text: """
  A custom manager for working with trees of objects.
  """
  import contextlib
  import functools
  from itertools import groupby
  
  from django.db import connections, models, router
  from django.db.models import (
      F,
      IntegerField,
      ManyToManyField,
      Max,
      OuterRef,
      Q,
      Subquery,
  )
  from django.utils.translation import gettext as _
  
  from mptt.compat import cached_field_value
  from mptt.exceptions import CantDisableUpdates, InvalidMove
  from mptt.querysets import TreeQuerySet
  from mptt.signals import node_moved
  from mptt.utils import _get_tree_model
  
  
  __all__ = ("TreeManager",)
  
  
  class SQCount(Subquery):
      template = "(SELECT count(*) FROM (%(subquery)s) _count)"
      output_field = IntegerField()
  
  
  def delegate_manager(method):
      """
      Delegate method calls to base manager, if exists.
      """
  
      @functools.wraps(method)
      def wrapped(self, *args, **kwargs):
          if self._base_manager:
              return getattr(self._base_manager, method.__name__)(*args, **kwargs)
          return method(self, *args, **kwargs)
  
      return wrapped
  
  
  class TreeManager(models.Manager.from_queryset(TreeQuerySet)):
  
      """
      A manager for working with trees of objects.
      """
  
      def contribute_to_class(self, model, name):
          super().contribute_to_class(model, name)
  
          if not model._meta.abstract:
              self.tree_model = _get_tree_model(model)
  
              self._base_manager = None
              if self.tree_model and self.tree_model is not model:
                  # _base_manager is the treemanager on tree_model
                  self._base_manager = self.tree_model._tree_manager
  
      def get_queryset(self, *args, **kwargs):
          """
          Ensures that this manager always returns nodes in tree order.
          """
          return (
              super()
              .get_queryset(*args, **kwargs)
              .order_by(self.tree_id_attr, self.left_attr)
          )
  
      def _get_queryset_relatives(self, queryset, direction, include_self):
          """
          Returns a queryset containing either the descendants
          ``direction == desc`` or the ancestors ``direction == asc`` of a given
          queryset.
  
          This function is not meant to be called directly, although there is no
          harm in doing so.
  
          Instead, it should be used via ``get_queryset_descendants()`` and/or
          ``get_queryset_ancestors()``.
  
          This function works by grouping contiguous siblings and using them to create
          a range that selects all nodes between the range, instead of querying for each
          node individually. Three variables are required when querying for ancestors or
          descendants: tree_id_attr, left_attr, right_attr. If we weren't using ranges
          and our queryset contained 100 results, the resulting SQL query would contain
          300 variables. However, when using ranges, if the same queryset contained 10
          sets of contiguous siblings, then the resulting SQL query should only contain
          30 variables.
  
          The attributes used to create the range are completely
          dependent upon whether you are ascending or descending the tree.
  
          * Ascending (ancestor nodes): select all nodes whose right_attr is greater
            than (or equal to, if include_self = True) the smallest right_attr within
            the set of contiguous siblings, and whose left_attr is less than (or equal
            to) the largest left_attr within the set of contiguous siblings.
  
          * Descending (descendant nodes): select all nodes whose left_attr is greater
            than (or equal to, if include_self = True) the smallest left_attr within
            the set of contiguous siblings, and whose right_attr is less than (or equal
            to) the largest right_attr within the set of contiguous siblings.
  
          The result is the more contiguous siblings in the original queryset, the fewer
          SQL variables will be required to execute the query.
          """
          assert self.model is queryset.model
  
          opts = queryset.model._mptt_meta
  
          filters = Q()
  
          e = "e" if include_self else ""
          max_op = "lt" + e
          min_op = "gt" + e
          if direction == "asc":
              max_attr = opts.left_attr
              min_attr = opts.right_attr
          elif direction == "desc":
              max_attr = opts.right_attr
              min_attr = opts.left_attr
  
          tree_key = opts.tree_id_attr
          min_key = "%s__%s" % (min_attr, min_op)
          max_key = "%s__%s" % (max_attr, max_op)
  
          q = queryset.order_by(opts.tree_id_attr, opts.parent_attr, opts.left_attr).only(
              opts.tree_id_attr,
              opts.left_attr,
              opts.right_attr,
              min_attr,
              max_attr,
              opts.parent_attr,
              # These fields are used by MPTTModel.update_mptt_cached_fields()
              *[f.lstrip("-") for f in opts.order_insertion_by]
          )
  
          if not q:
              return self.none()
  
          for group in groupby(
              q,
              key=lambda n: (
                  getattr(n, opts.tree_id_attr),
                  getattr(n, opts.parent_attr + "_id"),
              ),
          ):
              next_lft = None
              for node in list(group[1]):
                  tree, lft, rght, min_val, max_val = (
                      getattr(node, opts.tree_id_attr),
                      getattr(node, opts.left_attr),
                      getattr(node, opts.right_attr),
                      getattr(node, min_attr),
                      getattr(node, max_attr),
                  )
                  if next_lft is None:
                      next_lft = rght + 1
                      min_max = {"min": min_val, "max": max_val}
                  elif lft == next_lft:
                      if min_val < min_max["min"]:
                          min_max["min"] = min_val
                      if max_val > min_max["max"]:
                          min_max["max"] = max_val
                      next_lft = rght + 1
                  elif lft != next_lft:
                      filters |= Q(
                          **{
                              tree_key: tree,
                              min_key: min_max["min"],
                              max_key: min_max["max"],
                          }
                      )
                      min_max = {"min": min_val, "max": max_val}
                      next_lft = rght + 1
              filters |= Q(
                  **{
                      tree_key: tree,
                      min_key: min_max["min"],
                      max_key: min_max["max"],
                  }
              )
  
          return self.filter(filters)
  
      def get_queryset_descendants(self, queryset, include_self=False):
          """
          Returns a queryset containing the descendants of all nodes in the
          given queryset.
  
