FunctionalAndReactiveDomainModelingCreatingAccountUsingSmartConstructors.scala

import java.util.{Date, Calendar}
import util.{Try, Success, Failure}

type Amount = BigDecimal

def today = Calendar.getInstance.getTime

case class Balance(amount: Amount = 0)

sealed trait Account {
  def no: String
  def name: String
  def dateOfOpen: Option[Date]
  def dateOfClose: Option[Date]
  def balance: Balance
}

final case class CheckingAccount private (no: String,
                                          name: String,
                                          dateOfOpen: Option[Date],
                                          dateOfClose: Option[Date],
                                          balance: Balance)
    extends Account

final case class SavingsAccount private (no: String,
                                         name: String,
                                         rateOfInterest: Amount,
                                         dateOfOpen: Option[Date],
                                         dateOfClose: Option[Date],
                                         balance: Balance)
    extends Account

object Account {
  def checkingAccount(no: String,
                      name: String,
                      openDate: Option[Date],
                      closeDate: Option[Date],
                      balance: Balance): Try[Account] = {
    closeDateCheck(openDate, closeDate).map { d =>
      CheckingAccount(no, name, Some(d._1), d._2, balance)
    }
  }
  
  def savingsAccount(no: String,
                     name: String,
                     rate: BigDecimal,
                     openDate: Option[Date],
                     closeDate: Option[Date],
                     balance: Balance): Try[Account] = {
    closeDateCheck(openDate, closeDate).map { d =>
      if (rate <= BigDecimal(0))
        throw new Exception(s"Interest rate $rate must be > 0")
      else
        SavingsAccount(no, name, rate, Some(d._1), d._2, balance)
    }
  }
  
  private def closeDateCheck(
      openDate: Option[Date],
      closeDate: Option[Date]): Try[(Date, Option[Date])] = {
    val od = openDate.getOrElse(today)
    closeDate
      .map { cd =>
        if (cd before od)
          Failure(
            new Exception(
              s"Close date [$cd] cannot be earlier than open date [$od]"))
        else Success((od, Some(cd)))
      }
      .getOrElse {
        Success((od, closeDate))
      }
  }
}