from authens.backends import ENSCASBackend as AuthENSBackend
from authens.utils import parse_entrance_year


class ENSCASBackend(AuthENSBackend):
    # Override AuthENS backend user creation to implement the @<promo> logic

    def get_free_username(self, cas_login, attributes):
        entrance_year = parse_entrance_year(attributes.get("homeDirectory"))
        if entrance_year is None:
            return super().get_free_username(cas_login, attributes)
        entrance_year %= 100
        return "%s@%02d" % (cas_login, entrance_year)