/backup/util/dbops/restore_dbops.class.php

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<?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/>.

/**
 * @package    moodlecore
 * @subpackage backup-dbops
 * @copyright  2010 onwards Eloy Lafuente (stronk7) {@link http://stronk7.com}
 * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
 */

/**
 * Base abstract class for all the helper classes providing DB operations
 *
 * TODO: Finish phpdocs
 */
abstract class restore_dbops {
    /**
     * Keep cache of backup records.
     * @var array
     * @todo MDL-25290 static should be replaced with MUC code.
     */
    private static $backupidscache = array();
    /**
     * Keep track of backup ids which are cached.
     * @var array
     * @todo MDL-25290 static should be replaced with MUC code.
     */
    private static $backupidsexist = array();
    /**
     * Count is expensive, so manually keeping track of
     * backupidscache, to avoid memory issues.
     * @var int
     * @todo MDL-25290 static should be replaced with MUC code.
     */
    private static $backupidscachesize = 2048;
    /**
     * Count is expensive, so manually keeping track of
     * backupidsexist, to avoid memory issues.
     * @var int
     * @todo MDL-25290 static should be replaced with MUC code.
     */
    private static $backupidsexistsize = 10240;
    /**
     * Slice backupids cache to add more data.
     * @var int
     * @todo MDL-25290 static should be replaced with MUC code.
     */
    private static $backupidsslice = 512;

    /**
     * Return one array containing all the tasks that have been included
     * in the restore process. Note that these tasks aren't built (they
     * haven't steps nor ids data available)
     */
    public static function get_included_tasks($restoreid) {
        $rc = restore_controller_dbops::load_controller($restoreid);
        $tasks = $rc->get_plan()->get_tasks();
        $includedtasks = array();
        foreach ($tasks as $key => $task) {
            // Calculate if the task is being included
            $included = false;
            // blocks, based in blocks setting and parent activity/course
            if ($task instanceof restore_block_task) {
                if (!$task->get_setting_value('blocks')) { // Blocks not included, continue
                    continue;
                }
                $parent = basename(dirname(dirname($task->get_taskbasepath())));
                if ($parent == 'course') { // Parent is course, always included if present
                    $included = true;

                } else { // Look for activity_included setting
                    $included = $task->get_setting_value($parent . '_included');
                }

            // ativities, based on included setting
            } else if ($task instanceof restore_activity_task) {
                $included = $task->get_setting_value('included');

            // sections, based on included setting
            } else if ($task instanceof restore_section_task) {
                $included = $task->get_setting_value('included');

            // course always included if present
            } else if ($task instanceof restore_course_task) {
                $included = true;
            }

            // If included, add it
            if ($included) {
                $includedtasks[] = clone($task); // A clone is enough. In fact we only need the basepath.
            }
        }
        $rc->destroy(); // Always need to destroy.

        return $includedtasks;
    }

    /**
     * Load one inforef.xml file to backup_ids table for future reference
     *
     * @param string $restoreid Restore id
     * @param string $inforeffile File path
     * @param \core\progress\base $progress Progress tracker
     */
    public static function load_inforef_to_tempids($restoreid, $inforeffile,
            \core\progress\base $progress = null) {

        if (!file_exists($inforeffile)) { // Shouldn't happen ever, but...
            throw new backup_helper_exception('missing_inforef_xml_file', $inforeffile);
        }

        // Set up progress tracking (indeterminate).
        if (!$progress) {
            $progress = new \core\progress\none();
        }
        $progress->start_progress('Loading inforef.xml file');

        // Let's parse, custom processor will do its work, sending info to DB
        $xmlparser = new progressive_parser();
        $xmlparser->set_file($inforeffile);
        $xmlprocessor = new restore_inforef_parser_processor($restoreid);
        $xmlparser->set_processor($xmlprocessor);
        $xmlparser->set_progress($progress);
        $xmlparser->process();

        // Finish progress
        $progress->end_progress();
    }

    /**
     * Load the needed role.xml file to backup_ids table for future reference
     */
    public static function load_roles_to_tempids($restoreid, $rolesfile) {

        if (!file_exists($rolesfile)) { // Shouldn't happen ever, but...
            throw new backup_helper_exception('missing_roles_xml_file', $rolesfile);
        }
        // Let's parse, custom processor will do its work, sending info to DB
        $xmlparser = new progressive_parser();
        $xmlparser->set_file($rolesfile);
        $xmlprocessor = new restore_roles_parser_processor($restoreid);
        $xmlparser->set_processor($xmlprocessor);
        $xmlparser->process();
    }

    /**
     * Precheck the loaded roles, return empty array if everything is ok, and
     * array with 'errors', 'warnings' elements (suitable to be used by restore_prechecks)
     * with any problem found. At the same time, store all the mapping into backup_ids_temp
     * and also put the information into $rolemappings (controller->info), so it can be reworked later by
     * post-precheck stages while at the same time accept modified info in the same object coming from UI
     */
    public static function precheck_included_roles($restoreid, $courseid, $userid, $samesite, $rolemappings) {
        global $DB;

