function wiki_extend_navigation(navigation_node $navref, $course, $module, $cm)
{
    global $CFG, $PAGE, $USER;
    require_once $CFG->dirroot . '/mod/wiki/locallib.php';
    $context = context_module::instance($cm->id);
    $url = $PAGE->url;
    $userid = 0;
    if ($module->wikimode == 'individual') {
        $userid = $USER->id;
    }
    if (!($wiki = wiki_get_wiki($cm->instance))) {
        return false;
    }
    if (!($gid = groups_get_activity_group($cm))) {
        $gid = 0;
    }
    if (!($subwiki = wiki_get_subwiki_by_group($cm->instance, $gid, $userid))) {
        return null;
    } else {
        $swid = $subwiki->id;
    }
    $pageid = $url->param('pageid');
    $cmid = $url->param('id');
    if (empty($pageid) && !empty($cmid)) {
        // wiki main page
        $page = wiki_get_page_by_title($swid, $wiki->firstpagetitle);
        $pageid = $page->id;
    }
    if (wiki_can_create_pages($context)) {
        $link = new moodle_url('/mod/wiki/create.php', array('action' => 'new', 'swid' => $swid));
        $node = $navref->add(get_string('newpage', 'wiki'), $link, navigation_node::TYPE_SETTING);
    }
    if (is_numeric($pageid)) {
        if (has_capability('mod/wiki:viewpage', $context)) {
            $link = new moodle_url('/mod/wiki/view.php', array('pageid' => $pageid));
            $node = $navref->add(get_string('view', 'wiki'), $link, navigation_node::TYPE_SETTING);
        }
        if (wiki_user_can_edit($subwiki)) {
            $link = new moodle_url('/mod/wiki/edit.php', array('pageid' => $pageid));
            $node = $navref->add(get_string('edit', 'wiki'), $link, navigation_node::TYPE_SETTING);
        }
        if (has_capability('mod/wiki:viewcomment', $context)) {
            $link = new moodle_url('/mod/wiki/comments.php', array('pageid' => $pageid));
            $node = $navref->add(get_string('comments', 'wiki'), $link, navigation_node::TYPE_SETTING);
        }
        if (has_capability('mod/wiki:viewpage', $context)) {
            $link = new moodle_url('/mod/wiki/history.php', array('pageid' => $pageid));
            $node = $navref->add(get_string('history', 'wiki'), $link, navigation_node::TYPE_SETTING);
        }
        if (has_capability('mod/wiki:viewpage', $context)) {
            $link = new moodle_url('/mod/wiki/map.php', array('pageid' => $pageid));
            $node = $navref->add(get_string('map', 'wiki'), $link, navigation_node::TYPE_SETTING);
        }
        if (has_capability('mod/wiki:viewpage', $context)) {
            $link = new moodle_url('/mod/wiki/files.php', array('pageid' => $pageid));
            $node = $navref->add(get_string('files', 'wiki'), $link, navigation_node::TYPE_SETTING);
        }
        if (has_capability('mod/wiki:managewiki', $context)) {
            $link = new moodle_url('/mod/wiki/admin.php', array('pageid' => $pageid));
            $node = $navref->add(get_string('admin', 'wiki'), $link, navigation_node::TYPE_SETTING);
        }
    }
}

