class ThemeSettings

class ThemeSettings extends DestinationBase implements ContainerFactoryPluginInterface {
  
  /**
   * The configuration factory.
   *
   * @var \Drupal\Core\Config\ConfigFactoryInterface
   */
  protected $configFactory;
  
  /**
   * Constructs a theme settings destination object.
   *
   * @param array $configuration
   *   Plugin configuration.
   * @param string $plugin_id
   *   The plugin ID.
   * @param mixed $plugin_definition
   *   The plugin definition.
   * @param \Drupal\migrate\Plugin\MigrationInterface $migration
   *   The current migration.
   * @param \Drupal\Core\Config\ConfigFactoryInterface $config_factory
   *   The configuration factory.
   */
  public function __construct(array $configuration, $plugin_id, $plugin_definition, MigrationInterface $migration, ConfigFactoryInterface $config_factory) {
    parent::__construct($configuration, $plugin_id, $plugin_definition, $migration);
    $this->configFactory = $config_factory;
  }
  
  /**
   * {@inheritdoc}
   */
  public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition, ?MigrationInterface $migration = NULL) {
    return new static($configuration, $plugin_id, $plugin_definition, $migration, $container->get('config.factory'));
  }
  
  /**
   * {@inheritdoc}
   */
  public function import(Row $row, array $old_destination_id_values = []) {
    $imported = FALSE;
    $config = $this->configFactory
      ->getEditable($row->getDestinationProperty('configuration_name'));
    $theme_settings = $row->getDestination();
    // Remove keys not in theme settings.
    unset($theme_settings['configuration_name']);
    unset($theme_settings['theme_name']);
    unset($theme_settings['legacy_theme_name']);
    if (isset($theme_settings)) {
      theme_settings_convert_to_config($theme_settings, $config);
      $config->save();
      $imported = TRUE;
    }
    return $imported;
  }
  
  /**
   * {@inheritdoc}
   */
  public function getIds() {
    $ids['name']['type'] = 'string';
    return $ids;
  }
  
  /**
   * {@inheritdoc}
   */
  public function fields() {
    // Theme settings vary by theme, so no specific fields are defined.
    return [];
  }

}