Gilded Rose Kata in Scala

GildedRose.scala

package com.gildedrose

case class AgedBrie(var sellWithin: Int, var value: Int)
  extends Item("Aged Brie", sellWithin, value)

case class BackstagePass(var sellWithin: Int, var value: Int)
  extends Item("Backstage passes to a TAFKAL80ETC concert", sellWithin, value)

case class Sulfuras(var sellWithin: Int, var value: Int)
  extends Item("Sulfuras, Hand of Ragnaros", sellWithin, value)

object Services {
  val sellInUpdater = new DefaultSellInUpdater
  val qualityUpdater = new DefaultQualityUpdater
}

class GildedRose(val items: Array[Item]) {
  import Services._

  def updateQuality() = items.foreach {
    case item@AgedBrie(_, _) => new GildedRoseUpdater()(sellInUpdater, new IncrementingQualityUpdater()).update(item)
    case item@BackstagePass(_, _) => new GildedRoseUpdater()(sellInUpdater, new BackstagePassQualityUpdater()).update(item)
    case Sulfuras(_, _) =>
    case item => new GildedRoseUpdater()(sellInUpdater, qualityUpdater).update(item)
  }
}

trait QualityUpdater {
  def apply(item: Item)
}

class DefaultQualityUpdater extends QualityUpdater {
  def apply(item: Item): Unit = {
    item.quality = item.quality - (if (item.sellIn >= 0) 1 else 2)
    item.quality = Math.max(item.quality, 0)
  }
}

class IncrementingQualityUpdater extends QualityUpdater {
  def apply(item: Item): Unit = {
    item.quality = Math.min(item.quality + 1, 50)
  }
}

class BackstagePassQualityUpdater extends QualityUpdater {
  def apply(item: Item): Unit = {
    item.quality = item.quality + (
      if (item.sellIn > 10) 1
      else if (item.sellIn > 5) 2
      else if (item.sellIn > 0) 3
      else -item.quality
      )
  }
}

trait SellInUpdater {
  def apply(item: Item)
}

class DefaultSellInUpdater extends SellInUpdater {
  def apply(item: Item): Unit = {
    item.sellIn = item.sellIn - 1
  }
}

class GildedRoseUpdater (
  implicit val sellInUpdater: SellInUpdater,
  implicit val qualityUpdater: QualityUpdater) {

  def update(item: Item): Unit = {
    sellInUpdater(item)
    qualityUpdater(item)
  }
}