/** Scorer applies the scoring rules to compute a score */
public class Scorer
{
    private int ball;
    private int[] rolls = new int[21];
    private int currentRoll = 0;

    /** Add one roll to our collection */
    public void addRoll(int pins)
    {
        rolls[currentRoll++] = pins;
    }

    /** Compute the score for a given frame (cumulative) */
    public int scoreForFrame(int theFrame)
    {
        ball = 0;
        int score=0;
        // Iterate from the start to the given frame 
        for (int currentFrame = 0; currentFrame < theFrame; currentFrame++)
        {
            if (strike())
            {
                score += 10 + nextTwoBalls();
            }
            else if (spare())
            {
                score += 10 + nextBall();
            }
            else
            {
                score += twoBallsInFrame();
            }
        }

        return score;
    }

    private boolean strike()
    {
        if (rolls[ball] == 10)
        {
            ball++;
            return true;
        }
        return false;
    }

    private boolean spare()
    {
        if ((rolls[ball] + rolls[ball+1]) == 10)
        {
            ball += 2;
            return true;
        }
        return false;
    }

    private int nextTwoBalls()
    {
        return rolls[ball] + rolls[ball+1];
    }

    private int nextBall()
    {
        return rolls[ball];
    }

    private int twoBallsInFrame()
    {
        return rolls[ball++] + rolls[ball++];
    }

}