Test.scala

case class Currency(code: String)

object RateProvider {
  sealed trait Command
  case object Provide extends Command

  sealed trait Message
  case class CurrencyRate(curreny: Currency, rate: Double)
}

class RateProvider(currency: Currency, storage: ActorRef) extends Actor {
  import RateProvider._

  private val random = new java.util.Random()
  
  def receive = {
    case Provide => storage ! CurrencyRate(currency, random.nextDouble)
  }

  override def preStart(): Unit = {
    context.system.scheduler.schedule(100 millis, 100 millis, self, Provide)
  }
}

object Storage {
  sealed trait Command 
  case object NotifyTraders extends Command

  case object Put(id: Stirng, currency: Currency, rate: Double)
  case object Call(id: Stirng, currency: Currency, rate: Double)
}

class Storage(traders: Seq[ActorRef]) extends Actor {
  def receive = {
    case rate: CurrencyRate => // implement
    case NotifyTraders => latestRate foreach { rate =>
      traders foreach (_)
    }
  }

  def latestRate: Future[CurrencyRate] = ??? // Implement query to db

  override def preStart(): Unit = {
    context.system.scheduler.schedule(100 millis, 100 millis, self, Provide)
  }
}

class Traider(id: String, currencies: Seq[Currency], storage: ActorRef) extends Actor {
  private def random = new java.util.Random()

  def receive = {
    case RateProvider.CurrencyRate(currency, rate) if cirrencies contais currency =>
      if (random.nextBoolean) {
        random.match {
          case v if v > 50 => storage ! Put(id, currency, rate)
          case _ => storage ! Call(id, currency, rate)
        }
      }
  }
}