comment.module

<?php

/**
 * @file
 * Enables users to comment on published content.
 *
 * When enabled, the Comment module creates a discussion board for each Drupal
 * node. Users can post comments to discuss a forum topic, story, collaborative
 * book page, etc.
 */

use Drupal\node\Plugin\Core\Entity\Node;
use Drupal\entity\Plugin\Core\Entity\EntityDisplay;
use Drupal\file\Plugin\Core\Entity\File;
use Drupal\Core\Entity\EntityInterface;
use Symfony\Component\HttpFoundation\Request;
use Symfony\Component\HttpKernel\Exception\NotFoundHttpException;
use Symfony\Component\HttpKernel\HttpKernelInterface;

/**
 * Comment is awaiting approval.
 */
const COMMENT_NOT_PUBLISHED = 0;

/**
 * Comment is published.
 */
const COMMENT_PUBLISHED = 1;

/**
 * Comments are displayed in a flat list - expanded.
 */
const COMMENT_MODE_FLAT = 0;

/**
 * Comments are displayed as a threaded list - expanded.
 */
const COMMENT_MODE_THREADED = 1;

/**
 * Anonymous posters cannot enter their contact information.
 */
const COMMENT_ANONYMOUS_MAYNOT_CONTACT = 0;

/**
 * Anonymous posters may leave their contact information.
 */
const COMMENT_ANONYMOUS_MAY_CONTACT = 1;

/**
 * Anonymous posters are required to leave their contact information.
 */
const COMMENT_ANONYMOUS_MUST_CONTACT = 2;

/**
 * Comment form should be displayed on a separate page.
 */
const COMMENT_FORM_SEPARATE_PAGE = 0;

/**
 * Comment form should be shown below post or list of comments.
 */
const COMMENT_FORM_BELOW = 1;

/**
 * Comments for this node are hidden.
 */
const COMMENT_NODE_HIDDEN = 0;

/**
 * Comments for this node are closed.
 */
const COMMENT_NODE_CLOSED = 1;

/**
 * Comments for this node are open.
 */
const COMMENT_NODE_OPEN = 2;

use Drupal\comment\Plugin\Core\Entity\Comment;

/**
 * Implements hook_help().
 */
function comment_help($path, $arg) {
  switch ($path) {
    case 'admin/help#comment':
      $output = '<h3>' . t('About') . '</h3>';
      $output .= '<p>' . t('The Comment module allows users to comment on site content, set commenting defaults and permissions, and moderate comments. For more information, see the online handbook entry for <a href="@comment">Comment module</a>.', array('@comment' => 'http://drupal.org/documentation/modules/comment')) . '</p>';
      $output .= '<h3>' . t('Uses') . '</h3>';
      $output .= '<dl>';
      $output .= '<dt>' . t('Default and custom settings') . '</dt>';
      $output .= '<dd>' . t("Each <a href='@content-type'>content type</a> can have its own default comment settings configured as: <em>Open</em> to allow new comments, <em>Hidden</em> to hide existing comments and prevent new comments, or <em>Closed</em> to view existing comments, but prevent new comments. These defaults will apply to all new content created (changes to the settings on existing content must be done manually). Other comment settings can also be customized per content type, and can be overridden for any given item of content. When a comment has no replies, it remains editable by its author, as long as the author has a user account and is logged in.", array('@content-type' => url('admin/structure/types'))) . '</dd>';
      $output .= '<dt>' . t('Comment approval') . '</dt>';
      $output .= '<dd>' . t("Comments from users who have the <em>Skip comment approval</em> permission are published immediately. All other comments are placed in the <a href='@comment-approval'>Unapproved comments</a> queue, until a user who has permission to <em>Administer comments</em> publishes or deletes them. Published comments can be bulk managed on the <a href='@admin-comment'>Published comments</a> administration page.", array('@comment-approval' => url('admin/content/comment/approval'), '@admin-comment' => url('admin/content/comment'))) . '</dd>';
      $output .= '</dl>';
      return $output;
  }
}

