text: import json
  import logging
  from collections import defaultdict
  from io import StringIO
  from urllib.parse import urlparse
  
  from django.conf import settings
  from django.contrib.auth.models import Group, Permission
  from django.contrib.contenttypes.models import ContentType
  from django.core import checks
  from django.core.cache import cache
  from django.core.exceptions import ValidationError
  from django.core.handlers.base import BaseHandler
  from django.core.handlers.wsgi import WSGIRequest
  from django.db import models, transaction
  from django.db.models import Q, Value
  from django.db.models.functions import Concat, Substr
  from django.http import Http404
  from django.template.response import TemplateResponse
  from django.urls import reverse
  from django.utils import timezone
  from django.utils.functional import cached_property
  from django.utils.text import capfirst, slugify
  from django.utils.translation import ugettext_lazy as _
  from modelcluster.models import ClusterableModel, get_all_child_relations
  from treebeard.mp_tree import MP_Node
  
  from wagtail.core.query import PageQuerySet, TreeQuerySet
  from wagtail.core.signals import page_published, page_unpublished
  from wagtail.core.sites import get_site_for_hostname
  from wagtail.core.url_routing import RouteResult
  from wagtail.core.utils import WAGTAIL_APPEND_SLASH, camelcase_to_underscore, resolve_model_string
  from wagtail.search import index
  
  logger = logging.getLogger('wagtail.core')
  
  PAGE_TEMPLATE_VAR = 'page'
  
  
  class SiteManager(models.Manager):
      def get_by_natural_key(self, hostname, port):
          return self.get(hostname=hostname, port=port)
  
  
  class Site(models.Model):
      hostname = models.CharField(verbose_name=_('hostname'), max_length=255, db_index=True)
      port = models.IntegerField(
          verbose_name=_('port'),
          default=80,
          help_text=_(
              "Set this to something other than 80 if you need a specific port number to appear in URLs"
              " (e.g. development on port 8000). Does not affect request handling (so port forwarding still works)."
          )
      )
      site_name = models.CharField(
          verbose_name=_('site name'),
          max_length=255,
          null=True,
          blank=True,
          help_text=_("Human-readable name for the site.")
      )
      root_page = models.ForeignKey('Page', verbose_name=_('root page'), related_name='sites_rooted_here', on_delete=models.CASCADE)
      is_default_site = models.BooleanField(
          verbose_name=_('is default site'),
          default=False,
          help_text=_(
              "If true, this site will handle requests for all other hostnames that do not have a site entry of their own"
          )
      )
  
      objects = SiteManager()
  
      class Meta:
          unique_together = ('hostname', 'port')
          verbose_name = _('site')
          verbose_name_plural = _('sites')
  
      def natural_key(self):
          return (self.hostname, self.port)
  
      def __str__(self):
          if self.site_name:
              return(
                  self.site_name +
                  (" [default]" if self.is_default_site else "")
              )
          else:
              return(
                  self.hostname +
                  ("" if self.port == 80 else (":%d" % self.port)) +
                  (" [default]" if self.is_default_site else "")
              )
  
      @staticmethod
      def find_for_request(request):
          """
          Find the site object responsible for responding to this HTTP
          request object. Try:
  
          * unique hostname first
          * then hostname and port
          * if there is no matching hostname at all, or no matching
            hostname:port combination, fall back to the unique default site,
            or raise an exception
  
          NB this means that high-numbered ports on an extant hostname may
          still be routed to a different hostname which is set as the default
          """
  
          try:
              hostname = request.get_host().split(':')[0]
          except KeyError:
              hostname = None
  
          try:
              port = request.get_port()
          except (AttributeError, KeyError):
              port = request.META.get('SERVER_PORT')
  
          return get_site_for_hostname(hostname, port)
  
      @property
      def root_url(self):
          if self.port == 80:
              return 'http://%s' % self.hostname
          elif self.port == 443:
              return 'https://%s' % self.hostname
          else:
              return 'http://%s:%d' % (self.hostname, self.port)
  
      def clean_fields(self, exclude=None):
          super().clean_fields(exclude)
          # Only one site can have the is_default_site flag set
          try:
              default = Site.objects.get(is_default_site=True)
          except Site.DoesNotExist:
              pass
          except Site.MultipleObjectsReturned:
              raise
          else:
              if self.is_default_site and self.pk != default.pk:
                  raise ValidationError(
                      {'is_default_site': [
                          _(
                              "%(hostname)s is already configured as the default site."
                              " You must unset that before you can save this site as default."
                          )
                          % {'hostname': default.hostname}
                      ]}
                  )
  
      @staticmethod
      def get_site_root_paths():
          """
          Return a list of (id, root_path, root_url) tuples, most specific path
          first - used to translate url_paths into actual URLs with hostnames
          """
          result = cache.get('wagtail_site_root_paths')
  
          if result is None:
              result = [
                  (site.id, site.root_page.url_path, site.root_url)
                  for site in Site.objects.select_related('root_page').order_by(
                      '-root_page__url_path', '-is_default_site', 'hostname')
              ]
              cache.set('wagtail_site_root_paths', result, 3600)
  
          return result
  
  
  PAGE_MODEL_CLASSES = []
  
  
  def get_page_models():
      """
      Returns a list of all non-abstract Page model classes defined in this project.
      """
      return PAGE_MODEL_CLASSES
  
  
  def get_default_page_content_type():
      """
      Returns the content type to use as a default for pages whose content type
      has been deleted.
      """
      return ContentType.objects.get_for_model(Page)
  
  
  class BasePageManager(models.Manager):
      def get_queryset(self):
          return self._queryset_class(self.model).order_by('path')
  
  
  PageManager = BasePageManager.from_queryset(PageQuerySet)
  
  
  class PageBase(models.base.ModelBase):
      """Metaclass for Page"""
      def __init__(cls, name, bases, dct):
          super(PageBase, cls).__init__(name, bases, dct)
  
          if 'template' not in dct:
              # Define a default template path derived from the app name and model name
              cls.template = "%s/%s.html" % (cls._meta.app_label, camelcase_to_underscore(name))
  
          if 'ajax_template' not in dct:
              cls.ajax_template = None
  
          cls._clean_subpage_models = None  # to be filled in on first call to cls.clean_subpage_models
          cls._clean_parent_page_models = None  # to be filled in on first call to cls.clean_parent_page_models
  
          # All pages should be creatable unless explicitly set otherwise.
          # This attribute is not inheritable.
          if 'is_creatable' not in dct:
              cls.is_creatable = not cls._meta.abstract
  
          if not cls._meta.abstract:
              # register this type in the list of page content types
              PAGE_MODEL_CLASSES.append(cls)
  
  
  class AbstractPage(MP_Node):
      """
      Abstract superclass for Page. According to Django's inheritance rules, managers set on
      abstract models are inherited by subclasses, but managers set on concrete models that are extended
      via multi-table inheritance are not. We therefore need to attach PageManager to an abstract
      superclass to ensure that it is retained by subclasses of Page.
      """
      objects = PageManager()
  
      class Meta:
          abstract = True
  
  
  class Page(AbstractPage, index.Indexed, ClusterableModel, metaclass=PageBase):
      title = models.CharField(
          verbose_name=_('title'),
          max_length=255,
          help_text=_("The page title as you'd like it to be seen by the public")
      )
      # to reflect title of a current draft in the admin UI
      draft_title = models.CharField(
          max_length=255,
          editable=False
      )
      slug = models.SlugField(
          verbose_name=_('slug'),
          allow_unicode=True,
          max_length=255,
          help_text=_("The name of the page as it will appear in URLs e.g http://domain.com/blog/[my-slug]/")
      )
      content_type = models.ForeignKey(
          'contenttypes.ContentType',
          verbose_name=_('content type'),
          related_name='pages',
          on_delete=models.SET(get_default_page_content_type)
      )
      live = models.BooleanField(verbose_name=_('live'), default=True, editable=False)
      has_unpublished_changes = models.BooleanField(
          verbose_name=_('has unpublished changes'),
          default=False,
          editable=False
      )
      url_path = models.TextField(verbose_name=_('URL path'), blank=True, editable=False)
      owner = models.ForeignKey(
          settings.AUTH_USER_MODEL,
          verbose_name=_('owner'),
          null=True,
          blank=True,
          editable=True,
          on_delete=models.SET_NULL,
          related_name='owned_pages'
      )
  
