<?php

// This file is part of Moodle - http://moodle.org/
//
// Moodle is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// Moodle is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with Moodle. If not, see <http://www.gnu.org/licenses/>.

/**
 * This contains functions and classes that will be used by scripts in wiki module
 *
 * @package mod_wiki
 * @copyright 2009 Marc Alier, Jordi Piguillem marc.alier@upc.edu
 * @copyright 2009 Universitat Politecnica de Catalunya http://www.upc.edu
 *
 * @author Jordi Piguillem
 * @author Marc Alier
 * @author David Jimenez
 * @author Josep Arus
 * @author Daniel Serrano
 * @author Kenneth Riba
 *
 * @license http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
 */

defined('MOODLE_INTERNAL') || die();

require_once($CFG->dirroot . '/mod/wiki/lib.php');
require_once($CFG->dirroot . '/mod/wiki/parser/parser.php');
require_once($CFG->libdir . '/filelib.php');

define('WIKI_REFRESH_CACHE_TIME', 30); // @TODO: To be deleted.
define('FORMAT_CREOLE', '37');
define('FORMAT_NWIKI', '38');
define('NO_VALID_RATE', '-999');
define('IMPROVEMENT', '+');
define('EQUAL', '=');
define('WORST', '-');

define('LOCK_TIMEOUT', 30);

/**
 * Get a wiki instance
 * @param int $wikiid the instance id of wiki
 */
function wiki_get_wiki($wikiid) {
    global $DB;

    return $DB->get_record('wiki', array('id' => $wikiid));
}

/**
 * Get sub wiki instances with same wiki id
 * @param int $wikiid
 */
function wiki_get_subwikis($wikiid) {
    global $DB;
    return $DB->get_records('wiki_subwikis', array('wikiid' => $wikiid));
}

/**
 * Get a sub wiki instance by wiki id and group id
 * @param int $wikiid
 * @param int $groupid
 * @return object
 */
function wiki_get_subwiki_by_group($wikiid, $groupid, $userid = 0) {
    global $DB;
    return $DB->get_record('wiki_subwikis', array('wikiid' => $wikiid, 'groupid' => $groupid, 'userid' => $userid));
}

/**
 * Get a sub wiki instace by instance id
 * @param int $subwikiid
 * @return object
 */
function wiki_get_subwiki($subwikiid) {
    global $DB;
    return $DB->get_record('wiki_subwikis', array('id' => $subwikiid));

}

/**
 * Add a new sub wiki instance
 * @param int $wikiid
 * @param int $groupid
 * @return int $insertid
 */
function wiki_add_subwiki($wikiid, $groupid, $userid = 0) {
    global $DB;

    $record = new StdClass();
    $record->wikiid = $wikiid;
    $record->groupid = $groupid;
    $record->userid = $userid;

    $insertid = $DB->insert_record('wiki_subwikis', $record);
    return $insertid;
}

/**
 * Get a wiki instance by pageid
 * @param int $pageid
 * @return object
 */
function wiki_get_wiki_from_pageid($pageid) {
    global $DB;

    $sql = "SELECT w.*
            FROM {wiki} w, {wiki_subwikis} s, {wiki_pages} p
            WHERE p.id = ? AND
            p.subwikiid = s.id AND
            s.wikiid = w.id";

    return $DB->get_record_sql($sql, array($pageid));
}

/**
 * Get a wiki page by pageid
 * @param int $pageid
 * @return object
 */
function wiki_get_page($pageid) {
    global $DB;
    return $DB->get_record('wiki_pages', array('id' => $pageid));
}

/**
 * Get latest version of wiki page
 * @param int $pageid
 * @return object
 */
function wiki_get_current_version($pageid) {
    global $DB;

    // @TODO: Fix this query
    $sql = "SELECT *
            FROM {wiki_versions}
            WHERE pageid = ?
            ORDER BY version DESC";
    $records = $DB->get_records_sql($sql, array($pageid), 0, 1);
    return array_pop($records);

}

/**
 * Alias of wiki_get_current_version
 * @TODO, does the exactly same thing as wiki_get_current_version, should be removed
 * @param int $pageid
 * @return object
 */
function wiki_get_last_version($pageid) {
    return wiki_get_current_version($pageid);
}

/**
 * Get page section
 * @param int $pageid
 * @param string $section
 */
function wiki_get_section_page($page, $section) {

    $version = wiki_get_current_version($page->id);
    return wiki_parser_proxy::get_section($version->content, $version->contentformat, $section);
}

/**
 * Get a wiki page by page title
 * @param int $swid, sub wiki id
 * @param string $title
 * @return object
 */
function wiki_get_page_by_title($swid, $title) {
    global $DB;
    return $DB->get_record('wiki_pages', array('subwikiid' => $swid, 'title' => $title));
}

/**
 * Get a version record by record id
 * @param int $versionid, the version id
 * @return object
 */
function wiki_get_version($versionid) {
    global $DB;
    return $DB->get_record('wiki_versions', array('id' => $versionid));
}

/**
 * Get first page of wiki instace
 * @param int $subwikiid
 * @param int $module, wiki instance object
 */
function wiki_get_first_page($subwikid, $module = null) {
    global $DB, $USER;

    $sql = "SELECT p.*
            FROM {wiki} w, {wiki_subwikis} s, {wiki_pages} p
            WHERE s.id = ? AND
            s.wikiid = w.id AND
            w.firstpagetitle = p.title AND
            p.subwikiid = s.id";
    return $DB->get_record_sql($sql, array($subwikid));
}

function wiki_save_section($wikipage, $sectiontitle, $sectioncontent, $userid) {

    $wiki = wiki_get_wiki_from_pageid($wikipage->id);
    $cm = get_coursemodule_from_instance('wiki', $wiki->id);
    $context = context_module::instance($cm->id);

    if (has_capability('mod/wiki:editpage', $context)) {
        $version = wiki_get_current_version($wikipage->id);
        $content = wiki_parser_proxy::get_section($version->content, $version->contentformat, $sectiontitle, true);

        $newcontent = $content[0] . $sectioncontent . $content[2];

        return wiki_save_page($wikipage, $newcontent, $userid);
    } else {
        return false;
    }
}

/**
 * Save page content
 * @param object $wikipage
 * @param string $newcontent
 * @param int $userid
 */
function wiki_save_page($wikipage, $newcontent, $userid) {
    global $DB;

    $wiki = wiki_get_wiki_from_pageid($wikipage->id);
    $cm = get_coursemodule_from_instance('wiki', $wiki->id);
    $context = context_module::instance($cm->id);

    if (has_capability('mod/wiki:editpage', $context)) {
        $version = wiki_get_current_version($wikipage->id);

        $version->content = $newcontent;
        $version->userid = $userid;
        $version->version++;
        $version->timecreated = time();
        $version->id = $DB->insert_record('wiki_versions', $version);

        $wikipage->timemodified = $version->timecreated;
        $wikipage->userid = $userid;
        $return = wiki_refresh_cachedcontent($wikipage, $newcontent);
        $event = \mod_wiki\event\page_updated::create(
                array(
                    'context' => $context,
                    'objectid' => $wikipage->id,
                    'relateduserid' => $userid,
                    'other' => array(
                        'newcontent' => $newcontent
                        )
                    ));
        $event->add_record_snapshot('wiki', $wiki);
        $event->add_record_snapshot('wiki_pages', $wikipage);
        $event->add_record_snapshot('wiki_versions', $version);
        $event->trigger();
        return $return;
    } else {
        return false;
    }
}

function wiki_refresh_cachedcontent($page, $newcontent = null) {
    global $DB;

