from django.contrib.auth.models import User
from cashonly.models import Account


class CashBackend(object):
    def authenticate(self, card_number=None, pin=None):
        if not card_number.isdigit():
            raise ValueError('card_number has to consist of digits only!')

        if len(pin) > 0 and not pin.isdigit():
            raise ValueError('pin has to consist of digits only or \
                has to be empty!')

        try:
            account = Account.objects.get(card_number=card_number)
        except Account.DoesNotExist:
            return None

        if account.check_pin(pin):
            return account.user

        return None