      seo_title = models.CharField(
          verbose_name=_("page title"),
          max_length=255,
          blank=True,
          help_text=_("Optional. 'Search Engine Friendly' title. This will appear at the top of the browser window.")
      )
  
      show_in_menus_default = False
      show_in_menus = models.BooleanField(
          verbose_name=_('show in menus'),
          default=False,
          help_text=_("Whether a link to this page will appear in automatically generated menus")
      )
      search_description = models.TextField(verbose_name=_('search description'), blank=True)
  
      go_live_at = models.DateTimeField(
          verbose_name=_("go live date/time"),
          blank=True,
          null=True
      )
      expire_at = models.DateTimeField(
          verbose_name=_("expiry date/time"),
          blank=True,
          null=True
      )
      expired = models.BooleanField(verbose_name=_('expired'), default=False, editable=False)
  
      locked = models.BooleanField(verbose_name=_('locked'), default=False, editable=False)
  
      first_published_at = models.DateTimeField(
          verbose_name=_('first published at'),
          blank=True,
          null=True,
          db_index=True
      )
      last_published_at = models.DateTimeField(
          verbose_name=_('last published at'),
          null=True,
          editable=False
      )
      latest_revision_created_at = models.DateTimeField(
          verbose_name=_('latest revision created at'),
          null=True,
          editable=False
      )
      live_revision = models.ForeignKey(
          'PageRevision',
          related_name='+',
          verbose_name='live revision',
          on_delete=models.SET_NULL,
          null=True,
          blank=True,
          editable=False
      )
  
      search_fields = [
          index.SearchField('title', partial_match=True, boost=2),
          index.AutocompleteField('title'),
          index.FilterField('title'),
          index.FilterField('id'),
          index.FilterField('live'),
          index.FilterField('owner'),
          index.FilterField('content_type'),
          index.FilterField('path'),
          index.FilterField('depth'),
          index.FilterField('locked'),
          index.FilterField('show_in_menus'),
          index.FilterField('first_published_at'),
          index.FilterField('last_published_at'),
          index.FilterField('latest_revision_created_at'),
      ]
  
      # Do not allow plain Page instances to be created through the Wagtail admin
      is_creatable = False
  
      # An array of additional field names that will not be included when a Page is copied.
      exclude_fields_in_copy = []
  
      # Define these attributes early to avoid masking errors. (Issue #3078)
      # The canonical definition is in wagtailadmin.edit_handlers.
      content_panels = []
      promote_panels = []
      settings_panels = []
  
      def __init__(self, *args, **kwargs):
          super().__init__(*args, **kwargs)
          if not self.id:
              # this model is being newly created
              # rather than retrieved from the db;
              if not self.content_type_id:
                  # set content type to correctly represent the model class
                  # that this was created as
                  self.content_type = ContentType.objects.get_for_model(self)
              if 'show_in_menus' not in kwargs:
                  # if the value is not set on submit refer to the model setting
                  self.show_in_menus = self.show_in_menus_default
  
      def __str__(self):
          return self.title
  
      def set_url_path(self, parent):
          """
          Populate the url_path field based on this page's slug and the specified parent page.
          (We pass a parent in here, rather than retrieving it via get_parent, so that we can give
          new unsaved pages a meaningful URL when previewing them; at that point the page has not
          been assigned a position in the tree, as far as treebeard is concerned.
          """
          if parent:
              self.url_path = parent.url_path + self.slug + '/'
          else:
              # a page without a parent is the tree root, which always has a url_path of '/'
              self.url_path = '/'
  
          return self.url_path
  
      @staticmethod
      def _slug_is_available(slug, parent_page, page=None):
          """
          Determine whether the given slug is available for use on a child page of
          parent_page. If 'page' is passed, the slug is intended for use on that page
          (and so it will be excluded from the duplicate check).
          """
          if parent_page is None:
              # the root page's slug can be whatever it likes...
              return True
  
          siblings = parent_page.get_children()
          if page:
              siblings = siblings.not_page(page)
  
          return not siblings.filter(slug=slug).exists()
  
      def _get_autogenerated_slug(self, base_slug):
          candidate_slug = base_slug
          suffix = 1
          parent_page = self.get_parent()
  
          while not Page._slug_is_available(candidate_slug, parent_page, self):
              # try with incrementing suffix until we find a slug which is available
              suffix += 1
              candidate_slug = "%s-%d" % (base_slug, suffix)
  
          return candidate_slug
  
      def full_clean(self, *args, **kwargs):
          # Apply fixups that need to happen before per-field validation occurs
  
          if not self.slug:
              # Try to auto-populate slug from title
              base_slug = slugify(self.title, allow_unicode=True)
  
              # only proceed if we get a non-empty base slug back from slugify
              if base_slug:
                  self.slug = self._get_autogenerated_slug(base_slug)
  
          if not self.draft_title:
              self.draft_title = self.title
  
          super().full_clean(*args, **kwargs)
  
      def clean(self):
          super().clean()
          if not Page._slug_is_available(self.slug, self.get_parent(), self):
              raise ValidationError({'slug': _("This slug is already in use")})
  
      @transaction.atomic
      # ensure that changes are only committed when we have updated all descendant URL paths, to preserve consistency
      def save(self, *args, **kwargs):
          self.full_clean()
  
          update_descendant_url_paths = False
          is_new = self.id is None
  
          if is_new:
              # we are creating a record. If we're doing things properly, this should happen
              # through a treebeard method like add_child, in which case the 'path' field
              # has been set and so we can safely call get_parent
              self.set_url_path(self.get_parent())
          else:
              # Check that we are committing the slug to the database
              # Basically: If update_fields has been specified, and slug is not included, skip this step
              if not ('update_fields' in kwargs and 'slug' not in kwargs['update_fields']):
                  # see if the slug has changed from the record in the db, in which case we need to
                  # update url_path of self and all descendants
                  old_record = Page.objects.get(id=self.id)
                  if old_record.slug != self.slug:
                      self.set_url_path(self.get_parent())
                      update_descendant_url_paths = True
                      old_url_path = old_record.url_path
                      new_url_path = self.url_path
  
          result = super().save(*args, **kwargs)
  
          if update_descendant_url_paths:
              self._update_descendant_url_paths(old_url_path, new_url_path)
  
          # Check if this is a root page of any sites and clear the 'wagtail_site_root_paths' key if so
          if Site.objects.filter(root_page=self).exists():
              cache.delete('wagtail_site_root_paths')
  
          # Log
          if is_new:
              cls = type(self)
              logger.info(
                  "Page created: \"%s\" id=%d content_type=%s.%s path=%s",
                  self.title,
                  self.id,
                  cls._meta.app_label,
                  cls.__name__,
                  self.url_path
              )
  
          return result
  
      def delete(self, *args, **kwargs):
          # Ensure that deletion always happens on an instance of Page, not a specific subclass. This
          # works around a bug in treebeard <= 3.0 where calling SpecificPage.delete() fails to delete
          # child pages that are not instances of SpecificPage
          if type(self) is Page:
              # this is a Page instance, so carry on as we were
              return super().delete(*args, **kwargs)
          else:
              # retrieve an actual Page instance and delete that instead of self
              return Page.objects.get(id=self.id).delete(*args, **kwargs)
  
      @classmethod
      def check(cls, **kwargs):
          errors = super(Page, cls).check(**kwargs)
  
          # Check that foreign keys from pages are not configured to cascade
          # This is the default Django behaviour which must be explicitly overridden
          # to prevent pages disappearing unexpectedly and the tree being corrupted
  
