text: from django.apps import apps
  from django.conf import settings
  from django.contrib import auth
  from django.contrib.auth.base_user import AbstractBaseUser, BaseUserManager
  from django.contrib.auth.hashers import make_password
  from django.contrib.contenttypes.models import ContentType
  from django.core.exceptions import PermissionDenied
  from django.core.mail import send_mail
  from django.db import models
  from django.db.models.manager import EmptyManager
  from django.utils import timezone
  from django.utils.translation import gettext_lazy as _
  
  from .validators import UnicodeUsernameValidator
  
  
  def update_last_login(sender, user, **kwargs):
      """
      A signal receiver which updates the last_login date for
      the user logging in.
      """
      user.last_login = timezone.now()
      user.save(update_fields=['last_login'])
  
  
  class PermissionManager(models.Manager):
      use_in_migrations = True
  
      def get_by_natural_key(self, codename, app_label, model):
          return self.get(
              codename=codename,
              content_type=ContentType.objects.db_manager(self.db).get_by_natural_key(app_label, model),
          )
  
  
  class Permission(models.Model):
      """
      The permissions system provides a way to assign permissions to specific
      users and groups of users.
  
      The permission system is used by the Django admin site, but may also be
      useful in your own code. The Django admin site uses permissions as follows:
  
          - The "add" permission limits the user's ability to view the "add" form
            and add an object.
          - The "change" permission limits a user's ability to view the change
            list, view the "change" form and change an object.
          - The "delete" permission limits the ability to delete an object.
          - The "view" permission limits the ability to view an object.
  
      Permissions are set globally per type of object, and per specific object
      instance. It is possible to say "Mary may change news stories," and it's
      now possible to say "Mary may change news stories, and also only the
      ones she created herself" and/or "Mary may only change news stories that have a
      certain status or publication date."
  
      The permissions listed above are automatically created for each model.
      """
      name = models.CharField(_('name'), max_length=255)
      content_type = models.ForeignKey(
          ContentType,
          models.CASCADE,
          verbose_name=_('content type'),
      )
      codename = models.CharField(_('codename'), max_length=100)
      created_by = models.ForeignKey(settings.AUTH_USER_MODEL, on_delete=models.CASCADE, editable=False, null=True, blank=True)
      objects = PermissionManager()
  
      class Meta:
          verbose_name = _('permission')
          verbose_name_plural = _('permissions')
          unique_together = [['content_type', 'codename']]
          ordering = ['content_type__app_label', 'content_type__model', 'codename']
  
      def __str__(self):
          return '%s | %s' % (self.content_type, self.name)
  
      def natural_key(self):
          return (self.codename,) + self.content_type.natural_key()
      natural_key.dependencies = ['contenttypes.contenttype']
  
  
  class GroupManager(models.Manager):
      """
      The manager for the auth's Group model.
      """
      use_in_migrations = True
  
      def get_by_natural_key(self, name):
          return self.get(name=name)
  
  
  class Group(models.Model):
      """
      Groups are a generic way of categorizing users to apply permissions, or
      some other label, to those users. A user can belong to any number of
      groups.
  
      A user in a group automatically has all the permissions granted to that
      group. For example, if the group 'Site editors' has the permission
      can_edit_home_page, any user in that group will have that permission.
  
      Beyond permissions, groups are a convenient way to categorize users to
      apply some label, or extended functionality, to them. For example, you
      could create a group 'Special users', and you could write code that would
      do special things to those users -- such as giving them access to a
      members-only portion of your site, or sending them members-only email
      messages.
      """
      name = models.CharField(_('name'), max_length=150, unique=True)
      permissions = models.ManyToManyField(
          Permission,
          verbose_name=_('permissions'),
          blank=True,
      )
  
      objects = GroupManager()
  
      class Meta:
          verbose_name = _('group')
          verbose_name_plural = _('groups')
  
      def __str__(self):
          return self.name
  
      def natural_key(self):
          return (self.name,)
  
  
  class UserManager(BaseUserManager):
      use_in_migrations = True
  
      def _create_user(self, username, email, password, **extra_fields):
          """
          Create and save a user with the given username, email, and password.
          """
          if not username:
              raise ValueError('The given username must be set')
          email = self.normalize_email(email)
          # Lookup the real model class from the global app registry so this
          # manager method can be used in migrations. This is fine because
          # managers are by definition working on the real model.
          GlobalUserModel = apps.get_model(self.model._meta.app_label, self.model._meta.object_name)
          username = GlobalUserModel.normalize_username(username)
          user = self.model(username=username, email=email, **extra_fields)
          user.password = make_password(password)
          user.save(using=self._db)
          return user
  
      def create_user(self, username, email=None, password=None, **extra_fields):
          extra_fields.setdefault('is_staff', False)
          extra_fields.setdefault('is_superuser', False)
          return self._create_user(username, email, password, **extra_fields)
  
      def create_superuser(self, username, email=None, password=None, **extra_fields):
          extra_fields.setdefault('is_staff', True)
          extra_fields.setdefault('is_superuser', True)
  
          if extra_fields.get('is_staff') is not True:
              raise ValueError('Superuser must have is_staff=True.')
          if extra_fields.get('is_superuser') is not True:
              raise ValueError('Superuser must have is_superuser=True.')
  
