@staticmethod
def add(year, unit, limit, quarter):
    """ Compose a string of the next time period

        :param int year: date year
        :param int unit: number of the week/month/quarter
        :param int limit: maximum unit possible
        :param bool quarter: True if quarter format is required
        """
    string = '{}-Q{}' if quarter else '{}-{:02}'
    if unit == limit:
        return string.format(year + 1, 1)
    else:
        return string.format(year, unit + 1)
