PE4.scala

.onCommand[WithdrawCmd, WithdrawalResponse]{
  case (WithdrawCmd(time, description, amount), ctx, state) =>
    if(state.balance - amount >= 0)
      ctx.thenPersist(WithdrawEvt(time, description, amount)){ _ =>
        ctx.reply(SuccessfulWithdrawalResponse(state.balance - amount))
      }
    else {
      ctx.reply(FailedWithdrawalResponse(s"Insufficient funds (current balance ${state.balance})"))
      ctx.done
    }