          # get names of foreign keys pointing to parent classes (such as page_ptr)
          field_exceptions = [field.name
                              for model in [cls] + list(cls._meta.get_parent_list())
                              for field in model._meta.parents.values() if field]
  
          for field in cls._meta.fields:
              if isinstance(field, models.ForeignKey) and field.name not in field_exceptions:
                  if field.remote_field.on_delete == models.CASCADE:
                      errors.append(
                          checks.Warning(
                              "Field hasn't specified on_delete action",
                              hint="Set on_delete=models.SET_NULL and make sure the field is nullable or set on_delete=models.PROTECT. Wagtail does not allow simple database CASCADE because it will corrupt its tree storage.",
                              obj=field,
                              id='wagtailcore.W001',
                          )
                      )
  
          if not isinstance(cls.objects, PageManager):
              errors.append(
                  checks.Error(
                      "Manager does not inherit from PageManager",
                      hint="Ensure that custom Page managers inherit from wagtail.core.models.PageManager",
                      obj=cls,
                      id='wagtailcore.E002',
                  )
              )
  
          try:
              cls.clean_subpage_models()
          except (ValueError, LookupError) as e:
              errors.append(
                  checks.Error(
                      "Invalid subpage_types setting for %s" % cls,
                      hint=str(e),
                      id='wagtailcore.E002'
                  )
              )
  
          try:
              cls.clean_parent_page_models()
          except (ValueError, LookupError) as e:
              errors.append(
                  checks.Error(
                      "Invalid parent_page_types setting for %s" % cls,
                      hint=str(e),
                      id='wagtailcore.E002'
                  )
              )
  
          return errors
  
      def _update_descendant_url_paths(self, old_url_path, new_url_path):
          (Page.objects
              .filter(path__startswith=self.path)
              .exclude(pk=self.pk)
              .update(url_path=Concat(
                  Value(new_url_path),
                  Substr('url_path', len(old_url_path) + 1))))
  
      #: Return this page in its most specific subclassed form.
      @cached_property
      def specific(self):
          """
          Return this page in its most specific subclassed form.
          """
          # the ContentType.objects manager keeps a cache, so this should potentially
          # avoid a database lookup over doing self.content_type. I think.
          content_type = ContentType.objects.get_for_id(self.content_type_id)
          model_class = content_type.model_class()
          if model_class is None:
              # Cannot locate a model class for this content type. This might happen
              # if the codebase and database are out of sync (e.g. the model exists
              # on a different git branch and we haven't rolled back migrations before
              # switching branches); if so, the best we can do is return the page
              # unchanged.
              return self
          elif isinstance(self, model_class):
              # self is already the an instance of the most specific class
              return self
          else:
              return content_type.get_object_for_this_type(id=self.id)
  
      #: Return the class that this page would be if instantiated in its
      #: most specific form
      @cached_property
      def specific_class(self):
          """
          Return the class that this page would be if instantiated in its
          most specific form
          """
          content_type = ContentType.objects.get_for_id(self.content_type_id)
          return content_type.model_class()
  
      def route(self, request, path_components):
          if path_components:
              # request is for a child of this page
              child_slug = path_components[0]
              remaining_components = path_components[1:]
  
              try:
                  subpage = self.get_children().get(slug=child_slug)
              except Page.DoesNotExist:
                  raise Http404
  
              return subpage.specific.route(request, remaining_components)
  
          else:
              # request is for this very page
              if self.live:
                  return RouteResult(self)
              else:
                  raise Http404
  
      def get_admin_display_title(self):
          """
          Return the title for this page as it should appear in the admin backend;
          override this if you wish to display extra contextual information about the page,
          such as language. By default, returns ``draft_title``.
          """
          # Fall back on title if draft_title is blank (which may happen if the page was created
          # in a fixture or migration that didn't explicitly handle draft_title)
          return self.draft_title or self.title
  
      def save_revision(self, user=None, submitted_for_moderation=False, approved_go_live_at=None, changed=True):
          self.full_clean()
  
          # Create revision
          revision = self.revisions.create(
              content_json=self.to_json(),
              user=user,
              submitted_for_moderation=submitted_for_moderation,
              approved_go_live_at=approved_go_live_at,
          )
  
          update_fields = []
  
          self.latest_revision_created_at = revision.created_at
          update_fields.append('latest_revision_created_at')
  
          self.draft_title = self.title
          update_fields.append('draft_title')
  
          if changed:
              self.has_unpublished_changes = True
              update_fields.append('has_unpublished_changes')
  
          if update_fields:
              self.save(update_fields=update_fields)
  
          # Log
          logger.info("Page edited: \"%s\" id=%d revision_id=%d", self.title, self.id, revision.id)
  
          if submitted_for_moderation:
              logger.info("Page submitted for moderation: \"%s\" id=%d revision_id=%d", self.title, self.id, revision.id)
  
          return revision
  
      def get_latest_revision(self):
          return self.revisions.order_by('-created_at', '-id').first()
  
      def get_latest_revision_as_page(self):
          if not self.has_unpublished_changes:
              # Use the live database copy in preference to the revision record, as:
              # 1) this will pick up any changes that have been made directly to the model,
              #    such as automated data imports;
              # 2) it ensures that inline child objects pick up real database IDs even if
              #    those are absent from the revision data. (If this wasn't the case, the child
              #    objects would be recreated with new IDs on next publish - see #1853)
              return self.specific
  
          latest_revision = self.get_latest_revision()
  
          if latest_revision:
              return latest_revision.as_page_object()
          else:
              return self.specific
  
      def unpublish(self, set_expired=False, commit=True):
          if self.live:
              self.live = False
              self.has_unpublished_changes = True
              self.live_revision = None
  
              if set_expired:
                  self.expired = True
  
              if commit:
                  self.save()
  
              page_unpublished.send(sender=self.specific_class, instance=self.specific)
  
              logger.info("Page unpublished: \"%s\" id=%d", self.title, self.id)
  
              self.revisions.update(approved_go_live_at=None)
  
      def get_context(self, request, *args, **kwargs):
          return {
              PAGE_TEMPLATE_VAR: self,
              'self': self,
              'request': request,
          }
  
      def get_template(self, request, *args, **kwargs):
          if request.is_ajax():
              return self.ajax_template or self.template
          else:
              return self.template
  
      def serve(self, request, *args, **kwargs):
          request.is_preview = getattr(request, 'is_preview', False)
  
          return TemplateResponse(
              request,
              self.get_template(request, *args, **kwargs),
              self.get_context(request, *args, **kwargs)
          )
  
      def is_navigable(self):
          """
          Return true if it's meaningful to browse subpages of this page -
          i.e. it currently has subpages,
          or it's at the top level (this rule necessary for empty out-of-the-box sites to have working navigation)
          """
          return (not self.is_leaf()) or self.depth == 2
  
      def _get_site_root_paths(self, request=None):
          """
          Return ``Site.get_site_root_paths()``, using the cached copy on the
          request object if available.
          """
          # if we have a request, use that to cache site_root_paths; otherwise, use self
          cache_object = request if request else self
          try:
              return cache_object._wagtail_cached_site_root_paths
          except AttributeError:
              cache_object._wagtail_cached_site_root_paths = Site.get_site_root_paths()
              return cache_object._wagtail_cached_site_root_paths
  
      def get_url_parts(self, request=None):
          """
          Determine the URL for this page and return it as a tuple of
          ``(site_id, site_root_url, page_url_relative_to_site_root)``.
          Return None if the page is not routable.
  
          This is used internally by the ``full_url``, ``url``, ``relative_url``
          and ``get_site`` properties and methods; pages with custom URL routing
          should override this method in order to have those operations return
          the custom URLs.
  
          Accepts an optional keyword argument ``request``, which may be used
          to avoid repeated database / cache lookups. Typically, a page model
          that overrides ``get_url_parts`` should not need to deal with
          ``request`` directly, and should just pass it to the original method
          when calling ``super``.
          """
  
          possible_sites = [
              (pk, path, url)
              for pk, path, url in self._get_site_root_paths(request)
              if self.url_path.startswith(path)
          ]
  
          if not possible_sites:
              return None
  
          site_id, root_path, root_url = possible_sites[0]
  
          if hasattr(request, 'site'):
              for site_id, root_path, root_url in possible_sites:
                  if site_id == request.site.pk:
                      break
              else:
                  site_id, root_path, root_url = possible_sites[0]
  
          page_path = reverse(
              'wagtail_serve', args=(self.url_path[len(root_path):],))
  
          # Remove the trailing slash from the URL reverse generates if
          # WAGTAIL_APPEND_SLASH is False and we're not trying to serve
          # the root path
          if not WAGTAIL_APPEND_SLASH and page_path != '/':
              page_path = page_path.rstrip('/')
  
          return (site_id, root_url, page_path)
  
      def get_full_url(self, request=None):
          """Return the full URL (including protocol / domain) to this page, or None if it is not routable"""
          url_parts = self.get_url_parts(request=request)
  
          if url_parts is None:
              # page is not routable
              return
  
          site_id, root_url, page_path = url_parts
  
          return root_url + page_path
  
      full_url = property(get_full_url)
  
      def get_url(self, request=None, current_site=None):
          """
          Return the 'most appropriate' URL for referring to this page from the pages we serve,
          within the Wagtail backend and actual website templates;
          this is the local URL (starting with '/') if we're only running a single site
          (i.e. we know that whatever the current page is being served from, this link will be on the
          same domain), and the full URL (with domain) if not.
          Return None if the page is not routable.
  
