trait CodeMirrorPluginTrait in The CodeMirror Editor 8

trait CodeMirrorPluginTrait {

  /**
   * Returns a list of buttons available for CodeMirror.
   *
   * @return array
   *   A list of buttons.
   */
  protected static function getAvailableButtons() {
    return [
      'bold',
      'italic',
      'underline',
      'strike-through',
      'list-numbered',
      'list-bullet',
      'link',
      'horizontal-rule',
      'undo',
      'redo',
      'clear-formatting',
      'enlarge',
      'shrink',
    ];
  }

  /**
   * Returns the default settings for CodeMirror plugin.
   *
   * @return array
   *   A list of default settings, keyed by the setting name.
   */
  protected static function getDefaultCodeMirrorSettings() {
    return [
      'mode' => 'text/html',
      'toolbar' => TRUE,
      'buttons' => static::getAvailableButtons(),
      'lineWrapping' => FALSE,
      'lineNumbers' => FALSE,
      'foldGutter' => FALSE,
      'autoCloseTags' => TRUE,
      'styleActiveLine' => FALSE,
    ];
  }

  /**
   * Returns a form to configure settings for the CodeMirror plugin.
   *
   * @param array $settings
   *   The plugin settings.
   * @param array $keys
   *   If provided only specified form elements will be rendered.
   *
   * @return array
   *   The form definition for the plugin settings.
   */
  protected static function buildCodeMirrorSettingsForm(array $settings, array $keys = NULL) {
    $form = [];
    if (!$keys || in_array('mode', $keys)) {
      $definitions = \Drupal::service('plugin.manager.codemirror_mode')
        ->getDefinitions();
      $enabled_modes = \Drupal::config('codemirror_editor.settings')
        ->get('language_modes');
      $options = [];
      foreach ($definitions as $mode => $definition) {
        if (in_array($mode, $enabled_modes)) {
          ksort($definition['mime_types']);
          foreach ($definition['mime_types'] as $mime_type) {
            $options[$definition['label']][$mime_type] = $mime_type;
          }
        }
      }
      $form['mode'] = [
        '#type' => 'select',
        '#title' => t('Language mode'),
        '#default_value' => $settings['mode'],
        '#options' => $options,
      ];
    }
    if (!$keys || in_array('toolbar', $keys)) {
      $form['toolbar'] = [
        '#title' => t('Load toolbar'),
        '#type' => 'checkbox',
        '#default_value' => $settings['toolbar'],
      ];
    }
    if (!$keys || in_array('buttons', $keys)) {
      $form['buttons'] = [
        '#type' => 'select',
        '#multiple' => TRUE,
        '#title' => t('Toolbar buttons'),
        '#default_value' => $settings['buttons'],
        '#options' => array_combine(static::getAvailableButtons(), static::getAvailableButtons()),
        '#value_callback' => [
          static::class,
          'setButtonsValue',
        ],
        '#states' => [
          'visible' => [
            ':input[name$="[settings_edit_form][settings][toolbar]"]' => [
              'checked' => TRUE,
            ],
          ],
        ],
        '#description' => t('Buttons that will be available inside the toolbar.'),
      ];
    }
    if (!$keys || in_array('lineWrapping', $keys)) {
      $form['lineWrapping'] = [
        '#title' => t('Line wrapping'),
        '#type' => 'checkbox',
        '#default_value' => $settings['lineWrapping'],
      ];
    }
    if (!$keys || in_array('lineNumbers', $keys)) {
      $form['lineNumbers'] = [
        '#title' => t('Line numbers'),
        '#type' => 'checkbox',
        '#default_value' => $settings['lineNumbers'],
      ];
    }
    if (!$keys || in_array('foldGutter', $keys)) {
      $form['foldGutter'] = [
        '#title' => t('Fold gutter'),
        '#type' => 'checkbox',
        '#default_value' => $settings['foldGutter'],
      ];
    }
    if (!$keys || in_array('autoCloseTags', $keys)) {
      $form['autoCloseTags'] = [
        '#title' => t('Auto close tags'),
        '#type' => 'checkbox',
        '#default_value' => $settings['autoCloseTags'],
      ];
    }
    if (!$keys || in_array('styleActiveLine', $keys)) {
      $form['styleActiveLine'] = [
        '#title' => t('Style active line'),
        '#type' => 'checkbox',
        '#default_value' => $settings['styleActiveLine'],
      ];
    }
    return $form;
  }

  /**
   * Returns formatted boolean setting value.
   *
   * @param string $key
   *   Plugin setting key to format.
   *
   * @return string
   *   Format settings value.
   */
  protected function formatBoolean($key) {
    return $this->settings[$key] ? $this
      ->t('Yes') : $this
      ->t('No');
  }

  /**
   * Normalizes language mode.
   *
   * @param string $mode
   *   Language mode to normalize.
   *
   * @return string
   *   Normalized language mode.
   */
  protected static function normalizeMode($mode) {
    return \Drupal::service('plugin.manager.codemirror_mode')
      ->normalizeMode($mode);
  }

  /**
   * Value callback for CodeMirror buttons.
   *
   * Prevent buttons from being stored in config with keyed values.
   *
   * @param array $element
   *   An associative array containing the properties of the element.
   * @param mixed $input
   *   The incoming input to populate the form element. If this is FALSE,
   *   the element's default value should be returned.
   * @param \Drupal\Core\Form\FormStateInterface $form_state
   *   The current state of the form.
   *
   * @return mixed
   *   The value to assign to the element.
   */
  public static function setButtonsValue(array &$element, $input, FormStateInterface $form_state) {
    if ($input === FALSE) {
      return $element['#default_value'] ?? [];
    }
    return $input;
  }

}