text: from __future__ import unicode_literals
  
  import logging
  
  from django.db import models
  from django.utils.encoding import python_2_unicode_compatible
  from django.utils.functional import cached_property
  from django.utils.module_loading import import_string
  from django.utils.translation import force_text
  from django.utils.translation import ugettext_lazy as _
  
  from mayan.apps.documents.models import DocumentType, DocumentVersion
  
  from .managers import DocumentTypeSettingsManager
  
  logger = logging.getLogger(__name__)
  
  
  @python_2_unicode_compatible
  class StoredDriver(models.Model):
      driver_path = models.CharField(
          max_length=255, verbose_name=_('Driver path')
      )
      internal_name = models.CharField(
          db_index=True, max_length=128, verbose_name=_('Internal name')
      )
  
      class Meta:
          ordering = ('internal_name',)
          verbose_name = _('Driver')
          verbose_name_plural = _('Drivers')
  
      def __str__(self):
          return force_text(self.driver_label)
  
      @cached_property
      def driver_class(self):
          return import_string(self.driver_path)
  
      @cached_property
      def driver_label(self):
          return self.driver_class.label
  
  
  class DocumentTypeSettings(models.Model):
      """
      Model to store the file metadata settings for a document type.
      """
      document_type = models.OneToOneField(
          on_delete=models.CASCADE, related_name='file_metadata_settings',
          to=DocumentType, unique=True, verbose_name=_('Document type')
      )
      auto_process = models.BooleanField(
          default=True, verbose_name=_(
              'Automatically queue newly created documents for processing.'
          )
      )
  
      objects = DocumentTypeSettingsManager()
  
      class Meta:
          verbose_name = _('Document type settings')
          verbose_name_plural = _('Document types settings')
  
      def natural_key(self):
          return self.document_type.natural_key()
      natural_key.dependencies = ['documents.DocumentType']
  
  
  @python_2_unicode_compatible
  class DocumentVersionDriverEntry(models.Model):
      driver = models.ForeignKey(
          on_delete=models.CASCADE, related_name='driver_entries',
          to=StoredDriver, verbose_name=_('Driver')
      )
      document_version = models.ForeignKey(
          on_delete=models.CASCADE, related_name='file_metadata_drivers',
          to=DocumentVersion, verbose_name=_('Document version')
      )
  
      class Meta:
          ordering = ('document_version', 'driver')
          unique_together = ('driver', 'document_version')
          verbose_name = _('Document version driver entry')
          verbose_name_plural = _('Document version driver entries')
  
      def __str__(self):
          return force_text(self.driver)
  
      def get_attribute_count(self):
          return self.entries.count()
      get_attribute_count.short_description = _('Attribute count')
  
  
  @python_2_unicode_compatible
  class FileMetadataEntry(models.Model):
      document_version_driver_entry = models.ForeignKey(
          on_delete=models.CASCADE, related_name='entries',
          to=DocumentVersionDriverEntry,
          verbose_name=_('Document version driver entry')
      )
  
      key = models.CharField(
          db_index=True, help_text=_('Name of the file metadata entry.'),
          max_length=255, verbose_name=_('Key')
      )
      value = models.CharField(
          db_index=True, help_text=_('Value of the file metadata entry.'),
          max_length=255, verbose_name=_('Value')
      )
  
      class Meta:
          ordering = ('key', 'value')
          verbose_name = _('File metadata entry')
          verbose_name_plural = _('File metadata entries')
  
      def __str__(self):
          return '{}: {}: {}'.format(
              self.document_version_driver_entry, self.key, self.value
          )
  