    $version = wiki_get_current_version($page->id);
    if (empty($version)) {
        return null;
    }
    if (!isset($newcontent)) {
        $newcontent = $version->content;
    }

    $options = array('swid' => $page->subwikiid, 'pageid' => $page->id);
    $parseroutput = wiki_parse_content($version->contentformat, $newcontent, $options);
    $page->cachedcontent = $parseroutput['toc'] . $parseroutput['parsed_text'];
    $page->timerendered = time();
    $DB->update_record('wiki_pages', $page);

    wiki_refresh_page_links($page, $parseroutput['link_count']);

    return array('page' => $page, 'sections' => $parseroutput['repeated_sections'], 'version' => $version->version);
}

/**
 * Restore a page with specified version.
 *
 * @param stdClass $wikipage wiki page record
 * @param stdClass $version wiki page version to restore
 * @param context_module $context context of wiki module
 * @return stdClass restored page
 */
function wiki_restore_page($wikipage, $version, $context) {
    $return = wiki_save_page($wikipage, $version->content, $version->userid);
    $event = \mod_wiki\event\page_version_restored::create(
            array(
                'context' => $context,
                'objectid' => $version->id,
                'other' => array(
                    'pageid' => $wikipage->id
                    )
                ));
    $event->add_record_snapshot('wiki_versions', $version);
    $event->trigger();
    return $return['page'];
}

function wiki_refresh_page_links($page, $links) {
    global $DB;

    $DB->delete_records('wiki_links', array('frompageid' => $page->id));
    foreach ($links as $linkname => $linkinfo) {

        $newlink = new stdClass();
        $newlink->subwikiid = $page->subwikiid;
        $newlink->frompageid = $page->id;

        if ($linkinfo['new']) {
            $newlink->tomissingpage = $linkname;
        } else {
            $newlink->topageid = $linkinfo['pageid'];
        }

        try {
            $DB->insert_record('wiki_links', $newlink);
        } catch (dml_exception $e) {
            debugging($e->getMessage());
        }

    }
}

/**
 * Create a new wiki page, if the page exists, return existing pageid
 * @param int $swid
 * @param string $title
 * @param string $format
 * @param int $userid
 */
function wiki_create_page($swid, $title, $format, $userid) {
    global $DB;
    $subwiki = wiki_get_subwiki($swid);
    $cm = get_coursemodule_from_instance('wiki', $subwiki->wikiid);
    $context = context_module::instance($cm->id);
    require_capability('mod/wiki:editpage', $context);
    // if page exists
    if ($page = wiki_get_page_by_title($swid, $title)) {
        return $page->id;
    }

    // Creating a new empty version
    $version = new stdClass();
    $version->content = '';
    $version->contentformat = $format;
    $version->version = 0;
    $version->timecreated = time();
    $version->userid = $userid;

    $versionid = null;
    $versionid = $DB->insert_record('wiki_versions', $version);

    // Createing a new empty page
    $page = new stdClass();
    $page->subwikiid = $swid;
    $page->title = $title;
    $page->cachedcontent = '';
    $page->timecreated = $version->timecreated;
    $page->timemodified = $version->timecreated;
    $page->timerendered = $version->timecreated;
    $page->userid = $userid;
    $page->pageviews = 0;
    $page->readonly = 0;

    $pageid = $DB->insert_record('wiki_pages', $page);

    // Setting the pageid
    $version->id = $versionid;
    $version->pageid = $pageid;
    $DB->update_record('wiki_versions', $version);

    $event = \mod_wiki\event\page_created::create(
            array(
                'context' => $context,
                'objectid' => $pageid
                )
            );
    $event->trigger();

    wiki_make_cache_expire($page->title);
    return $pageid;
}

function wiki_make_cache_expire($pagename) {
    global $DB;

    $sql = "UPDATE {wiki_pages}
            SET timerendered = 0
            WHERE id IN ( SELECT l.frompageid
                FROM {wiki_links} l
                WHERE l.tomissingpage = ?
            )";
    $DB->execute ($sql, array($pagename));
}

/**
 * Get a specific version of page
 * @param int $pageid
 * @param int $version
 */
function wiki_get_wiki_page_version($pageid, $version) {
    global $DB;
    return $DB->get_record('wiki_versions', array('pageid' => $pageid, 'version' => $version));
}

/**
 * Get version list
 * @param int $pageid
 * @param int $limitfrom
 * @param int $limitnum
 */
function wiki_get_wiki_page_versions($pageid, $limitfrom, $limitnum) {
    global $DB;
    return $DB->get_records('wiki_versions', array('pageid' => $pageid), 'version DESC', '*', $limitfrom, $limitnum);
}

/**
 * Count the number of page version
 * @param int $pageid
 */
function wiki_count_wiki_page_versions($pageid) {
    global $DB;
    return $DB->count_records('wiki_versions', array('pageid' => $pageid));
}

/**
 * Get linked from page
 * @param int $pageid
 */
function wiki_get_linked_to_pages($pageid) {
    global $DB;
    return $DB->get_records('wiki_links', array('frompageid' => $pageid));
}

/**
 * Get linked from page
 * @param int $pageid
 */
function wiki_get_linked_from_pages($pageid) {
    global $DB;
    return $DB->get_records('wiki_links', array('topageid' => $pageid));
}

/**
 * Get pages which user have been edited
 * @param int $swid
 * @param int $userid
 */
function wiki_get_contributions($swid, $userid) {
    global $DB;

    $sql = "SELECT v.*
            FROM {wiki_versions} v, {wiki_pages} p
            WHERE p.subwikiid = ? AND
            v.pageid = p.id AND
            v.userid = ?";

    return $DB->get_records_sql($sql, array($swid, $userid));
}

/**
 * Get missing or empty pages in wiki
 * @param int $swid sub wiki id
 */
function wiki_get_missing_or_empty_pages($swid) {
    global $DB;

    $sql = "SELECT DISTINCT p.title, p.id, p.subwikiid
            FROM {wiki} w, {wiki_subwikis} s, {wiki_pages} p
            WHERE s.wikiid = w.id and
            s.id = ? and
            w.firstpagetitle != p.title and
            p.subwikiid = ? and
            1 =  (SELECT count(*)
                FROM {wiki_versions} v
                WHERE v.pageid = p.id)
            UNION
            SELECT DISTINCT l.tomissingpage as title, 0 as id, l.subwikiid
            FROM {wiki_links} l
            WHERE l.subwikiid = ? and
            l.topageid = 0";

    return $DB->get_records_sql($sql, array($swid, $swid, $swid));
}

/**
 * Get pages list in wiki
 * @param int $swid sub wiki id
 * @param string $sort How to sort the pages. By default, title ASC.
 */
function wiki_get_page_list($swid, $sort = 'title ASC') {
    global $DB;
    $records = $DB->get_records('wiki_pages', array('subwikiid' => $swid), $sort);
    return $records;
}

/**
 * Return a list of orphaned wikis for one specific subwiki
 * @global object
 * @param int $swid sub wiki id
 */
function wiki_get_orphaned_pages($swid) {
    global $DB;

