class MachineName

class MachineName extends FieldPluginBase {
  
  /**
   * Stores the available options.
   *
   * @var array
   */
  protected $valueOptions;
  public function getValueOptions() {
    if (isset($this->valueOptions)) {
      return;
    }
    if (isset($this->definition['options callback']) && is_callable($this->definition['options callback'])) {
      if (isset($this->definition['options arguments']) && is_array($this->definition['options arguments'])) {
        $this->valueOptions = call_user_func_array($this->definition['options callback'], $this->definition['options arguments']);
      }
      else {
        $this->valueOptions = call_user_func($this->definition['options callback']);
      }
    }
    else {
      $this->valueOptions = [];
    }
  }
  
  /**
   * {@inheritdoc}
   */
  protected function defineOptions() {
    $options = parent::defineOptions();
    $options['machine_name'] = [
      'default' => FALSE,
    ];
    return $options;
  }
  
  /**
   * {@inheritdoc}
   */
  public function buildOptionsForm(&$form, FormStateInterface $form_state) {
    parent::buildOptionsForm($form, $form_state);
    $form['machine_name'] = [
      '#title' => $this->t('Output machine name'),
      '#description' => $this->t('Display field as machine name.'),
      '#type' => 'checkbox',
      '#default_value' => !empty($this->options['machine_name']),
    ];
  }
  
  /**
   * {@inheritdoc}
   */
  public function preRender(&$values) {
    $this->getValueOptions();
  }
  
  /**
   * {@inheritdoc}
   */
  public function render(ResultRow $values) {
    $value = $values->{$this->field_alias};
    if (!empty($this->options['machine_name']) || !isset($this->valueOptions[$value])) {
      $result = $this->sanitizeValue($value);
    }
    else {
      $result = $this->valueOptions[$value];
    }
    return $result;
  }

}