HarryPotterBasket

/**
 * Created by helen on 20/08/15.
 */
object HarryPotterBasket {
  val pricingStrategies = List(TwoBooksPricingStrategy)

  def calculate(basket: List[HarryPotterSeries]): Double = {
    pricingStrategies.map(_.price(basket)).head.price.get
  }

  def calculate1(basket: PricingApplication) : Double = {
    if (basket.remaining.isEmpty)
      basket.price
    else
      //Todo: Get remaining basket and find strategy that matches.
  }
}

sealed trait HarryPotterSeries

case object HarryPotterAndThePhilisophersStone extends HarryPotterSeries
case object HarryPotterAndTheChamberOfSecrets extends HarryPotterSeries
case object HarryPotterAndThePrisonerOfAsakban extends HarryPotterSeries
case object HarryPotterAndTheGobletOfFire extends HarryPotterSeries
case object HarryPotterAndTheOrderOfThePheniox extends HarryPotterSeries
case object HarryPotterAndTheHalfBloodPrince extends HarryPotterSeries
case object HarryPotterAndTheDeathlyHallows extends HarryPotterSeries

sealed trait HarryPotterPricingStrategy {
  def price(basket : List[HarryPotterSeries]) : PricingApplication
}

case object TwoBooksPricingStrategy extends HarryPotterPricingStrategy {
  def price(basket: List[HarryPotterSeries]) = {
    if(basket.toSet.size >= 2) {
      val firstBook = basket.head
      PricingApplication(Some(15.20), Lists.removeFirst(basket.tail)(_ == firstBook))
    } else {
      PricingApplication(Option.empty, basket)
    }
  }
}

case object OneBookPricingStrategy extends HarryPotterPricingStrategy {
  def price(basket: List[HarryPotterSeries]) = {
    if (basket.nonEmpty) PricingApplication(Some(8), basket.tail)
    else PricingApplication(None, basket);
  }
}

case class PricingApplication(price: Option[Double], remaining: List[HarryPotterSeries])

object Lists {
  def removeFirst[T](list: List[T])(predicate: (T) => Boolean): List[T] = {
    val (before, atAndAfter) = list span (x => !predicate(x))
    before ::: atAndAfter.drop(1)
  }
}

HarryPotterBasketTest

/**
 * Created by helen on 20/08/15.
 */
import org.scalatest.Matchers._

class HarryPotterBasketTest extends org.scalatest.FunSuite {

  test("should apply discount for 2 books") {
    val basket = List(HarryPotterAndThePhilisophersStone, HarryPotterAndTheOrderOfThePheniox)
    HarryPotterBasket.calculate(basket) should be (15.2)
  }

  test("should apply discount for 3 books of 2 types") {
    val basket = List(HarryPotterAndTheChamberOfSecrets, HarryPotterAndTheChamberOfSecrets, HarryPotterAndTheGobletOfFire)
    HarryPotterBasket.calculate(basket) should be (23.2)
  }

}