    $sql = "SELECT p.id, p.title
            FROM {wiki_pages} p, {wiki} w , {wiki_subwikis} s
            WHERE p.subwikiid = ?
            AND s.id = ?
            AND w.id = s.wikiid
            AND p.title != w.firstpagetitle
            AND p.id NOT IN (SELECT topageid FROM {wiki_links} WHERE subwikiid = ?)";

    return $DB->get_records_sql($sql, array($swid, $swid, $swid));
}

/**
 * Search wiki title
 * @param int $swid sub wiki id
 * @param string $search
 */
function wiki_search_title($swid, $search) {
    global $DB;

    return $DB->get_records_select('wiki_pages', "subwikiid = ? AND title LIKE ?", array($swid, '%'.$search.'%'));
}

/**
 * Search wiki content
 * @param int $swid sub wiki id
 * @param string $search
 */
function wiki_search_content($swid, $search) {
    global $DB;

    return $DB->get_records_select('wiki_pages', "subwikiid = ? AND cachedcontent LIKE ?", array($swid, '%'.$search.'%'));
}

/**
 * Search wiki title and content
 * @param int $swid sub wiki id
 * @param string $search
 */
function wiki_search_all($swid, $search) {
    global $DB;

    return $DB->get_records_select('wiki_pages', "subwikiid = ? AND (cachedcontent LIKE ? OR title LIKE ?)", array($swid, '%'.$search.'%', '%'.$search.'%'));
}

/**
 * Get user data
 */
function wiki_get_user_info($userid) {
    global $DB;
    return $DB->get_record('user', array('id' => $userid));
}

/**
 * Increase page view nubmer
 * @param int $page, database record
 */
function wiki_increment_pageviews($page) {
    global $DB;

    $page->pageviews++;
    $DB->update_record('wiki_pages', $page);
}

//----------------------------------------------------------
//----------------------------------------------------------

/**
 * Text format supported by wiki module
 */
function wiki_get_formats() {
    return array('html', 'creole', 'nwiki');
}

/**
 * Parses a string with the wiki markup language in $markup.
 *
 * @return Array or false when something wrong has happened.
 *
 * Returned array contains the following fields:
 *     'parsed_text' => String. Contains the parsed wiki content.
 *     'unparsed_text' => String. Constains the original wiki content.
 *     'link_count' => Array of array('destination' => ..., 'new' => "is new?"). Contains the internal wiki links found in the wiki content.
 *      'deleted_sections' => the list of deleted sections.
 *              '' =>
 *
 * @author Josep Arús Pous
 **/
function wiki_parse_content($markup, $pagecontent, $options = array()) {
    global $PAGE;

    $subwiki = wiki_get_subwiki($options['swid']);
    $cm = get_coursemodule_from_instance("wiki", $subwiki->wikiid);
    $context = context_module::instance($cm->id);

    $parser_options = array(
        'link_callback' => '/mod/wiki/locallib.php:wiki_parser_link',
        'link_callback_args' => array('swid' => $options['swid']),
        'table_callback' => '/mod/wiki/locallib.php:wiki_parser_table',
        'real_path_callback' => '/mod/wiki/locallib.php:wiki_parser_real_path',
        'real_path_callback_args' => array(
            'context' => $context,
            'component' => 'mod_wiki',
            'filearea' => 'attachments',
            'subwikiid'=> $subwiki->id,
            'pageid' => $options['pageid']
        ),
        'pageid' => $options['pageid'],
        'pretty_print' => (isset($options['pretty_print']) && $options['pretty_print']),
        'printable' => (isset($options['printable']) && $options['printable'])
    );

    return wiki_parser_proxy::parse($pagecontent, $markup, $parser_options);
}

/**
 * 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=' . $swid . '&amp;title=' . urlencode($link) . '&amp;action=new', 'new' => true, 'link_info' => array('link' => $link, 'new' => true, 'pageid' => 0));
        }
    }
}

/**
 * Returns the table fully parsed (HTML)
 *
 * @return HTML for the table $table
 * @author Josep Arús Pous
 *
 **/
function wiki_parser_table($table) {
    global $OUTPUT;

    $htmltable = new html_table();

    $headers = $table[0];
    $htmltable->head = array();
    foreach ($headers as $h) {
        $htmltable->head[] = $h[1];
    }

    array_shift($table);
    $htmltable->data = array();
    foreach ($table as $row) {
        $row_data = array();
        foreach ($row as $r) {
            $row_data[] = $r[1];
        }
        $htmltable->data[] = $row_data;
    }

    return html_writer::table($htmltable);
}

/**
 * Returns an absolute path link, unless there is no such link.
 *
 * @param string $url Link's URL or filename
 * @param stdClass $context filearea params
 * @param string $component The component the file is associated with
 * @param string $filearea The filearea the file is stored in
 * @param int $swid Sub wiki id
 *
 * @return string URL for files full path
 */

function wiki_parser_real_path($url, $context, $component, $filearea, $swid) {
    global $CFG;

    if (preg_match("/^(?:http|ftp)s?\:\/\//", $url)) {
        return $url;
    } else {

        $file = 'pluginfile.php';
        if (!$CFG->slasharguments) {
            $file = $file . '?file=';
        }
        $baseurl = "$CFG->wwwroot/$file/{$context->id}/$component/$filearea/$swid/";
        // it is a file in current file area
        return $baseurl . $url;
    }
}

/**
 * Returns the token used by a wiki language to represent a given tag or "object" (bold -> **)
 *
 * @return A string when it has only one token at the beginning (f. ex. lists). An array composed by 2 strings when it has 2 tokens, one at the beginning and one at the end (f. ex. italics). Returns false otherwise.
 * @author Josep Arús Pous
 **/
function wiki_parser_get_token($markup, $name) {

    return wiki_parser_proxy::get_token($name, $markup);
}

/**
 * Checks if current user can view a subwiki
 *
 * @param stdClass $subwiki usually record from {wiki_subwikis}. Must contain fields 'wikiid', 'groupid', 'userid'.
 *     If it also contains fields 'course' and 'groupmode' from table {wiki} it will save extra DB query.
 * @param stdClass $wiki optional wiki object if known
 * @return bool
 */
function wiki_user_can_view($subwiki, $wiki = null) {
    global $USER;

    if (empty($wiki) || $wiki->id != $subwiki->wikiid) {
        $wiki = wiki_get_wiki($subwiki->wikiid);
    }
    $modinfo = get_fast_modinfo($wiki->course);
    if (!isset($modinfo->instances['wiki'][$subwiki->wikiid])) {
        // Module does not exist.
        return false;
    }
    $cm = $modinfo->instances['wiki'][$subwiki->wikiid];
    if (!$cm->uservisible) {
        // The whole module is not visible to the current user.
        return false;
    }
    $context = context_module::instance($cm->id);

