class CommentItem

class CommentItem extends FieldItemBase implements CommentItemInterface {
  
  /**
   * {@inheritdoc}
   */
  public static function defaultStorageSettings() {
    return [
      'comment_type' => '',
    ] + parent::defaultStorageSettings();
  }
  
  /**
   * {@inheritdoc}
   */
  public static function defaultFieldSettings() {
    return [
      'default_mode' => CommentManagerInterface::COMMENT_MODE_THREADED,
      'per_page' => 50,
      'form_location' => CommentItemInterface::FORM_BELOW,
      'anonymous' => AnonymousContact::Forbidden->value,
      'preview' => CommentPreviewMode::Optional->value,
    ] + parent::defaultFieldSettings();
  }
  
  /**
   * {@inheritdoc}
   */
  public static function propertyDefinitions(FieldStorageDefinitionInterface $field_definition) {
    $properties['status'] = DataDefinition::create('integer')->setLabel(new TranslatableMarkup('Comment status'))
      ->setRequired(TRUE);
    $properties['cid'] = DataDefinition::create('integer')->setLabel(new TranslatableMarkup('Last comment ID'));
    $properties['last_comment_timestamp'] = DataDefinition::create('integer')->setLabel(new TranslatableMarkup('Last comment timestamp'))
      ->setDescription(new TranslatableMarkup('The time that the last comment was created.'));
    $properties['last_comment_name'] = DataDefinition::create('string')->setLabel(new TranslatableMarkup('Last comment name'))
      ->setDescription(new TranslatableMarkup('The name of the user posting the last comment.'));
    $properties['last_comment_uid'] = DataDefinition::create('integer')->setLabel(new TranslatableMarkup('Last comment user ID'));
    $properties['comment_count'] = DataDefinition::create('integer')->setLabel(new TranslatableMarkup('Number of comments'))
      ->setDescription(new TranslatableMarkup('The number of comments.'));
    return $properties;
  }
  
  /**
   * {@inheritdoc}
   */
  public static function schema(FieldStorageDefinitionInterface $field_definition) {
    return [
      'columns' => [
        'status' => [
          'description' => 'Whether comments are allowed on this entity: 0 = no, 1 = closed (read only), 2 = open (read/write).',
          'type' => 'int',
          'default' => 0,
        ],
      ],
      'indexes' => [],
      'foreign keys' => [],
    ];
  }
  
  /**
   * {@inheritdoc}
   */
  public function fieldSettingsForm(array $form, FormStateInterface $form_state) {
    $element = [];
    $settings = $this->getSettings();
    $anonymous_user = new AnonymousUserSession();
    $element['default_mode'] = [
      '#type' => 'checkbox',
      '#title' => $this->t('Threading'),
      '#default_value' => $settings['default_mode'],
      '#description' => $this->t('Show comment replies in a threaded list.'),
    ];
    $element['per_page'] = [
      '#type' => 'number',
      '#title' => $this->t('Comments per page'),
      '#default_value' => $settings['per_page'],
      '#required' => TRUE,
      '#min' => 0,
      '#max' => 1000,
      '#description' => $this->t('Enter 0 to show all comments.'),
    ];
    $element['anonymous'] = [
      '#type' => 'select',
      '#title' => $this->t('Anonymous commenting'),
      '#default_value' => $settings['anonymous'],
      '#options' => AnonymousContact::asOptions(),
      '#access' => $anonymous_user->hasPermission('post comments'),
    ];
    $element['form_location'] = [
      '#type' => 'checkbox',
      '#title' => $this->t('Show reply form on the same page as comments'),
      '#default_value' => $settings['form_location'],
    ];
    $element['preview'] = [
      '#type' => 'radios',
      '#title' => $this->t('Preview comment'),
      '#default_value' => $settings['preview'],
      '#options' => CommentPreviewMode::asOptions(),
    ];
    return $element;
  }
  
  /**
   * {@inheritdoc}
   */
  public static function mainPropertyName() {
    return 'status';
  }
  
  /**
   * {@inheritdoc}
   */
  public function isEmpty() {
    // There is always a value for this field, it is one of the values of the
    // \Drupal\comment\CommentingStatus enum.
    return FALSE;
  }
  
  /**
   * {@inheritdoc}
   */
  public function storageSettingsForm(array &$form, FormStateInterface $form_state, $has_data) {
    $element = [];
    // @todo Inject entity storage once typed-data supports container injection.
    //   See https://www.drupal.org/node/2053415 for more details.
    $comment_types = CommentType::loadMultiple();
    $options = [];
    $entity_type = $this->getEntity()
      ->getEntityTypeId();
    foreach ($comment_types as $comment_type) {
      if ($comment_type->getTargetEntityTypeId() == $entity_type) {
        $options[$comment_type->id()] = $comment_type->label();
      }
    }
    $element['comment_type'] = [
      '#type' => 'select',
      '#title' => $this->t('Comment type'),
      '#options' => $options,
      '#required' => TRUE,
      '#description' => $this->t('Select the Comment type to use for this comment field. Manage the comment types from the <a href=":url">administration overview page</a>.', [
        ':url' => Url::fromRoute('entity.comment_type.collection')->toString(),
      ]),
      '#default_value' => $this->getSetting('comment_type'),
      '#disabled' => $has_data,
    ];
    return $element;
  }
  
  /**
   * {@inheritdoc}
   */
  public static function generateSampleValue(FieldDefinitionInterface $field_definition) {
    $statuses = array_column(CommentingStatus::cases(), 'value');
    return [
      'status' => $statuses[mt_rand(0, count($statuses) - 1)],
    ];
  }

}