        $problems = array(); // To store warnings/errors

        // Get loaded roles from backup_ids
        $rs = $DB->get_recordset('backup_ids_temp', array('backupid' => $restoreid, 'itemname' => 'role'), '', 'itemid, info');
        foreach ($rs as $recrole) {
            // If the rolemappings->modified flag is set, that means that we are coming from
            // manually modified mappings (by UI), so accept those mappings an put them to backup_ids
            if ($rolemappings->modified) {
                $target = $rolemappings->mappings[$recrole->itemid]->targetroleid;
                self::set_backup_ids_record($restoreid, 'role', $recrole->itemid, $target);

            // Else, we haven't any info coming from UI, let's calculate the mappings, matching
            // in multiple ways and checking permissions. Note mapping to 0 means "skip"
            } else {
                $role = (object)backup_controller_dbops::decode_backup_temp_info($recrole->info);
                $match = self::get_best_assignable_role($role, $courseid, $userid, $samesite);
                // Send match to backup_ids
                self::set_backup_ids_record($restoreid, 'role', $recrole->itemid, $match);
                // Build the rolemappings element for controller
                unset($role->id);
                unset($role->nameincourse);
                $role->targetroleid = $match;
                $rolemappings->mappings[$recrole->itemid] = $role;
                // Prepare warning if no match found
                if (!$match) {
                    $problems['warnings'][] = get_string('cannotfindassignablerole', 'backup', $role->name);
                }
            }
        }
        $rs->close();
        return $problems;
    }

    /**
     * Return cached backup id's
     *
     * @param int $restoreid id of backup
     * @param string $itemname name of the item
     * @param int $itemid id of item
     * @return array backup id's
     * @todo MDL-25290 replace static backupids* with MUC code
     */
    protected static function get_backup_ids_cached($restoreid, $itemname, $itemid) {
        global $DB;

        $key = "$itemid $itemname $restoreid";

        // If record exists in cache then return.
        if (isset(self::$backupidsexist[$key]) && isset(self::$backupidscache[$key])) {
            // Return a copy of cached data, to avoid any alterations in cached data.
            return clone self::$backupidscache[$key];
        }

        // Clean cache, if it's full.
        if (self::$backupidscachesize <= 0) {
            // Remove some records, to keep memory in limit.
            self::$backupidscache = array_slice(self::$backupidscache, self::$backupidsslice, null, true);
            self::$backupidscachesize = self::$backupidscachesize + self::$backupidsslice;
        }
        if (self::$backupidsexistsize <= 0) {
            self::$backupidsexist = array_slice(self::$backupidsexist, self::$backupidsslice, null, true);
            self::$backupidsexistsize = self::$backupidsexistsize + self::$backupidsslice;
        }

        // Retrive record from database.
        $record = array(
            'backupid' => $restoreid,
            'itemname' => $itemname,
            'itemid'   => $itemid
        );
        if ($dbrec = $DB->get_record('backup_ids_temp', $record)) {
            self::$backupidsexist[$key] = $dbrec->id;
            self::$backupidscache[$key] = $dbrec;
            self::$backupidscachesize--;
            self::$backupidsexistsize--;
            return $dbrec;
        } else {
            return false;
        }
    }

    /**
     * Cache backup ids'
     *
     * @param int $restoreid id of backup
     * @param string $itemname name of the item
     * @param int $itemid id of item
     * @param array $extrarecord extra record which needs to be updated
     * @return void
     * @todo MDL-25290 replace static BACKUP_IDS_* with MUC code
     */
    protected static function set_backup_ids_cached($restoreid, $itemname, $itemid, $extrarecord) {
        global $DB;

        $key = "$itemid $itemname $restoreid";

        $record = array(
            'backupid' => $restoreid,
            'itemname' => $itemname,
            'itemid'   => $itemid,
        );

        // If record is not cached then add one.
        if (!isset(self::$backupidsexist[$key])) {
            // If we have this record in db, then just update this.
            if ($existingrecord = $DB->get_record('backup_ids_temp', $record)) {
                self::$backupidsexist[$key] = $existingrecord->id;
                self::$backupidsexistsize--;
                self::update_backup_cached_record($record, $extrarecord, $key, $existingrecord);
            } else {
                // Add new record to cache and db.
                $recorddefault = array (
                    'newitemid' => 0,
                    'parentitemid' => null,
                    'info' => null);
                $record = array_merge($record, $recorddefault, $extrarecord);
                $record['id'] = $DB->insert_record('backup_ids_temp', $record);
                self::$backupidsexist[$key] = $record['id'];
                self::$backupidsexistsize--;
                if (self::$backupidscachesize > 0) {
                    // Cache new records if we haven't got many yet.
                    self::$backupidscache[$key] = (object) $record;
                    self::$backupidscachesize--;
                }
            }
        } else {
            self::update_backup_cached_record($record, $extrarecord, $key);
        }
    }

