pekko/akka-docs/src/test/scala/docs/cluster/FactorialBackend.scala

/*
 * Copyright (C) 2018-2020 Lightbend Inc. <https://www.lightbend.com>
 */

package scala.docs.cluster

import scala.annotation.tailrec
import scala.concurrent.Future
import com.typesafe.config.ConfigFactory
import akka.actor.Actor
import akka.actor.ActorLogging
import akka.actor.ActorSystem
import akka.actor.Props
import akka.pattern.pipe

//#backend
class FactorialBackend extends Actor with ActorLogging {

  import context.dispatcher

  def receive = {
    case (n: Int) =>
      Future(factorial(n))
        .map { result =>
          (n, result)
        }
        .pipeTo(sender())
  }

  def factorial(n: Int): BigInt = {
    @tailrec def factorialAcc(acc: BigInt, n: Int): BigInt = {
      if (n <= 1) acc
      else factorialAcc(acc * n, n - 1)
    }
    factorialAcc(BigInt(1), n)
  }

}
//#backend

object FactorialBackend {
  def main(args: Array[String]): Unit = {
    // Override the configuration of the port when specified as program argument
    val port = if (args.isEmpty) "0" else args(0)
    val config = ConfigFactory
      .parseString(s"akka.remote.classic.netty.tcp.port=$port")
      .withFallback(ConfigFactory.parseString("akka.cluster.roles = [backend]"))
      .withFallback(ConfigFactory.load("factorial"))

    val system = ActorSystem("ClusterSystem", config)
    system.actorOf(Props[FactorialBackend], name = "factorialBackend")

    system.actorOf(Props[MetricsListener], name = "metricsListener")
  }
}