    Behaviors
      .receive[Command] { (context, message) =>
        message match {
          case SpawnJob(jobName) =>
            context.log.info("Spawning job {}!", jobName)
            context.spawn(Job(jobName), name = jobName)
            Behaviors.same
          case GracefulShutdown =>
            context.log.info("Initiating graceful shutdown...")
            // perform graceful stop, executing cleanup before final system termination
            // behavior executing cleanup is passed as a parameter to Actor.stopped
            Behaviors.stopped { () =>
              cleanup(context.system.log)
            }
        }
      }
      .receiveSignal {
        case (context, PostStop) =>
          context.log.info("Master Control Program stopped")
          Behaviors.same
      }
  }
}

  object GreetStarter {
    import Messages._
    def apply(): Behavior[SayHi] = {
      Behaviors.setup { ctx =>
        val props = DispatcherSelector.fromConfig("akka.actor.default-blocking-io-dispatcher")
        val helloActor = ctx.spawn(HelloActor(), "hello-actor",props)
        val greeter = ctx.spawn(Greeter(helloActor), "greeter")
        ctx.watch(greeter)
        ctx.watchWith(helloActor,StopWorker("something happend"))
        Behaviors.receiveMessage { who =>
          if (who.name == "stop") {
            ctx.stop(helloActor)
            ctx.stop(greeter)
            Behaviors.stopped
          } else {
            greeter ! who
            Behaviors.same
          }
        }.receiveSignal {
            case (context, Terminated(ref)) =>
              context.log.info("{} stopped!", ref.path.name)
              Behaviors.same
          }
      }
    }
  }

  trait Receive[T] extends Behavior[T] {
    def receiveSignal(onSignal: PartialFunction[(ActorContext[T], Signal), Behavior[T]]): Behavior[T]
  }
trait Signal
/**
 * Lifecycle signal that is fired upon restart of the Actor before replacing
 * the behavior with the fresh one (i.e. this signal is received within the
 * behavior that failed).
 */
sealed abstract class PreRestart extends Signal
case object PreRestart extends PreRestart {
  def instance: PreRestart = this
}
/**
 * Lifecycle signal that is fired after this actor and all its child actors
 * (transitively) have terminated. The [[Terminated]] signal is only sent to
 * registered watchers after this signal has been processed.
 */
sealed abstract class PostStop extends Signal
// comment copied onto object for better hints in IDEs
/**
 * Lifecycle signal that is fired after this actor and all its child actors
 * (transitively) have terminated. The [[Terminated]] signal is only sent to
 * registered watchers after this signal has been processed.
 */
case object PostStop extends PostStop {
  def instance: PostStop = this
}
object Terminated {
  def apply(ref: ActorRef[Nothing]): Terminated = new Terminated(ref)
  def unapply(t: Terminated): Option[ActorRef[Nothing]] = Some(t.ref)
}