          Accepts an optional but recommended ``request`` keyword argument that, if provided, will
          be used to cache site-level URL information (thereby avoiding repeated database / cache
          lookups) and, via the ``request.site`` attribute, determine whether a relative or full URL
          is most appropriate.
          """
          # ``current_site`` is purposefully undocumented, as one can simply pass the request and get
          # a relative URL based on ``request.site``. Nonetheless, support it here to avoid
          # copy/pasting the code to the ``relative_url`` method below.
          if current_site is None and request is not None:
              current_site = getattr(request, 'site', None)
          url_parts = self.get_url_parts(request=request)
  
          if url_parts is None:
              # page is not routable
              return
  
          site_id, root_url, page_path = url_parts
  
          if (current_site is not None and site_id == current_site.id) or len(self._get_site_root_paths(request)) == 1:
              # the site matches OR we're only running a single site, so a local URL is sufficient
              return page_path
          else:
              return root_url + page_path
  
      url = property(get_url)
  
      def relative_url(self, current_site, request=None):
          """
          Return the 'most appropriate' URL for this page taking into account the site we're currently on;
          a local URL if the site matches, or a fully qualified one otherwise.
          Return None if the page is not routable.
  
          Accepts an optional but recommended ``request`` keyword argument that, if provided, will
          be used to cache site-level URL information (thereby avoiding repeated database / cache
          lookups).
          """
          return self.get_url(request=request, current_site=current_site)
  
      def get_site(self):
          """
          Return the Site object that this page belongs to.
          """
  
          url_parts = self.get_url_parts()
  
          if url_parts is None:
              # page is not routable
              return
  
          site_id, root_url, page_path = url_parts
  
          return Site.objects.get(id=site_id)
  
      @classmethod
      def get_indexed_objects(cls):
          content_type = ContentType.objects.get_for_model(cls)
          return super(Page, cls).get_indexed_objects().filter(content_type=content_type)
  
      def get_indexed_instance(self):
          # This is accessed on save by the wagtailsearch signal handler, and in edge
          # cases (e.g. loading test fixtures), may be called before the specific instance's
          # entry has been created. In those cases, we aren't ready to be indexed yet, so
          # return None.
          try:
              return self.specific
          except self.specific_class.DoesNotExist:
              return None
  
      @classmethod
      def clean_subpage_models(cls):
          """
          Returns the list of subpage types, normalised as model classes.
          Throws ValueError if any entry in subpage_types cannot be recognised as a model name,
          or LookupError if a model does not exist (or is not a Page subclass).
          """
          if cls._clean_subpage_models is None:
              subpage_types = getattr(cls, 'subpage_types', None)
              if subpage_types is None:
                  # if subpage_types is not specified on the Page class, allow all page types as subpages
                  cls._clean_subpage_models = get_page_models()
              else:
                  cls._clean_subpage_models = [
                      resolve_model_string(model_string, cls._meta.app_label)
                      for model_string in subpage_types
                  ]
  
                  for model in cls._clean_subpage_models:
                      if not issubclass(model, Page):
                          raise LookupError("%s is not a Page subclass" % model)
  
          return cls._clean_subpage_models
  
      @classmethod
      def clean_parent_page_models(cls):
          """
          Returns the list of parent page types, normalised as model classes.
          Throws ValueError if any entry in parent_page_types cannot be recognised as a model name,
          or LookupError if a model does not exist (or is not a Page subclass).
          """
  
          if cls._clean_parent_page_models is None:
              parent_page_types = getattr(cls, 'parent_page_types', None)
              if parent_page_types is None:
                  # if parent_page_types is not specified on the Page class, allow all page types as subpages
                  cls._clean_parent_page_models = get_page_models()
              else:
                  cls._clean_parent_page_models = [
                      resolve_model_string(model_string, cls._meta.app_label)
                      for model_string in parent_page_types
                  ]
  
                  for model in cls._clean_parent_page_models:
                      if not issubclass(model, Page):
                          raise LookupError("%s is not a Page subclass" % model)
  
          return cls._clean_parent_page_models
  
      @classmethod
      def allowed_parent_page_models(cls):
          """
          Returns the list of page types that this page type can be a subpage of,
          as a list of model classes
          """
          return [
              parent_model for parent_model in cls.clean_parent_page_models()
              if cls in parent_model.clean_subpage_models()
          ]
  
      @classmethod
      def allowed_subpage_models(cls):
          """
          Returns the list of page types that this page type can have as subpages,
          as a list of model classes
          """
          return [
              subpage_model for subpage_model in cls.clean_subpage_models()
              if cls in subpage_model.clean_parent_page_models()
          ]
  
      @classmethod
      def creatable_subpage_models(cls):
          """
          Returns the list of page types that may be created under this page type,
          as a list of model classes
          """
          return [
              page_model for page_model in cls.allowed_subpage_models()
              if page_model.is_creatable
          ]
  
      @classmethod
      def can_exist_under(cls, parent):
          """
          Checks if this page type can exist as a subpage under a parent page
          instance.
  
          See also: :func:`Page.can_create_at` and :func:`Page.can_move_to`
          """
          return cls in parent.specific_class.allowed_subpage_models()
  
      @classmethod
      def can_create_at(cls, parent):
          """
          Checks if this page type can be created as a subpage under a parent
          page instance.
          """
          return cls.is_creatable and cls.can_exist_under(parent)
  
      def can_move_to(self, parent):
          """
          Checks if this page instance can be moved to be a subpage of a parent
          page instance.
          """
          return self.can_exist_under(parent)
  
      @classmethod
      def get_verbose_name(cls):
          """
          Returns the human-readable "verbose name" of this page model e.g "Blog page".
          """
          # This is similar to doing cls._meta.verbose_name.title()
          # except this doesn't convert any characters to lowercase
          return capfirst(cls._meta.verbose_name)
  
      @property
      def status_string(self):
          if not self.live:
              if self.expired:
                  return _("expired")
              elif self.approved_schedule:
                  return _("scheduled")
              else:
                  return _("draft")
          else:
              if self.approved_schedule:
                  return _("live + scheduled")
              elif self.has_unpublished_changes:
                  return _("live + draft")
              else:
                  return _("live")
  
      @property
      def approved_schedule(self):
          return self.revisions.exclude(approved_go_live_at__isnull=True).exists()
  
      def has_unpublished_subtree(self):
          """
          An awkwardly-defined flag used in determining whether unprivileged editors have
          permission to delete this article. Returns true if and only if this page is non-live,
          and it has no live children.
          """
          return (not self.live) and (not self.get_descendants().filter(live=True).exists())
  
      @transaction.atomic  # only commit when all descendants are properly updated
      def move(self, target, pos=None):
          """
          Extension to the treebeard 'move' method to ensure that url_path is updated too.
          """
          old_url_path = Page.objects.get(id=self.id).url_path
          super().move(target, pos=pos)
          # treebeard's move method doesn't actually update the in-memory instance, so we need to work
          # with a freshly loaded one now
          new_self = Page.objects.get(id=self.id)
          new_url_path = new_self.set_url_path(new_self.get_parent())
          new_self.save()
          new_self._update_descendant_url_paths(old_url_path, new_url_path)
  
          # Log
          logger.info("Page moved: \"%s\" id=%d path=%s", self.title, self.id, new_url_path)
  
      def copy(self, recursive=False, to=None, update_attrs=None, copy_revisions=True, keep_live=True, user=None):
          # Fill dict with self.specific values
          specific_self = self.specific
          default_exclude_fields = ['id', 'path', 'depth', 'numchild', 'url_path', 'path', 'index_entries']
          exclude_fields = default_exclude_fields + specific_self.exclude_fields_in_copy
          specific_dict = {}
  
          for field in specific_self._meta.get_fields():
              # Ignore explicitly excluded fields
              if field.name in exclude_fields:
                  continue
  
