bowling.scala

import scala.collection.mutable._

class BowlingGame(val reverseRolls: List[Int]) {
  def roll(pins: Int) = {
    if(pins == 10)
      new BowlingGame(0 :: pins :: reverseRolls)
    else
      new BowlingGame(pins :: reverseRolls)
  }

  lazy val rolls = reverseRolls.reverse

  def score() = {
    (0 to 9).map(_ * 2).foldLeft(0)((score, frameIndex) => {
      if(isStrike(frameIndex))
        score + 10 + strikeBonus(frameIndex)
      else if(isSpare(frameIndex))
        score + 10 + spareBonus(frameIndex)
      else
        score + sumOfBallsInFrame(frameIndex)
    })
  }

  private def isStrike(index: Int) = rolls(index) == 10
  private def isSpare(index: Int) = sumOfBallsInFrame(index) == 10
  private def sumOfBallsInFrame(index: Int) = rolls(index) + rolls(index+1)
  private def spareBonus(index: Int) = rolls(index+2)
  private def strikeBonus(index: Int) = {
    if(isStrike(index+2)) rolls(index+2) + rolls(index+4) else rolls(index+2) + rolls(index+3)
  }
}