class StylesCombo

class StylesCombo extends CKEditorPluginBase implements CKEditorPluginConfigurableInterface {

  /**
   * Implements \Drupal\ckeditor\Plugin\CKEditorPluginInterface::isInternal().
   */
  public function isInternal() {
    return TRUE;
  }

  /**
   * Implements \Drupal\ckeditor\Plugin\CKEditorPluginInterface::getFile().
   */
  public function getFile() {

    // This plugin is already part of Drupal core's CKEditor build.
    return FALSE;
  }

  /**
   * Implements \Drupal\ckeditor\Plugin\CKEditorPluginInterface::getConfig().
   */
  public function getConfig(Editor $editor) {
    $config = array();
    $styles = $editor->settings['plugins']['stylescombo']['styles'];
    $config['stylesSet'] = $this
      ->generateStylesSetSetting($styles);
    return $config;
  }

  /**
   * Implements \Drupal\ckeditor\Plugin\CKEditorPluginButtonsInterface::getButtons().
   */
  public function getButtons() {
    return array(
      'Styles' => array(
        'label' => t('Font style'),
        'image_alternative' => '<a href="#" role="button" aria-label="' . t('Styles') . '"><span class="ckeditor-button-dropdown">' . t('Styles') . '<span class="ckeditor-button-arrow"></span></span></a>',
      ),
    );
  }

  /**
   * Implements \Drupal\ckeditor\Plugin\CKEditorPluginConfigurableInterface::settingsForm().
   */
  public function settingsForm(array $form, array &$form_state, Editor $editor) {

    // Defaults.
    $config = array(
      'styles' => '',
    );
    if (isset($editor->settings['plugins']['stylescombo'])) {
      $config = $editor->settings['plugins']['stylescombo'];
    }
    $form['styles'] = array(
      '#title' => t('Styles'),
      '#title_display' => 'invisible',
      '#type' => 'textarea',
      '#default_value' => $config['styles'],
      '#description' => t('A list of classes that will be provided in the "Styles" dropdown. Enter one class on each line in the format: element.class|Label. Example: h1.title|Title.<br />These styles should be available in your theme\'s CSS file.'),
      '#attached' => array(
        'library' => array(
          array(
            'ckeditor',
            'drupal.ckeditor.stylescombo.admin',
          ),
        ),
      ),
      '#element_validate' => array(
        array(
          $this,
          'validateStylesValue',
        ),
      ),
    );
    return $form;
  }

  /**
   * #element_validate handler for the "styles" element in settingsForm().
   */
  public function validateStylesValue(array $element, array &$form_state) {
    if ($this
      ->generateStylesSetSetting($element['#value']) === FALSE) {
      form_error($element, t('The provided list of styles is syntactically incorrect.'));
    }
  }

  /**
   * Builds the "stylesSet" configuration part of the CKEditor JS settings.
   *
   * @see getConfig()
   *
   * @param string $styles
   *   The "styles" setting.
   * @return array|FALSE
   *   An array containing the "stylesSet" configuration, or FALSE when the
   *   syntax is invalid.
   */
  protected function generateStylesSetSetting($styles) {
    $styles_set = array();

    // Early-return when empty.
    $styles = trim($styles);
    if (empty($styles)) {
      return $styles_set;
    }
    $styles = str_replace(array(
      "\r\n",
      "\r",
    ), "\n", $styles);
    foreach (explode("\n", $styles) as $style) {
      $style = trim($style);

      // Ignore empty lines in between non-empty lines.
      if (empty($style)) {
        continue;
      }

      // Validate syntax: element.class[.class...]|label pattern expected.
      if (!preg_match('@^ *[a-zA-Z0-9]+ *(\\.[a-zA-Z0-9_-]+ *)+\\| *.+ *$@', $style)) {
        return FALSE;
      }

      // Parse.
      list($selector, $label) = explode('|', $style);
      $classes = explode('.', $selector);
      $element = array_shift($classes);

      // Build the data structure CKEditor's stylescombo plugin expects.
      // @see http://docs.cksource.com/CKEditor_3.x/Developers_Guide/Styles
      $styles_set[] = array(
        'name' => trim($label),
        'element' => trim($element),
        'attributes' => array(
          'class' => implode(' ', array_map('trim', $classes)),
        ),
      );
    }
    return $styles_set;
  }

}