case class SiteId(val v: String) extends AnyVal {
    override def toString = v.toString
  }

  case class ItemId(val v: String) extends AnyVal {
    override def toString = v.toString
  }

  case class Item(siteId: SiteId, itemId: ItemId, price: Option[Double])


  def getFirstOccurrence(archive: RDD[(Timestamp, Item)], availableNow: RDD[(Item, Boolean)])(implicit parallel: Int) = {
    val occurance = archive
      .map { case (existAt, item) => ((item.siteId, item.itemId), existAt) }
      .reduceByKey{ case (tsA, tsB) => if (tsA.toMillis < tsB.toMillis) tsA else tsB}
      .join(availableNow.map{case (item, isAvailable) => ((item.siteId, item.itemId), isAvailable)})
      .filter{case ((siteId, itemId), (_, isAvailable)) => isAvailable}
      .map{ case ((siteId, itemId), (createdAt, _)) => (siteId, itemId, createdAt)}
  }