/**
 * Implements hook_entity_view_mode_info().
 */
function comment_entity_view_mode_info() {
  $view_modes['comment']['full'] = array(
    'label' => t('Full comment'),
  );
  return $view_modes;
}

/**
 * Implements hook_entity_bundle_info().
 */
function comment_entity_bundle_info() {
  $bundles = array();
  foreach (node_type_get_names() as $type => $name) {
    $bundles['comment']['comment_node_' . $type] = array(
      'label' => t('@node_type comment', array('@node_type' => $name)),
      // Provide the node type/bundle name for other modules, so it does not
      // have to be extracted manually from the bundle name.
      'node bundle' => $type,
      'admin' => array(
        // Place the Field UI paths for comments one level below the
        // corresponding paths for nodes, so that they appear in the same set
        // of local tasks. Note that the paths use a different placeholder name
        // and thus a different menu loader callback, so that Field UI page
        // callbacks get a comment bundle name from the node type in the URL.
        // See comment_node_type_load() and comment_menu_alter().
        'path' => 'admin/structure/types/manage/%comment_node_type/comment',
        'bundle argument' => 4,
        'real path' => 'admin/structure/types/manage/' . $type . '/comment',
      ),
    );
  }
  return $bundles;
}

/**
 * Loads the comment bundle name corresponding a given content type.
 *
 * This function is used as a menu loader callback in comment_menu().
 *
 * @param $name
 *   The machine name of the node type whose comment fields are to be edited.
 *
 * @return
 *   The comment bundle name corresponding to the node type.
 *
 * @see comment_menu_alter()
 */
function comment_node_type_load($name) {
  if ($type = node_type_load($name)) {
    return 'comment_node_' . $type->type;
  }
}

/**
 * Entity URI callback.
 */
function comment_uri(Comment $comment) {
  return array(
    'path' => 'comment/' . $comment->id(),
    'options' => array('fragment' => 'comment-' . $comment->id()),
  );
}

/**
 * Implements hook_field_extra_fields().
 */
function comment_field_extra_fields() {
  $return = array();

  foreach (node_type_get_types() as $type) {
    if (variable_get('comment_subject_field_' . $type->type, 1) == 1) {
      $return['comment']['comment_node_' . $type->type] = array(
        'form' => array(
          'author' => array(
            'label' => t('Author'),
            'description' => t('Author textfield'),
            'weight' => -2,
          ),
          'subject' => array(
            'label' => t('Subject'),
            'description' => t('Subject textfield'),
            'weight' => -1,
          ),
        ),
      );
    }
  }

  return $return;
}

/**
 * Implements hook_theme().
 */
function comment_theme() {
  return array(
    'comment_block' => array(
      'variables' => array('number' => NULL),
    ),
    'comment_preview' => array(
      'variables' => array('comment' => NULL),
    ),
    'comment' => array(
      'template' => 'comment',
      'render element' => 'elements',
    ),
    'comment_post_forbidden' => array(
      'variables' => array('node' => NULL),
    ),
    'comment_wrapper' => array(
      'template' => 'comment-wrapper',
      'render element' => 'content',
    ),
  );
}