              # Ignore reverse relations
              if field.auto_created:
                  continue
  
              # Ignore m2m relations - they will be copied as child objects
              # if modelcluster supports them at all (as it does for tags)
              if field.many_to_many:
                  continue
  
              # Ignore parent links (page_ptr)
              if isinstance(field, models.OneToOneField) and field.remote_field.parent_link:
                  continue
  
              specific_dict[field.name] = getattr(specific_self, field.name)
  
          # New instance from prepared dict values, in case the instance class implements multiple levels inheritance
          page_copy = self.specific_class(**specific_dict)
  
          if not keep_live:
              page_copy.live = False
              page_copy.has_unpublished_changes = True
              page_copy.live_revision = None
              page_copy.first_published_at = None
              page_copy.last_published_at = None
  
          if user:
              page_copy.owner = user
  
          if update_attrs:
              for field, value in update_attrs.items():
                  setattr(page_copy, field, value)
  
          if to:
              if recursive and (to == self or to.is_descendant_of(self)):
                  raise Exception("You cannot copy a tree branch recursively into itself")
              page_copy = to.add_child(instance=page_copy)
          else:
              page_copy = self.add_sibling(instance=page_copy)
  
          # A dict that maps child objects to their new ids
          # Used to remap child object ids in revisions
          child_object_id_map = defaultdict(dict)
  
          # Copy child objects
          specific_self = self.specific
          for child_relation in get_all_child_relations(specific_self):
              accessor_name = child_relation.get_accessor_name()
              parental_key_name = child_relation.field.attname
              child_objects = getattr(specific_self, accessor_name, None)
  
              if child_objects:
                  for child_object in child_objects.all():
                      old_pk = child_object.pk
                      child_object.pk = None
                      setattr(child_object, parental_key_name, page_copy.id)
                      child_object.save()
  
                      # Add mapping to new primary key (so we can apply this change to revisions)
                      child_object_id_map[accessor_name][old_pk] = child_object.pk
  
          # Copy revisions
          if copy_revisions:
              for revision in self.revisions.all():
                  revision.pk = None
                  revision.submitted_for_moderation = False
                  revision.approved_go_live_at = None
                  revision.page = page_copy
  
                  # Update ID fields in content
                  revision_content = json.loads(revision.content_json)
                  revision_content['pk'] = page_copy.pk
  
                  for child_relation in get_all_child_relations(specific_self):
                      accessor_name = child_relation.get_accessor_name()
                      try:
                          child_objects = revision_content[accessor_name]
                      except KeyError:
                          # KeyErrors are possible if the revision was created
                          # before this child relation was added to the database
                          continue
  
                      for child_object in child_objects:
                          child_object[child_relation.field.name] = page_copy.pk
  
                          # Remap primary key to copied versions
                          # If the primary key is not recognised (eg, the child object has been deleted from the database)
                          # set the primary key to None
                          child_object['pk'] = child_object_id_map[accessor_name].get(child_object['pk'], None)
  
                  revision.content_json = json.dumps(revision_content)
  
                  # Save
                  revision.save()
  
          # Create a new revision
          # This code serves a few purposes:
          # * It makes sure update_attrs gets applied to the latest revision
          # * It bumps the last_revision_created_at value so the new page gets ordered as if it was just created
          # * It sets the user of the new revision so it's possible to see who copied the page by looking at its history
          latest_revision = page_copy.get_latest_revision_as_page()
  
          if update_attrs:
              for field, value in update_attrs.items():
                  setattr(latest_revision, field, value)
  
          latest_revision_as_page_revision = latest_revision.save_revision(user=user, changed=False)
          if keep_live:
              page_copy.live_revision = latest_revision_as_page_revision
              page_copy.last_published_at = latest_revision_as_page_revision.created_at
              page_copy.first_published_at = latest_revision_as_page_revision.created_at
              page_copy.save()
  
          # Log
          logger.info("Page copied: \"%s\" id=%d from=%d", page_copy.title, page_copy.id, self.id)
  
          # Copy child pages
          if recursive:
              for child_page in self.get_children():
                  child_page.specific.copy(
                      recursive=True,
                      to=page_copy,
                      copy_revisions=copy_revisions,
                      keep_live=keep_live,
                      user=user
                  )
  
          return page_copy
  
      copy.alters_data = True
  
      def permissions_for_user(self, user):
          """
          Return a PagePermissionsTester object defining what actions the user can perform on this page
          """
          user_perms = UserPagePermissionsProxy(user)
          return user_perms.for_page(self)
  
      def dummy_request(self, original_request=None, **meta):
          """
          Construct a HttpRequest object that is, as far as possible, representative of ones that would
          receive this page as a response. Used for previewing / moderation and any other place where we
          want to display a view of this page in the admin interface without going through the regular
          page routing logic.
  
          If you pass in a real request object as original_request, additional information (e.g. client IP, cookies)
          will be included in the dummy request.
          """
          url = self.full_url
          if url:
              url_info = urlparse(url)
              hostname = url_info.hostname
              path = url_info.path
              port = url_info.port or 80
              scheme = url_info.scheme
          else:
              # Cannot determine a URL to this page - cobble one together based on
              # whatever we find in ALLOWED_HOSTS
              try:
                  hostname = settings.ALLOWED_HOSTS[0]
                  if hostname == '*':
                      # '*' is a valid value to find in ALLOWED_HOSTS[0], but it's not a valid domain name.
                      # So we pretend it isn't there.
                      raise IndexError
              except IndexError:
                  hostname = 'localhost'
              path = '/'
              port = 80
              scheme = 'http'
  
          dummy_values = {
              'REQUEST_METHOD': 'GET',
              'PATH_INFO': path,
              'SERVER_NAME': hostname,
              'SERVER_PORT': port,
              'SERVER_PROTOCOL': 'HTTP/1.1',
              'HTTP_HOST': hostname,
              'wsgi.version': (1, 0),
              'wsgi.input': StringIO(),
              'wsgi.errors': StringIO(),
              'wsgi.url_scheme': scheme,
              'wsgi.multithread': True,
              'wsgi.multiprocess': True,
              'wsgi.run_once': False,
          }
  
          # Add important values from the original request object, if it was provided.
          HEADERS_FROM_ORIGINAL_REQUEST = [
              'REMOTE_ADDR', 'HTTP_X_FORWARDED_FOR', 'HTTP_COOKIE', 'HTTP_USER_AGENT', 'HTTP_AUTHORIZATION',
              'wsgi.version', 'wsgi.multithread', 'wsgi.multiprocess', 'wsgi.run_once',
          ]
          if settings.SECURE_PROXY_SSL_HEADER:
              HEADERS_FROM_ORIGINAL_REQUEST.append(settings.SECURE_PROXY_SSL_HEADER[0])
          if original_request:
              for header in HEADERS_FROM_ORIGINAL_REQUEST:
                  if header in original_request.META:
                      dummy_values[header] = original_request.META[header]
  
          # Add additional custom metadata sent by the caller.
          dummy_values.update(**meta)
  
          request = WSGIRequest(dummy_values)
  
          # Add a flag to let middleware know that this is a dummy request.
          request.is_dummy = True
  
          # Apply middleware to the request
          # Note that Django makes sure only one of the middleware settings are
          # used in a project
          if hasattr(settings, 'MIDDLEWARE'):
              handler = BaseHandler()
              handler.load_middleware()
              handler._middleware_chain(request)
          elif hasattr(settings, 'MIDDLEWARE_CLASSES'):
              # Pre Django 1.10 style - see http://www.mellowmorning.com/2011/04/18/mock-django-request-for-testing/
              handler = BaseHandler()
              handler.load_middleware()
              # call each middleware in turn and throw away any responses that they might return
              for middleware_method in handler._request_middleware:
                  middleware_method(request)
  
          return request
  
      DEFAULT_PREVIEW_MODES = [('', _('Default'))]
  
      @property
      def preview_modes(self):
          """
          A list of (internal_name, display_name) tuples for the modes in which
          this page can be displayed for preview/moderation purposes. Ordinarily a page
          will only have one display mode, but subclasses of Page can override this -
          for example, a page containing a form might have a default view of the form,
          and a post-submission 'thankyou' page
          """
          return Page.DEFAULT_PREVIEW_MODES
  
      @property
      def default_preview_mode(self):
          return self.preview_modes[0][0]
  
      def serve_preview(self, request, mode_name):
          """
          Return an HTTP response for use in page previews. Normally this would be equivalent
          to self.serve(request), since we obviously want the preview to be indicative of how
          it looks on the live site. However, there are a couple of cases where this is not
          appropriate, and custom behaviour is required:
  
          1) The page has custom routing logic that derives some additional required
          args/kwargs to be passed to serve(). The routing mechanism is bypassed when
          previewing, so there's no way to know what args we should pass. In such a case,
          the page model needs to implement its own version of serve_preview.
  