          If ``include_self=True``, nodes in ``queryset`` will also
          be included in the result.
          """
          return self._get_queryset_relatives(queryset, "desc", include_self)
  
      def get_queryset_ancestors(self, queryset, include_self=False):
          """
          Returns a queryset containing the ancestors
          of all nodes in the given queryset.
  
          If ``include_self=True``, nodes in ``queryset`` will also
          be included in the result.
          """
          return self._get_queryset_relatives(queryset, "asc", include_self)
  
      @contextlib.contextmanager
      def disable_mptt_updates(self):
          """
          Context manager. Disables mptt updates.
  
          NOTE that this context manager causes inconsistencies! MPTT model
          methods are not guaranteed to return the correct results.
  
          When to use this method:
              If used correctly, this method can be used to speed up bulk
              updates.
  
              This doesn't do anything clever. It *will* mess up your tree.  You
              should follow this method with a call to ``TreeManager.rebuild()``
              to ensure your tree stays sane, and you should wrap both calls in a
              transaction.
  
              This is best for updates that span a large part of the table.  If
              you are doing localised changes (one tree, or a few trees) consider
              using ``delay_mptt_updates``.
  
              If you are making only minor changes to your tree, just let the
              updates happen.
  
          Transactions:
              This doesn't enforce any transactional behavior.  You should wrap
              this in a transaction to ensure database consistency.
  
          If updates are already disabled on the model, this is a noop.
  
          Usage::
  
              with transaction.atomic():
                  with MyNode.objects.disable_mptt_updates():
                      ## bulk updates.
                  MyNode.objects.rebuild()
          """
          # Error cases:
          if self.model._meta.abstract:
              #  an abstract model. Design decision needed - do we disable
              #  updates for all concrete models that derive from this model?  I
              #  vote no - that's a bit implicit and it's a weird use-case
              #  anyway.  Open to further discussion :)
              raise CantDisableUpdates(
                  "You can't disable/delay mptt updates on %s,"
                  " it's an abstract model" % self.model.__name__
              )
          elif self.model._meta.proxy:
              #  a proxy model. disabling updates would implicitly affect other
              #  models using the db table. Caller should call this on the
              #  manager for the concrete model instead, to make the behavior
              #  explicit.
              raise CantDisableUpdates(
                  "You can't disable/delay mptt updates on %s, it's a proxy"
                  " model. Call the concrete model instead." % self.model.__name__
              )
          elif self.tree_model is not self.model:
              #  a multiple-inheritance child of an MPTTModel.  Disabling
              #  updates may affect instances of other models in the tree.
              raise CantDisableUpdates(
                  "You can't disable/delay mptt updates on %s, it doesn't"
                  " contain the mptt fields." % self.model.__name__
              )
  
          if not self.model._mptt_updates_enabled:
              # already disabled, noop.
              yield
          else:
              self.model._set_mptt_updates_enabled(False)
              try:
                  yield
              finally:
                  self.model._set_mptt_updates_enabled(True)
  
      @contextlib.contextmanager
      def delay_mptt_updates(self):
          """
          Context manager. Delays mptt updates until the end of a block of bulk
          processing.
  
          NOTE that this context manager causes inconsistencies! MPTT model
          methods are not guaranteed to return the correct results until the end
          of the context block.
  
          When to use this method:
              If used correctly, this method can be used to speed up bulk
              updates.  This is best for updates in a localised area of the db
              table, especially if all the updates happen in a single tree and
              the rest of the forest is left untouched.  No subsequent rebuild is
              necessary.
  
              ``delay_mptt_updates`` does a partial rebuild of the modified trees
              (not the whole table).  If used indiscriminately, this can actually
              be much slower than just letting the updates occur when they're
              required.
  
              The worst case occurs when every tree in the table is modified just
              once.  That results in a full rebuild of the table, which can be
              *very* slow.
  
              If your updates will modify most of the trees in the table (not a
              small number of trees), you should consider using
              ``TreeManager.disable_mptt_updates``, as it does much fewer
              queries.
  
          Transactions:
              This doesn't enforce any transactional behavior.  You should wrap
              this in a transaction to ensure database consistency.
  
          Exceptions:
              If an exception occurs before the processing of the block, delayed
              updates will not be applied.
  