/**
 * Implements hook_menu().
 */
function comment_menu() {
  $items['admin/content/comment'] = array(
    'title' => 'Comments',
    'description' => 'List and edit site comments and the comment approval queue.',
    'page callback' => 'comment_admin',
    'access arguments' => array('administer comments'),
    'type' => MENU_LOCAL_TASK | MENU_NORMAL_ITEM,
    'file' => 'comment.admin.inc',
  );
  // Tabs begin here.
  $items['admin/content/comment/new'] = array(
    'title' => 'Published comments',
    'type' => MENU_DEFAULT_LOCAL_TASK,
    'weight' => -10,
  );
  $items['admin/content/comment/approval'] = array(
    'title' => 'Unapproved comments',
    'title callback' => 'comment_count_unpublished',
    'page arguments' => array('approval'),
    'access arguments' => array('administer comments'),
    'type' => MENU_LOCAL_TASK,
  );
  $items['comment/%'] = array(
    'title' => 'Comment permalink',
    'page callback' => 'comment_permalink',
    'page arguments' => array(1),
    'access arguments' => array('access comments'),
  );
  $items['comment/%/view'] = array(
    'title' => 'View comment',
    'type' => MENU_DEFAULT_LOCAL_TASK,
    'weight' => -10,
  );
  // Every other comment path uses %, but this one loads the comment directly,
  // so we don't end up loading it twice (in the page and access callback).
  $items['comment/%comment/edit'] = array(
    'title' => 'Edit',
    'page callback' => 'comment_edit_page',
    'page arguments' => array(1),
    'access callback' => 'comment_access',
    'access arguments' => array('edit', 1),
    'type' => MENU_LOCAL_TASK,
    'weight' => 0,
  );
  $items['comment/%/approve'] = array(
    'title' => 'Approve',
    'page callback' => 'comment_approve',
    'page arguments' => array(1),
    'access arguments' => array('administer comments'),
    'file' => 'comment.pages.inc',
    'weight' => 1,
  );
  $items['comment/%/delete'] = array(
    'title' => 'Delete',
    'page callback' => 'comment_confirm_delete_page',
    'page arguments' => array(1),
    'access arguments' => array('administer comments'),
    'type' => MENU_LOCAL_TASK,
    'file' => 'comment.admin.inc',
    'weight' => 2,
  );
  $items['comment/reply/%node'] = array(
    'title' => 'Add new comment',
    'page callback' => 'comment_reply',
    'page arguments' => array(2),
    'access callback' => 'node_access',
    'access arguments' => array('view', 2),
    'file' => 'comment.pages.inc',
  );

  return $items;
}

/**
 * Implements hook_menu_alter().
 */
function comment_menu_alter(&$items) {
  // Add comments to the description for admin/content.
  $items['admin/content']['description'] = 'Administer content and comments.';

  // Adjust the Field UI tabs on admin/structure/types/manage/[node-type].
  // See comment_entity_bundle_info().
  $items['admin/structure/types/manage/%comment_node_type/comment/fields']['title'] = 'Comment fields';
  $items['admin/structure/types/manage/%comment_node_type/comment/fields']['weight'] = 3;
  $items['admin/structure/types/manage/%comment_node_type/comment/display']['title'] = 'Comment display';
  $items['admin/structure/types/manage/%comment_node_type/comment/display']['weight'] = 4;
}

/**
 * Returns a menu title which includes the number of unapproved comments.
 */
function comment_count_unpublished() {
  $count = db_query('SELECT COUNT(cid) FROM {comment} WHERE status = :status', array(
    ':status' => COMMENT_NOT_PUBLISHED,
  ))->fetchField();
  return t('Unapproved comments (@count)', array('@count' => $count));
}

/**
 * Implements hook_node_type_insert().
 *
 * Creates a comment body field for a node type created while the Comment module
 * is enabled. For node types created before the Comment module is enabled,
 * hook_modules_enabled() serves to create the body fields.
 *
 * @see comment_modules_enabled()
 */
function comment_node_type_insert($info) {
  _comment_body_field_create($info);
}

/**
 * Implements hook_node_type_update().
 */
function comment_node_type_update($info) {
  if (!empty($info->old_type) && $info->type != $info->old_type) {
    field_attach_rename_bundle('comment', 'comment_node_' . $info->old_type, 'comment_node_' . $info->type);
  }
}

/**
 * Implements hook_node_type_delete().
 */
function comment_node_type_delete($info) {
  field_attach_delete_bundle('comment', 'comment_node_' . $info->type);
  $settings = array(
    'comment',
    'comment_default_mode',
    'comment_default_per_page',
    'comment_anonymous',
    'comment_subject_field',
    'comment_preview',
    'comment_form_location',
  );
  foreach ($settings as $setting) {
    variable_del($setting . '_' . $info->type);
  }
}