          2) The page has several different renderings that we would like to be able to see
          when previewing - for example, a form page might have one rendering that displays
          the form, and another rendering to display a landing page when the form is posted.
          This can be done by setting a custom preview_modes list on the page model -
          Wagtail will allow the user to specify one of those modes when previewing, and
          pass the chosen mode_name to serve_preview so that the page model can decide how
          to render it appropriately. (Page models that do not specify their own preview_modes
          list will always receive an empty string as mode_name.)
  
          Any templates rendered during this process should use the 'request' object passed
          here - this ensures that request.user and other properties are set appropriately for
          the wagtail user bar to be displayed. This request will always be a GET.
          """
          request.is_preview = True
  
          return self.serve(request)
  
      def get_cached_paths(self):
          """
          This returns a list of paths to invalidate in a frontend cache
          """
          return ['/']
  
      def get_sitemap_urls(self, request=None):
          return [
              {
                  'location': self.get_full_url(request),
                  # fall back on latest_revision_created_at if last_published_at is null
                  # (for backwards compatibility from before last_published_at was added)
                  'lastmod': (self.last_published_at or self.latest_revision_created_at),
              }
          ]
  
      def get_static_site_paths(self):
          """
          This is a generator of URL paths to feed into a static site generator
          Override this if you would like to create static versions of subpages
          """
          # Yield path for this page
          yield '/'
  
          # Yield paths for child pages
          for child in self.get_children().live():
              for path in child.specific.get_static_site_paths():
                  yield '/' + child.slug + path
  
      def get_ancestors(self, inclusive=False):
          return Page.objects.ancestor_of(self, inclusive)
  
      def get_descendants(self, inclusive=False):
          return Page.objects.descendant_of(self, inclusive)
  
      def get_siblings(self, inclusive=True):
          return Page.objects.sibling_of(self, inclusive)
  
      def get_next_siblings(self, inclusive=False):
          return self.get_siblings(inclusive).filter(path__gte=self.path).order_by('path')
  
      def get_prev_siblings(self, inclusive=False):
          return self.get_siblings(inclusive).filter(path__lte=self.path).order_by('-path')
  
      def get_view_restrictions(self):
          """Return a query set of all page view restrictions that apply to this page"""
          return PageViewRestriction.objects.filter(page__in=self.get_ancestors(inclusive=True))
  
      password_required_template = getattr(settings, 'PASSWORD_REQUIRED_TEMPLATE', 'wagtailcore/password_required.html')
  
      def serve_password_required_response(self, request, form, action_url):
          """
          Serve a response indicating that the user has been denied access to view this page,
          and must supply a password.
          form = a Django form object containing the password input
              (and zero or more hidden fields that also need to be output on the template)
          action_url = URL that this form should be POSTed to
          """
          context = self.get_context(request)
          context['form'] = form
          context['action_url'] = action_url
          return TemplateResponse(request, self.password_required_template, context)
  
      class Meta:
          verbose_name = _('page')
          verbose_name_plural = _('pages')
  
  
  class Orderable(models.Model):
      sort_order = models.IntegerField(null=True, blank=True, editable=False)
      sort_order_field = 'sort_order'
  
      class Meta:
          abstract = True
          ordering = ['sort_order']
  
  
  class SubmittedRevisionsManager(models.Manager):
      def get_queryset(self):
          return super().get_queryset().filter(submitted_for_moderation=True)
  
  
  class PageRevision(models.Model):
      page = models.ForeignKey('Page', verbose_name=_('page'), related_name='revisions', on_delete=models.CASCADE)
      submitted_for_moderation = models.BooleanField(
          verbose_name=_('submitted for moderation'),
          default=False,
          db_index=True
      )
      created_at = models.DateTimeField(db_index=True, verbose_name=_('created at'))
      user = models.ForeignKey(
          settings.AUTH_USER_MODEL, verbose_name=_('user'), null=True, blank=True,
          on_delete=models.SET_NULL
      )
      content_json = models.TextField(verbose_name=_('content JSON'))
      approved_go_live_at = models.DateTimeField(verbose_name=_('approved go live at'), null=True, blank=True)
  
      objects = models.Manager()
      submitted_revisions = SubmittedRevisionsManager()
  
      def save(self, *args, **kwargs):
          # Set default value for created_at to now
          # We cannot use auto_now_add as that will override
          # any value that is set before saving
          if self.created_at is None:
              self.created_at = timezone.now()
  
          super().save(*args, **kwargs)
          if self.submitted_for_moderation:
              # ensure that all other revisions of this page have the 'submitted for moderation' flag unset
              self.page.revisions.exclude(id=self.id).update(submitted_for_moderation=False)
  
      def as_page_object(self):
          obj = self.page.specific_class.from_json(self.content_json)
  
          # Override the possibly-outdated tree parameter fields from this revision object
          # with up-to-date values
          obj.pk = self.page.pk
          obj.path = self.page.path
          obj.depth = self.page.depth
          obj.numchild = self.page.numchild
  
          # Populate url_path based on the revision's current slug and the parent page as determined
          # by path
          obj.set_url_path(self.page.get_parent())
  
          # also copy over other properties which are meaningful for the page as a whole, not a
          # specific revision of it
          obj.draft_title = self.page.draft_title
          obj.live = self.page.live
          obj.has_unpublished_changes = self.page.has_unpublished_changes
          obj.owner = self.page.owner
          obj.locked = self.page.locked
          obj.latest_revision_created_at = self.page.latest_revision_created_at
          obj.first_published_at = self.page.first_published_at
  
          return obj
  
      def approve_moderation(self):
          if self.submitted_for_moderation:
              logger.info("Page moderation approved: \"%s\" id=%d revision_id=%d", self.page.title, self.page.id, self.id)
              self.publish()
  
      def reject_moderation(self):
          if self.submitted_for_moderation:
              logger.info("Page moderation rejected: \"%s\" id=%d revision_id=%d", self.page.title, self.page.id, self.id)
              self.submitted_for_moderation = False
              self.save(update_fields=['submitted_for_moderation'])
  
      def is_latest_revision(self):
          if self.id is None:
              # special case: a revision without an ID is presumed to be newly-created and is thus
              # newer than any revision that might exist in the database
              return True
          latest_revision = PageRevision.objects.filter(page_id=self.page_id).order_by('-created_at', '-id').first()
          return (latest_revision == self)
  
      def publish(self):
          page = self.as_page_object()
          if page.go_live_at and page.go_live_at > timezone.now():
              page.has_unpublished_changes = True
              # Instead set the approved_go_live_at of this revision
              self.approved_go_live_at = page.go_live_at
              self.save()
              # And clear the the approved_go_live_at of any other revisions
              page.revisions.exclude(id=self.id).update(approved_go_live_at=None)
              # if we are updating a currently live page skip the rest
              if page.live_revision:
                  return
              # if we have a go_live in the future don't make the page live
              page.live = False
          else:
              page.live = True
              # at this point, the page has unpublished changes iff there are newer revisions than this one
              page.has_unpublished_changes = not self.is_latest_revision()
              # If page goes live clear the approved_go_live_at of all revisions
              page.revisions.update(approved_go_live_at=None)
          page.expired = False  # When a page is published it can't be expired
  
