shopping cart kata

ShoppingCart.scala

case class MultiPrice(qty: Int, price: Int)
case class PriceData(
  itemPrices: Map[Char, Int],
  multiPrices: Map[Char, MultiPrice]
)

object ShoppingCart {

  def checkout(basket: String, priceData: PriceData): Int = {
    val itemCounts = basket.groupBy(identity).mapValues(_.length)
    itemCounts.foldLeft(0) { case (acc, (sku, qty)) => 
      acc + totalPerItem(sku, qty, priceData)
    }
  }

  def totalPerItem(sku: Char, count: Int, priceData: PriceData): Int = {
    val itemPrice = priceData.itemPrices(sku) // throws on error
    priceData.multiPrices.get(sku) match {
      case None     => itemPrice * count
      case Some(mp) => count / mp.qty * mp.price + count % mp.qty * itemPrice
    }
  }
}

object Tests {
  val pd: PriceData = PriceData(
    Map('A' -> 50, 'B' -> 30, 'C' -> 20, 'D' -> 15),
    Map(
      'A' -> MultiPrice(3, 130),
      'B' -> MultiPrice(2, 45)
    )
  )
}

class MutableShoppingCart(priceData: PriceData) {
  private var basket: List[Char] = Nil
  
  def scan(sku: Char): Unit = basket = sku +: basket
  def checkout: Int = ShoppingCart.checkout(basket.mkString, priceData)
}