MainCheckout

object MainCheckout {
  def main(args: Array[String]) = {
    val priceList: List[Item] = List(
      Item("A", 50, Some(SpecialOffer(3, 130))),
      Item("B", 30, Some(SpecialOffer(2, 45))),
      Item("C", 20),
      Item("D", 15)
    )

    val transaction = Transaction(priceList)
    println("Please enter a series of SKUs, separated by commas. For example: A,B,C")
    val skus =  scala.io.StdIn.readLine()
    val total = transaction.calculateTotal(skus)
    println(s"Total is: $total")
  }
}

case class Item(sku: String, standardPrice: Int, specialOffer: Option[SpecialOffer] = None)

case class SpecialOffer(multiplier: Int, price: Int)

case class ItemsWithQuantities(item: Item, quantity: Int) {
  val totalPrice: Int = {
    item.specialOffer match {
      case Some(offer: SpecialOffer) =>
        val quantityOfSpecialOffers = quantity / offer.multiplier
        val quantityOfStandardPrice = quantity % offer.multiplier
        quantityOfSpecialOffers * offer.price + quantityOfStandardPrice * item.standardPrice
      case None => quantity * item.standardPrice
    }
  }
}

case class Transaction(priceList: List[Item]) {
  def calculateTotal(itemsSkusAsString: String): Int = {
    val itemSkus: List[String] = itemsSkusAsString.split(",").toList
    val items: List[Item] = itemSkus.map(itemSku => convertToItemFromSku(itemSku))
    val groupedItemsWithQuantities: List[ItemsWithQuantities] = convertToItemsWithQuantities(items)
    totalForItems(groupedItemsWithQuantities)
  }

  private def convertToItemFromSku(sku: String): Item = {
    priceList.find(price => price.sku.equals(sku)) match {
      case Some(item) => item
      case _ => throw ItemNotFoundException()
    }
  }

  private def convertToItemsWithQuantities(itemList: List[Item]): List[ItemsWithQuantities] = {
    val groupedItems: List[List[Item]] = itemList.groupBy(_.sku).values.toList
    groupedItems.map(item => ItemsWithQuantities(item.head, item.length))
  }

  private def totalForItems(items: List[ItemsWithQuantities]) = {
    items.map(_.totalPrice).sum
  }
}

case class ItemNotFoundException() extends Exception("Sorry, this item has not been recognised. Please wait for assistance.")