/**
 * This function is the parser callback to parse wiki links.
 *
 * It returns the necesary information to print a link.
 *
 * NOTE: Empty pages and non-existent pages must be print in red color.
 *
 * !!!!!! IMPORTANT !!!!!!
 * It is critical that you call format_string on the content before it is used.
 *
 * @param string|page_wiki $link name of a page
 * @param array $options
 * @return array Array('content' => string, 'url' => string, 'new' => bool, 'link_info' => array)
 *
 * @TODO Doc return and options
 */
function wiki_parser_link($link, $options = null)
{
    global $CFG;
    if (is_object($link)) {
        $parsedlink = array('content' => $link->title, 'url' => $CFG->wwwroot . '/mod/wiki/view.php?pageid=' . $link->id, 'new' => false, 'link_info' => array('link' => $link->title, 'pageid' => $link->id, 'new' => false));
        $version = wiki_get_current_version($link->id);
        if ($version->version == 0) {
            $parsedlink['new'] = true;
        }
        return $parsedlink;
    } else {
        $swid = $options['swid'];
        if ($page = wiki_get_page_by_title($swid, $link)) {
            $parsedlink = array('content' => $link, 'url' => $CFG->wwwroot . '/mod/wiki/view.php?pageid=' . $page->id, 'new' => false, 'link_info' => array('link' => $link, 'pageid' => $page->id, 'new' => false));
            $version = wiki_get_current_version($page->id);
            if ($version->version == 0) {
                $parsedlink['new'] = true;
            }
            return $parsedlink;
        } else {
            return array('content' => $link, 'url' => $CFG->wwwroot . '/mod/wiki/create.php?swid=' . $swid . '&title=' . urlencode($link) . '&action=new', 'new' => true, 'link_info' => array('link' => $link, 'new' => true, 'pageid' => 0));
        }
    }
}

        $manageandedit = $manage && $edit;

        if ($groupmode == VISIBLEGROUPS and ($modeanduser || $modeandgroupmember) and !$manageandedit) {
            print_error('nocontent','wiki');
        }

        $params = array('wid' => $wiki->id, 'group' => $gid, 'uid' => $uid, 'title' => $title);
        $url = new moodle_url('/mod/wiki/create.php', $params);
        redirect($url);
    }

    // Checking is there is a page with this title. If it does not exists, redirect to first page
    if (!$page = wiki_get_page_by_title($subwiki->id, $title)) {
        $params = array('wid' => $wiki->id, 'group' => $gid, 'uid' => $uid, 'title' => $wiki->firstpagetitle);
        // Check to see if the first page has been created
        if (!wiki_get_page_by_title($subwiki->id, $wiki->firstpagetitle)) {
            $url = new moodle_url('/mod/wiki/create.php', $params);
        } else {
            $url = new moodle_url('/mod/wiki/view.php', $params);
        }
        redirect($url);
    }

    //    /*
    //     * Case 3:
    //     *
    //     * A user switches group when is 'reading' a non-existent page.
    //     *
    //     * URL Params: wid -> wiki id
    //     *             title -> page title
    //     *             currentgroup -> group id

