public List<String> getLessons(String grade, String year) {
    List<String> lessons = new ArrayList<String>();

    if (StringUtils.equalsIgnoreCase(grade, SIXTH_GRADE)) {
      int hi_friends = 2;

      for (String lesson : sixthGradeLessons()) {
        lessons.add(HI_FRIENDS_PREFIX + hi_friends + CONJUNCTION + lesson);
      }
    } else if (StringUtils.equalsIgnoreCase(grade, FIFTH_GRADE)) {
      int hi_friends = 1;

      for (String lesson : fifthGradeLessons()) {
        lessons.add(HI_FRIENDS_PREFIX + hi_friends + CONJUNCTION + lesson);
      }
    } else {
      List<String> grades = Arrays.asList(StringUtils.split(grade, CONJUNCTION));
      List<LessonPost> posts = postDAO.getByYearGradeLessonKeyword(year, grades, null);

      for (LessonPost post : posts) {
        String uuid = post.getUuid();
        if (StringUtils.containsIgnoreCase(uuid, LESSONS_PREFIX)) {
          int index = uuid.lastIndexOf(LESSONS_PREFIX) + LESSONS_PREFIX.length();
          String name = uuid.substring(index);

          lessons.add(name);
        }
      }
    }
    return lessons;
  }
  private int getLessonNumber(String lessonString) {
    int index = HI_FRIENDS_PREFIX.length() + 1 + 1 + LESSONS_PREFIX.length();
    String lesson = StringUtils.substring(lessonString, index, index + 1);

    return Integer.parseInt(lesson);
  }