    // Working depending on activity groupmode
    switch (groups_get_activity_groupmode($cm)) {
    case NOGROUPS:

        if ($wiki->wikimode == 'collaborative') {
            // Collaborative Mode:
            // There is one wiki for all the class.
            //
            // Only view capbility needed
            return has_capability('mod/wiki:viewpage', $context);
        } else if ($wiki->wikimode == 'individual') {
            // Individual Mode:
            // Each person owns a wiki.
            if ($subwiki->userid == $USER->id) {
                // Only the owner of the wiki can view it
                return has_capability('mod/wiki:viewpage', $context);
            } else { // User has special capabilities
                // User must have:
                //      mod/wiki:viewpage capability
                // and
                //      mod/wiki:managewiki capability
                $view = has_capability('mod/wiki:viewpage', $context);
                $manage = has_capability('mod/wiki:managewiki', $context);

                return $view && $manage;
            }
        } else {
            //Error
            return false;
        }
    case SEPARATEGROUPS:
        // Collaborative and Individual Mode
        //
        // Collaborative Mode:
        //      There is one wiki per group.
        // Individual Mode:
        //      Each person owns a wiki.
        if ($wiki->wikimode == 'collaborative' || $wiki->wikimode == 'individual') {
            // Only members of subwiki group could view that wiki
            if (in_array($subwiki->groupid, $modinfo->get_groups($cm->groupingid))) {
                // Only view capability needed
                return has_capability('mod/wiki:viewpage', $context);

            } else { // User is not part of that group
                // User must have:
                //      mod/wiki:managewiki capability
                // or
                //      moodle/site:accessallgroups capability
                // and
                //      mod/wiki:viewpage capability
                $view = has_capability('mod/wiki:viewpage', $context);
                $manage = has_capability('mod/wiki:managewiki', $context);
                $access = has_capability('moodle/site:accessallgroups', $context);
                return ($manage || $access) && $view;
            }
        } else {
            //Error
            return false;
        }
    case VISIBLEGROUPS:
        // Collaborative and Individual Mode
        //
        // Collaborative Mode:
        //      There is one wiki per group.
        // Individual Mode:
        //      Each person owns a wiki.
        if ($wiki->wikimode == 'collaborative' || $wiki->wikimode == 'individual') {
            // Everybody can read all wikis
            //
            // Only view capability needed
            return has_capability('mod/wiki:viewpage', $context);
        } else {
            //Error
            return false;
        }
    default: // Error
        return false;
    }
}

/**
 * Checks if current user can edit a subwiki
 *
 * @param $subwiki
 */
function wiki_user_can_edit($subwiki) {
    global $USER;

    $wiki = wiki_get_wiki($subwiki->wikiid);
    $cm = get_coursemodule_from_instance('wiki', $wiki->id);
    $context = context_module::instance($cm->id);

    // Working depending on activity groupmode
    switch (groups_get_activity_groupmode($cm)) {
    case NOGROUPS:

        if ($wiki->wikimode == 'collaborative') {
            // Collaborative Mode:
            // There is a wiki for all the class.
            //
            // Only edit capbility needed
            return has_capability('mod/wiki:editpage', $context);
        } else if ($wiki->wikimode == 'individual') {
            // Individual Mode
            // There is a wiki per user

            // Only the owner of that wiki can edit it
            if ($subwiki->userid == $USER->id) {
                return has_capability('mod/wiki:editpage', $context);
            } else { // Current user is not the owner of that wiki.

                // User must have:
                //      mod/wiki:editpage capability
                // and
                //      mod/wiki:managewiki capability
                $edit = has_capability('mod/wiki:editpage', $context);
                $manage = has_capability('mod/wiki:managewiki', $context);

                return $edit && $manage;
            }
        } else {
            //Error
            return false;
        }
    case SEPARATEGROUPS:
        if ($wiki->wikimode == 'collaborative') {
            // Collaborative Mode:
            // There is one wiki per group.
            //
            // Only members of subwiki group could edit that wiki
            if (groups_is_member($subwiki->groupid)) {
                // Only edit capability needed
                return has_capability('mod/wiki:editpage', $context);
            } else { // User is not part of that group
                // User must have:
                //      mod/wiki:managewiki capability
                // and
                //      moodle/site:accessallgroups capability
                // and
                //      mod/wiki:editpage capability
                $manage = has_capability('mod/wiki:managewiki', $context);
                $access = has_capability('moodle/site:accessallgroups', $context);
                $edit = has_capability('mod/wiki:editpage', $context);
                return $manage && $access && $edit;
            }
        } else if ($wiki->wikimode == 'individual') {
            // Individual Mode:
            // Each person owns a wiki.
            //
            // Only the owner of that wiki can edit it
            if ($subwiki->userid == $USER->id) {
                return has_capability('mod/wiki:editpage', $context);
            } else { // Current user is not the owner of that wiki.
                // User must have:
                //      mod/wiki:managewiki capability
                // and
                //      moodle/site:accessallgroups capability
                // and
                //      mod/wiki:editpage capability
                $manage = has_capability('mod/wiki:managewiki', $context);
                $access = has_capability('moodle/site:accessallgroups', $context);
                $edit = has_capability('mod/wiki:editpage', $context);
                return $manage && $access && $edit;
            }
        } else {
            //Error
            return false;
        }
    case VISIBLEGROUPS:
        if ($wiki->wikimode == 'collaborative') {
            // Collaborative Mode:
            // There is one wiki per group.
            //
            // Only members of subwiki group could edit that wiki
            if (groups_is_member($subwiki->groupid)) {
                // Only edit capability needed
                return has_capability('mod/wiki:editpage', $context);
            } else { // User is not part of that group
                // User must have:
                //      mod/wiki:managewiki capability
                // and
                //      mod/wiki:editpage capability
                $manage = has_capability('mod/wiki:managewiki', $context);
                $edit = has_capability('mod/wiki:editpage', $context);
                return $manage && $edit;
            }
        } else if ($wiki->wikimode == 'individual') {
            // Individual Mode:
            // Each person owns a wiki.
            //
            // Only the owner of that wiki can edit it
            if ($subwiki->userid == $USER->id) {
                return has_capability('mod/wiki:editpage', $context);
            } else { // Current user is not the owner of that wiki.
                // User must have:
                //      mod/wiki:managewiki capability
                // and
                //      mod/wiki:editpage capability
                $manage = has_capability('mod/wiki:managewiki', $context);
                $edit = has_capability('mod/wiki:editpage', $context);
                return $manage && $edit;
            }
        } else {
            //Error
            return false;
        }
    default: // Error
        return false;
    }
}

//----------------
// Locks
//----------------

/**
 * Checks if a page-section is locked.
 *
 * @return true if the combination of section and page is locked, FALSE otherwise.
 */
function wiki_is_page_section_locked($pageid, $userid, $section = null) {
    global $DB;

    $sql = "pageid = ? AND lockedat > ? AND userid != ?";
    $params = array($pageid, time(), $userid);

    if (!empty($section)) {
        $sql .= " AND (sectionname = ? OR sectionname IS null)";
        $params[] = $section;
    }

    return $DB->record_exists_select('wiki_locks', $sql, $params);
}

/**
 * Inserts or updates a wiki_locks record.
 */
function wiki_set_lock($pageid, $userid, $section = null, $insert = false) {
    global $DB;

    if (wiki_is_page_section_locked($pageid, $userid, $section)) {
        return false;
    }

    $params = array('pageid' => $pageid, 'userid' => $userid, 'sectionname' => $section);

    $lock = $DB->get_record('wiki_locks', $params);

    if (!empty($lock)) {
        $DB->update_record('wiki_locks', array('id' => $lock->id, 'lockedat' => time() + LOCK_TIMEOUT));
    } else if ($insert) {
        $DB->insert_record('wiki_locks',
            array('pageid' => $pageid, 'sectionname' => $section, 'userid' => $userid, 'lockedat' => time() + LOCK_TIMEOUT));
    }

    return true;
}

/**
 * Deletes wiki_locks that are not in use. (F.Ex. after submitting the changes). If no userid is present, it deletes ALL the wiki_locks of a specific page.
 *
 * @param int $pageid page id.
 * @param int $userid id of user for which lock is deleted.
 * @param string $section section to be deleted.
 * @param bool $delete_from_db deleted from db.
 * @param bool $delete_section_and_page delete section and page version.
 */
function wiki_delete_locks($pageid, $userid = null, $section = null, $delete_from_db = true, $delete_section_and_page = false) {
    global $DB;

