ContinuousIntegration/TDD-pure-function/src/main/java/de/edu/hsfulda/ciip/tdd/BownlingCalculator.java

package de.edu.hsfulda.ciip.tdd;

import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class BownlingCalculator {
	private static final int SINGLE_DIGIT = 0;
	private static final int STRIKE_SECOND_NEXT_THROW = 2;
	private static final int STRIKE_NEXT_THROW = 1;
	private static final String STRIKE = "X (\\d)(\\d)";
	private static final int PINS_IN_FRAME = 10;
	private static final String SPARE = "(\\d)/ (\\d)";
	private static final String INCOMPLETE_FRAME = "\\d";

	@FunctionalInterface
	private interface FrameCalculator {
		int evaluate(Matcher frameStructure);
	}

	private static final int SPARE_FRAME_FOLLOWING_THROW = 2;
	private static final int SPARE_FRAME_FIRST_THROW = 1;

	public int evaluate(String listOfThrows) {
		int sum = 0;
		sum += evaluateFrames(listOfThrows, INCOMPLETE_FRAME,
				singleDigit -> convertMatchToInt(singleDigit, SINGLE_DIGIT));
		sum += evaluateFrames(listOfThrows, SPARE, // trailing line comments for formatting
				spare -> PINS_IN_FRAME //
						- convertMatchToInt(spare, SPARE_FRAME_FIRST_THROW)
						+ convertMatchToInt(spare, SPARE_FRAME_FOLLOWING_THROW));
		sum += evaluateFrames(listOfThrows, STRIKE, //
				strike -> PINS_IN_FRAME //
						+ convertMatchToInt(strike, STRIKE_NEXT_THROW) //
						+ convertMatchToInt(strike, STRIKE_SECOND_NEXT_THROW));
		return sum;
	}

	private int convertMatchToInt(Matcher strike, int groupIndex) {
		return Integer.parseInt(strike.group(groupIndex));
	}

	private int evaluateFrames(String listOfThrows, String frameStructurePattern, FrameCalculator frameCalculator) {
		Matcher singleDigit = Pattern.compile(frameStructurePattern).matcher(listOfThrows);
		int frameValue = 0;
		while (singleDigit.find()) {
			frameValue += frameCalculator.evaluate(singleDigit);
		}
		return frameValue;
	}

}