class CommentWidget

class CommentWidget extends WidgetBase {
    
    /**
     * {@inheritdoc}
     */
    public function formElement(FieldItemListInterface $items, $delta, array $element, array &$form, FormStateInterface $form_state) {
        $entity = $items->getEntity();
        $element['status'] = [
            '#type' => 'radios',
            '#title' => $this->t('Comments'),
            '#title_display' => 'invisible',
            '#default_value' => $items->status,
            '#options' => [
                CommentItemInterface::OPEN => $this->t('Open'),
                CommentItemInterface::CLOSED => $this->t('Closed'),
                CommentItemInterface::HIDDEN => $this->t('Hidden'),
            ],
            CommentItemInterface::OPEN => [
                '#description' => $this->t('Users with the "Post comments" permission can post comments.'),
            ],
            CommentItemInterface::CLOSED => [
                '#description' => $this->t('Users cannot post comments, but existing comments will be displayed.'),
            ],
            CommentItemInterface::HIDDEN => [
                '#description' => $this->t('Comments are hidden from view.'),
            ],
        ];
        // If the entity doesn't have any comments, the "hidden" option makes no
        // sense, so don't even bother presenting it to the user unless this is the
        // default value widget on the field settings form.
        if (!$this->isDefaultValueWidget($form_state) && !$items->comment_count) {
            $element['status'][CommentItemInterface::HIDDEN]['#access'] = FALSE;
            // Also adjust the description of the "closed" option.
            $element['status'][CommentItemInterface::CLOSED]['#description'] = $this->t('Users cannot post comments.');
        }
        // If the advanced settings tabs-set is available (normally rendered in the
        // second column on wide-resolutions), place the field as a details element
        // in this tab-set.
        if (isset($form['advanced'])) {
            // Get default value from the field.
            $field_default_values = $this->fieldDefinition
                ->getDefaultValue($entity);
            // Override widget title to be helpful for end users.
            $element['#title'] = $this->t('Comment settings');
            $element += [
                '#type' => 'details',
                // Open the details when the selected value is different to the stored
                // default values for the field.
'#open' => $items->status != $field_default_values[0]['status'],
                '#group' => 'advanced',
                '#attributes' => [
                    'class' => [
                        'comment-' . Html::getClass($entity->getEntityTypeId()) . '-settings-form',
                    ],
                ],
                '#attached' => [
                    'library' => [
                        'comment/drupal.comment',
                    ],
                ],
            ];
        }
        return $element;
    }
    
    /**
     * {@inheritdoc}
     */
    public function massageFormValues(array $values, array $form, FormStateInterface $form_state) {
        // Add default values for statistics properties because we don't want to
        // have them in form.
        foreach ($values as &$value) {
            $value += [
                'cid' => 0,
                'last_comment_timestamp' => 0,
                'last_comment_name' => '',
                'last_comment_uid' => 0,
                'comment_count' => 0,
            ];
        }
        return $values;
    }

}