          Usage::
  
              with transaction.atomic():
                  with MyNode.objects.delay_mptt_updates():
                      ## bulk updates.
          """
          with self.disable_mptt_updates():
              if self.model._mptt_is_tracking:
                  # already tracking, noop.
                  yield
              else:
                  self.model._mptt_start_tracking()
                  try:
                      yield
                  except Exception:
                      # stop tracking, but discard results
                      self.model._mptt_stop_tracking()
                      raise
                  results = self.model._mptt_stop_tracking()
                  partial_rebuild = self.partial_rebuild
                  for tree_id in results:
                      partial_rebuild(tree_id)
  
      @property
      def parent_attr(self):
          return self.model._mptt_meta.parent_attr
  
      @property
      def left_attr(self):
          return self.model._mptt_meta.left_attr
  
      @property
      def right_attr(self):
          return self.model._mptt_meta.right_attr
  
      @property
      def tree_id_attr(self):
          return self.model._mptt_meta.tree_id_attr
  
      @property
      def level_attr(self):
          return self.model._mptt_meta.level_attr
  
      def _translate_lookups(self, **lookups):
          new_lookups = {}
          join_parts = "__".join
          for k, v in lookups.items():
              parts = k.split("__")
              new_parts = []
              new_parts__append = new_parts.append
              for part in parts:
                  new_parts__append(getattr(self, part + "_attr", part))
              new_lookups[join_parts(new_parts)] = v
          return new_lookups
  
      @delegate_manager
      def _mptt_filter(self, qs=None, **filters):
          """
          Like ``self.filter()``, but translates name-agnostic filters for MPTT
          fields.
          """
          if qs is None:
              qs = self
          return qs.filter(**self._translate_lookups(**filters))
  
      @delegate_manager
      def _mptt_update(self, qs=None, **items):
          """
          Like ``self.update()``, but translates name-agnostic MPTT fields.
          """
          if qs is None:
              qs = self
          return qs.update(**self._translate_lookups(**items))
  
      def _get_connection(self, **hints):
          return connections[router.db_for_write(self.model, **hints)]
  
      def add_related_count(
          self,
          queryset,
          rel_model,
          rel_field,
          count_attr,
          cumulative=False,
          extra_filters={},
      ):
          """
          Adds a related item count to a given ``QuerySet`` using its
          ``extra`` method, for a ``Model`` class which has a relation to
          this ``Manager``'s ``Model`` class.
  
          Arguments:
  
          ``rel_model``
             A ``Model`` class which has a relation to this `Manager``'s
             ``Model`` class.
  
          ``rel_field``
             The name of the field in ``rel_model`` which holds the
             relation.
  
          ``count_attr``
             The name of an attribute which should be added to each item in
             this ``QuerySet``, containing a count of how many instances
             of ``rel_model`` are related to it through ``rel_field``.
  
          ``cumulative``
             If ``True``, the count will be for each item and all of its
             descendants, otherwise it will be for each item itself.
  
          ``extra_filters``
             Dict with aditional parameters filtering the related queryset.
          """
          if cumulative:
              subquery_filters = {
                  rel_field + "__tree_id": OuterRef(self.tree_id_attr),
                  rel_field + "__lft__gte": OuterRef(self.left_attr),
                  rel_field + "__lft__lte": OuterRef(self.right_attr),
              }
          else:
              current_rel_model = rel_model
              for rel_field_part in rel_field.split("__"):
                  current_mptt_field = current_rel_model._meta.get_field(rel_field_part)
                  current_rel_model = current_mptt_field.related_model
              mptt_field = current_mptt_field
  
              if isinstance(mptt_field, ManyToManyField):
                  field_name = "pk"
              else:
                  field_name = mptt_field.remote_field.field_name
  
              subquery_filters = {
                  rel_field: OuterRef(field_name),
              }
          subquery = rel_model.objects.filter(**subquery_filters, **extra_filters).values(
              "pk"
          )
          return queryset.annotate(**{count_attr: SQCount(subquery)})
  
      @delegate_manager
      def insert_node(
          self,
          node,
          target,
          position="last-child",
          save=False,
          allow_existing_pk=False,
          refresh_target=True,
      ):
          """
          Sets up the tree state for ``node`` (which has not yet been
          inserted into in the database) so it will be positioned relative
          to a given ``target`` node as specified by ``position`` (when
          appropriate) it is inserted, with any necessary space already
          having been made for it.
  
          A ``target`` of ``None`` indicates that ``node`` should be
          the last root node.
  
          If ``save`` is ``True``, ``node``'s ``save()`` method will be
          called before it is returned.
  
          NOTE: This is a low-level method; it does NOT respect
          ``MPTTMeta.order_insertion_by``.  In most cases you should just
          set the node's parent and let mptt call this during save.
          """
  
          if node.pk and not allow_existing_pk and self.filter(pk=node.pk).exists():
              raise ValueError(_("Cannot insert a node which has already been saved."))
  
          if target is None:
              tree_id = self._get_next_tree_id()
              setattr(node, self.left_attr, 1)
              setattr(node, self.right_attr, 2)
              setattr(node, self.level_attr, 0)
              setattr(node, self.tree_id_attr, tree_id)
              setattr(node, self.parent_attr, None)
          elif target.is_root_node() and position in ["left", "right"]:
              if refresh_target:
                  # Ensure mptt values on target are not stale.
                  target._mptt_refresh()
  
              target_tree_id = getattr(target, self.tree_id_attr)
              if position == "left":
                  tree_id = target_tree_id
                  space_target = target_tree_id - 1
              else:
                  tree_id = target_tree_id + 1
                  space_target = target_tree_id
              self._create_tree_space(space_target)
  
              setattr(node, self.left_attr, 1)
              setattr(node, self.right_attr, 2)
              setattr(node, self.level_attr, 0)
              setattr(node, self.tree_id_attr, tree_id)
              setattr(node, self.parent_attr, None)
          else:
              setattr(node, self.left_attr, 0)
              setattr(node, self.level_attr, 0)
  
              if refresh_target:
                  # Ensure mptt values on target are not stale.
                  target._mptt_refresh()
  