          return self._create_user(username, email, password, **extra_fields)
  
      def with_perm(self, perm, is_active=True, include_superusers=True, backend=None, obj=None):
          if backend is None:
              backends = auth._get_backends(return_tuples=True)
              if len(backends) == 1:
                  backend, _ = backends[0]
              else:
                  raise ValueError(
                      'You have multiple authentication backends configured and '
                      'therefore must provide the `backend` argument.'
                  )
          elif not isinstance(backend, str):
              raise TypeError(
                  'backend must be a dotted import path string (got %r).'
                  % backend
              )
          else:
              backend = auth.load_backend(backend)
          if hasattr(backend, 'with_perm'):
              return backend.with_perm(
                  perm,
                  is_active=is_active,
                  include_superusers=include_superusers,
                  obj=obj,
              )
          return self.none()
  
  
  # A few helper functions for common logic between User and AnonymousUser.
  def _user_get_permissions(user, obj, from_name):
      permissions = set()
      name = 'get_%s_permissions' % from_name
      for backend in auth.get_backends():
          if hasattr(backend, name):
              permissions.update(getattr(backend, name)(user, obj))
      return permissions
  
  
  def _user_has_perm(user, perm, obj):
      """
      A backend can raise `PermissionDenied` to short-circuit permission checking.
      """
      for backend in auth.get_backends():
          if not hasattr(backend, 'has_perm'):
              continue
          try:
              if backend.has_perm(user, perm, obj):
                  return True
          except PermissionDenied:
              return False
      return False
  
  
  def _user_has_module_perms(user, app_label):
      """
      A backend can raise `PermissionDenied` to short-circuit permission checking.
      """
      for backend in auth.get_backends():
          if not hasattr(backend, 'has_module_perms'):
              continue
          try:
              if backend.has_module_perms(user, app_label):
                  return True
          except PermissionDenied:
              return False
      return False
  
  
  class PermissionsMixin(models.Model):
      """
      Add the fields and methods necessary to support the Group and Permission
      models using the ModelBackend.
      """
      is_superuser = models.BooleanField(
          _('superuser status'),
          default=False,
          help_text=_(
              'Designates that this user has all permissions without '
              'explicitly assigning them.'
          ),
      )
      groups = models.ManyToManyField(
          Group,
          verbose_name=_('groups'),
          blank=True,
          help_text=_(
              'The groups this user belongs to. A user will get all permissions '
              'granted to each of their groups.'
          ),
          related_name="user_set",
          related_query_name="user",
      )
      user_permissions = models.ManyToManyField(
          Permission,
          verbose_name=_('user permissions'),
          blank=True,
          help_text=_('Specific permissions for this user.'),
          related_name="user_set",
          related_query_name="user",
      )
  
      class Meta:
          abstract = True
  
      def get_user_permissions(self, obj=None):
          """
          Return a list of permission strings that this user has directly.
          Query all available auth backends. If an object is passed in,
          return only permissions matching this object.
          """
          return _user_get_permissions(self, obj, 'user')
  
      def get_group_permissions(self, obj=None):
          """
          Return a list of permission strings that this user has through their
          groups. Query all available auth backends. If an object is passed in,
          return only permissions matching this object.
          """
          return _user_get_permissions(self, obj, 'group')
  
      def get_all_permissions(self, obj=None):
          return _user_get_permissions(self, obj, 'all')
  
      def has_perm(self, perm, obj=None):
          """
          Return True if the user has the specified permission. Query all
          available auth backends, but return immediately if any backend returns
          True. Thus, a user who has permission from a single auth backend is
          assumed to have permission in general. If an object is provided, check
          permissions for that object.
          """
          # Active superusers have all permissions.
          if self.is_active and self.is_superuser:
              return True
  
          # Otherwise we need to check the backends.
          return _user_has_perm(self, perm, obj)
  
      def has_perms(self, perm_list, obj=None):
          """
          Return True if the user has each of the specified permissions. If
          object is passed, check if the user has all required perms for it.
          """
          return all(self.has_perm(perm, obj) for perm in perm_list)
  
      def has_module_perms(self, app_label):
          """
          Return True if the user has any permissions in the given app label.
          Use similar logic as has_perm(), above.
          """
          # Active superusers have all permissions.
          if self.is_active and self.is_superuser:
              return True
  
          return _user_has_module_perms(self, app_label)
  
  
  class AbstractUser(AbstractBaseUser, PermissionsMixin):
      """
      An abstract base class implementing a fully featured User model with
      admin-compliant permissions.
  
