class CommentSelection

class CommentSelection extends DefaultSelection {
    
    /**
     * {@inheritdoc}
     */
    protected function buildEntityQuery($match = NULL, $match_operator = 'CONTAINS') {
        $query = parent::buildEntityQuery($match, $match_operator);
        // Adding the 'comment_access' tag is sadly insufficient for comments:
        // core requires us to also know about the concept of 'published' and
        // 'unpublished'.
        if (!$this->currentUser
            ->hasPermission('administer comments')) {
            $query->condition('status', CommentInterface::PUBLISHED);
        }
        return $query;
    }
    
    /**
     * {@inheritdoc}
     */
    public function createNewEntity($entity_type_id, $bundle, $label, $uid) {
        $comment = parent::createNewEntity($entity_type_id, $bundle, $label, $uid);
        // In order to create a referenceable comment, it needs to published.
        
        /** @var \Drupal\comment\CommentInterface $comment */
        $comment->setPublished();
        return $comment;
    }
    
    /**
     * {@inheritdoc}
     */
    public function validateReferenceableNewEntities(array $entities) {
        $entities = parent::validateReferenceableNewEntities($entities);
        // Mirror the conditions checked in buildEntityQuery().
        if (!$this->currentUser
            ->hasPermission('administer comments')) {
            $entities = array_filter($entities, function ($comment) {
                
                /** @var \Drupal\comment\CommentInterface $comment */
                return $comment->isPublished();
            });
        }
        return $entities;
    }
    
    /**
     * {@inheritdoc}
     */
    public function validateReferenceableEntities(array $ids) {
        $result = [];
        if ($ids) {
            $target_type = $this->configuration['target_type'];
            $entity_type = $this->entityTypeManager
                ->getDefinition($target_type);
            $query = $this->buildEntityQuery();
            // Mirror the conditions checked in buildEntityQuery().
            if (!$this->currentUser
                ->hasPermission('administer comments')) {
                $query->condition('status', 1);
            }
            $result = $query->condition($entity_type->getKey('id'), $ids, 'IN')
                ->execute();
        }
        return $result;
    }
    
    /**
     * {@inheritdoc}
     */
    public function entityQueryAlter(SelectInterface $query) {
        parent::entityQueryAlter($query);
        $tables = $query->getTables();
        $data_table = 'comment_field_data';
        if (!isset($tables['comment_field_data']['alias'])) {
            // If no conditions join against the comment data table, it should be
            // joined manually to allow node access processing.
            $query->innerJoin($data_table, NULL, "[base_table].[cid] = [{$data_table}].[cid] AND [{$data_table}].[default_langcode] = 1");
        }
        // Historically, comments were always linked to 'node' entities, but that is
        // no longer the case, as the 'node' module might not even be enabled.
        // Comments can now be linked to any entity and they can also be referenced
        // by other entities, so we won't have a single table to join to. That
        // actually means that we can no longer optimize the query on those cases.
        // However, the most common case remains to be comment replies, and in this
        // case, we can get the host entity type if the 'entity' value is present
        // and perform the extra joins and alterations needed.
        $comment = $this->getConfiguration()['entity'];
        if ($comment instanceof CommentInterface) {
            $host_entity_type_id = $comment->getCommentedEntityTypeId();
            
            /** @var \Drupal\Core\Entity\EntityTypeInterface $host_entity_type */
            $host_entity_type = $this->entityTypeManager
                ->getDefinition($host_entity_type_id);
            $host_entity_field_data_table = $host_entity_type->getDataTable();
            // Not all entities have a data table, so check first.
            if ($host_entity_field_data_table) {
                $id_key = $host_entity_type->getKey('id');
                // The Comment module doesn't implement per-comment access, so it
                // checks instead that the user has access to the host entity.
                $entity_alias = $query->innerJoin($host_entity_field_data_table, 'n', "[%alias].[{$id_key}] = [{$data_table}].[entity_id] AND [{$data_table}].[entity_type] = '{$host_entity_type_id}'");
                // Pass the query to the entity access control.
                $this->reAlterQuery($query, $host_entity_type_id . '_access', $entity_alias);
                // Additional checks for "node" entities.
                if ($host_entity_type_id === 'node') {
                    // Passing the query to node_query_node_access_alter() is sadly
                    // insufficient for nodes.
                    // @see \Drupal\node\Plugin\EntityReferenceSelection\NodeSelection::buildEntityQuery()
                    if (!$this->currentUser
                        ->hasPermission('bypass node access') && !$this->moduleHandler
                        ->hasImplementations('node_grants')) {
                        $query->condition($entity_alias . '.status', 1);
                    }
                }
            }
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function getReferenceableEntities($match = NULL, $match_operator = 'CONTAINS', $limit = 0) {
        $target_type = $this->getConfiguration()['target_type'];
        $query = $this->buildEntityQuery($match, $match_operator);
        if ($limit > 0) {
            $query->range(0, $limit);
        }
        $result = $query->execute();
        if (empty($result)) {
            return [];
        }
        $options = [];
        $entities = $this->entityTypeManager
            ->getStorage($target_type)
            ->loadMultiple($result);
        foreach ($entities as $entity_id => $entity) {
            // Additional access check as comments might be attached to entities
            // which the current user does not have access to.
            if ($entity->access('view', $this->currentUser)) {
                $bundle = $entity->bundle();
                $options[$bundle][$entity_id] = Html::escape($this->entityRepository
                    ->getTranslationFromContext($entity)
                    ->label() ?? '');
            }
        }
        return $options;
    }
    
    /**
     * {@inheritdoc}
     */
    public function countReferenceableEntities($match = NULL, $match_operator = 'CONTAINS') {
        $options = $this->getReferenceableEntities($match, $match_operator);
        return count($options, COUNT_RECURSIVE) - count($options);
    }

}