          # Set first_published_at, last_published_at and live_revision
          # if the page is being published now
          if page.live:
              now = timezone.now()
              page.last_published_at = now
              page.live_revision = self
  
              if page.first_published_at is None:
                  page.first_published_at = now
          else:
              # Unset live_revision if the page is going live in the future
              page.live_revision = None
  
          page.save()
          self.submitted_for_moderation = False
          page.revisions.update(submitted_for_moderation=False)
  
          if page.live:
              page_published.send(sender=page.specific_class, instance=page.specific, revision=self)
  
              logger.info("Page published: \"%s\" id=%d revision_id=%d", page.title, page.id, self.id)
          elif page.go_live_at:
              logger.info(
                  "Page scheduled for publish: \"%s\" id=%d revision_id=%d go_live_at=%s",
                  page.title,
                  page.id,
                  self.id,
                  page.go_live_at.isoformat()
              )
  
      def get_previous(self):
          return self.get_previous_by_created_at(page=self.page)
  
      def get_next(self):
          return self.get_next_by_created_at(page=self.page)
  
      def __str__(self):
          return '"' + str(self.page) + '" at ' + str(self.created_at)
  
      class Meta:
          verbose_name = _('page revision')
          verbose_name_plural = _('page revisions')
  
  
  PAGE_PERMISSION_TYPES = [
      ('add', _("Add"), _("Add/edit pages you own")),
      ('edit', _("Edit"), _("Edit any page")),
      ('publish', _("Publish"), _("Publish any page")),
      ('bulk_delete', _("Bulk delete"), _("Delete pages with children")),
      ('lock', _("Lock"), _("Lock/unlock any page")),
  ]
  
  PAGE_PERMISSION_TYPE_CHOICES = [
      (identifier, long_label)
      for identifier, short_label, long_label in PAGE_PERMISSION_TYPES
  ]
  
  
  class GroupPagePermission(models.Model):
      group = models.ForeignKey(Group, verbose_name=_('group'), related_name='page_permissions', on_delete=models.CASCADE)
      page = models.ForeignKey('Page', verbose_name=_('page'), related_name='group_permissions', on_delete=models.CASCADE)
      permission_type = models.CharField(
          verbose_name=_('permission type'),
          max_length=20,
          choices=PAGE_PERMISSION_TYPE_CHOICES
      )
  
      class Meta:
          unique_together = ('group', 'page', 'permission_type')
          verbose_name = _('group page permission')
          verbose_name_plural = _('group page permissions')
  
      def __str__(self):
          return "Group %d ('%s') has permission '%s' on page %d ('%s')" % (
              self.group.id, self.group,
              self.permission_type,
              self.page.id, self.page
          )
  
  
  class UserPagePermissionsProxy:
      """Helper object that encapsulates all the page permission rules that this user has
      across the page hierarchy."""
  
      def __init__(self, user):
          self.user = user
  
          if user.is_active and not user.is_superuser:
              self.permissions = GroupPagePermission.objects.filter(group__user=self.user).select_related('page')
  
      def revisions_for_moderation(self):
          """Return a queryset of page revisions awaiting moderation that this user has publish permission on"""
  
          # Deal with the trivial cases first...
          if not self.user.is_active:
              return PageRevision.objects.none()
          if self.user.is_superuser:
              return PageRevision.submitted_revisions.all()
  
          # get the list of pages for which they have direct publish permission
          # (i.e. they can publish any page within this subtree)
          publishable_pages = [perm.page for perm in self.permissions if perm.permission_type == 'publish']
          if not publishable_pages:
              return PageRevision.objects.none()
  
          # compile a filter expression to apply to the PageRevision.submitted_revisions manager:
          # return only those pages whose paths start with one of the publishable_pages paths
          only_my_sections = Q(page__path__startswith=publishable_pages[0].path)
          for page in publishable_pages[1:]:
              only_my_sections = only_my_sections | Q(page__path__startswith=page.path)
  
          # return the filtered queryset
          return PageRevision.submitted_revisions.filter(only_my_sections)
  
      def for_page(self, page):
          """Return a PagePermissionTester object that can be used to query whether this user has
          permission to perform specific tasks on the given page"""
          return PagePermissionTester(self, page)
  
      def editable_pages(self):
          """Return a queryset of the pages that this user has permission to edit"""
          # Deal with the trivial cases first...
          if not self.user.is_active:
              return Page.objects.none()
          if self.user.is_superuser:
              return Page.objects.all()
  
          editable_pages = Page.objects.none()
  
          for perm in self.permissions.filter(permission_type='add'):
              # user has edit permission on any subpage of perm.page
              # (including perm.page itself) that is owned by them
              editable_pages |= Page.objects.descendant_of(perm.page, inclusive=True).filter(owner=self.user)
  
          for perm in self.permissions.filter(permission_type='edit'):
              # user has edit permission on any subpage of perm.page
              # (including perm.page itself) regardless of owner
              editable_pages |= Page.objects.descendant_of(perm.page, inclusive=True)
  
          return editable_pages
  
      def can_edit_pages(self):
          """Return True if the user has permission to edit any pages"""
          return self.editable_pages().exists()
  
      def publishable_pages(self):
          """Return a queryset of the pages that this user has permission to publish"""
          # Deal with the trivial cases first...
          if not self.user.is_active:
              return Page.objects.none()
          if self.user.is_superuser:
              return Page.objects.all()
  
          publishable_pages = Page.objects.none()
  
          for perm in self.permissions.filter(permission_type='publish'):
              # user has publish permission on any subpage of perm.page
              # (including perm.page itself)
              publishable_pages |= Page.objects.descendant_of(perm.page, inclusive=True)
  
          return publishable_pages
  
      def can_publish_pages(self):
          """Return True if the user has permission to publish any pages"""
          return self.publishable_pages().exists()
  
  
  class PagePermissionTester:
      def __init__(self, user_perms, page):
          self.user = user_perms.user
          self.user_perms = user_perms
          self.page = page
          self.page_is_root = page.depth == 1  # Equivalent to page.is_root()
  
          if self.user.is_active and not self.user.is_superuser:
              self.permissions = set(
                  perm.permission_type for perm in user_perms.permissions
                  if self.page.path.startswith(perm.page.path)
              )
  
      def can_add_subpage(self):
          if not self.user.is_active:
              return False
          specific_class = self.page.specific_class
          if specific_class is None or not specific_class.creatable_subpage_models():
              return False
          return self.user.is_superuser or ('add' in self.permissions)
  
      def can_edit(self):
          if not self.user.is_active:
              return False
          if self.page_is_root:  # root node is not a page and can never be edited, even by superusers
              return False
          return (
              self.user.is_superuser or
              ('edit' in self.permissions) or
              ('add' in self.permissions and self.page.owner_id == self.user.pk)
          )
  
      def can_delete(self):
          if not self.user.is_active:
              return False
          if self.page_is_root:  # root node is not a page and can never be deleted, even by superusers
              return False
  
          if self.user.is_superuser:
              # superusers require no further checks
              return True
  
          # if the user does not have bulk_delete permission, they may only delete leaf pages
          if 'bulk_delete' not in self.permissions and not self.page.is_leaf():
              return False
  
          if 'edit' in self.permissions:
              # if the user does not have publish permission, we also need to confirm that there
              # are no published pages here
              if 'publish' not in self.permissions:
                  pages_to_delete = self.page.get_descendants(inclusive=True)
                  if pages_to_delete.live().exists():
                      return False
  
              return True
  
          elif 'add' in self.permissions:
              pages_to_delete = self.page.get_descendants(inclusive=True)
              if 'publish' in self.permissions:
                  # we don't care about live state, but all pages must be owned by this user
                  # (i.e. eliminating pages owned by this user must give us the empty set)
                  return not pages_to_delete.exclude(owner=self.user).exists()
              else:
                  # all pages must be owned by this user and non-live
                  # (i.e. eliminating non-live pages owned by this user must give us the empty set)
                  return not pages_to_delete.exclude(live=False, owner=self.user).exists()
  
          else:
              return False
  
      def can_unpublish(self):
          if not self.user.is_active:
              return False
          if (not self.page.live) or self.page_is_root:
              return False
          if self.page.locked:
              return False
  
          return self.user.is_superuser or ('publish' in self.permissions)
  
      def can_publish(self):
          if not self.user.is_active:
              return False
          if self.page_is_root:
              return False
  
          return self.user.is_superuser or ('publish' in self.permissions)
  
      def can_set_view_restrictions(self):
          return self.can_publish()
  
      def can_unschedule(self):
          return self.can_publish()
  
      def can_lock(self):
          return self.user.is_superuser or ('lock' in self.permissions)
  
      def can_publish_subpage(self):
          """
          Niggly special case for creating and publishing a page in one go.
          Differs from can_publish in that we want to be able to publish subpages of root, but not
          to be able to publish root itself. (Also, can_publish_subpage returns false if the page
          does not allow subpages at all.)
          """
          if not self.user.is_active:
              return False
          specific_class = self.page.specific_class
          if specific_class is None or not specific_class.creatable_subpage_models():
              return False
  
          return self.user.is_superuser or ('publish' in self.permissions)
  
      def can_reorder_children(self):
          """
          Keep reorder permissions the same as publishing, since it immediately affects published pages
          (and the use-cases for a non-admin needing to do it are fairly obscure...)
          """
          return self.can_publish_subpage()
  
      def can_move(self):
          """
          Moving a page should be logically equivalent to deleting and re-adding it (and all its children).
          As such, the permission test for 'can this be moved at all?' should be the same as for deletion.
          (Further constraints will then apply on where it can be moved *to*.)
          """
          return self.can_delete()
  
      def can_copy(self):
          return not self.page_is_root
  
      def can_move_to(self, destination):
          # reject the logically impossible cases first
          if self.page == destination or destination.is_descendant_of(self.page):
              return False
  
