text: """
  Generic models which provide extra functionality over base Django model types.
  """
  
  from __future__ import unicode_literals
  
  import re
  import os
  import logging
  
  from django.db import models
  from django.conf import settings
  from django.contrib.auth.models import User
  from django.contrib.contenttypes.models import ContentType
  from django.utils.translation import gettext_lazy as _
  from django.core.exceptions import ValidationError
  
  from django.db.models.signals import pre_delete
  from django.dispatch import receiver
  
  from mptt.models import MPTTModel, TreeForeignKey
  from mptt.exceptions import InvalidMove
  
  from InvenTree.fields import InvenTreeURLField
  from InvenTree.validators import validate_tree_name
  
  
  logger = logging.getLogger('inventree')
  
  
  def rename_attachment(instance, filename):
      """
      Function for renaming an attachment file.
      The subdirectory for the uploaded file is determined by the implementing class.
  
          Args:
          instance: Instance of a PartAttachment object
          filename: name of uploaded file
  
      Returns:
          path to store file, format: '<subdir>/<id>/filename'
      """
  
      # Construct a path to store a file attachment for a given model type
      return os.path.join(instance.getSubdir(), filename)
  
  
  class DataImportMixin(object):
      """
      Model mixin class which provides support for 'data import' functionality.
  
      Models which implement this mixin should provide information on the fields available for import
      """
  
      # Define a map of fields avaialble for import
      IMPORT_FIELDS = {}
  
      @classmethod
      def get_import_fields(cls):
          """
          Return all available import fields
  
          Where information on a particular field is not explicitly provided,
          introspect the base model to (attempt to) find that information.
  
          """
          fields = cls.IMPORT_FIELDS
  
          for name, field in fields.items():
  
              # Attempt to extract base field information from the model
              base_field = None
  
              for f in cls._meta.fields:
                  if f.name == name:
                      base_field = f
                      break
  
              if base_field:
                  if 'label' not in field:
                      field['label'] = base_field.verbose_name
  
                  if 'help_text' not in field:
                      field['help_text'] = base_field.help_text
  
              fields[name] = field
  
          return fields
  
      @classmethod
      def get_required_import_fields(cls):
          """ Return all *required* import fields """
          fields = {}
  
          for name, field in cls.get_import_fields().items():
              required = field.get('required', False)
  
              if required:
                  fields[name] = field
  
          return fields
  
  
  class ReferenceIndexingMixin(models.Model):
      """
      A mixin for keeping track of numerical copies of the "reference" field.
  
      !!DANGER!! always add `ReferenceIndexingSerializerMixin`to all your models serializers to
      ensure the reference field is not too big
  
      Here, we attempt to convert a "reference" field value (char) to an integer,
      for performing fast natural sorting.
  
      This requires extra database space (due to the extra table column),
      but is required as not all supported database backends provide equivalent casting.
  
      This mixin adds a field named 'reference_int'.
  
      - If the 'reference' field can be cast to an integer, it is stored here
      - If the 'reference' field *starts* with an integer, it is stored here
      - Otherwise, we store zero
      """
  
      class Meta:
          abstract = True
  
      def rebuild_reference_field(self):
  
          reference = getattr(self, 'reference', '')
  
          self.reference_int = extract_int(reference)
  
      reference_int = models.BigIntegerField(default=0)
  
  
  def extract_int(reference, clip=0x7fffffff):
      # Default value if we cannot convert to an integer
      ref_int = 0
  
      # Look at the start of the string - can it be "integerized"?
      result = re.match(r"^(\d+)", reference)
  
      if result and len(result.groups()) == 1:
          ref = result.groups()[0]
          try:
              ref_int = int(ref)
          except:
              ref_int = 0
  
      # Ensure that the returned values are within the range that can be stored in an IntegerField
      # Note: This will result in large values being "clipped"
      if clip is not None:
          if ref_int > clip:
              ref_int = clip
          elif ref_int < -clip:
              ref_int = -clip
  
      return ref_int
  
  
  class InvenTreeAttachment(models.Model):
      """ Provides an abstracted class for managing file attachments.
  