 /**
 * Creates a comment_body field instance for a given node type.
 *
 * @param $info
 *   An object representing the content type. The only property that is
 *   currently used is $info->type, which is the machine name of the content
 *   type for which the body field (instance) is to be created.
 */
function _comment_body_field_create($info) {
  // Create the field if needed.
  if (!field_read_field('comment_body', array('include_inactive' => TRUE))) {
    $field = array(
      'field_name' => 'comment_body',
      'type' => 'text_long',
      'entity_types' => array('comment'),
    );
    field_create_field($field);
  }
  // Create the instance if needed.
  if (!field_read_instance('comment', 'comment_body', 'comment_node_' . $info->type, array('include_inactive' => TRUE))) {
    field_attach_create_bundle('comment', 'comment_node_' . $info->type);
    // Attaches the body field by default.
    $instance = array(
      'field_name' => 'comment_body',
      'label' => 'Comment',
      'entity_type' => 'comment',
      'bundle' => 'comment_node_' . $info->type,
      'settings' => array('text_processing' => 1),
      'required' => TRUE,
    );
    field_create_instance($instance);
    entity_get_display('comment', 'comment_node_' . $info->type, 'default')
      ->setComponent('comment_body', array(
        'label' => 'hidden',
        'type' => 'text_default',
        'weight' => 0,
      ))
      ->save();
  }
}

/**
 * Implements hook_permission().
 */
function comment_permission() {
  return array(
    'administer comments' => array(
      'title' => t('Administer comments and comment settings'),
    ),
    'access comments' => array(
      'title' => t('View comments'),
    ),
    'post comments' => array(
      'title' => t('Post comments'),
    ),
    'skip comment approval' => array(
      'title' => t('Skip comment approval'),
    ),
    'edit own comments' => array(
      'title' => t('Edit own comments'),
    ),
  );
}

/**
 * Redirects comment links to the correct page depending on comment settings.
 *
 * Since comments are paged there is no way to guarantee which page a comment
 * appears on. Comment paging and threading settings may be changed at any time.
 * With threaded comments, an individual comment may move between pages as
 * comments can be added either before or after it in the overall discussion.
 * Therefore we use a central routing function for comment links, which
 * calculates the page number based on current comment settings and returns
 * the full comment view with the pager set dynamically.
 *
 * @param $cid
 *   A comment identifier.
 *
 * @return
 *   The comment listing set to the page on which the comment appears.
 */
function comment_permalink($cid) {
  if (($comment = comment_load($cid)) && ($node = $comment->nid->entity)) {

    // Find the current display page for this comment.
    $page = comment_get_display_page($comment->id(), $node->type);

    // @todo: Cleaner sub request handling.
    $request = drupal_container()->get('request');
    $subrequest = Request::create('/node/' . $node->nid, 'GET', $request->query->all(), $request->cookies->all(), array(), $request->server->all());
    $subrequest->query->set('page', $page);
    // @todo: Convert the pager to use the request object.
    $_GET['page'] = $page;
    return drupal_container()->get('http_kernel')->handle($subrequest, HttpKernelInterface::SUB_REQUEST);
  }
  throw new NotFoundHttpException();
}

/**
 * Finds the most recent comments that are available to the current user.
 *
 * @param integer $number
 *   (optional) The maximum number of comments to find. Defaults to 10.
 *
 * @return
 *   An array of comment objects or an empty array if there are no recent
 *   comments visible to the current user.
 */
function comment_get_recent($number = 10) {
  $query = db_select('comment', 'c');
  $query->innerJoin('node', 'n', 'n.nid = c.nid');
  $query->addTag('node_access');
  $query->addMetaData('base_table', 'comment');
  $comments = $query
    ->fields('c')
    ->condition('c.status', COMMENT_PUBLISHED)
    ->condition('n.status', NODE_PUBLISHED)
    ->orderBy('c.created', 'DESC')
    // Additionally order by cid to ensure that comments with the same timestamp
    // are returned in the exact order posted.
    ->orderBy('c.cid', 'DESC')
    ->range(0, $number)
    ->execute()
    ->fetchAll();