 /**
  * Creates a new page.
  *
  * @param string $title New page title.
  * @param string $content Page contents.
  * @param int $contentformat Page contents format. If an invalid format is provided, default wiki format is used.
  * @param int $subwikiid The Subwiki ID where to store the page.
  * @param int $wikiid Page\'s wiki ID. Used if subwiki does not exists.
  * @param int $userid Subwiki\'s user ID. Used if subwiki does not exists.
  * @param int $groupid Subwiki\'s group ID. Used if subwiki does not exists.
  * @return array of warnings and page data.
  * @since Moodle 3.1
  */
 public static function new_page($title, $content, $contentformat = null, $subwikiid = null, $wikiid = null, $userid = null, $groupid = null)
 {
     global $USER;
     $params = self::validate_parameters(self::new_page_parameters(), array('title' => $title, 'content' => $content, 'contentformat' => $contentformat, 'subwikiid' => $subwikiid, 'wikiid' => $wikiid, 'userid' => $userid, 'groupid' => $groupid));
     $warnings = array();
     // Get wiki and subwiki instances.
     if (!empty($params['subwikiid'])) {
         if (!($subwiki = wiki_get_subwiki($params['subwikiid']))) {
             throw new moodle_exception('incorrectsubwikiid', 'wiki');
         }
         if (!($wiki = wiki_get_wiki($subwiki->wikiid))) {
             throw new moodle_exception('incorrectwikiid', 'wiki');
         }
         // Permission validation.
         $cm = get_coursemodule_from_instance('wiki', $wiki->id, $wiki->course);
         $context = context_module::instance($cm->id);
         self::validate_context($context);
     } else {
         if (!($wiki = wiki_get_wiki($params['wikiid']))) {
             throw new moodle_exception('incorrectwikiid', 'wiki');
         }
         // Permission validation.
         $cm = get_coursemodule_from_instance('wiki', $wiki->id, $wiki->course);
         $context = context_module::instance($cm->id);
         self::validate_context($context);
         // Determine groupid and userid to use.
         list($groupid, $userid) = self::determine_group_and_user($cm, $wiki, $params['groupid'], $params['userid']);
         // Get subwiki and validate it.
         $subwiki = wiki_get_subwiki_by_group_and_user_with_validation($wiki, $groupid, $userid);
         if ($subwiki === false) {
             // User cannot view page.
             throw new moodle_exception('cannoteditpage', 'wiki');
         } else {
             if ($subwiki->id < 0) {
                 // Subwiki needed to check edit permissions.
                 if (!wiki_user_can_edit($subwiki)) {
                     throw new moodle_exception('cannoteditpage', 'wiki');
                 }
                 // Subwiki does not exists and it can be created.
                 $swid = wiki_add_subwiki($wiki->id, $groupid, $userid);
                 if (!($subwiki = wiki_get_subwiki($swid))) {
                     throw new moodle_exception('incorrectsubwikiid', 'wiki');
                 }
             }
         }
     }
     // Subwiki needed to check edit permissions.
     if (!wiki_user_can_edit($subwiki)) {
         throw new moodle_exception('cannoteditpage', 'wiki');
     }
     if ($page = wiki_get_page_by_title($subwiki->id, $params['title'])) {
         throw new moodle_exception('pageexists', 'wiki');
     }
     // Ignore invalid formats and use default instead.
     if (!$params['contentformat'] || $wiki->forceformat) {
         $params['contentformat'] = $wiki->defaultformat;
     } else {
         $formats = wiki_get_formats();
         if (!in_array($params['contentformat'], $formats)) {
             $params['contentformat'] = $wiki->defaultformat;
         }
     }
     $newpageid = wiki_create_page($subwiki->id, $params['title'], $params['contentformat'], $USER->id);
     if (!($page = wiki_get_page($newpageid))) {
         throw new moodle_exception('incorrectpageid', 'wiki');
     }
     // Save content.
     $save = wiki_save_page($page, $params['content'], $USER->id);
     if (!$save) {
         throw new moodle_exception('savingerror', 'wiki');
     }
     $result = array();
     $result['pageid'] = $page->id;
     $result['warnings'] = $warnings;
     return $result;
 }

             $gid = 0;
             $uid = 0;
         } else {
             $gid = $currentgroup;
             $uid = 0;
         }
     }
 }
 // Getting subwiki instance. If it does not exists, redirect to create page
 if (!($subwiki = wiki_get_subwiki_by_group($wiki->id, $gid, $uid))) {
     $params = array('wid' => $wiki->id, 'gid' => $gid, 'uid' => $uid, 'title' => $title);
     $url = new moodle_url('/mod/wiki/create.php', $params);
     redirect($url);
 }
 // Checking is there is a page with this title. If it does not exists, redirect to first page
 if (!($page = wiki_get_page_by_title($subwiki->id, $title))) {
     $params = array('wid' => $wiki->id, 'gid' => $gid, 'uid' => $uid, 'title' => $wiki->firstpagetitle);
     $url = new moodle_url('/mod/wiki/view.php', $params);
     redirect($url);
 }
 //    /*
 //     * Case 3:
 //     *
 //     * A user switches group when is 'reading' a non-existent page.
 //     *
 //     * URL Params: wid -> wiki id
 //     *             title -> page title
 //     *             currentgroup -> group id
 //     *
 //     */
 //} elseif ($wid && $title && $currentgroup) {