              (
                  space_target,
                  level,
                  left,
                  parent,
                  right_shift,
              ) = self._calculate_inter_tree_move_values(node, target, position)
  
              tree_id = getattr(target, self.tree_id_attr)
              self._create_space(2, space_target, tree_id)
  
              setattr(node, self.left_attr, -left)
              setattr(node, self.right_attr, -left + 1)
              setattr(node, self.level_attr, -level)
              setattr(node, self.tree_id_attr, tree_id)
              setattr(node, self.parent_attr, parent)
  
              if parent:
                  self._post_insert_update_cached_parent_right(parent, right_shift)
  
          if save:
              node.save()
          return node
  
      @delegate_manager
      def _move_node(
          self, node, target, position="last-child", save=True, refresh_target=True
      ):
          if self.tree_model._mptt_is_tracking:
              # delegate to insert_node and clean up the gaps later.
              return self.insert_node(
                  node,
                  target,
                  position=position,
                  save=save,
                  allow_existing_pk=True,
                  refresh_target=refresh_target,
              )
          else:
              if target is None:
                  if node.is_child_node():
                      self._make_child_root_node(node)
              elif target.is_root_node() and position in ("left", "right"):
                  self._make_sibling_of_root_node(node, target, position)
              else:
                  if node.is_root_node():
                      self._move_root_node(node, target, position)
                  else:
                      self._move_child_node(node, target, position)
  
      def move_node(self, node, target, position="last-child"):
          """
          Moves ``node`` relative to a given ``target`` node as specified
          by ``position`` (when appropriate), by examining both nodes and
          calling the appropriate method to perform the move.
  
          A ``target`` of ``None`` indicates that ``node`` should be
          turned into a root node.
  
          Valid values for ``position`` are ``'first-child'``,
          ``'last-child'``, ``'left'`` or ``'right'``.
  
          ``node`` will be modified to reflect its new tree state in the
          database.
  
          This method explicitly checks for ``node`` being made a sibling
          of a root node, as this is a special case due to our use of tree
          ids to order root nodes.
  
          NOTE: This is a low-level method; it does NOT respect
          ``MPTTMeta.order_insertion_by``.  In most cases you should just
          move the node yourself by setting node.parent.
          """
          self._move_node(node, target, position=position)
          node.save()
          node_moved.send(
              sender=node.__class__, instance=node, target=target, position=position
          )
  
      @delegate_manager
      def root_node(self, tree_id):
          """
          Returns the root node of the tree with the given id.
          """
          return self._mptt_filter(tree_id=tree_id, parent=None).get()
  
      @delegate_manager
      def root_nodes(self):
          """
          Creates a ``QuerySet`` containing root nodes.
          """
          return self._mptt_filter(parent=None)
  
      @delegate_manager
      def rebuild(self):
          """
          Rebuilds all trees in the database table using `parent` link.
          """
          opts = self.model._mptt_meta
  
          qs = self._mptt_filter(parent=None)
          if opts.order_insertion_by:
              qs = qs.order_by(*opts.order_insertion_by)
          pks = qs.values_list("pk", flat=True)
  
          rebuild_helper = self._rebuild_helper
          idx = 0
          for pk in pks:
              idx += 1
              rebuild_helper(pk, 1, idx)
  
      rebuild.alters_data = True
  
      @delegate_manager
      def partial_rebuild(self, tree_id):
          """
          Partially rebuilds a tree i.e. It rebuilds only the tree with given
          ``tree_id`` in database table using ``parent`` link.
          """
          opts = self.model._mptt_meta
  
          qs = self._mptt_filter(parent=None, tree_id=tree_id)
          if opts.order_insertion_by:
              qs = qs.order_by(*opts.order_insertion_by)
          pks = qs.values_list("pk", flat=True)
          if not pks:
              return
          if len(pks) > 1:
              raise RuntimeError(
                  "More than one root node with tree_id %d. That's invalid,"
                  " do a full rebuild." % tree_id
              )
  
          self._rebuild_helper(pks[0], 1, tree_id)
  
      @delegate_manager
      def build_tree_nodes(self, data, target=None, position="last-child"):
          """
          Load a tree from a nested dictionary for bulk insert, returning an
          array of records. Use to efficiently insert many nodes within a tree
          without an expensive `rebuild`.
  