  return $comments ? $comments : array();
}

/**
 * Calculates the page number for the first new comment.
 *
 * @param $num_comments
 *   Number of comments.
 * @param $new_replies
 *   Number of new replies.
 * @param Drupal\node\Node $node
 *   The first new comment node.
 *
 * @return
 *   "page=X" if the page number is greater than zero; empty string otherwise.
 */
function comment_new_page_count($num_comments, $new_replies, Node $node) {
  $mode = variable_get('comment_default_mode_' . $node->type, COMMENT_MODE_THREADED);
  $comments_per_page = variable_get('comment_default_per_page_' . $node->type, 50);
  $pagenum = NULL;
  $flat = $mode == COMMENT_MODE_FLAT ? TRUE : FALSE;
  if ($num_comments <= $comments_per_page) {
    // Only one page of comments.
    $pageno = 0;
  }
  elseif ($flat) {
    // Flat comments.
    $count = $num_comments - $new_replies;
    $pageno = $count / $comments_per_page;
  }
  else {
    // Threaded comments: we build a query with a subquery to find the first
    // thread with a new comment.

    // 1. Find all the threads with a new comment.
    $unread_threads_query = db_select('comment')
      ->fields('comment', array('thread'))
      ->condition('nid', $node->nid)
      ->condition('status', COMMENT_PUBLISHED)
      ->orderBy('created', 'DESC')
      ->orderBy('cid', 'DESC')
      ->range(0, $new_replies);

    // 2. Find the first thread.
    $first_thread = db_select($unread_threads_query, 'thread')
      ->fields('thread', array('thread'))
      ->orderBy('SUBSTRING(thread, 1, (LENGTH(thread) - 1))')
      ->range(0, 1)
      ->execute()
      ->fetchField();

    // Remove the final '/'.
    $first_thread = substr($first_thread, 0, -1);

    // Find the number of the first comment of the first unread thread.
    $count = db_query('SELECT COUNT(*) FROM {comment} WHERE nid = :nid AND status = :status AND SUBSTRING(thread, 1, (LENGTH(thread) - 1)) < :thread', array(
      ':status' => COMMENT_PUBLISHED,
      ':nid' => $node->nid,
      ':thread' => $first_thread,
    ))->fetchField();

    $pageno = $count / $comments_per_page;
  }

  if ($pageno >= 1) {
    $pagenum = array('page' => intval($pageno));
  }

  return $pagenum;
}

/**
 * Returns HTML for a list of recent comments.
 *
 * @ingroup themeable
 */
function theme_comment_block($variables) {
  $items = array();
  $number = $variables['number'];
  foreach (comment_get_recent($number) as $comment) {
    $items[] = l($comment->subject, 'comment/' . $comment->cid, array('fragment' => 'comment-' . $comment->cid)) . '&nbsp;<span>' . t('@time ago', array('@time' => format_interval(REQUEST_TIME - $comment->changed))) . '</span>';
  }

  if ($items) {
    return theme('item_list', array('items' => $items));
  }
  else {
    return t('No comments available.');
  }
}

/**
 * Implements hook_node_view().
 */
function comment_node_view(Node $node, EntityDisplay $display, $view_mode) {
  $links = array();

