import akka.actor._



case class Ping(target: ActorRef)

case class Pong(target: ActorRef)

case class Zong(target: ActorRef)



class Player(private val NUMBER_OF_RALLIES: Int) extends Actor{

  private var receivedBallCounter = 0



  def receive = {

      case Ping(targetPlayerRef) => {

        println("ping")

        receivedBallCounter += 1



        if ( receivedBallCounter < NUMBER_OF_RALLIES ) {

          targetPlayerRef ! Pong(self)

        }

        else {

          targetPlayerRef ! Pong(self)

          targetPlayerRef ! PoisonPill

        }

      }



      case Pong(targetPlayerRef) => {

        println("pong")

        receivedBallCounter += 1



        if ( receivedBallCounter < NUMBER_OF_RALLIES ) {

          targetPlayerRef ! Ping(self)

        }

        else {

          targetPlayerRef ! PoisonPill

        }

      }



      case _ => {

        println("Unhandled message")

      }

  }

}



val NUMBER_OF_RALLIES = 5

val actorSystem = ActorSystem("PingPongTraining")

val player1 = actorSystem.actorOf(Props(classOf[Player], NUMBER_OF_RALLIES))

val player2 = actorSystem.actorOf(Props(classOf[Player], NUMBER_OF_RALLIES))

player1 ! Zong(player2)

player1 ! Ping(player2)

player1 ! Zong(player2)

actorSystem.shutdown



/********************* POISON_PILL ********************* 

 * A PoisonPill message will stop an actor when the message is processed.

 * A PoisonPill message is queued just like an ordinary message

 * and will be handled after other messages queued ahead of it in its mailbox.

 */



/********************* context.stop(self) ********************* 

 * The difference is in which messages get processed before this sequence starts.

 * In the case of the stop call, the message currently being processed is completed first,

 * with all others discarded. 

 */



/********************* Console output *********************

 * scala> :load 12_1.scala

 * Loading 12_1.scala...

 * import akka.actor._

 * defined class Ping

 * defined class Pong

 * defined class Zong

 * defined class Player

 * NUMBER_OF_RALLIES: Int = 5

 * actorSystem: akka.actor.ActorSystem = akka://PingPongTraining

 * player1: akka.actor.ActorRef = Actor[akka://PingPongTraining/user/$a#-1157019602]

 * player2: akka.actor.ActorRef = Actor[akka://PingPongTraining/user/$b#-546795948]

 * Unhandled message

 * ping

 * pong

 * ping

 * pong

 * ping

 * pong

 * ping

 * pong

 * ping

 * pong

 * [INFO] [01/15/2018 22:07:07.545] [PingPongTraining-akka.actor.default-dispatcher-5] [akka://PingPongTraining/user/$a] Message [$line233.$read$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$Zong] from Actor[akka://PingPongTraining/deadLetters] to Actor[akka://PingPongTraining/user/$a#-1157019602] was not delivered. [1] dead letters encountered. This logging can be turned off or adjusted with configuration settings 'akka.log-dead-letters' and 'akka.log-dead-letters-during-shutdown'.

 *  */