class CommentLinkBuilder

class CommentLinkBuilder implements CommentLinkBuilderInterface {
  use StringTranslationTrait;

  /**
   * Current user.
   *
   * @var \Drupal\Core\Session\AccountInterface
   */
  protected $currentUser;

  /**
   * Comment manager service.
   *
   * @var \Drupal\comment\CommentManagerInterface
   */
  protected $commentManager;

  /**
   * Module handler service.
   *
   * @var \Drupal\Core\Extension\ModuleHandlerInterface
   */
  protected $moduleHandler;

  /**
   * The entity type manager service.
   *
   * @var \Drupal\Core\Entity\EntityTypeManagerInterface
   */
  protected $entityTypeManager;

  /**
   * Constructs a new CommentLinkBuilder object.
   *
   * @param \Drupal\Core\Session\AccountInterface $current_user
   *   Current user.
   * @param \Drupal\comment\CommentManagerInterface $comment_manager
   *   Comment manager service.
   * @param \Drupal\Core\Extension\ModuleHandlerInterface $module_handler
   *   Module handler service.
   * @param \Drupal\Core\StringTranslation\TranslationInterface $string_translation
   *   String translation service.
   * @param \Drupal\Core\Entity\EntityTypeManagerInterface $entity_type_manager
   *   The entity type manager.
   */
  public function __construct(AccountInterface $current_user, CommentManagerInterface $comment_manager, ModuleHandlerInterface $module_handler, TranslationInterface $string_translation, EntityTypeManagerInterface $entity_type_manager) {
    $this->currentUser = $current_user;
    $this->commentManager = $comment_manager;
    $this->moduleHandler = $module_handler;
    $this->stringTranslation = $string_translation;
    $this->entityTypeManager = $entity_type_manager;
  }

  /**
   * {@inheritdoc}
   */
  public function buildCommentedEntityLinks(FieldableEntityInterface $entity, array &$context) {
    $entity_links = [];
    $view_mode = $context['view_mode'];
    if ($view_mode == 'search_index' || $view_mode == 'search_result' || $view_mode == 'print' || $view_mode == 'rss') {

      // Do not add any links if the entity is displayed for:
      // - search indexing.
      // - constructing a search result excerpt.
      // - print.
      // - rss.
      return [];
    }
    $fields = $this->commentManager
      ->getFields($entity
      ->getEntityTypeId());
    foreach ($fields as $field_name => $detail) {

      // Skip fields that the entity does not have.
      if (!$entity
        ->hasField($field_name)) {
        continue;
      }
      $links = [];
      $commenting_status = $entity
        ->get($field_name)->status;
      if ($commenting_status != CommentItemInterface::HIDDEN) {

        // Entity has commenting status open or closed.
        $field_definition = $entity
          ->getFieldDefinition($field_name);
        if ($view_mode == 'teaser') {

          // Teaser view: display the number of comments that have been posted,
          // or a link to add new comments if the user has permission, the
          // entity is open to new comments, and there currently are none.
          if ($this->currentUser
            ->hasPermission('access comments')) {
            if (!empty($entity
              ->get($field_name)->comment_count)) {
              $links['comment-comments'] = [
                'title' => $this
                  ->formatPlural($entity
                  ->get($field_name)->comment_count, '1 comment', '@count comments'),
                'attributes' => [
                  'title' => $this
                    ->t('Jump to the first comment.'),
                ],
                'fragment' => 'comments',
                'url' => $entity
                  ->toUrl(),
              ];
              if ($this->moduleHandler
                ->moduleExists('history')) {
                $links['comment-new-comments'] = [
                  'title' => '',
                  'url' => Url::fromRoute('<current>'),
                  'attributes' => [
                    'class' => 'hidden',
                    'title' => $this
                      ->t('Jump to the first new comment.'),
                    'data-history-node-last-comment-timestamp' => $entity
                      ->get($field_name)->last_comment_timestamp,
                    'data-history-node-field-name' => $field_name,
                  ],
                ];
              }
            }
          }