  if ($node->comment != COMMENT_NODE_HIDDEN) {
    if ($view_mode == 'rss') {
      // Add a comments RSS element which is a URL to the comments of this node.
      $node->rss_elements[] = array(
        'key' => 'comments',
        'value' => url('node/' . $node->nid, array('fragment' => 'comments', 'absolute' => TRUE))
      );
    }
    elseif ($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 node
      // is open to new comments, and there currently are none.
      if (user_access('access comments')) {
        if (!empty($node->comment_count)) {
          $links['comment-comments'] = array(
            'title' => format_plural($node->comment_count, '1 comment', '@count comments'),
            'href' => "node/$node->nid",
            'attributes' => array('title' => t('Jump to the first comment of this posting.')),
            'fragment' => 'comments',
            'html' => TRUE,
          );
          // Show a link to the first new comment.
          if ($new = comment_num_new($node->nid)) {
            $links['comment-new-comments'] = array(
              'title' => format_plural($new, '1 new comment', '@count new comments'),
              'href' => "node/$node->nid",
              'query' => comment_new_page_count($node->comment_count, $new, $node),
              'attributes' => array('title' => t('Jump to the first new comment of this posting.')),
              'fragment' => 'new',
              'html' => TRUE,
            );
          }
        }
      }
      if ($node->comment == COMMENT_NODE_OPEN) {
        $comment_form_location = variable_get('comment_form_location_' . $node->type, COMMENT_FORM_BELOW);
        if (user_access('post comments')) {
          $links['comment-add'] = array(
            'title' => t('Add new comment'),
            'href' => "node/$node->nid",
            'attributes' => array('title' => t('Add a new comment to this page.')),
            'fragment' => 'comment-form',
          );
          if ($comment_form_location == COMMENT_FORM_SEPARATE_PAGE) {
            $links['comment-add']['href'] = "comment/reply/$node->nid";
          }
        }
        else {
          $links['comment-forbidden'] = array(
            'title' => theme('comment_post_forbidden', array('node' => $node)),
            'html' => TRUE,
          );
        }
      }
    }
    elseif ($view_mode != 'search_index' && $view_mode != 'search_result') {
      // Node in other view modes: add a "post comment" link if the user is
      // allowed to post comments and if this node is allowing new comments.
      // But we don't want this link if we're building the node for search
      // indexing or constructing a search result excerpt.
      if ($node->comment == COMMENT_NODE_OPEN) {
        $comment_form_location = variable_get('comment_form_location_' . $node->type, COMMENT_FORM_BELOW);
        if (user_access('post comments')) {
          // Show the "post comment" link if the form is on another page, or
          // if there are existing comments that the link will skip past.
          if ($comment_form_location == COMMENT_FORM_SEPARATE_PAGE || (!empty($node->comment_count) && user_access('access comments'))) {
            $links['comment-add'] = array(
              'title' => t('Add new comment'),
              'attributes' => array('title' => t('Share your thoughts and opinions related to this posting.')),
              'href' => "node/$node->nid",
              'fragment' => 'comment-form',
            );
            if ($comment_form_location == COMMENT_FORM_SEPARATE_PAGE) {
              $links['comment-add']['href'] = "comment/reply/$node->nid";
            }
          }
        }
        else {
          $links['comment-forbidden'] = array(
            'title' => theme('comment_post_forbidden', array('node' => $node)),
            'html' => TRUE,
          );
        }
      }
    }

    $node->content['links']['comment'] = array(
      '#theme' => 'links__node__comment',
      '#links' => $links,
      '#attributes' => array('class' => array('links', 'inline')),
    );

    // Only append comments when we are building a node on its own node detail
    // page. We compare $node and $page_node to ensure that comments are not
    // appended to other nodes shown on the page, for example a node_reference
    // displayed in 'full' view mode within another node.
    if ($node->comment && $view_mode == 'full' && node_is_page($node) && empty($node->in_preview)) {
      $node->content['comments'] = comment_node_page_additions($node);
    }
  }
}

/**
 * Builds the comment-related elements for node detail pages.
 *
 * @param Drupal\node\Node $node
 *   The node entity for which to build the comment-related elements.
 *
 * @return
 *   A renderable array representing the comment-related page elements for the
 *   node.
 */
function comment_node_page_additions(Node $node) {
  $additions = array();