      An attachment can be either an uploaded file, or an external URL
  
      Attributes:
          attachment: File
          comment: String descriptor for the attachment
          user: User associated with file upload
          upload_date: Date the file was uploaded
      """
  
      def getSubdir(self):
          """
          Return the subdirectory under which attachments should be stored.
          Note: Re-implement this for each subclass of InvenTreeAttachment
          """
  
          return "attachments"
  
      def save(self, *args, **kwargs):
          # Either 'attachment' or 'link' must be specified!
          if not self.attachment and not self.link:
              raise ValidationError({
                  'attachment': _('Missing file'),
                  'link': _('Missing external link'),
              })
  
          super().save(*args, **kwargs)
  
      def __str__(self):
          if self.attachment is not None:
              return os.path.basename(self.attachment.name)
          else:
              return str(self.link)
  
      attachment = models.FileField(upload_to=rename_attachment, verbose_name=_('Attachment'),
                                    help_text=_('Select file to attach'),
                                    blank=True, null=True
                                    )
  
      link = InvenTreeURLField(
          blank=True, null=True,
          verbose_name=_('Link'),
          help_text=_('Link to external URL')
      )
  
      comment = models.CharField(blank=True, max_length=100, verbose_name=_('Comment'), help_text=_('File comment'))
  
      user = models.ForeignKey(
          User,
          on_delete=models.SET_NULL,
          blank=True, null=True,
          verbose_name=_('User'),
          help_text=_('User'),
      )
  
      upload_date = models.DateField(auto_now_add=True, null=True, blank=True, verbose_name=_('upload date'))
  
      @property
      def basename(self):
          if self.attachment:
              return os.path.basename(self.attachment.name)
          else:
              return None
  
      @basename.setter
      def basename(self, fn):
          """
          Function to rename the attachment file.
  
          - Filename cannot be empty
          - Filename cannot contain illegal characters
          - Filename must specify an extension
          - Filename cannot match an existing file
          """
  
          fn = fn.strip()
  
          if len(fn) == 0:
              raise ValidationError(_('Filename must not be empty'))
  
          attachment_dir = os.path.join(
              settings.MEDIA_ROOT,
              self.getSubdir()
          )
  
          old_file = os.path.join(
              settings.MEDIA_ROOT,
              self.attachment.name
          )
  
          new_file = os.path.join(
              settings.MEDIA_ROOT,
              self.getSubdir(),
              fn
          )
  
          new_file = os.path.abspath(new_file)
  
          # Check that there are no directory tricks going on...
          if not os.path.dirname(new_file) == attachment_dir:
              logger.error(f"Attempted to rename attachment outside valid directory: '{new_file}'")
              raise ValidationError(_("Invalid attachment directory"))
  
          # Ignore further checks if the filename is not actually being renamed
          if new_file == old_file:
              return
  
          forbidden = ["'", '"', "#", "@", "!", "&", "^", "<", ">", ":", ";", "/", "\\", "|", "?", "*", "%", "~", "`"]
  
          for c in forbidden:
              if c in fn:
                  raise ValidationError(_(f"Filename contains illegal character '{c}'"))
  
          if len(fn.split('.')) < 2:
              raise ValidationError(_("Filename missing extension"))
  
          if not os.path.exists(old_file):
              logger.error(f"Trying to rename attachment '{old_file}' which does not exist")
              return
  
          if os.path.exists(new_file):
              raise ValidationError(_("Attachment with this filename already exists"))
  
          try:
              os.rename(old_file, new_file)
              self.attachment.name = os.path.join(self.getSubdir(), fn)
              self.save()
          except:
              raise ValidationError(_("Error renaming file"))
  
      class Meta:
          abstract = True
  
  
  class InvenTreeTree(MPTTModel):
      """ Provides an abstracted self-referencing tree model for data categories.
  