          ::
  
              records = MyModel.objects.build_tree_nodes({
                  'id': 7,
                  'name': 'parent',
                  'children': [
                      {
                          'id': 8,
                          'parent_id': 7,
                          'name': 'child',
                          'children': [
                              {
                                  'id': 9,
                                  'parent_id': 8,
                                  'name': 'grandchild',
                              }
                          ]
                      }
                  ]
              })
              MyModel.objects.bulk_create(records)
  
          """
          opts = self.model._mptt_meta
          if target:
              tree_id = target.tree_id
              if position in ("left", "right"):
                  level = getattr(target, opts.level_attr)
                  if position == "left":
                      cursor = getattr(target, opts.left_attr)
                  else:
                      cursor = getattr(target, opts.right_attr) + 1
              else:
                  level = getattr(target, opts.level_attr) + 1
                  if position == "first-child":
                      cursor = getattr(target, opts.left_attr) + 1
                  else:
                      cursor = getattr(target, opts.right_attr)
          else:
              tree_id = self._get_next_tree_id()
              cursor = 1
              level = 0
  
          stack = []
  
          def treeify(data, cursor=1, level=0):
              data = dict(data)
              children = data.pop("children", [])
              node = self.model(**data)
              stack.append(node)
              setattr(node, opts.tree_id_attr, tree_id)
              setattr(node, opts.level_attr, level)
              setattr(node, opts.left_attr, cursor)
              for child in children:
                  cursor = treeify(child, cursor=cursor + 1, level=level + 1)
              cursor += 1
              setattr(node, opts.right_attr, cursor)
              return cursor
  
          treeify(data, cursor=cursor, level=level)
  
          if target:
              self._create_space(2 * len(stack), cursor - 1, tree_id)
  
          return stack
  
      def _rebuild_helper(self, pk, left, tree_id, level=0):
          opts = self.model._mptt_meta
          right = left + 1
  
          qs = self._mptt_filter(parent__pk=pk)
          if opts.order_insertion_by:
              qs = qs.order_by(*opts.order_insertion_by)
          child_ids = qs.values_list("pk", flat=True)
  
          rebuild_helper = self._rebuild_helper
          for child_id in child_ids:
              right = rebuild_helper(child_id, right, tree_id, level + 1)
  
          qs = self.model._default_manager.db_manager(self.db).filter(pk=pk)
          self._mptt_update(qs, left=left, right=right, level=level, tree_id=tree_id)
  
          return right + 1
  
      def _post_insert_update_cached_parent_right(self, instance, right_shift, seen=None):
          setattr(
              instance, self.right_attr, getattr(instance, self.right_attr) + right_shift
          )
          parent = cached_field_value(instance, self.parent_attr)
          if parent:
              if not seen:
                  seen = set()
              seen.add(instance)
              if parent in seen:
                  # detect infinite recursion and throw an error
                  raise InvalidMove
              self._post_insert_update_cached_parent_right(parent, right_shift, seen=seen)
  
      def _calculate_inter_tree_move_values(self, node, target, position):
          """
          Calculates values required when moving ``node`` relative to
          ``target`` as specified by ``position``.
          """
          left = getattr(node, self.left_attr)
          level = getattr(node, self.level_attr)
          target_left = getattr(target, self.left_attr)
          target_right = getattr(target, self.right_attr)
          target_level = getattr(target, self.level_attr)
  
          if position == "last-child" or position == "first-child":
              if position == "last-child":
                  space_target = target_right - 1
              else:
                  space_target = target_left
              level_change = level - target_level - 1
              parent = target
          elif position == "left" or position == "right":
              if position == "left":
                  space_target = target_left - 1
              else:
                  space_target = target_right
              level_change = level - target_level
              parent = getattr(target, self.parent_attr)
          else:
              raise ValueError(_("An invalid position was given: %s.") % position)
  
          left_right_change = left - space_target - 1
  
          right_shift = 0
          if parent:
              right_shift = 2 * (node.get_descendant_count() + 1)
  
          return space_target, level_change, left_right_change, parent, right_shift
  
      def _close_gap(self, size, target, tree_id):
          """
          Closes a gap of a certain ``size`` after the given ``target``
          point in the tree identified by ``tree_id``.
          """
          self._manage_space(-size, target, tree_id)
  
      def _create_space(self, size, target, tree_id):
          """
          Creates a space of a certain ``size`` after the given ``target``
          point in the tree identified by ``tree_id``.
          """
          self._manage_space(size, target, tree_id)
  
      def _create_tree_space(self, target_tree_id, num_trees=1):
          """
          Creates space for a new tree by incrementing all tree ids
          greater than ``target_tree_id``.
          """
          qs = self._mptt_filter(tree_id__gt=target_tree_id)
          self._mptt_update(qs, tree_id=F(self.tree_id_attr) + num_trees)
          self.tree_model._mptt_track_tree_insertions(target_tree_id + 1, num_trees)
  
      def _get_next_tree_id(self):
          """
          Determines the next largest unused tree id for the tree managed
          by this manager.
          """
          max_tree_id = list(self.aggregate(Max(self.tree_id_attr)).values())[0]
          max_tree_id = max_tree_id or 0
          return max_tree_id + 1
  
      def _inter_tree_move_and_close_gap(
          self, node, level_change, left_right_change, new_tree_id
      ):
          """
          Removes ``node`` from its current tree, with the given set of
          changes being applied to ``node`` and its descendants, closing
          the gap left by moving ``node`` as it does so.
          """
          connection = self._get_connection(instance=node)
          qn = connection.ops.quote_name
  