    $wiki = wiki_get_wiki_from_pageid($pageid);
    $cm = get_coursemodule_from_instance('wiki', $wiki->id);
    $context = context_module::instance($cm->id);

    $params = array('pageid' => $pageid);

    if (!empty($userid)) {
        $params['userid'] = $userid;
    }

    if (!empty($section)) {
        $params['sectionname'] = $section;
    }

    if ($delete_from_db) {
        $DB->delete_records('wiki_locks', $params);
        if ($delete_section_and_page && !empty($section)) {
            $params['sectionname'] = null;
            $DB->delete_records('wiki_locks', $params);
        }
        $event = \mod_wiki\event\page_locks_deleted::create(
        array(
            'context' => $context,
            'objectid' => $pageid,
            'relateduserid' => $userid,
            'other' => array(
                'section' => $section
                )
            ));
        // No need to add snapshot, as important data is section, userid and pageid, which is part of event.
        $event->trigger();
    } else {
        $DB->set_field('wiki_locks', 'lockedat', time(), $params);
    }
}

/**
 * Deletes wiki_locks that expired 1 hour ago.
 */
function wiki_delete_old_locks() {
    global $DB;

    $DB->delete_records_select('wiki_locks', "lockedat < ?", array(time() - 3600));
}

/**
 * Deletes wiki_links. It can be sepecific link or links attached in subwiki
 *
 * @global mixed $DB database object
 * @param int $linkid id of the link to be deleted
 * @param int $topageid links to the specific page
 * @param int $frompageid links from specific page
 * @param int $subwikiid links to subwiki
 */
function wiki_delete_links($linkid = null, $topageid = null, $frompageid = null, $subwikiid = null) {
    global $DB;
    $params = array();

    // if link id is givien then don't check for anything else
    if (!empty($linkid)) {
        $params['id'] = $linkid;
    } else {
        if (!empty($topageid)) {
            $params['topageid'] = $topageid;
        }
        if (!empty($frompageid)) {
            $params['frompageid'] = $frompageid;
        }
        if (!empty($subwikiid)) {
            $params['subwikiid'] = $subwikiid;
        }
    }

    //Delete links if any params are passed, else nothing to delete.
    if (!empty($params)) {
        $DB->delete_records('wiki_links', $params);
    }
}

/**
 * Delete wiki synonyms related to subwikiid or page
 *
 * @param int $subwikiid id of sunbwiki
 * @param int $pageid id of page
 */
function wiki_delete_synonym($subwikiid, $pageid = null) {
    global $DB;

    $params = array('subwikiid' => $subwikiid);
    if (!is_null($pageid)) {
        $params['pageid'] = $pageid;
    }
    $DB->delete_records('wiki_synonyms', $params, IGNORE_MISSING);
}

/**
 * Delete pages and all related data
 *
 * @param mixed $context context in which page needs to be deleted.
 * @param mixed $pageids id's of pages to be deleted
 * @param int $subwikiid id of the subwiki for which all pages should be deleted
 */
function wiki_delete_pages($context, $pageids = null, $subwikiid = null) {
    global $DB, $CFG;

    if (!empty($pageids) && is_int($pageids)) {
       $pageids = array($pageids);
    } else if (!empty($subwikiid)) {
        $pageids = wiki_get_page_list($subwikiid);
    }

    //If there is no pageid then return as we can't delete anything.
    if (empty($pageids)) {
        return;
    }

    /// Delete page and all it's relevent data
    foreach ($pageids as $pageid) {
        if (is_object($pageid)) {
            $pageid = $pageid->id;
        }

        //Delete page comments
        $comments = wiki_get_comments($context->id, $pageid);
        foreach ($comments as $commentid => $commentvalue) {
            wiki_delete_comment($commentid, $context, $pageid);
        }

        //Delete page tags
        core_tag_tag::remove_all_item_tags('mod_wiki', 'wiki_pages', $pageid);

        //Delete Synonym
        wiki_delete_synonym($subwikiid, $pageid);

        //Delete all page versions
        wiki_delete_page_versions(array($pageid=>array(0)), $context);

        //Delete all page locks
        wiki_delete_locks($pageid);

        //Delete all page links
        wiki_delete_links(null, $pageid);

        $params = array('id' => $pageid);

        // Get page before deleting.
        $page = $DB->get_record('wiki_pages', $params);

        //Delete page
        $DB->delete_records('wiki_pages', $params);

        // Trigger page_deleted event.
        $event = \mod_wiki\event\page_deleted::create(
                array(
                    'context' => $context,
                    'objectid' => $pageid,
                    'other' => array('subwikiid' => $subwikiid)
                    ));
        $event->add_record_snapshot('wiki_pages', $page);
        $event->trigger();
    }
}

/**
 * Delete specificed versions of a page or versions created by users
 * if version is 0 then it will remove all versions of the page
 *
 * @param array $deleteversions delete versions for a page
 * @param context_module $context module context
 */
function wiki_delete_page_versions($deleteversions, $context = null) {
    global $DB;

    /// delete page-versions
    foreach ($deleteversions as $id => $versions) {
        $params = array('pageid' => $id);
        if (is_null($context)) {
            $wiki = wiki_get_wiki_from_pageid($id);
            $cm = get_coursemodule_from_instance('wiki', $wiki->id);
            $context = context_module::instance($cm->id);
        }
        // Delete all versions, if version specified is 0.
        if (in_array(0, $versions)) {
            $oldversions = $DB->get_records('wiki_versions', $params);
            $DB->delete_records('wiki_versions', $params, IGNORE_MISSING);
        } else {
            list($insql, $param) = $DB->get_in_or_equal($versions);
            $insql .= ' AND pageid = ?';
            array_push($param, $params['pageid']);
            $oldversions = $DB->get_recordset_select('wiki_versions', 'version ' . $insql, $param);
            $DB->delete_records_select('wiki_versions', 'version ' . $insql, $param);
        }
        foreach ($oldversions as $version) {
            // Trigger page version deleted event.
            $event = \mod_wiki\event\page_version_deleted::create(
                    array(
                        'context' => $context,
                        'objectid' => $version->id,
                        'other' => array(
                            'pageid' => $id
                        )
                    ));
            $event->add_record_snapshot('wiki_versions', $version);
            $event->trigger();
        }
    }
}

function wiki_get_comment($commentid){
    global $DB;
    return $DB->get_record('comments', array('id' => $commentid));
}

/**
 * Returns all comments by context and pageid
 *
 * @param int $contextid Current context id
 * @param int $pageid Current pageid
 **/
function wiki_get_comments($contextid, $pageid) {
    global $DB;

    return $DB->get_records('comments', array('contextid' => $contextid, 'itemid' => $pageid, 'commentarea' => 'wiki_page'), 'timecreated ASC');
}

