class AssignOwnerNode

class AssignOwnerNode extends ConfigurableActionBase implements ContainerFactoryPluginInterface {
    
    /**
     * The database connection.
     *
     * @var \Drupal\Core\Database\Connection
     */
    protected $connection;
    
    /**
     * Constructs a new AssignOwnerNode action.
     *
     * @param array $configuration
     *   A configuration array containing information about the plugin instance.
     * @param string $plugin_id
     *   The plugin ID for the plugin instance.
     * @param mixed $plugin_definition
     *   The plugin implementation definition.
     * @param \Drupal\Core\Database\Connection $connection
     *   The database connection.
     */
    public function __construct(array $configuration, $plugin_id, $plugin_definition, Connection $connection) {
        parent::__construct($configuration, $plugin_id, $plugin_definition);
        $this->connection = $connection;
    }
    
    /**
     * {@inheritdoc}
     */
    public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition) {
        return new static($configuration, $plugin_id, $plugin_definition, $container->get('database'));
    }
    
    /**
     * {@inheritdoc}
     */
    public function execute($entity = NULL) {
        
        /** @var \Drupal\node\NodeInterface $entity */
        $entity->setOwnerId($this->configuration['owner_uid'])
            ->save();
    }
    
    /**
     * {@inheritdoc}
     */
    public function defaultConfiguration() {
        return [
            'owner_uid' => '',
        ];
    }
    
    /**
     * {@inheritdoc}
     */
    public function buildConfigurationForm(array $form, FormStateInterface $form_state) {
        $description = $this->t('The username of the user to which you would like to assign ownership.');
        $count = $this->connection
            ->query("SELECT COUNT(*) FROM {users}")
            ->fetchField();
        // Use dropdown for fewer than 200 users; textbox for more than that.
        if (intval($count) < 200) {
            $options = [];
            $result = $this->connection
                ->query("SELECT [uid], [name] FROM {users_field_data} WHERE [uid] > 0 AND [default_langcode] = 1 ORDER BY [name]");
            foreach ($result as $data) {
                $options[$data->uid] = $data->name;
            }
            $form['owner_uid'] = [
                '#type' => 'select',
                '#title' => $this->t('Username'),
                '#default_value' => $this->configuration['owner_uid'],
                '#options' => $options,
                '#description' => $description,
            ];
        }
        else {
            $form['owner_uid'] = [
                '#type' => 'entity_autocomplete',
                '#title' => $this->t('Username'),
                '#target_type' => 'user',
                '#selection_settings' => [
                    'include_anonymous' => FALSE,
                ],
                '#default_value' => User::load($this->configuration['owner_uid']),
                // Validation is done in static::validateConfigurationForm().
'#validate_reference' => FALSE,
                '#size' => '6',
                '#maxlength' => '60',
                '#description' => $description,
            ];
        }
        return $form;
    }
    
    /**
     * {@inheritdoc}
     */
    public function validateConfigurationForm(array &$form, FormStateInterface $form_state) {
        $exists = (bool) $this->connection
            ->queryRange('SELECT 1 FROM {users_field_data} WHERE [uid] = :uid AND [default_langcode] = 1', 0, 1, [
            ':uid' => $form_state->getValue('owner_uid'),
        ])
            ->fetchField();
        if (!$exists) {
            $form_state->setErrorByName('owner_uid', $this->t('Enter a valid username.'));
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function submitConfigurationForm(array &$form, FormStateInterface $form_state) {
        $this->configuration['owner_uid'] = $form_state->getValue('owner_uid');
    }
    
    /**
     * {@inheritdoc}
     */
    public function access($object, AccountInterface $account = NULL, $return_as_object = FALSE) {
        
        /** @var \Drupal\node\NodeInterface $object */
        $result = $object->access('update', $account, TRUE)
            ->andIf($object->getOwner()
            ->access('edit', $account, TRUE));
        return $return_as_object ? $result : $result->isAllowed();
    }

}