PosFoldOverPricersVerboseFolding.scala

private def total(quantity: Int, tierPrice: TierPrice, unitPrice: UnitPrice): BigDecimal = {
  // initial value
  var total = BigDecimal(0)

  // iteration 1 - tier price
  val tiers = quantity / tierPrice.quantity
  val tierPriceAmount = tiers * tierPrice.price
  // accumulator to pass to the iteration 2  
  val remainingQuantityAfterTierPrice = quantity % tierPrice.quantity
  total = total + tierPriceAmount

  // iteration 2 - unit price
  val unitPriceAmount =  remainingQuantityAfterTierPrice * unitPrice.price
  // accumulator to return from folding
  val remainingQuantityAfterUnitPrice = 0
  total = total + unitPriceAmount
  
  // remaining quanity can be ignored, we return only the total part of the accumulator
  total
}