/**
 * Add comments ro database
 *
 * @param object $context. Current context
 * @param int $pageid. Current pageid
 * @param string $content. Content of the comment
 * @param string editor. Version of editor we are using.
 **/
function wiki_add_comment($context, $pageid, $content, $editor) {
    global $CFG;
    require_once($CFG->dirroot . '/comment/lib.php');

    list($context, $course, $cm) = get_context_info_array($context->id);
    $cmt = new stdclass();
    $cmt->context = $context;
    $cmt->itemid = $pageid;
    $cmt->area = 'wiki_page';
    $cmt->course = $course;
    $cmt->component = 'mod_wiki';

    $manager = new comment($cmt);

    if ($editor == 'creole') {
        $manager->add($content, FORMAT_CREOLE);
    } else if ($editor == 'html') {
        $manager->add($content, FORMAT_HTML);
    } else if ($editor == 'nwiki') {
        $manager->add($content, FORMAT_NWIKI);
    }

}

/**
 * Delete comments from database
 *
 * @param $idcomment. Id of comment which will be deleted
 * @param $context. Current context
 * @param $pageid. Current pageid
 **/
function wiki_delete_comment($idcomment, $context, $pageid) {
    global $CFG;
    require_once($CFG->dirroot . '/comment/lib.php');

    list($context, $course, $cm) = get_context_info_array($context->id);
    $cmt = new stdClass();
    $cmt->context = $context;
    $cmt->itemid = $pageid;
    $cmt->area = 'wiki_page';
    $cmt->course = $course;
    $cmt->component = 'mod_wiki';

    $manager = new comment($cmt);
    $manager->delete($idcomment);

}

/**
 * Delete al comments from wiki
 *
 **/
function wiki_delete_comments_wiki() {
    global $PAGE, $DB;

    $cm = $PAGE->cm;
    $context = context_module::instance($cm->id);

    $table = 'comments';
    $select = 'contextid = ?';

    $DB->delete_records_select($table, $select, array($context->id));

}

function wiki_add_progress($pageid, $oldversionid, $versionid, $progress) {
    global $DB;
    for ($v = $oldversionid + 1; $v <= $versionid; $v++) {
        $user = wiki_get_wiki_page_id($pageid, $v);

        $DB->insert_record('wiki_progress', array('userid' => $user->userid, 'pageid' => $pageid, 'versionid' => $v, 'progress' => $progress));
    }
}

function wiki_get_wiki_page_id($pageid, $id) {
    global $DB;
    return $DB->get_record('wiki_versions', array('pageid' => $pageid, 'id' => $id));
}

function wiki_print_page_content($page, $context, $subwikiid) {
    global $OUTPUT, $CFG;

    if ($page->timerendered + WIKI_REFRESH_CACHE_TIME < time()) {
        $content = wiki_refresh_cachedcontent($page);
        $page = $content['page'];
    }

    if (isset($content)) {
        $box = '';
        foreach ($content['sections'] as $s) {
            $box .= '<p>' . get_string('repeatedsection', 'wiki', $s) . '</p>';
        }

        if (!empty($box)) {
            echo $OUTPUT->box($box);
        }
    }
    $html = file_rewrite_pluginfile_urls($page->cachedcontent, 'pluginfile.php', $context->id, 'mod_wiki', 'attachments', $subwikiid);
    $html = format_text($html, FORMAT_MOODLE, array('overflowdiv'=>true, 'allowid'=>true));
    echo $OUTPUT->box($html);

    echo $OUTPUT->tag_list(core_tag_tag::get_item_tags('mod_wiki', 'wiki_pages', $page->id),
            null, 'wiki-tags');

    wiki_increment_pageviews($page);
}

/**
 * This function trims any given text and returns it with some dots at the end
 *
 * @param string $text
 * @param string $limit
 *
 * @return string
 */
function wiki_trim_string($text, $limit = 25) {

    if (core_text::strlen($text) > $limit) {
        $text = core_text::substr($text, 0, $limit) . '...';
    }

    return $text;
}

/**
 * Prints default edit form fields and buttons
 *
 * @param string $format Edit form format (html, creole...)
 * @param integer $version Version number. A negative number means no versioning.
 */

function wiki_print_edit_form_default_fields($format, $pageid, $version = -1, $upload = false, $deleteuploads = array()) {
    global $CFG, $PAGE, $OUTPUT;

    echo '<input type="hidden" name="sesskey" value="' . sesskey() . '" />';

    if ($version >= 0) {
        echo '<input type="hidden" name="version" value="' . $version . '" />';
    }

    echo '<input type="hidden" name="format" value="' . $format . '"/>';

    //attachments
    require_once($CFG->dirroot . '/lib/form/filemanager.php');

    $filemanager = new MoodleQuickForm_filemanager('attachments', get_string('wikiattachments', 'wiki'), array('id' => 'attachments'), array('subdirs' => false, 'maxfiles' => 99, 'maxbytes' => $CFG->maxbytes));

    $value = file_get_submitted_draft_itemid('attachments');
    if (!empty($value) && !$upload) {
        $filemanager->setValue($value);
    }

    echo "<fieldset class=\"wiki-upload-section clearfix\"><legend class=\"ftoggler\">" . get_string("uploadtitle", 'wiki') . "</legend>";

    echo $OUTPUT->container_start('container');
    print $filemanager->toHtml();
    echo $OUTPUT->container_end();

    $cm = $PAGE->cm;
    $context = context_module::instance($cm->id);

    echo $OUTPUT->container_start('container wiki-upload-table');
    wiki_print_upload_table($context, 'wiki_upload', $pageid, $deleteuploads);
    echo $OUTPUT->container_end();

    echo "</fieldset>";

    echo '<input class="wiki_button" type="submit" name="editoption" value="' . get_string('save', 'wiki') . '"/>';
    echo '<input class="wiki_button" type="submit" name="editoption" value="' . get_string('upload', 'wiki') . '"/>';
    echo '<input class="wiki_button" type="submit" name="editoption" value="' . get_string('preview') . '"/>';
    echo '<input class="wiki_button" type="submit" name="editoption" value="' . get_string('cancel') . '" />';
}

/**
 * Prints a table with the files attached to a wiki page
 * @param object $context
 * @param string $filearea
 * @param int $fileitemid
 * @param array deleteuploads
 */
function wiki_print_upload_table($context, $filearea, $fileitemid, $deleteuploads = array()) {
    global $CFG, $OUTPUT;

    $htmltable = new html_table();

    $htmltable->head = array(get_string('deleteupload', 'wiki'), get_string('uploadname', 'wiki'), get_string('uploadactions', 'wiki'));

    $fs = get_file_storage();
    $files = $fs->get_area_files($context->id, 'mod_wiki', $filearea, $fileitemid); //TODO: this is weird (skodak)

    foreach ($files as $file) {
        if (!$file->is_directory()) {
            $checkbox = '<input type="checkbox" name="deleteupload[]", value="' . $file->get_pathnamehash() . '"';

            if (in_array($file->get_pathnamehash(), $deleteuploads)) {
                $checkbox .= ' checked="checked"';
            }

            $checkbox .= " />";

            $htmltable->data[] = array($checkbox, '<a href="' . file_encode_url($CFG->wwwroot . '/pluginfile.php', '/' . $context->id . '/wiki_upload/' . $fileitemid . '/' . $file->get_filename()) . '">' . $file->get_filename() . '</a>', "");
        }
    }

    print '<h3 class="upload-table-title">' . get_string('uploadfiletitle', 'wiki') . "</h3>";
    print html_writer::table($htmltable);
}