          # reject moves that are forbidden by subpage_types / parent_page_types rules
          # (these rules apply to superusers too)
          if not self.page.specific.can_move_to(destination):
              return False
  
          # shortcut the trivial 'everything' / 'nothing' permissions
          if not self.user.is_active:
              return False
          if self.user.is_superuser:
              return True
  
          # check that the page can be moved at all
          if not self.can_move():
              return False
  
          # Inspect permissions on the destination
          destination_perms = self.user_perms.for_page(destination)
  
          # we always need at least add permission in the target
          if 'add' not in destination_perms.permissions:
              return False
  
          if self.page.live or self.page.get_descendants().filter(live=True).exists():
              # moving this page will entail publishing within the destination section
              return ('publish' in destination_perms.permissions)
          else:
              # no publishing required, so the already-tested 'add' permission is sufficient
              return True
  
      def can_copy_to(self, destination, recursive=False):
          # reject the logically impossible cases first
          # recursive can't copy to the same tree otherwise it will be on infinite loop
          if recursive and (self.page == destination or destination.is_descendant_of(self.page)):
              return False
  
          # shortcut the trivial 'everything' / 'nothing' permissions
          if not self.user.is_active:
              return False
          if self.user.is_superuser:
              return True
  
          # Inspect permissions on the destination
          destination_perms = self.user_perms.for_page(destination)
  
          if not destination.specific_class.creatable_subpage_models():
              return False
  
          # we always need at least add permission in the target
          if 'add' not in destination_perms.permissions:
              return False
  
          return True
  
      def can_view_revisions(self):
          return not self.page_is_root
  
  
  class BaseViewRestriction(models.Model):
      NONE = 'none'
      PASSWORD = 'password'
      GROUPS = 'groups'
      LOGIN = 'login'
  
      RESTRICTION_CHOICES = (
          (NONE, _("Public")),
          (LOGIN, _("Private, accessible to logged-in users")),
          (PASSWORD, _("Private, accessible with the following password")),
          (GROUPS, _("Private, accessible to users in specific groups")),
      )
  
      restriction_type = models.CharField(
          max_length=20, choices=RESTRICTION_CHOICES)
      password = models.CharField(verbose_name=_('password'), max_length=255, blank=True)
      groups = models.ManyToManyField(Group, verbose_name=_('groups'), blank=True)
  
      def accept_request(self, request):
          if self.restriction_type == BaseViewRestriction.PASSWORD:
              passed_restrictions = request.session.get(self.passed_view_restrictions_session_key, [])
              if self.id not in passed_restrictions:
                  return False
  
          elif self.restriction_type == BaseViewRestriction.LOGIN:
              if not request.user.is_authenticated:
                  return False
  
          elif self.restriction_type == BaseViewRestriction.GROUPS:
              if not request.user.is_superuser:
                  current_user_groups = request.user.groups.all()
  
                  if not any(group in current_user_groups for group in self.groups.all()):
                      return False
  
          return True
  
      def mark_as_passed(self, request):
          """
          Update the session data in the request to mark the user as having passed this
          view restriction
          """
          has_existing_session = (settings.SESSION_COOKIE_NAME in request.COOKIES)
          passed_restrictions = request.session.setdefault(self.passed_view_restrictions_session_key, [])
          if self.id not in passed_restrictions:
              passed_restrictions.append(self.id)
              request.session[self.passed_view_restrictions_session_key] = passed_restrictions
          if not has_existing_session:
              # if this is a session we've created, set it to expire at the end
              # of the browser session
              request.session.set_expiry(0)
  
      class Meta:
          abstract = True
          verbose_name = _('view restriction')
          verbose_name_plural = _('view restrictions')
  
  
  class PageViewRestriction(BaseViewRestriction):
      page = models.ForeignKey(
          'Page', verbose_name=_('page'), related_name='view_restrictions', on_delete=models.CASCADE
      )
  
      passed_view_restrictions_session_key = 'passed_page_view_restrictions'
  
      class Meta:
          verbose_name = _('page view restriction')
          verbose_name_plural = _('page view restrictions')
  
  
  class BaseCollectionManager(models.Manager):
      def get_queryset(self):
          return TreeQuerySet(self.model).order_by('path')
  
  
  CollectionManager = BaseCollectionManager.from_queryset(TreeQuerySet)
  
  
  class CollectionViewRestriction(BaseViewRestriction):
      collection = models.ForeignKey(
          'Collection',
          verbose_name=_('collection'),
          related_name='view_restrictions',
          on_delete=models.CASCADE
      )
  
      passed_view_restrictions_session_key = 'passed_collection_view_restrictions'
  
      class Meta:
          verbose_name = _('collection view restriction')
          verbose_name_plural = _('collection view restrictions')
  
  
  class Collection(MP_Node):
      """
      A location in which resources such as images and documents can be grouped
      """
      name = models.CharField(max_length=255, verbose_name=_('name'))
  
      objects = CollectionManager()
  
      def __str__(self):
          return self.name
  
      def get_ancestors(self, inclusive=False):
          return Collection.objects.ancestor_of(self, inclusive)
  
      def get_descendants(self, inclusive=False):
          return Collection.objects.descendant_of(self, inclusive)
  
      def get_siblings(self, inclusive=True):
          return Collection.objects.sibling_of(self, inclusive)
  
      def get_next_siblings(self, inclusive=False):
          return self.get_siblings(inclusive).filter(path__gte=self.path).order_by('path')
  
      def get_prev_siblings(self, inclusive=False):
          return self.get_siblings(inclusive).filter(path__lte=self.path).order_by('-path')
  
      def get_view_restrictions(self):
          """Return a query set of all collection view restrictions that apply to this collection"""
          return CollectionViewRestriction.objects.filter(collection__in=self.get_ancestors(inclusive=True))
  
      class Meta:
          verbose_name = _('collection')
          verbose_name_plural = _('collections')
  
  
  def get_root_collection_id():
      return Collection.get_first_root_node().id
  
  
  class CollectionMember(models.Model):
      """
      Base class for models that are categorised into collections
      """
      collection = models.ForeignKey(
          Collection,
          default=get_root_collection_id,
          verbose_name=_('collection'),
          related_name='+',
          on_delete=models.CASCADE
      )
  
      search_fields = [
          index.FilterField('collection'),
      ]
  
      class Meta:
          abstract = True
  
  
  class GroupCollectionPermission(models.Model):
      """
      A rule indicating that a group has permission for some action (e.g. "create document")
      within a specified collection.
      """
      group = models.ForeignKey(
          Group,
          verbose_name=_('group'),
          related_name='collection_permissions',
          on_delete=models.CASCADE
      )
      collection = models.ForeignKey(
          Collection,
          verbose_name=_('collection'),
          related_name='group_permissions',
          on_delete=models.CASCADE
      )
      permission = models.ForeignKey(
          Permission,
          verbose_name=_('permission'),
          on_delete=models.CASCADE
      )
  
      def __str__(self):
          return "Group %d ('%s') has permission '%s' on collection %d ('%s')" % (
              self.group.id, self.group,
              self.permission,
              self.collection.id, self.collection
          )
  
      class Meta:
          unique_together = ('group', 'collection', 'permission')
          verbose_name = _('group collection permission')
          verbose_name_plural = _('group collection permissions')
  