  // Only attempt to render comments if the node has visible comments.
  // Unpublished comments are not included in $node->comment_count, so show
  // comments unconditionally if the user is an administrator.
  if (($node->comment_count && user_access('access comments')) || user_access('administer comments')) {
    $mode = variable_get('comment_default_mode_' . $node->type, COMMENT_MODE_THREADED);
    $comments_per_page = variable_get('comment_default_per_page_' . $node->type, 50);
    if ($cids = comment_get_thread($node, $mode, $comments_per_page)) {
      $comments = comment_load_multiple($cids);
      comment_prepare_thread($comments);
      $build = comment_view_multiple($comments);
      $build['pager']['#theme'] = 'pager';
      $additions['comments'] = $build;
    }
  }

  // Append comment form if needed.
  if (user_access('post comments') && $node->comment == COMMENT_NODE_OPEN && (variable_get('comment_form_location_' . $node->type, COMMENT_FORM_BELOW) == COMMENT_FORM_BELOW)) {
    $additions['comment_form'] = comment_add($node);
  }

  if ($additions) {
    $additions += array(
      '#theme' => 'comment_wrapper__node_' . $node->type,
      '#node' => $node,
      'comments' => array(),
      'comment_form' => array(),
    );
  }

  return $additions;
}

/**
 * Returns a rendered form to comment the given node.
 *
 * @param Drupal\node\Node $node
 *   The node entity to be commented.
 * @param int $pid
 *   (optional) Some comments are replies to other comments. In those cases,
 *   $pid is the parent comment's comment ID. Defaults to NULL.
 *
 * @return array
 *   The renderable array for the comment addition form.
 */
function comment_add(Node $node, $pid = NULL) {
  $values = array('nid' => $node->nid, 'pid' => $pid, 'node_type' => 'comment_node_' . $node->type);
  $comment = entity_create('comment', $values);
  return entity_get_form($comment);
}

/**
 * Retrieves comments for a thread.
 *
 * @param Drupal\node\Node $node
 *   The node whose comment(s) needs rendering.
 * @param $mode
 *   The comment display mode; COMMENT_MODE_FLAT or COMMENT_MODE_THREADED.
 * @param $comments_per_page
 *   The amount of comments to display per page.
 *
 * @return
 *   An array of the IDs of the comment to be displayed.
 *
 * To display threaded comments in the correct order we keep a 'thread' field
 * and order by that value. This field keeps this data in
 * a way which is easy to update and convenient to use.
 *
 * A "thread" value starts at "1". If we add a child (A) to this comment,
 * we assign it a "thread" = "1.1". A child of (A) will have "1.1.1". Next
 * brother of (A) will get "1.2". Next brother of the parent of (A) will get
 * "2" and so on.
 *
 * First of all note that the thread field stores the depth of the comment:
 * depth 0 will be "X", depth 1 "X.X", depth 2 "X.X.X", etc.
 *
 * Now to get the ordering right, consider this example:
 *
 * 1
 * 1.1
 * 1.1.1
 * 1.2
 * 2
 *
 * If we "ORDER BY thread ASC" we get the above result, and this is the
 * natural order sorted by time. However, if we "ORDER BY thread DESC"
 * we get:
 *
 * 2
 * 1.2
 * 1.1.1
 * 1.1
 * 1
 *
 * Clearly, this is not a natural way to see a thread, and users will get
 * confused. The natural order to show a thread by time desc would be:
 *
 * 2
 * 1
 * 1.2
 * 1.1
 * 1.1.1
 *
 * which is what we already did before the standard pager patch. To achieve
 * this we simply add a "/" at the end of each "thread" value. This way, the
 * thread fields will look like this:
 *
 * 1/
 * 1.1/
 * 1.1.1/
 * 1.2/
 * 2/
 *
 * we add "/" since this char is, in ASCII, higher than every number, so if
 * now we "ORDER BY thread DESC" we get the correct order. However this would
 * spoil the reverse ordering, "ORDER BY thread ASC" -- here, we do not need
 * to consider the trailing "/" so we use a substring only.
 */
function comment_get_thread(Node $node, $mode, $comments_per_page) {
  $query = db_select('comment', 'c')
    ->extend('Drupal\Core\Database\Query\PagerSelectExtender');
  $query->addField('c', 'cid');
  $query
    ->condition('c.nid', $node->nid)
    ->addTag('node_access')
    ->addTag('comment_filter')
    ->addMetaData('base_table', 'comment')
    ->addMetaData('node', $node)
    ->limit($comments_per_page);