/**
 * Generate wiki's page tree
 *
 * @param page_wiki $page. A wiki page object
 * @param navigation_node $node. Starting navigation_node
 * @param array $keys. An array to store keys
 * @return an array with all tree nodes
 */
function wiki_build_tree($page, $node, &$keys) {
    $content = array();
    static $icon = null;
    if ($icon === null) {
        // Substitute the default navigation icon with empty image.
        $icon = new pix_icon('spacer', '');
    }
    $pages = wiki_get_linked_pages($page->id);
    foreach ($pages as $p) {
        $key = $page->id . ':' . $p->id;
        if (in_array($key, $keys)) {
            break;
        }
        array_push($keys, $key);
        $l = wiki_parser_link($p);
        $link = new moodle_url('/mod/wiki/view.php', array('pageid' => $p->id));
        // navigation_node::get_content will format the title for us
        $nodeaux = $node->add($p->title, $link, null, null, null, $icon);
        if ($l['new']) {
            $nodeaux->add_class('wiki_newentry');
        }
        wiki_build_tree($p, $nodeaux, $keys);
    }
    $content[] = $node;
    return $content;
}

/**
 * Get linked pages from page
 * @param int $pageid
 */
function wiki_get_linked_pages($pageid) {
    global $DB;

    $sql = "SELECT p.id, p.title
            FROM {wiki_pages} p
            JOIN {wiki_links} l ON l.topageid = p.id
            WHERE l.frompageid = ?
            ORDER BY p.title ASC";
    return $DB->get_records_sql($sql, array($pageid));
}

/**
 * Get updated pages from wiki
 * @param int $pageid
 */
function wiki_get_updated_pages_by_subwiki($swid) {
    global $DB, $USER;

    $sql = "SELECT *
            FROM {wiki_pages}
            WHERE subwikiid = ? AND timemodified > ?
            ORDER BY timemodified DESC";
    return $DB->get_records_sql($sql, array($swid, $USER->lastlogin));
}

/**
 * Check if the user can create pages in a certain wiki.
 * @param context $context Wiki's context.
 * @param integer|stdClass $user A user id or object. By default (null) checks the permissions of the current user.
 * @return bool True if user can create pages, false otherwise.
 * @since Moodle 3.1
 */
function wiki_can_create_pages($context, $user = null) {
    return has_capability('mod/wiki:createpage', $context, $user);
}

/**
 * Get a sub wiki instance by wiki id, group id and user id.
 * If the wiki doesn't exist in DB it will return an isntance with id -1.
 *
 * @param int $wikiid  Wiki ID.
 * @param int $groupid Group ID.
 * @param int $userid  User ID.
 * @return object      Subwiki instance.
 * @since Moodle 3.1
 */
function wiki_get_possible_subwiki_by_group($wikiid, $groupid, $userid = 0) {
    if (!$subwiki = wiki_get_subwiki_by_group($wikiid, $groupid, $userid)) {
        $subwiki = new stdClass();
        $subwiki->id = -1;
        $subwiki->wikiid = $wikiid;
        $subwiki->groupid = $groupid;
        $subwiki->userid = $userid;
    }
    return $subwiki;
}

/**
 * Get all the possible subwikis visible to the user in a wiki.
 * It will return all the subwikis that can be created in a wiki, even if they don't exist in DB yet.
 *
 * @param  stdClass $wiki          Wiki to get the subwikis from.
 * @param  cm_info|stdClass $cm    Optional. The course module object.
 * @param  context_module $context Optional. Context of wiki module.
 * @return array                   List of subwikis.
 * @since Moodle 3.1
 */
function wiki_get_visible_subwikis($wiki, $cm = null, $context = null) {
    global $USER;

    $subwikis = array();

    if (empty($wiki) or !is_object($wiki)) {
        // Wiki not valid.
        return $subwikis;
    }

    if (empty($cm)) {
        $cm = get_coursemodule_from_instance('wiki', $wiki->id);
    }
    if (empty($context)) {
        $context = context_module::instance($cm->id);
    }

    if (!has_capability('mod/wiki:viewpage', $context)) {
        return $subwikis;
    }

    $manage = has_capability('mod/wiki:managewiki', $context);

    if (!$groupmode = groups_get_activity_groupmode($cm)) {
        // No groups.
        if ($wiki->wikimode == 'collaborative') {
            // Only 1 subwiki.
            $subwikis[] = wiki_get_possible_subwiki_by_group($wiki->id, 0, 0);
        } else if ($wiki->wikimode == 'individual') {
            // There's 1 subwiki per user.
            if ($manage) {
                // User can view all subwikis.
                $users = get_enrolled_users($context);
                foreach ($users as $user) {
                    $subwikis[] = wiki_get_possible_subwiki_by_group($wiki->id, 0, $user->id);
                }
            } else {
                // User can only see his subwiki.
                $subwikis[] = wiki_get_possible_subwiki_by_group($wiki->id, 0, $USER->id);
            }
        }
    } else {
        if ($wiki->wikimode == 'collaborative') {
            // 1 subwiki per group.
            $aag = has_capability('moodle/site:accessallgroups', $context);
            if ($aag || $groupmode == VISIBLEGROUPS) {
                // User can see all groups.
                $allowedgroups = groups_get_all_groups($cm->course, 0, $cm->groupingid);
                $allparticipants = new stdClass();
                $allparticipants->id = 0;
                array_unshift($allowedgroups, $allparticipants); // Add all participants.
            } else {
                // User can only see the groups he belongs to.
                $allowedgroups = groups_get_all_groups($cm->course, $USER->id, $cm->groupingid);
            }

            foreach ($allowedgroups as $group) {
                $subwikis[] = wiki_get_possible_subwiki_by_group($wiki->id, $group->id, 0);
            }
        } else if ($wiki->wikimode == 'individual') {
            // 1 subwiki per user and group.

            if ($manage || $groupmode == VISIBLEGROUPS) {
                // User can view all subwikis.
                $users = get_enrolled_users($context);
                foreach ($users as $user) {
                    // Get all the groups this user belongs to.
                    $groups = groups_get_all_groups($cm->course, $user->id);
                    if (!empty($groups)) {
                        foreach ($groups as $group) {
                            $subwikis[] = wiki_get_possible_subwiki_by_group($wiki->id, $group->id, $user->id);
                        }
                    } else {
                        // User doesn't belong to any group, add it to group 0.
                        $subwikis[] = wiki_get_possible_subwiki_by_group($wiki->id, 0, $user->id);
                    }
                }
            } else {
                // The user can only see the subwikis of the groups he belongs.
                $allowedgroups = groups_get_all_groups($cm->course, $USER->id, $cm->groupingid);
                foreach ($allowedgroups as $group) {
                    $users = groups_get_members($group->id);
                    foreach ($users as $user) {
                        $subwikis[] = wiki_get_possible_subwiki_by_group($wiki->id, $group->id, $user->id);
                    }
                }
            }
        }
    }

    return $subwikis;
}

/**
 * Utility function for getting a subwiki by group and user, validating that the user can view it.
 * If the subwiki doesn't exists in DB yet it'll have id -1.
 *
 * @param stdClass $wiki The wiki.
 * @param int $groupid Group ID. 0 means the subwiki doesn't use groups.
 * @param int $userid User ID. 0 means the subwiki doesn't use users.
 * @return stdClass Subwiki. If it doesn't exists in DB yet it'll have id -1. If the user can't view the
 *                  subwiki this function will return false.
 * @since  Moodle 3.1
 * @throws moodle_exception
 */
function wiki_get_subwiki_by_group_and_user_with_validation($wiki, $groupid, $userid) {
    global $USER, $DB;