          opts = self.model._meta
          inter_tree_move_query = """
          UPDATE %(table)s
          SET %(level)s = CASE
                  WHEN %(left)s >= %%s AND %(left)s <= %%s
                      THEN %(level)s - %%s
                  ELSE %(level)s END,
              %(tree_id)s = CASE
                  WHEN %(left)s >= %%s AND %(left)s <= %%s
                      THEN %%s
                  ELSE %(tree_id)s END,
              %(left)s = CASE
                  WHEN %(left)s >= %%s AND %(left)s <= %%s
                      THEN %(left)s - %%s
                  WHEN %(left)s > %%s
                      THEN %(left)s - %%s
                  ELSE %(left)s END,
              %(right)s = CASE
                  WHEN %(right)s >= %%s AND %(right)s <= %%s
                      THEN %(right)s - %%s
                  WHEN %(right)s > %%s
                      THEN %(right)s - %%s
                  ELSE %(right)s END
          WHERE %(tree_id)s = %%s""" % {
              "table": qn(self.tree_model._meta.db_table),
              "level": qn(opts.get_field(self.level_attr).column),
              "left": qn(opts.get_field(self.left_attr).column),
              "tree_id": qn(opts.get_field(self.tree_id_attr).column),
              "right": qn(opts.get_field(self.right_attr).column),
          }
  
          left = getattr(node, self.left_attr)
          right = getattr(node, self.right_attr)
          gap_size = right - left + 1
          gap_target_left = left - 1
          params = [
              left,
              right,
              level_change,
              left,
              right,
              new_tree_id,
              left,
              right,
              left_right_change,
              gap_target_left,
              gap_size,
              left,
              right,
              left_right_change,
              gap_target_left,
              gap_size,
              getattr(node, self.tree_id_attr),
          ]
  
          cursor = connection.cursor()
          cursor.execute(inter_tree_move_query, params)
  
      def _make_child_root_node(self, node, new_tree_id=None):
          """
          Removes ``node`` from its tree, making it the root node of a new
          tree.
  
          If ``new_tree_id`` is not specified a new tree id will be
          generated.
  
          ``node`` will be modified to reflect its new tree state in the
          database.
          """
          left = getattr(node, self.left_attr)
          right = getattr(node, self.right_attr)
          level = getattr(node, self.level_attr)
          if not new_tree_id:
              new_tree_id = self._get_next_tree_id()
          left_right_change = left - 1
  
          self._inter_tree_move_and_close_gap(node, level, left_right_change, new_tree_id)
  
          # Update the node to be consistent with the updated
          # tree in the database.
          setattr(node, self.left_attr, left - left_right_change)
          setattr(node, self.right_attr, right - left_right_change)
          setattr(node, self.level_attr, 0)
          setattr(node, self.tree_id_attr, new_tree_id)
          setattr(node, self.parent_attr, None)
          node._mptt_cached_fields[self.parent_attr] = None
  
      def _make_sibling_of_root_node(self, node, target, position):
          """
          Moves ``node``, making it a sibling of the given ``target`` root
          node as specified by ``position``.
  
          ``node`` will be modified to reflect its new tree state in the
          database.
  
          Since we use tree ids to reduce the number of rows affected by
          tree mangement during insertion and deletion, root nodes are not
          true siblings; thus, making an item a sibling of a root node is
          a special case which involves shuffling tree ids around.
          """
          if node == target:
              raise InvalidMove(_("A node may not be made a sibling of itself."))
  
          opts = self.model._meta
          tree_id = getattr(node, self.tree_id_attr)
          target_tree_id = getattr(target, self.tree_id_attr)
  
          if node.is_child_node():
              if position == "left":
                  space_target = target_tree_id - 1
                  new_tree_id = target_tree_id
              elif position == "right":
                  space_target = target_tree_id
                  new_tree_id = target_tree_id + 1
              else:
                  raise ValueError(_("An invalid position was given: %s.") % position)
  
              self._create_tree_space(space_target)
              if tree_id > space_target:
                  # The node's tree id has been incremented in the
                  # database - this change must be reflected in the node
                  # object for the method call below to operate on the
                  # correct tree.
                  setattr(node, self.tree_id_attr, tree_id + 1)
              self._make_child_root_node(node, new_tree_id)
          else:
              if position == "left":
                  if target_tree_id > tree_id:
                      left_sibling = target.get_previous_sibling()
                      if node == left_sibling:
                          return
                      new_tree_id = getattr(left_sibling, self.tree_id_attr)
                      lower_bound, upper_bound = tree_id, new_tree_id
                      shift = -1
                  else:
                      new_tree_id = target_tree_id
                      lower_bound, upper_bound = new_tree_id, tree_id
                      shift = 1
              elif position == "right":
                  if target_tree_id > tree_id:
                      new_tree_id = target_tree_id
                      lower_bound, upper_bound = tree_id, target_tree_id
                      shift = -1
                  else:
                      right_sibling = target.get_next_sibling()
                      if node == right_sibling:
                          return
                      new_tree_id = getattr(right_sibling, self.tree_id_attr)
                      lower_bound, upper_bound = new_tree_id, tree_id
                      shift = 1
              else:
                  raise ValueError(_("An invalid position was given: %s.") % position)
  
              connection = self._get_connection(instance=node)
              qn = connection.ops.quote_name
  
