from django.contribu.auth.backends import ModelBackend
from django.contrib.auth import get_user_model

class UsernameOrEmailBackend(ModelBackend):
    """ An authentication backend which will allow users to login using
        either their username or their email.

        In settings.py, add:

            AUTHENTICATION_BACKENDS = [
                'mypackage.backends.UsernameOrEmailBackend',
            ]
    """

    def authenticate(self, username=None, password=None, **kwargs):
        UserModel = get_user_model()
        if username is None:
            username = kwargs.get(UserModel.USERNAME_FIELD)
        filter_field = "email" if "@" in username else UserModel.USERNAME_FIELD
        try:
            user = UserModel._default_manager.get(**{filter_field: username})
            if user.check_password(password):
                return user
        except UserModel.DoesNotExist:
            # Run the default password hasher once to reduce the timing
            # difference between an existing and a non-existing user (#20760).
            UserModel().set_password(password)