Third ieration : Stalls can have different charging algorithm.

Scenario3.scala

package iteration.third

import java.util.Date

object Scenario3 {
  def main(args: Array[String]) = {

    def payMethodNormal(t: Ticket) = (t.outTime.getTime - t.inTime.getTime).toInt
    def payMethodDouble(t: Ticket) = (t.outTime.getTime - t.inTime.getTime).toInt * 2

    val pa0 = new ParkingArea(
      List(
        new Stall(0, true, payMethodNormal),
        new Stall(0, true, payMethodDouble)))

    val (pa1, t1) = pa0.checkin(0)
    println(s"t1 = ${t1}")
    val (pa2, t2) = pa1.checkin(0)
    println(s"t2 = ${t2}")
    val (pa3, t3) = pa2.checkout(0, t1)
    println(s"t3 = ${t3}")
    println(s"amount = ${pa3.amount}")
    val (pa4, t4) = pa3.checkin(1)
    println(s"t4 = ${t4}")
    val (pa5, t5) = pa4.checkout(1, t4)
    println(s"t5 = ${t5}")
    println(s"amount = ${pa5.amount}")

  }
}

class Stall(val amount: Int, val isFree: Boolean, val payMethod: (Ticket) => Int) {
  override def toString = s"amount=${amount} isFree=${isFree}"
}

class Ticket(val area: Stall, val inTime: Date, val outTime: Date) {
  override def toString = { s"area = ${area} inTime=${inTime}, outTime=${outTime}" }
}

class ParkingArea(stalls: List[Stall]) {
  def amount = stalls.map { s => s.amount }.sum

  def checkin(no: Int): (ParkingArea, Ticket) = {
    stalls(no).isFree match {
      case true => {
        val newStall = new Stall(stalls(no).amount, false, stalls(no).payMethod)
        (new ParkingArea(stalls.updated(no, newStall)), new Ticket(newStall, new Date, null))
      }
      case _ => (this, null)
    }
  }

  def checkout(no: Int, t: Ticket): (ParkingArea, Ticket) = {
    stalls(no) match {
      case s if t.area == s && !s.isFree => {
        val dummy = new Ticket(s, t.inTime, new Date)
        val newAmount = s.amount + s.payMethod(dummy)
        val newStall = new Stall(newAmount, true, s.payMethod)
        val newTicket = new Ticket(newStall, dummy.inTime, dummy.outTime)
        (new ParkingArea(stalls.updated(no, newStall)), newTicket)
      }
      case _ => (this, t)
    }
  }
}