  $count_query = db_select('comment', 'c');
  $count_query->addExpression('COUNT(*)');
  $count_query
    ->condition('c.nid', $node->nid)
    ->addTag('node_access')
    ->addTag('comment_filter')
    ->addMetaData('base_table', 'comment')
    ->addMetaData('node', $node);

  if (!user_access('administer comments')) {
    $query->condition('c.status', COMMENT_PUBLISHED);
    $count_query->condition('c.status', COMMENT_PUBLISHED);
  }
  if ($mode === COMMENT_MODE_FLAT) {
    $query->orderBy('c.cid', 'ASC');
  }
  else {
    // See comment above. Analysis reveals that this doesn't cost too
    // much. It scales much much better than having the whole comment
    // structure.
    $query->addExpression('SUBSTRING(c.thread, 1, (LENGTH(c.thread) - 1))', 'torder');
    $query->orderBy('torder', 'ASC');
  }

  $query->setCountQuery($count_query);
  $cids = $query->execute()->fetchCol();

  return $cids;
}

/**
 * Calculates the indentation level of each comment in a comment thread.
 *
 * This function loops over an array representing a comment thread. For each
 * comment, the function calculates the indentation level and saves it in the
 * 'divs' property of the comment object.
 *
 * @param array $comments
 *   An array of comment objects, keyed by comment ID.
 */
function comment_prepare_thread(&$comments) {
  // A flag stating if we are still searching for first new comment on the thread.
  $first_new = TRUE;

  // A counter that helps track how indented we are.
  $divs = 0;

  foreach ($comments as $key => $comment) {
    if ($first_new && $comment->new->value != MARK_READ) {
      // Assign the anchor only for the first new comment. This avoids duplicate
      // id attributes on a page.
      $first_new = FALSE;
      $comment->first_new = TRUE;
    }

    // The $divs element instructs #prefix whether to add an indent div or
    // close existing divs (a negative value).
    $comment->depth = count(explode('.', $comment->thread->value)) - 1;
    if ($comment->depth > $divs) {
      $comment->divs = 1;
      $divs++;
    }
    else {
      $comment->divs = $comment->depth - $divs;
      while ($comment->depth < $divs) {
        $divs--;
      }
    }
    $comments[$key] = $comment;
  }

  // The final comment must close up some hanging divs
  $comments[$key]->divs_final = $divs;
}

/**
 * Generates an array for rendering a comment.
 *
 * @param Drupal\comment\Comment $comment
 *   The comment object.
 * @param $view_mode
 *   View mode, e.g. 'full', 'teaser'...
 * @param $langcode
 *   (optional) A language code to use for rendering. Defaults to the global
 *   content language of the current request.
 *
 * @return
 *   An array as expected by drupal_render().
 */
function comment_view(Comment $comment, $view_mode = 'full', $langcode = NULL) {
  return entity_view($comment, $view_mode, $langcode);
}

/**
 * Adds reply, edit, delete, etc. links, depending on user permissions.
 *
 * @param Drupal\comment\Comment $comment
 *   The comment object.
 * @param Drupal\node\Node $node
 *   The node the comment is attached to.
 *
 * @return
 *   A structured array of links.
 */
function comment_links(Comment $comment, Node $node) {
  $links = array();
  if ($node->comment == COMMENT_NODE_OPEN) {
    if (user_access('administer comments') && user_access('post comments')) {
      $links['comment-delete'] = array(
        'title' => t('delete'),
        'href' => "comment/{$comment->id()}/delete",
        'html' => TRUE,
      );