Uebung-TDD-Pure-function/src/main/java/de/edu/hsfulda/ccip/tdd/purefunction/BowlingCalculator.java

package de.edu.hsfulda.ccip.tdd.purefunction;

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

public class BowlingCalculator {
	private static final String FOUL = "-";
	private static final int SPLIT_NEXT_ROLL = 2;
	private static final int STRIKE_NEXT_ROLL = 1;
	private static final int MAX_PIN_COUNT = 10;

	@FunctionalInterface
	interface FrameScorer {
		int score(Matcher frameMatcher);
	}

	private static final int INITIAL_SCORE = 0;
	private static final Pattern SINGLE_ROLL_PATTERN = Pattern.compile("\\d");
	private static final Pattern SPARE_PATTERN = Pattern.compile("(\\d)/ ([-\\d])");
	private static final Pattern STRIKE_PATTERN = Pattern.compile("X ([-\\d])([-\\d])");

	public int score(String rolls) {
		int score = INITIAL_SCORE;
		Matcher singleRollMatcher = SINGLE_ROLL_PATTERN.matcher(rolls);
		score = scoreFrameType(score, singleRollMatcher, matcher -> Integer.parseInt(singleRollMatcher.group()));

		Matcher spareMatcher = SPARE_PATTERN.matcher(rolls);
		score = scoreFrameType(score, spareMatcher, matcher -> scoreSpareFrame(spareMatcher));

		Matcher strikeMatcher = STRIKE_PATTERN.matcher(rolls);
		score = scoreFrameType(score, strikeMatcher, matcher -> scoreStrike(strikeMatcher));

		return score;
	}

	private int scoreStrike(Matcher strikeMatcher) {
		int frameScore = MAX_PIN_COUNT;
		for (int nextRollIndex = STRIKE_NEXT_ROLL; nextRollIndex <= STRIKE_NEXT_ROLL + 1; nextRollIndex++) {
			frameScore = addNextRollToCurrentFrame(strikeMatcher, frameScore, nextRollIndex);
		}
		return frameScore;
	}

	private int scoreSpareFrame(Matcher spareMatcher) {
		int frameScore = MAX_PIN_COUNT - Integer.parseInt(spareMatcher.group(1));
		int nextRollIndex = SPLIT_NEXT_ROLL;
		return addNextRollToCurrentFrame(spareMatcher, frameScore, nextRollIndex);
	}

	private int scoreFrameType(int score, Matcher scoreMatcher, FrameScorer frameScorer) {
		while (scoreMatcher.find()) {
			score += frameScorer.score(scoreMatcher);
		}
		return score;
	}

	private int addNextRollToCurrentFrame(Matcher frameMatcher, int frameScore, int nextRollIndex) {
		String nextRoll = frameMatcher.group(nextRollIndex);
		if (!FOUL.equalsIgnoreCase(nextRoll)) {
			frameScore += Integer.parseInt(nextRoll);
		}
		return frameScore;
	}
}