    // Get subwiki based on group and user.
    if (!$subwiki = wiki_get_subwiki_by_group($wiki->id, $groupid, $userid)) {

        // The subwiki doesn't exist.
        // Validate if user is valid.
        if ($userid != 0) {
            $user = core_user::get_user($userid, '*', MUST_EXIST);
            core_user::require_active_user($user);
        }

        // Validate that groupid is valid.
        if ($groupid != 0 && !groups_group_exists($groupid)) {
            throw new moodle_exception('cannotfindgroup', 'error');
        }

        // Valid data but subwiki not found. We'll simulate a subwiki object to check if the user would be able to see it
        // if it existed. If he's able to see it then we'll return an empty array because the subwiki has no pages.
        $subwiki = new stdClass();
        $subwiki->id = -1;
        $subwiki->wikiid = $wiki->id;
        $subwiki->userid = $userid;
        $subwiki->groupid = $groupid;
    }

    // Check that the user can view the subwiki. This function checks capabilities.
    if (!wiki_user_can_view($subwiki, $wiki)) {
        return false;
    }

    return $subwiki;
}

/**
 * Returns wiki pages tagged with a specified tag.
 *
 * This is a callback used by the tag area mod_wiki/wiki_pages to search for wiki pages
 * tagged with a specific tag.
 *
 * @param core_tag_tag $tag
 * @param bool $exclusivemode if set to true it means that no other entities tagged with this tag
 *             are displayed on the page and the per-page limit may be bigger
 * @param int $fromctx context id where the link was displayed, may be used by callbacks
 *            to display items in the same context first
 * @param int $ctx context id where to search for records
 * @param bool $rec search in subcontexts as well
 * @param int $page 0-based number of page being displayed
 * @return \core_tag\output\tagindex
 */
function mod_wiki_get_tagged_pages($tag, $exclusivemode = false, $fromctx = 0, $ctx = 0, $rec = 1, $page = 0) {
    global $OUTPUT;
    $perpage = $exclusivemode ? 20 : 5;

    // Build the SQL query.
    $ctxselect = context_helper::get_preload_record_columns_sql('ctx');
    $query = "SELECT wp.id, wp.title, ws.userid, ws.wikiid, ws.id AS subwikiid, ws.groupid, w.wikimode,
                    cm.id AS cmid, c.id AS courseid, c.shortname, c.fullname, $ctxselect
                FROM {wiki_pages} wp
                JOIN {wiki_subwikis} ws ON wp.subwikiid = ws.id
                JOIN {wiki} w ON w.id = ws.wikiid
                JOIN {modules} m ON m.name='wiki'
                JOIN {course_modules} cm ON cm.module = m.id AND cm.instance = w.id
                JOIN {tag_instance} tt ON wp.id = tt.itemid
                JOIN {course} c ON cm.course = c.id
                JOIN {context} ctx ON ctx.instanceid = cm.id AND ctx.contextlevel = :coursemodulecontextlevel
               WHERE tt.itemtype = :itemtype AND tt.tagid = :tagid AND tt.component = :component
                 AND cm.deletioninprogress = 0
                 AND wp.id %ITEMFILTER% AND c.id %COURSEFILTER%";

    $params = array('itemtype' => 'wiki_pages', 'tagid' => $tag->id, 'component' => 'mod_wiki',
        'coursemodulecontextlevel' => CONTEXT_MODULE);

    if ($ctx) {
        $context = $ctx ? context::instance_by_id($ctx) : context_system::instance();
        $query .= $rec ? ' AND (ctx.id = :contextid OR ctx.path LIKE :path)' : ' AND ctx.id = :contextid';
        $params['contextid'] = $context->id;
        $params['path'] = $context->path.'/%';
    }

    $query .= " ORDER BY ";
    if ($fromctx) {
        // In order-clause specify that modules from inside "fromctx" context should be returned first.
        $fromcontext = context::instance_by_id($fromctx);
        $query .= ' (CASE WHEN ctx.id = :fromcontextid OR ctx.path LIKE :frompath THEN 0 ELSE 1 END),';
        $params['fromcontextid'] = $fromcontext->id;
        $params['frompath'] = $fromcontext->path.'/%';
    }
    $query .= ' c.sortorder, cm.id, wp.id';

    $totalpages = $page + 1;

    // Use core_tag_index_builder to build and filter the list of items.
    $builder = new core_tag_index_builder('mod_wiki', 'wiki_pages', $query, $params, $page * $perpage, $perpage + 1);
    while ($item = $builder->has_item_that_needs_access_check()) {
        context_helper::preload_from_record($item);
        $courseid = $item->courseid;
        if (!$builder->can_access_course($courseid)) {
            $builder->set_accessible($item, false);
            continue;
        }
        $modinfo = get_fast_modinfo($builder->get_course($courseid));
        // Set accessibility of this item and all other items in the same course.
        $builder->walk(function ($taggeditem) use ($courseid, $modinfo, $builder) {
            if ($taggeditem->courseid == $courseid) {
                $accessible = false;
                if (($cm = $modinfo->get_cm($taggeditem->cmid)) && $cm->uservisible) {
                    $subwiki = (object)array('id' => $taggeditem->subwikiid, 'groupid' => $taggeditem->groupid,
                        'userid' => $taggeditem->userid, 'wikiid' => $taggeditem->wikiid);
                    $wiki = (object)array('id' => $taggeditem->wikiid, 'wikimode' => $taggeditem->wikimode,
                        'course' => $cm->course);
                    $accessible = wiki_user_can_view($subwiki, $wiki);
                }
                $builder->set_accessible($taggeditem, $accessible);
            }
        });
    }

    $items = $builder->get_items();
    if (count($items) > $perpage) {
        $totalpages = $page + 2; // We don't need exact page count, just indicate that the next page exists.
        array_pop($items);
    }

    // Build the display contents.
    if ($items) {
        $tagfeed = new core_tag\output\tagfeed();
        foreach ($items as $item) {
            context_helper::preload_from_record($item);
            $modinfo = get_fast_modinfo($item->courseid);
            $cm = $modinfo->get_cm($item->cmid);
            $pageurl = new moodle_url('/mod/wiki/view.php', array('pageid' => $item->id));
            $pagename = format_string($item->title, true, array('context' => context_module::instance($item->cmid)));
            $pagename = html_writer::link($pageurl, $pagename);
            $courseurl = course_get_url($item->courseid, $cm->sectionnum);
            $cmname = html_writer::link($cm->url, $cm->get_formatted_name());
            $coursename = format_string($item->fullname, true, array('context' => context_course::instance($item->courseid)));
            $coursename = html_writer::link($courseurl, $coursename);
            $icon = html_writer::link($pageurl, html_writer::empty_tag('img', array('src' => $cm->get_icon_url())));
            $tagfeed->add($icon, $pagename, $cmname.'<br>'.$coursename);
        }

        $content = $OUTPUT->render_from_template('core_tag/tagfeed',
                $tagfeed->export_for_template($OUTPUT));

        return new core_tag\output\tagindex($tag, 'mod_wiki', 'wiki_pages', $content,
                $exclusivemode, $fromctx, $ctx, $rec, $page, $totalpages);
    }
}