              root_sibling_query = """
              UPDATE %(table)s
              SET %(tree_id)s = CASE
                  WHEN %(tree_id)s = %%s
                      THEN %%s
                  ELSE %(tree_id)s + %%s END
              WHERE %(tree_id)s >= %%s AND %(tree_id)s <= %%s""" % {
                  "table": qn(self.tree_model._meta.db_table),
                  "tree_id": qn(opts.get_field(self.tree_id_attr).column),
              }
  
              cursor = connection.cursor()
              cursor.execute(
                  root_sibling_query,
                  [tree_id, new_tree_id, shift, lower_bound, upper_bound],
              )
              setattr(node, self.tree_id_attr, new_tree_id)
  
      def _manage_space(self, size, target, tree_id):
          """
          Manages spaces in the tree identified by ``tree_id`` by changing
          the values of the left and right columns by ``size`` after the
          given ``target`` point.
          """
          if self.tree_model._mptt_is_tracking:
              self.tree_model._mptt_track_tree_modified(tree_id)
          else:
              connection = self._get_connection()
              qn = connection.ops.quote_name
  
              opts = self.model._meta
              space_query = """
              UPDATE %(table)s
              SET %(left)s = CASE
                      WHEN %(left)s > %%s
                          THEN %(left)s + %%s
                      ELSE %(left)s END,
                  %(right)s = CASE
                      WHEN %(right)s > %%s
                          THEN %(right)s + %%s
                      ELSE %(right)s END
              WHERE %(tree_id)s = %%s
                AND (%(left)s > %%s OR %(right)s > %%s)""" % {
                  "table": qn(self.tree_model._meta.db_table),
                  "left": qn(opts.get_field(self.left_attr).column),
                  "right": qn(opts.get_field(self.right_attr).column),
                  "tree_id": qn(opts.get_field(self.tree_id_attr).column),
              }
              cursor = connection.cursor()
              cursor.execute(
                  space_query, [target, size, target, size, tree_id, target, target]
              )
  
      def _move_child_node(self, node, target, position):
          """
          Calls the appropriate method to move child node ``node``
          relative to the given ``target`` node as specified by
          ``position``.
          """
          tree_id = getattr(node, self.tree_id_attr)
          target_tree_id = getattr(target, self.tree_id_attr)
  
          if tree_id == target_tree_id:
              self._move_child_within_tree(node, target, position)
          else:
              self._move_child_to_new_tree(node, target, position)
  
      def _move_child_to_new_tree(self, node, target, position):
          """
          Moves child node ``node`` to a different tree, inserting it
          relative to the given ``target`` node in the new tree as
          specified by ``position``.
  
          ``node`` will be modified to reflect its new tree state in the
          database.
          """
          left = getattr(node, self.left_attr)
          right = getattr(node, self.right_attr)
          level = getattr(node, self.level_attr)
          new_tree_id = getattr(target, self.tree_id_attr)
  
          (
              space_target,
              level_change,
              left_right_change,
              parent,
              new_parent_right,
          ) = self._calculate_inter_tree_move_values(node, target, position)
  
          tree_width = right - left + 1
  
          # Make space for the subtree which will be moved
          self._create_space(tree_width, space_target, new_tree_id)
          # Move the subtree
          self._inter_tree_move_and_close_gap(
              node, level_change, left_right_change, new_tree_id
          )
  
          # Update the node to be consistent with the updated
          # tree in the database.
          setattr(node, self.left_attr, left - left_right_change)
          setattr(node, self.right_attr, right - left_right_change)
          setattr(node, self.level_attr, level - level_change)
          setattr(node, self.tree_id_attr, new_tree_id)
          setattr(node, self.parent_attr, parent)
  
          node._mptt_cached_fields[self.parent_attr] = parent.pk
  
      def _move_child_within_tree(self, node, target, position):
          """
          Moves child node ``node`` within its current tree relative to
          the given ``target`` node as specified by ``position``.
  
          ``node`` will be modified to reflect its new tree state in the
          database.
          """
          left = getattr(node, self.left_attr)
          right = getattr(node, self.right_attr)
          level = getattr(node, self.level_attr)
          width = right - left + 1
          tree_id = getattr(node, self.tree_id_attr)
          target_left = getattr(target, self.left_attr)
          target_right = getattr(target, self.right_attr)
          target_level = getattr(target, self.level_attr)
  
          if position == "last-child" or position == "first-child":
              if node == target:
                  raise InvalidMove(_("A node may not be made a child of itself."))
              elif left < target_left < right:
                  raise InvalidMove(
                      _("A node may not be made a child of any of its descendants.")
                  )
              if position == "last-child":
                  if target_right > right:
                      new_left = target_right - width
                      new_right = target_right - 1
                  else:
                      new_left = target_right
                      new_right = target_right + width - 1
              else:
                  if target_left > left:
                      new_left = target_left - width + 1
                      new_right = target_left
                  else:
                      new_left = target_left + 1
                      new_right = target_left + width
              level_change = level - target_level - 1
              parent = target
          elif position == "left" or position == "right":
              if node == target:
                  raise InvalidMove(_("A node may not be made a sibling of itself."))
              elif left < target_left < right:
                  raise InvalidMove(
                      _("A node may not be made a sibling of any of its descendants.")
                  )
              if position == "left":
                  if target_left > left:
                      new_left = target_left - width
                      new_right = target_left - 1
                  else:
                      new_left = target_left
                      new_right = target_left + width - 1
              else:
                  if target_right > right:
                      new_left = target_right - width + 1
                      new_right = target_right
                  else:
                      new_left = target_right + 1
                      new_right = target_right + width
              level_change = level - target_level
              parent = getattr(target, self.parent_attr)
          else:
              raise ValueError(_("An invalid position was given: %s.") % position)
  
