from itertools import chain
from types import MethodType

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

from .management import _get_builtin_permissions


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',
                )
            )

    if isinstance(cls().is_anonymous, MethodType):
        errors.append(
            checks.Critical(
                '%s.is_anonymous must be an attribute or property rather than '
                'a method. Ignoring this is a security issue as anonymous '
                'users will be treated as authenticated!' % cls,
                obj=cls,
                id='auth.C009',
            )
        )
    if isinstance(cls().is_authenticated, MethodType):
        errors.append(
            checks.Critical(
                '%s.is_authenticated must be an attribute or property rather '
                'than a method. Ignoring this is a security issue as anonymous '
                'users will be treated as authenticated!' % cls,
                obj=cls,
                id='auth.C010',
            )
        )
    return errors


def check_models_permissions(app_configs=None, **kwargs):
    if app_configs is None:
        models = apps.get_models()
    else:
        models = chain.from_iterable(app_config.get_models() for app_config in app_configs)

    Permission = apps.get_model('auth', 'Permission')
    permission_name_max_length = Permission._meta.get_field('name').max_length
    errors = []

    for model in models:
        opts = model._meta
        builtin_permissions = dict(_get_builtin_permissions(opts))
        # Check builtin permission name length.
        max_builtin_permission_name_length = (
            max(len(name) for name in builtin_permissions.values())
            if builtin_permissions else 0
        )
        if max_builtin_permission_name_length > permission_name_max_length:
            verbose_name_max_length = (
                permission_name_max_length - (max_builtin_permission_name_length - len(opts.verbose_name_raw))
            )
            errors.append(
                checks.Error(
                    "The verbose_name of model '%s.%s' must be at most %d characters "
                    "for its builtin permission names to be at most %d characters." % (
                        opts.app_label, opts.object_name, verbose_name_max_length, permission_name_max_length
                    ),
                    obj=model,
                    id='auth.E007',
                )
            )
        codenames = set()
        for codename, name in opts.permissions:
            # Check custom permission name length.
            if len(name) > permission_name_max_length:
                errors.append(
                    checks.Error(
                        "The permission named '%s' of model '%s.%s' is longer than %d characters." % (
                            name, opts.app_label, opts.object_name, permission_name_max_length
                        ),
                        obj=model,
                        id='auth.E008',
                    )
                )
            # Check custom permissions codename clashing.
            if codename in builtin_permissions:
                errors.append(
                    checks.Error(
                        "The permission codenamed '%s' clashes with a builtin permission "
                        "for model '%s.%s'." % (
                            codename, opts.app_label, opts.object_name
                        ),
                        obj=model,
                        id='auth.E005',
                    )
                )
            elif codename in codenames:
                errors.append(
                    checks.Error(
                        "The permission codenamed '%s' is duplicated for model '%s.%s'." % (
                            codename, opts.app_label, opts.object_name
                        ),
                        obj=model,
                        id='auth.E006',
                    )
                )
            codenames.add(codename)

    return errors