class TermSelection

class TermSelection extends DefaultSelection {
    
    /**
     * {@inheritdoc}
     */
    public function defaultConfiguration() {
        return [
            'sort' => [
                'field' => 'name',
                'direction' => 'asc',
            ],
        ] + parent::defaultConfiguration();
    }
    
    /**
     * {@inheritdoc}
     */
    public function buildConfigurationForm(array $form, FormStateInterface $form_state) {
        $form = parent::buildConfigurationForm($form, $form_state);
        // Sorting is not possible for taxonomy terms because we use
        // \Drupal\taxonomy\TermStorageInterface::loadTree() to retrieve matches.
        $form['sort']['#access'] = FALSE;
        return $form;
    }
    
    /**
     * {@inheritdoc}
     */
    public function getReferenceableEntities($match = NULL, $match_operator = 'CONTAINS', $limit = 0) {
        if ($match || $limit) {
            return parent::getReferenceableEntities($match, $match_operator, $limit);
        }
        $options = [];
        $bundles = $this->entityTypeBundleInfo
            ->getBundleInfo('taxonomy_term');
        $bundle_names = $this->getConfiguration()['target_bundles'] ?: array_keys($bundles);
        $has_admin_access = $this->currentUser
            ->hasPermission('administer taxonomy');
        $unpublished_terms = [];
        foreach ($bundle_names as $bundle) {
            if ($vocabulary = Vocabulary::load($bundle)) {
                
                /** @var \Drupal\taxonomy\TermInterface[] $terms */
                if ($terms = $this->entityTypeManager
                    ->getStorage('taxonomy_term')
                    ->loadTree($vocabulary->id(), 0, NULL, TRUE)) {
                    foreach ($terms as $term) {
                        if (!$has_admin_access && (!$term->isPublished() || in_array($term->parent->target_id, $unpublished_terms))) {
                            $unpublished_terms[] = $term->id();
                            continue;
                        }
                        $options[$vocabulary->id()][$term->id()] = str_repeat('-', $term->depth) . Html::escape($this->entityRepository
                            ->getTranslationFromContext($term)
                            ->label());
                    }
                }
            }
        }
        return $options;
    }
    
    /**
     * {@inheritdoc}
     */
    public function countReferenceableEntities($match = NULL, $match_operator = 'CONTAINS') {
        if ($match) {
            return parent::countReferenceableEntities($match, $match_operator);
        }
        $total = 0;
        $referenceable_entities = $this->getReferenceableEntities($match, $match_operator, 0);
        foreach ($referenceable_entities as $bundle => $entities) {
            $total += count($entities);
        }
        return $total;
    }
    
    /**
     * {@inheritdoc}
     */
    protected function buildEntityQuery($match = NULL, $match_operator = 'CONTAINS') {
        $query = parent::buildEntityQuery($match, $match_operator);
        // Adding the 'taxonomy_term_access' tag is sadly insufficient for terms:
        // core requires us to also know about the concept of 'published' and
        // 'unpublished'.
        if (!$this->currentUser
            ->hasPermission('administer taxonomy')) {
            $query->condition('status', 1);
        }
        return $query;
    }
    
    /**
     * {@inheritdoc}
     */
    public function createNewEntity($entity_type_id, $bundle, $label, $uid) {
        $term = parent::createNewEntity($entity_type_id, $bundle, $label, $uid);
        // In order to create a referenceable term, it needs to published.
        
        /** @var \Drupal\taxonomy\TermInterface $term */
        $term->setPublished();
        return $term;
    }
    
    /**
     * {@inheritdoc}
     */
    public function validateReferenceableNewEntities(array $entities) {
        $entities = parent::validateReferenceableNewEntities($entities);
        // Mirror the conditions checked in buildEntityQuery().
        if (!$this->currentUser
            ->hasPermission('administer taxonomy')) {
            $entities = array_filter($entities, function ($term) {
                
                /** @var \Drupal\taxonomy\TermInterface $term */
                return $term->isPublished();
            });
        }
        return $entities;
    }

}