          left_boundary = min(left, new_left)
          right_boundary = max(right, new_right)
          left_right_change = new_left - left
          gap_size = width
          if left_right_change > 0:
              gap_size = -gap_size
  
          connection = self._get_connection(instance=node)
          qn = connection.ops.quote_name
  
          opts = self.model._meta
          # The level update must come before the left update to keep
          # MySQL happy - left seems to refer to the updated value
          # immediately after its update has been specified in the query
          # with MySQL, but not with SQLite or Postgres.
          move_subtree_query = """
          UPDATE %(table)s
          SET %(level)s = CASE
                  WHEN %(left)s >= %%s AND %(left)s <= %%s
                    THEN %(level)s - %%s
                  ELSE %(level)s END,
              %(left)s = CASE
                  WHEN %(left)s >= %%s AND %(left)s <= %%s
                    THEN %(left)s + %%s
                  WHEN %(left)s >= %%s AND %(left)s <= %%s
                    THEN %(left)s + %%s
                  ELSE %(left)s END,
              %(right)s = CASE
                  WHEN %(right)s >= %%s AND %(right)s <= %%s
                    THEN %(right)s + %%s
                  WHEN %(right)s >= %%s AND %(right)s <= %%s
                    THEN %(right)s + %%s
                  ELSE %(right)s END
          WHERE %(tree_id)s = %%s""" % {
              "table": qn(self.tree_model._meta.db_table),
              "level": qn(opts.get_field(self.level_attr).column),
              "left": qn(opts.get_field(self.left_attr).column),
              "right": qn(opts.get_field(self.right_attr).column),
              "tree_id": qn(opts.get_field(self.tree_id_attr).column),
          }
  
          cursor = connection.cursor()
          cursor.execute(
              move_subtree_query,
              [
                  left,
                  right,
                  level_change,
                  left,
                  right,
                  left_right_change,
                  left_boundary,
                  right_boundary,
                  gap_size,
                  left,
                  right,
                  left_right_change,
                  left_boundary,
                  right_boundary,
                  gap_size,
                  tree_id,
              ],
          )
  
          # Update the node to be consistent with the updated
          # tree in the database.
          setattr(node, self.left_attr, new_left)
          setattr(node, self.right_attr, new_right)
          setattr(node, self.level_attr, level - level_change)
          setattr(node, self.parent_attr, parent)
          node._mptt_cached_fields[self.parent_attr] = parent.pk
  
      def _move_root_node(self, node, target, position):
          """
          Moves root node``node`` to a different tree, inserting it
          relative to the given ``target`` node as specified by
          ``position``.
  
          ``node`` will be modified to reflect its new tree state in the
          database.
          """
          left = getattr(node, self.left_attr)
          right = getattr(node, self.right_attr)
          level = getattr(node, self.level_attr)
          tree_id = getattr(node, self.tree_id_attr)
          new_tree_id = getattr(target, self.tree_id_attr)
          width = right - left + 1
  
          if node == target:
              raise InvalidMove(_("A node may not be made a child of itself."))
          elif tree_id == new_tree_id:
              raise InvalidMove(
                  _("A node may not be made a child of any of its descendants.")
              )
  
          (
              space_target,
              level_change,
              left_right_change,
              parent,
              right_shift,
          ) = self._calculate_inter_tree_move_values(node, target, position)
  
          # Create space for the tree which will be inserted
          self._create_space(width, space_target, new_tree_id)
  
          # Move the root node, making it a child node
          connection = self._get_connection(instance=node)
          qn = connection.ops.quote_name
  
          opts = self.model._meta
          move_tree_query = """
          UPDATE %(table)s
          SET %(level)s = %(level)s - %%s,
              %(left)s = %(left)s - %%s,
              %(right)s = %(right)s - %%s,
              %(tree_id)s = %%s
          WHERE %(left)s >= %%s AND %(left)s <= %%s
            AND %(tree_id)s = %%s""" % {
              "table": qn(self.tree_model._meta.db_table),
              "level": qn(opts.get_field(self.level_attr).column),
              "left": qn(opts.get_field(self.left_attr).column),
              "right": qn(opts.get_field(self.right_attr).column),
              "tree_id": qn(opts.get_field(self.tree_id_attr).column),
          }
  
          cursor = connection.cursor()
          cursor.execute(
              move_tree_query,
              [
                  level_change,
                  left_right_change,
                  left_right_change,
                  new_tree_id,
                  left,
                  right,
                  tree_id,
              ],
          )
  
          # Update the former root node to be consistent with the updated
          # tree in the database.
          setattr(node, self.left_attr, left - left_right_change)
          setattr(node, self.right_attr, right - left_right_change)
          setattr(node, self.level_attr, level - level_change)
          setattr(node, self.tree_id_attr, new_tree_id)
          setattr(node, self.parent_attr, parent)
          node._mptt_cached_fields[self.parent_attr] = parent.pk
  