class FileSelection

class FileSelection extends DefaultSelection {
    
    /**
     * {@inheritdoc}
     */
    protected function buildEntityQuery($match = NULL, $match_operator = 'CONTAINS') {
        $query = parent::buildEntityQuery($match, $match_operator);
        // Allow referencing :
        // - files with status "permanent"
        // - or files uploaded by the current user (since newly uploaded files only
        //   become "permanent" after the containing entity gets validated and
        //   saved.)
        $query->condition($query->orConditionGroup()
            ->condition('status', FileInterface::STATUS_PERMANENT)
            ->condition('uid', $this->currentUser
            ->id()));
        return $query;
    }
    
    /**
     * {@inheritdoc}
     */
    public function createNewEntity($entity_type_id, $bundle, $label, $uid) {
        $file = parent::createNewEntity($entity_type_id, $bundle, $label, $uid);
        // In order to create a referenceable file, it needs to have a "permanent"
        // status.
        
        /** @var \Drupal\file\FileInterface $file */
        $file->setPermanent();
        return $file;
    }
    
    /**
     * {@inheritdoc}
     */
    public function validateReferenceableNewEntities(array $entities) {
        $entities = parent::validateReferenceableNewEntities($entities);
        $entities = array_filter($entities, function ($file) {
            
            /** @var \Drupal\file\FileInterface $file */
            return $file->isPermanent() || $file->getOwnerId() === $this->currentUser
                ->id();
        });
        return $entities;
    }

}