Gets a NepDate object from gregorian calendar date

def from_ad_date(cls, date):
        """ Gets a NepDate object from gregorian calendar date """
        functions.check_valid_ad_range(date)
        days = values.START_EN_DATE - date

        # Add the required number of days to the start nepali date
        start_date = NepDate(values.START_NP_YEAR, 1, 1)
        # No need to update as addition already calls update
        return start_date + (date - values.START_EN_DATE)