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


UserModel = get_user_model()


class EmailOrUsernameBackend(ModelBackend):
    def authenticate(self, request, username=None, password=None, **kwargs):
        if username is None:
            username = kwargs.get(UserModel.USERNAME_FIELD)

        if username is None or password is None:
            return None

        user = self._get_user_by_username_or_email(username)
        if user is None:
            return None

        if user.check_password(password) and self.user_can_authenticate(user):
            return user

        return None

    def _get_user_by_username_or_email(self, value):
        try:
            return UserModel._default_manager.get_by_natural_key(value)
        except UserModel.DoesNotExist:
            email_field = UserModel.get_email_field_name()
            try:
                return UserModel._default_manager.get(**{f"{email_field}__iexact": value})
            except UserModel.DoesNotExist:
                return None
            except UserModel.MultipleObjectsReturned:
                return None