public class AchievementHandler {
    public ArrayList<Achievement> achievements

    public void completeAchievement(Achievement a) {
        if (a.getStatus() == AchievementStatus.IN_PROGRESS && achievements.contains(a)) {
            achievements.remove(a)
            a.setStatus(AchievementStatus.COMPLETE)
            achievements.add(a)
        }
    }
}