src/main/scala/me/rerun/akka/fsm/CoffeeMachine.scala

package me.rerun.akka.fsm

import akka.actor.FSM
import CoffeeMachine._
import CoffeeProtocol._
import org.slf4j.LoggerFactory

/**
 * Created by Arun on 12/25/15.
 */

object CoffeeMachine {

  sealed trait MachineState
  case object Open extends MachineState
  case object ReadyToBuy extends MachineState
  case object PoweredOff extends MachineState

  case class MachineData(currentTxTotal: Int, costOfCoffee: Int, coffeesLeft: Int)

}

object CoffeeProtocol {

  trait UserInteraction
  trait VendorInteraction

  case class Deposit(value: Int) extends UserInteraction
  case class Balance(value: Int) extends UserInteraction
  case object Cancel extends UserInteraction
  case object BrewCoffee extends UserInteraction
  case object GetCostOfCoffee extends UserInteraction

  case object ShutDownMachine extends VendorInteraction
  case object StartUpMachine extends VendorInteraction
  case class SetNumberOfCoffee(quantity: Int) extends VendorInteraction
  case class SetCostOfCoffee(price: Int) extends VendorInteraction
  case object GetNumberOfCoffee extends VendorInteraction

  case class MachineError(errorMsg:String)

}

class CoffeeMachine extends FSM[MachineState, MachineData] {

  private val logger = LoggerFactory.getLogger(classOf[CoffeeMachine])

  startWith(Open, MachineData(currentTxTotal = 0, costOfCoffee =  5, coffeesLeft = 10))

  when(Open) {
    case Event(_,MachineData(_,_,coffeesLeft)) if (coffeesLeft<=0) =>{
      logger.warn("No more coffee")
      sender ! MachineError("No more coffee")
      goto(PoweredOff)
    }
    case Event(Deposit(value), MachineData(currentTxTotal, costOfCoffee, coffeesLeft)) if (value + currentTxTotal) >= stateData.costOfCoffee => {
      goto(ReadyToBuy) using stateData.copy(currentTxTotal = currentTxTotal + value)
    }
    //If the total deposit is less than than the price of the coffee, then stay in the current state with the current deposit amount incremented.
    case Event(Deposit(value), MachineData(currentTxTotal, costOfCoffee, coffeesLeft)) if (value + currentTxTotal) < stateData.costOfCoffee => {
      val cumulativeValue = currentTxTotal + value
      logger.debug(s"staying at open with currentTxTotal $cumulativeValue")
      stay using stateData.copy(currentTxTotal = cumulativeValue)
    }
    case Event(SetNumberOfCoffee(quantity), _) => stay using stateData.copy(coffeesLeft = quantity)
    case Event(GetNumberOfCoffee, _) => sender ! (stateData.coffeesLeft); stay()
    case Event(SetCostOfCoffee(price), _) => stay using stateData.copy(costOfCoffee = price)
    case Event(GetCostOfCoffee, _) => sender ! (stateData.costOfCoffee); stay()
  }

  //Ignoring the case when user deposits cash during `ReadyToBuy` state
  when(ReadyToBuy) {
    case Event(BrewCoffee, MachineData(currentTxTotal, costOfCoffee, coffeesLeft)) => {
      val balanceToBeDispensed = currentTxTotal - costOfCoffee
      logger.debug(s"Balance is $balanceToBeDispensed")
      if (balanceToBeDispensed > 0) {
        sender ! Balance(value = balanceToBeDispensed)
        goto(Open) using stateData.copy(currentTxTotal = 0, coffeesLeft = coffeesLeft - 1)
      }
      else goto(Open) using stateData.copy(currentTxTotal = 0, coffeesLeft = coffeesLeft - 1)
    }
  }

  when(PoweredOff) {
    case (Event(StartUpMachine, _)) => goto(Open)
    case _ => {
      logger.warn("Machine Powered down.  Please start machine first with StartUpMachine")
      sender ! MachineError("Machine Powered down.  Please start machine first with StartUpMachine")
      stay()
    }
  }

  whenUnhandled {
    case Event(ShutDownMachine, MachineData(currentTxTotal, costOfCoffee, coffeesLeft)) => {
      sender ! Balance(value = currentTxTotal)
      goto(PoweredOff) using stateData.copy(currentTxTotal = 0)
    }
    case Event(Cancel, MachineData(currentTxTotal, _, _)) => {
      logger.debug(s"Balance is $currentTxTotal")
      sender ! Balance(value = currentTxTotal)
      goto(Open) using stateData.copy(currentTxTotal = 0)
    }
  }

  onTransition {
    case Open -> ReadyToBuy => logger.debug("From Transacting to ReadyToBuy")
    case ReadyToBuy -> Open => logger.debug("From ReadyToBuy to Open")
  }


}