      - Each Category has one parent Category, which can be blank (for a top-level Category).
      - Each Category can have zero-or-more child Categor(y/ies)
  
      Attributes:
          name: brief name
          description: longer form description
          parent: The item immediately above this one. An item with a null parent is a top-level item
      """
  
      def api_instance_filters(self):
          """
          Instance filters for InvenTreeTree models
          """
  
          return {
              'parent': {
                  'exclude_tree': self.pk,
              }
          }
  
      def save(self, *args, **kwargs):
  
          try:
              super().save(*args, **kwargs)
          except InvalidMove:
              raise ValidationError({
                  'parent': _("Invalid choice"),
              })
  
      class Meta:
          abstract = True
  
          # Names must be unique at any given level in the tree
          unique_together = ('name', 'parent')
  
      class MPTTMeta:
          order_insertion_by = ['name']
  
      name = models.CharField(
          blank=False,
          max_length=100,
          validators=[validate_tree_name],
          verbose_name=_("Name"),
          help_text=_("Name"),
      )
  
      description = models.CharField(
          blank=True,
          max_length=250,
          verbose_name=_("Description"),
          help_text=_("Description (optional)")
      )
  
      # When a category is deleted, graft the children onto its parent
      parent = TreeForeignKey('self',
                              on_delete=models.DO_NOTHING,
                              blank=True,
                              null=True,
                              verbose_name=_("parent"),
                              related_name='children')
  
      @property
      def item_count(self):
          """ Return the number of items which exist *under* this node in the tree.
  
          Here an 'item' is considered to be the 'leaf' at the end of each branch,
          and the exact nature here will depend on the class implementation.
  
          The default implementation returns zero
          """
          return 0
  
      def getUniqueParents(self):
          """ Return a flat set of all parent items that exist above this node.
          If any parents are repeated (which would be very bad!), the process is halted
          """
  
          return self.get_ancestors()
  
      def getUniqueChildren(self, include_self=True):
          """ Return a flat set of all child items that exist under this node.
          If any child items are repeated, the repetitions are omitted.
          """
  
          return self.get_descendants(include_self=include_self)
  
      @property
      def has_children(self):
          """ True if there are any children under this item """
          return self.getUniqueChildren(include_self=False).count() > 0
  
      def getAcceptableParents(self):
          """ Returns a list of acceptable parent items within this model
          Acceptable parents are ones which are not underneath this item.
          Setting the parent of an item to its own child results in recursion.
          """
  
          contents = ContentType.objects.get_for_model(type(self))
  
          available = contents.get_all_objects_for_this_type()
  
          # List of child IDs
          childs = self.getUniqueChildren()
  
          acceptable = [None]
  
          for a in available:
              if a.id not in childs:
                  acceptable.append(a)
  
          return acceptable
  
      @property
      def parentpath(self):
          """ Get the parent path of this category
  
          Returns:
              List of category names from the top level to the parent of this category
          """
  
          return [a for a in self.get_ancestors()]
  
      @property
      def path(self):
          """ Get the complete part of this category.
  
          e.g. ["Top", "Second", "Third", "This"]
  
          Returns:
              List of category names from the top level to this category
          """
          return self.parentpath + [self]
  
      @property
      def pathstring(self):
          """ Get a string representation for the path of this item.
  
          e.g. "Top/Second/Third/This"
          """
          return '/'.join([item.name for item in self.path])
  
      def __str__(self):
          """ String representation of a category is the full path to that category """
  
          return "{path} - {desc}".format(path=self.pathstring, desc=self.description)
  
  
  @receiver(pre_delete, sender=InvenTreeTree, dispatch_uid='tree_pre_delete_log')
  def before_delete_tree_item(sender, instance, using, **kwargs):
      """ Receives pre_delete signal from InvenTreeTree object.
  
      Before an item is deleted, update each child object to point to the parent of the object being deleted.
      """
  
      # Update each tree item below this one
      for child in instance.children.all():
          child.parent = instance.parent
          child.save()
  