parseDuration

package com.crossover.trial;

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

public class Solution {
    public class TimeParser {
        public LocalDateTime parseDuration(String duration, LocalDateTime now) {
            for (Matcher m = Pattern.compile("(\\d+) (\\w)s?").matcher(duration);m.find();)
                now = addTime(now, m.group(2), Integer.parseInt(m.group(1)));
            return now;
        }

        private LocalDateTime addTime(LocalDateTime now, String timeUnit, int amount) {
            switch (timeUnit) {
                case "minute": return now.minusMinutes(amount);
                case "hour":   return now.minusHours(amount);
                case "day":    return now.minusDays(amount);
                case "week":   return now.minusWeeks(amount);
                case "month":  return now.minusMonths(amount);
                case "year":   return now.minusYears(amount);
                default:       throw new IllegalArgumentException(timeUnit);
            }
        }
    }
}