          // Provide a link to new comment form.
          if ($commenting_status == CommentItemInterface::OPEN) {
            $comment_form_location = $field_definition
              ->getSetting('form_location');
            if ($this->currentUser
              ->hasPermission('post comments')) {
              $links['comment-add'] = [
                'title' => $this
                  ->t('Add new comment'),
                'language' => $entity
                  ->language(),
                'attributes' => [
                  'title' => $this
                    ->t('Share your thoughts and opinions.'),
                ],
                'fragment' => 'comment-form',
              ];
              if ($comment_form_location == CommentItemInterface::FORM_SEPARATE_PAGE) {
                $links['comment-add']['url'] = Url::fromRoute('comment.reply', [
                  'entity_type' => $entity
                    ->getEntityTypeId(),
                  'entity' => $entity
                    ->id(),
                  'field_name' => $field_name,
                ]);
              }
              else {
                $links['comment-add'] += [
                  'url' => $entity
                    ->toUrl(),
                ];
              }
            }
            elseif ($this->currentUser
              ->isAnonymous()) {
              $links['comment-forbidden'] = [
                'title' => $this->commentManager
                  ->forbiddenMessage($entity, $field_name),
              ];
            }
          }
        }
        else {

          // Entity in other view modes: add a "post comment" link if the user
          // is allowed to post comments and if this entity is allowing new
          // comments.
          if ($commenting_status == CommentItemInterface::OPEN) {
            $comment_form_location = $field_definition
              ->getSetting('form_location');
            if ($this->currentUser
              ->hasPermission('post comments')) {

              // Show the "post comment" link if the form is on another page, or
              // if there are existing comments that the link will skip past.
              if ($comment_form_location == CommentItemInterface::FORM_SEPARATE_PAGE || !empty($entity
                ->get($field_name)->comment_count) && $this->currentUser
                ->hasPermission('access comments')) {
                $links['comment-add'] = [
                  'title' => $this
                    ->t('Add new comment'),
                  'attributes' => [
                    'title' => $this
                      ->t('Share your thoughts and opinions.'),
                  ],
                  'fragment' => 'comment-form',
                ];
                if ($comment_form_location == CommentItemInterface::FORM_SEPARATE_PAGE) {
                  $links['comment-add']['url'] = Url::fromRoute('comment.reply', [
                    'entity_type' => $entity
                      ->getEntityTypeId(),
                    'entity' => $entity
                      ->id(),
                    'field_name' => $field_name,
                  ]);
                }
                else {
                  $links['comment-add']['url'] = $entity
                    ->toUrl();
                }
              }
            }
            elseif ($this->currentUser
              ->isAnonymous()) {
              $links['comment-forbidden'] = [
                'title' => $this->commentManager
                  ->forbiddenMessage($entity, $field_name),
              ];
            }
          }
        }
      }
      if (!empty($links)) {
        $entity_links['comment__' . $field_name] = [
          '#theme' => 'links__entity__comment__' . $field_name,
          '#links' => $links,
          '#attributes' => [
            'class' => [
              'links',
              'inline',
            ],
          ],
        ];
        if ($view_mode == 'teaser' && $this->moduleHandler
          ->moduleExists('history') && $this->currentUser
          ->isAuthenticated()) {
          $entity_links['comment__' . $field_name]['#cache']['contexts'][] = 'user';
          $entity_links['comment__' . $field_name]['#attached']['library'][] = 'comment/drupal.node-new-comments-link';

          // Embed the metadata for the "X new comments" link (if any) on this
          // entity.
          $entity_links['comment__' . $field_name]['#attached']['drupalSettings']['history']['lastReadTimestamps'][$entity
            ->id()] = history_read($entity
            ->id());
          $new_comments = $this->commentManager
            ->getCountNewComments($entity);
          if ($new_comments > 0) {
            $page_number = $this->entityTypeManager
              ->getStorage('comment')
              ->getNewCommentPageNumber($entity->{$field_name}->comment_count, $new_comments, $entity, $field_name);
            $query = $page_number ? [
              'page' => $page_number,
            ] : NULL;
            $value = [
              'new_comment_count' => (int) $new_comments,
              'first_new_comment_link' => $entity
                ->toUrl('canonical', [
                'query' => $query,
                'fragment' => 'new',
              ])
                ->toString(),
            ];
            $parents = [
              'comment',
              'newCommentsLinks',
              $entity
                ->getEntityTypeId(),
              $field_name,
              $entity
                ->id(),
            ];
            NestedArray::setValue($entity_links['comment__' . $field_name]['#attached']['drupalSettings'], $parents, $value);
          }
        }
      }
    }
    return $entity_links;
  }

}