# -*- coding: utf-8 -*-
from __future__ import unicode_literals

from django.apps import apps
from django.conf import settings
from django.core import checks


def check_user_model(app_configs=None, **kwargs):
    if app_configs is None:
        cls = apps.get_model(settings.AUTH_USER_MODEL)
    else:
        app_label, model_name = settings.AUTH_USER_MODEL.split('.')
        for app_config in app_configs:
            if app_config.label == app_label:
                cls = app_config.get_model(model_name)
                break
        else:
            # Checks might be run against a set of app configs that don't
            # include the specified user model. In this case we simply don't
            # perform the checks defined below.
            return []

    errors = []

    # Check that REQUIRED_FIELDS is a list
    if not isinstance(cls.REQUIRED_FIELDS, (list, tuple)):
        errors.append(
            checks.Error(
                "'REQUIRED_FIELDS' must be a list or tuple.",
                obj=cls,
                id='auth.E001',
            )
        )

    # Check that the USERNAME FIELD isn't included in REQUIRED_FIELDS.
    if cls.USERNAME_FIELD in cls.REQUIRED_FIELDS:
        errors.append(
            checks.Error(
                "The field named as the 'USERNAME_FIELD' "
                "for a custom user model must not be included in 'REQUIRED_FIELDS'.",
                obj=cls,
                id='auth.E002',
            )
        )

    # Check that the username field is unique
    if not cls._meta.get_field(cls.USERNAME_FIELD).unique:
        if (settings.AUTHENTICATION_BACKENDS ==
                ['django.contrib.auth.backends.ModelBackend']):
            errors.append(
                checks.Error(
                    "'%s.%s' must be unique because it is named as the 'USERNAME_FIELD'." % (
                        cls._meta.object_name, cls.USERNAME_FIELD
                    ),
                    obj=cls,
                    id='auth.E003',
                )
            )
        else:
            errors.append(
                checks.Warning(
                    "'%s.%s' is named as the 'USERNAME_FIELD', but it is not unique." % (
                        cls._meta.object_name, cls.USERNAME_FIELD
                    ),
                    hint='Ensure that your authentication backend(s) can handle non-unique usernames.',
                    obj=cls,
                    id='auth.W004',
                )
            )

    return errors