TaxCalculator.scala

object TaxCalculator {
  private val taxWindows = Seq(
    TaxForWindow(1, 5070, 10),
    TaxForWindow(5071, 8660, 14),
    TaxForWindow(8661, 14070, 23),
    TaxForWindow(14071, 21240, 30),
    TaxForWindow(21241, 40230, 33),
    TaxForWindow(40231, Int.MaxValue, 45))

  def calculate(salary: Double): Double = {
    require(salary >= 0)

    def windowsForSalary = taxWindows.reverse.dropWhile(_.from > salary)
    
    calculateInternal(salary, windowsForSalary)
  }

  private def taxForWindow(salary: Double, window: TaxForWindow): Double = (salary - (window.from - 1)) * window.percentage / 100

  private def calculateInternal(salary: Double, windows: Seq[TaxForWindow]): Double =
    windows match {
      case head :: tail => calculateInternal(head.from - 1, tail) + taxForWindow(salary, head)
      case Nil => 0
    }

  case class TaxForWindow(from: Double, to: Double, percentage: Double)
  
  def main(args: Array[String]): Unit = {
    println(calculate(50000))
  }
}