      Username and password are required. Other fields are optional.
      """
      username_validator = UnicodeUsernameValidator()
  
      username = models.CharField(
          _('username'),
          max_length=150,
          unique=True,
          help_text=_('Required. 150 characters or fewer. Letters, digits and @/./+/-/_ only.'),
          validators=[username_validator],
          error_messages={
              'unique': _("A user with that username already exists."),
          },
      )
      first_name = models.CharField(_('first name'), max_length=150, blank=True)
      last_name = models.CharField(_('last name'), max_length=150, blank=True)
      email = models.EmailField(_('email address'), blank=True)
      is_staff = models.BooleanField(
          _('staff status'),
          default=False,
          help_text=_('Designates whether the user can log into this admin site.'),
      )
      is_active = models.BooleanField(
          _('active'),
          default=True,
          help_text=_(
              'Designates whether this user should be treated as active. '
              'Unselect this instead of deleting accounts.'
          ),
      )
      date_joined = models.DateTimeField(_('date joined'), default=timezone.now)
  
      objects = UserManager()
  
      EMAIL_FIELD = 'email'
      USERNAME_FIELD = 'username'
      REQUIRED_FIELDS = ['email']
  
      class Meta:
          verbose_name = _('user')
          verbose_name_plural = _('users')
          abstract = True
  
      def clean(self):
          super().clean()
          self.email = self.__class__.objects.normalize_email(self.email)
  
      def get_full_name(self):
          """
          Return the first_name plus the last_name, with a space in between.
          """
          full_name = '%s %s' % (self.first_name, self.last_name)
          return full_name.strip()
  
      def get_short_name(self):
          """Return the short name for the user."""
          return self.first_name
  
      def email_user(self, subject, message, from_email=None, **kwargs):
          """Send an email to this user."""
          send_mail(subject, message, from_email, [self.email], **kwargs)
  
  
  class User(AbstractUser):
      """
      Users within the Django authentication system are represented by this
      model.
  
      Username and password are required. Other fields are optional.
      """
      class Meta(AbstractUser.Meta):
          swappable = 'AUTH_USER_MODEL'
  
  
  class AnonymousUser:
      id = None
      pk = None
      username = ''
      is_staff = False
      is_active = False
      is_superuser = False
      _groups = EmptyManager(Group)
      _user_permissions = EmptyManager(Permission)
  
      def __str__(self):
          return 'AnonymousUser'
  
      def __eq__(self, other):
          return isinstance(other, self.__class__)
  
      def __hash__(self):
          return 1  # instances always return the same hash value
  
      def __int__(self):
          raise TypeError('Cannot cast AnonymousUser to int. Are you trying to use it in place of User?')
  
      def save(self):
          raise NotImplementedError("Django doesn't provide a DB representation for AnonymousUser.")
  
      def delete(self):
          raise NotImplementedError("Django doesn't provide a DB representation for AnonymousUser.")
  
      def set_password(self, raw_password):
          raise NotImplementedError("Django doesn't provide a DB representation for AnonymousUser.")
  
      def check_password(self, raw_password):
          raise NotImplementedError("Django doesn't provide a DB representation for AnonymousUser.")
  
      @property
      def groups(self):
          return self._groups
  
      @property
      def user_permissions(self):
          return self._user_permissions
  
      def get_user_permissions(self, obj=None):
          return _user_get_permissions(self, obj, 'user')
  
      def get_group_permissions(self, obj=None):
          return set()
  
      def get_all_permissions(self, obj=None):
          return _user_get_permissions(self, obj, 'all')
  
      def has_perm(self, perm, obj=None):
          return _user_has_perm(self, perm, obj=obj)
  
      def has_perms(self, perm_list, obj=None):
          return all(self.has_perm(perm, obj) for perm in perm_list)
  
      def has_module_perms(self, module):
          return _user_has_module_perms(self, module)
  
      @property
      def is_anonymous(self):
          return True
  
      @property
      def is_authenticated(self):
          return False
  
      def get_username(self):
          return self.username
  