current-api.scala

package akka.persistence.typed.scaladsl

import akka.actor.typed.Behavior
import akka.persistence.typed.scaladsl.PersistentBehaviors.{CommandHandler, _}

class AccountSpec {

  sealed trait AccountCommand
  case object CreateAccount extends AccountCommand
  case class Deposit(amount: Double) extends AccountCommand
  case class Withdraw(amount: Double) extends AccountCommand
  case object CloseAccount extends AccountCommand

  sealed trait AccountEvent
  case object AccountCreated extends AccountEvent
  case class Deposited(amount: Double) extends AccountEvent
  case class Withdrawn(amount: Double) extends AccountEvent
  case object AccountClosed extends AccountEvent

  sealed trait Account
  case class OpenedAccount(balance: Double) extends Account
  case object ClosedAccount extends Account

  private def initial: CommandHandler[AccountCommand, AccountEvent, Option[Account]] =
    (_, _, cmd) =>
      cmd match {
        case CreateAccount ⇒ Effect.persist(AccountCreated)
      }

  private def openedAccountHandlers(acc: OpenedAccount): CommandHandler[AccountCommand, AccountEvent, Option[Account]] =
    (ctx, _, cmd) => cmd match {
      case Deposit(amount) ⇒ Effect.persist(Deposited(amount))

      case Withdraw(amount) if (acc.balance - amount) < 0.0 =>
            throw new RuntimeException("Insufficient balance")

      case Withdraw(amount) =>
        Effect
          .persist(Withdrawn(amount))
          .andThen { st => // can't even use a PF here because this method is overloaded
            st match { // need to pattern match because state is Account, Effect is invariant on State
              case Some(OpenedAccount(balance)) =>
                // do some side-effect using balance
                println(balance)
            }
          }
      case CloseAccount if acc.balance == 0.0 =>
        Effect.persist(AccountClosed)
      case CloseAccount  =>
            throw new RuntimeException("Account balance is not zero")

    }

  private def commandHandlers: CommandHandler[AccountCommand, AccountEvent, Option[Account]] =
    CommandHandler.byState {
      case None => CommandHandler.command {
        case CreateAccount => Effect.persist(AccountCreated)
      }
      case Some(acc@OpenedAccount(_)) => openedAccountHandlers(acc)
      case Some(ClosedAccount) => throw new RuntimeException("account already closed")
    }

  private def eventHandler(stateOpt: Option[Account], event: AccountEvent):Option[Account] =
    (stateOpt, event) match {

      case (None, AccountCreated) => Some(OpenedAccount(0.0))

      case (Some(acc@OpenedAccount(_)), Deposited(amount)) =>
        Some(acc.copy(balance = acc.balance + amount))

      case (Some(acc@OpenedAccount(_)), Withdrawn(amount)) =>
        Some(acc.copy(balance = acc.balance - amount))

      case (Some(acc@OpenedAccount(_)), AccountClosed) =>
        Some(ClosedAccount)

      // this or compiler warning. We should not need to do it
      case _ =>  throw new RuntimeException("this should never happen")
    }


  def behavior(accountNumber: String): Behavior[AccountCommand] =
    PersistentBehaviors.receive[AccountCommand, AccountEvent, Option[Account]](
      persistenceId = accountNumber,
      initialState = None,
      commandHandler = commandHandlers,
      eventHandler = eventHandler
    )
}

proposal-api.scala

package akka.persistence.typed.scaladsl

import akka.actor.typed.Behavior
import akka.persistence.typed.scaladsl.PersistentBehaviors.{CommandHandler, _}

class AccountSpec {

  sealed trait AccountCommand
  case object CreateAccount extends AccountCommand
  case class Deposit(amount: Double) extends AccountCommand
  case class Withdraw(amount: Double) extends AccountCommand
  case object CloseAccount extends AccountCommand

  sealed trait AccountEvent
  case object AccountCreated extends AccountEvent
  case class Deposited(amount: Double) extends AccountEvent
  case class Withdrawn(amount: Double) extends AccountEvent
  case object AccountClosed extends AccountEvent

  sealed trait Account
  case class OpenedAccount(balance: Double) extends Account
  case object ClosedAccount extends Account

  private def openedAccountHandler(acc: OpenedAccount): CommandHandler[AccountCommand, AccountEvent, Account] =
    (ctx, _, cmd) => cmd match {
      case Deposit(amount) ⇒ Effect.persist(Deposited(amount))

      case Withdraw(amount) if (acc.balance - amount) < 0.0 =>
        throw new RuntimeException("Insufficient balance")

      case Withdraw(amount) =>
        Effect
          .persist(Withdrawn(amount))
          .andThen { st => // can't even use a PF here because this method is overloaded
            st match { // need to pattern match because state is Account, Effect is invariant on State
              case OpenedAccount(balance) =>
                // do some side-effect using balance
                println(balance)
            }
          }

      case CloseAccount if acc.balance == 0.0 =>
        Effect.persist(AccountClosed)

      case CloseAccount  =>
        throw new RuntimeException("Account balance is not zero")

    }

  def openedAccountEvtHandler(acc: OpenedAccount): EventHandler[AccountEvent, Account] = {
      case Deposited(amount) =>
        acc.copy(balance = acc.balance + amount)

      case Withdrawn(amount) =>
        acc.copy(balance = acc.balance - amount)

      case AccountClosed => ClosedAccount

      // this or compiler warning. We should not need to do it
      case _ =>  throw new RuntimeException("this should never happen")
  }

  def behavior(accountNumber: String): Behavior[AccountCommand] =
    PersistentBehaviors[AccountCommand, AccountEvent, Account]
      .identifiedBy(accountNumber)
      .onCreation (
        commandHandler =  CommandHandler.command {
          case CreateAccount => Effect.persist(AccountCreated)
        },
        eventHandler = {
          case AccountCreated => OpenedAccount(0.0)
        }
      )
      .onUpdate (
        commandHandler = {
          case acc: OpenedAccount => openedAccountHandler(acc)
          case ClosedAccount => throw new RuntimeException("account already closed")
        },
        eventHandler = {
          case acc: OpenedAccount => openedAccountEvtHandler(acc)
        }
      )
}