ActionMaster.cs

using UnityEngine;
using System.Collections;

public class ActionMaster {

	public enum Action {Tidy, Reset, EndTurn, EndGame};

	public int[] bowlScore = new int[21];  // leave bowlScore[0] empty so i can check backwards.
	public int[] frameScore = new int[12]; // leave frameScore[0] empty.
	private int bowl = 1;
	private int frame = 1;
	public string result = "";
	private int ball = 1;
	private int thisScore;
	private int lastScore;
	private int scoreBeforeLast;

	// Because you can bowl three strikes on the last 'frame' I'm considering
	// them all 'frames' so the one strike per frame rule holds. 
	// I simply ignore those 'frames' when reporting the score.
	// Strike can only happen on ball 1 according to my rules, since I count 
	// additional strikes past frame 10 as additional frames.
	//
	// I consider this a reasonable alternative to having a special case for having 
	// a ball 3 and checking for strikes on ball 2 and ball 3 of frame 10.

	public Action Bowl (int pins)
	{
		if (pins < 0 || pins > 10)	{throw new UnityException ("Invalid Pins");}

		bowlScore[bowl] = pins;
		thisScore = bowlScore[bowl];
		lastScore = bowlScore[bowl - 1];
		if (bowl > 2) {scoreBeforeLast = bowlScore[bowl - 2];}

		// check what the quality is first.
		if (thisScore == 10) {result = "strike";}
		else if (ball == 2 && (lastScore + thisScore == 10)) {result = "spare";}
		else {result = "";}
	
		AddFrameScore ();

		if (frame == 12) {return Action.EndGame;}

		if (ball == 1) // First ball in frame
		{
			if (result == "strike") 
			{
				if (frame == 10) 
				{
					EndOfFrame ();
					return Action.Reset;
				}
				if (frame == 11 && lastScore == 10)
				{
					EndOfFrame ();
					return Action.Reset;
				}
				EndOfFrame ();
				return Action.EndTurn;
			}

			bowl += 1;
			ball = 2;
			return Action.Tidy;
		} 

		else if (ball == 2) // Second ball in frame
		{
			if (frame == 10)
			{
				if (result == "spare") {return Action.Reset;}
				if (result == "" && lastScore == 10) {return Action.Tidy;}
				if (result == "") {return Action.EndGame;}
			}
			EndOfFrame ();
			ball = 1;
			return Action.EndTurn;
		}

		throw new UnityException ("Something wrong happened");
	}

	private void EndOfFrame ()
	{
		bowl += 1;
		frame += 1;
	}

	private void AddFrameScore ()
	{
		// STRIKE?
		if (scoreBeforeLast == 10) // can only score a strike after two more bowls.
		{
			if (lastScore == 10) // if last TWO bowls were strikes the first strike was two frames ago.
			{
				frameScore[frame - 2] = frameScore[frame - 3] + thisScore + lastScore + scoreBeforeLast;
			} 
			else // two bowls ago was a strike, but last one wasn't then it's only one frame back.
			{
				frameScore[frame - 1] = frameScore[frame - 2] + thisScore + lastScore + scoreBeforeLast;
			}
		} 

		// SPARE?
		else if (ball == 1) // can only score a spare after one more bowl and only on ball 1.
		{
			if (scoreBeforeLast + lastScore == 10) // if last roll was a spare
			{
				frameScore[frame - 1] = frameScore[frame - 2] + thisScore + lastScore + scoreBeforeLast;
			}
		}

		// NO strike or spare
		if (result == "" && ball == 2)
		{
			frameScore[frame] = frameScore[frame - 1] + thisScore + lastScore; 
		}

		// If no conditions met - can't record a frame score yet.
	}
}