class Vocabulary

class Vocabulary extends ConfigEntityBundleBase implements VocabularyInterface {
  
  /**
   * The taxonomy vocabulary ID.
   *
   * @var string
   */
  protected $vid;
  
  /**
   * Name of the vocabulary.
   *
   * @var string
   */
  protected $name;
  
  /**
   * Description of the vocabulary.
   *
   * @var string
   */
  protected $description;
  
  /**
   * The weight of this vocabulary in relation to other vocabularies.
   *
   * @var int
   */
  protected $weight = 0;
  
  /**
   * {@inheritdoc}
   */
  public function id() {
    return $this->vid;
  }
  
  /**
   * {@inheritdoc}
   */
  public function getDescription() {
    return $this->description;
  }
  
  /**
   * {@inheritdoc}
   */
  public static function preDelete(EntityStorageInterface $storage, array $entities) {
    parent::preDelete($storage, $entities);
    // Only load terms without a parent, child terms will get deleted too.
    $term_storage = \Drupal::entityTypeManager()->getStorage('taxonomy_term');
    $terms = $term_storage->loadMultiple($storage->getToplevelTids(array_keys($entities)));
    $term_storage->delete($terms);
  }
  
  /**
   * {@inheritdoc}
   */
  public static function postDelete(EntityStorageInterface $storage, array $entities) {
    parent::postDelete($storage, $entities);
    // Reset caches.
    $storage->resetCache(array_keys($entities));
    if (reset($entities)->isSyncing()) {
      return;
    }
    $vocabularies = [];
    foreach ($entities as $vocabulary) {
      $vocabularies[$vocabulary->id()] = $vocabulary->id();
    }
    // Load all Taxonomy module fields and delete those which use only this
    // vocabulary.
    $field_storages = \Drupal::entityTypeManager()->getStorage('field_storage_config')
      ->loadByProperties([
      'module' => 'taxonomy',
    ]);
    foreach ($field_storages as $field_storage) {
      $modified_storage = FALSE;
      // Term reference fields may reference terms from more than one
      // vocabulary.
      foreach ($field_storage->getSetting('allowed_values') as $key => $allowed_value) {
        if (isset($vocabularies[$allowed_value['vocabulary']])) {
          $allowed_values = $field_storage->getSetting('allowed_values');
          unset($allowed_values[$key]);
          $field_storage->setSetting('allowed_values', $allowed_values);
          $modified_storage = TRUE;
        }
      }
      if ($modified_storage) {
        $allowed_values = $field_storage->getSetting('allowed_values');
        if (empty($allowed_values)) {
          $field_storage->delete();
        }
        else {
          // Update the field definition with the new allowed values.
          $field_storage->save();
        }
      }
    }
  }

}