 /**
  * Generates a page in wiki.
  *
  * @param stdClass wiki object returned from create_instance (if known)
  * @param stdClass|array $record data to insert as wiki entry.
  * @return stdClass
  * @throws coding_exception if neither $record->wikiid nor $wiki->id is specified
  */
 public function create_page($wiki, $record = array())
 {
     global $CFG, $USER;
     require_once $CFG->dirroot . '/mod/wiki/locallib.php';
     $this->pagecount++;
     $record = (array) $record + array('title' => 'wiki page ' . $this->pagecount, 'wikiid' => $wiki->id, 'subwikiid' => 0, 'group' => 0, 'content' => 'Wiki page content ' . $this->pagecount, 'format' => $wiki->defaultformat);
     if (empty($record['wikiid']) && empty($record['subwikiid'])) {
         throw new coding_exception('wiki page generator requires either wikiid or subwikiid');
     }
     if (!$record['subwikiid']) {
         if (!isset($record['userid'])) {
             $record['userid'] = $wiki->wikimode == 'individual' ? $USER->id : 0;
         }
         if ($subwiki = wiki_get_subwiki_by_group($record['wikiid'], $record['group'], $record['userid'])) {
             $record['subwikiid'] = $subwiki->id;
         } else {
             $record['subwikiid'] = wiki_add_subwiki($record['wikiid'], $record['group'], $record['userid']);
         }
     }
     if ($wikipage = wiki_get_page_by_title($record['subwikiid'], $record['title'])) {
         $rv = wiki_save_page($wikipage, $record['content'], $USER->id);
         return $rv['page'];
     }
     $pageid = wiki_create_page($record['subwikiid'], $record['title'], $record['format'], $USER->id);
     $wikipage = wiki_get_page($pageid);
     $rv = wiki_save_page($wikipage, $record['content'], $USER->id);
     return $rv['page'];
 }

 /**
  * Generates a page in wiki.
  *
  * @param stdClass wiki object returned from create_instance (if known)
  * @param stdClass|array $record data to insert as wiki entry.
  * @return stdClass
  * @throws coding_exception if neither $record->wikiid nor $wiki->id is specified
  */
 public function create_page($wiki, $record = array())
 {
     global $CFG, $USER;
     require_once $CFG->dirroot . '/mod/wiki/locallib.php';
     $this->pagecount++;
     $record = (array) $record + array('title' => 'wiki page ' . $this->pagecount, 'wikiid' => $wiki->id, 'subwikiid' => 0, 'group' => 0, 'content' => 'Wiki page content ' . $this->pagecount, 'format' => $wiki->defaultformat);
     if (empty($record['wikiid']) && empty($record['subwikiid'])) {
         throw new coding_exception('wiki page generator requires either wikiid or subwikiid');
     }
     if (!$record['subwikiid']) {
         if (!isset($record['userid'])) {
             $record['userid'] = $wiki->wikimode == 'individual' ? $USER->id : 0;
         }
         if ($subwiki = wiki_get_subwiki_by_group($record['wikiid'], $record['group'], $record['userid'])) {
             $record['subwikiid'] = $subwiki->id;
         } else {
             $record['subwikiid'] = wiki_add_subwiki($record['wikiid'], $record['group'], $record['userid']);
         }
     }
     $wikipage = wiki_get_page_by_title($record['subwikiid'], $record['title']);
     if (!$wikipage) {
         $pageid = wiki_create_page($record['subwikiid'], $record['title'], $record['format'], $USER->id);
         $wikipage = wiki_get_page($pageid);
     }
     $rv = wiki_save_page($wikipage, $record['content'], $USER->id);
     if (array_key_exists('tags', $record)) {
         $tags = is_array($record['tags']) ? $record['tags'] : preg_split('/,/', $record['tags']);
         if (empty($wiki->cmid)) {
             $cm = get_coursemodule_from_instance('wiki', $wiki->id, isset($wiki->course) ? $wiki->course : 0);
             $wiki->cmid = $cm->id;
         }
         core_tag_tag::set_item_tags('mod_wiki', 'wiki_pages', $wikipage->id, context_module::instance($wiki->cmid), $tags);
     }
     return $rv['page'];
 }