    /**
     * Updates existing backup record
     *
     * @param array $record record which needs to be updated
     * @param array $extrarecord extra record which needs to be updated
     * @param string $key unique key which is used to identify cached record
     * @param stdClass $existingrecord (optional) existing record
     */
    protected static function update_backup_cached_record($record, $extrarecord, $key, $existingrecord = null) {
        global $DB;
        // Update only if extrarecord is not empty.
        if (!empty($extrarecord)) {
            $extrarecord['id'] = self::$backupidsexist[$key];
            $DB->update_record('backup_ids_temp', $extrarecord);
            // Update existing cache or add new record to cache.
            if (isset(self::$backupidscache[$key])) {
                $record = array_merge((array)self::$backupidscache[$key], $extrarecord);
                self::$backupidscache[$key] = (object) $record;
            } else if (self::$backupidscachesize > 0) {
                if ($existingrecord) {
                    self::$backupidscache[$key] = $existingrecord;
                } else {
                    // Retrive record from database and cache updated records.
                    self::$backupidscache[$key] = $DB->get_record('backup_ids_temp', $record);
                }
                $record = array_merge((array)self::$backupidscache[$key], $extrarecord);
                self::$backupidscache[$key] = (object) $record;
                self::$backupidscachesize--;
            }
        }
    }

    /**
     * Reset the ids caches completely
     *
     * Any destructive operation (partial delete, truncate, drop or recreate) performed
     * with the backup_ids table must cause the backup_ids caches to be
     * invalidated by calling this method. See MDL-33630.
     *
     * Note that right now, the only operation of that type is the recreation
     * (drop & restore) of the table that may happen once the prechecks have ended. All
     * the rest of operations are always routed via {@link set_backup_ids_record()}, 1 by 1,
     * keeping the caches on sync.
     *
     * @todo MDL-25290 static should be replaced with MUC code.
     */
    public static function reset_backup_ids_cached() {
        // Reset the ids cache.
        $cachetoadd = count(self::$backupidscache);
        self::$backupidscache = array();
        self::$backupidscachesize = self::$backupidscachesize + $cachetoadd;
        // Reset the exists cache.
        $existstoadd = count(self::$backupidsexist);
        self::$backupidsexist = array();
        self::$backupidsexistsize = self::$backupidsexistsize + $existstoadd;
    }

    /**
     * Given one role, as loaded from XML, perform the best possible matching against the assignable
     * roles, using different fallback alternatives (shortname, archetype, editingteacher => teacher, defaultcourseroleid)
     * returning the id of the best matching role or 0 if no match is found
     */
    protected static function get_best_assignable_role($role, $courseid, $userid, $samesite) {
        global $CFG, $DB;

        // Gather various information about roles
        $coursectx = context_course::instance($courseid);
        $assignablerolesshortname = get_assignable_roles($coursectx, ROLENAME_SHORT, false, $userid);

        // Note: under 1.9 we had one function restore_samerole() that performed one complete
        // matching of roles (all caps) and if match was found the mapping was availabe bypassing
        // any assignable_roles() security. IMO that was wrong and we must not allow such
        // mappings anymore. So we have left that matching strategy out in 2.0

        // Empty assignable roles, mean no match possible
        if (empty($assignablerolesshortname)) {
            return 0;
        }

        // Match by shortname
        if ($match = array_search($role->shortname, $assignablerolesshortname)) {
            return $match;
        }

        // Match by archetype
        list($in_sql, $in_params) = $DB->get_in_or_equal(array_keys($assignablerolesshortname));
        $params = array_merge(array($role->archetype), $in_params);
        if ($rec = $DB->get_record_select('role', "archetype = ? AND id $in_sql", $params, 'id', IGNORE_MULTIPLE)) {
            return $rec->id;
        }

        // Match editingteacher to teacher (happens a lot, from 1.9)
        if ($role->shortname == 'editingteacher' && in_array('teacher', $assignablerolesshortname)) {
            return array_search('teacher', $assignablerolesshortname);
        }

        // No match, return 0
        return 0;
    }


    /**
     * Process the loaded roles, looking for their best mapping or skipping
     * Any error will cause exception. Note this is one wrapper over
     * precheck_included_roles, that contains all the logic, but returns
     * errors/warnings instead and is executed as part of the restore prechecks
     */
     public static function process_included_roles($restoreid, $courseid, $userid, $samesite, $rolemappings) {
        global $DB;

        // Just let precheck_included_roles() to do all the hard work
        $problems = self::precheck_included_roles($restoreid, $courseid, $userid, $samesite, $rolemappings);

        // With problems of type error, throw exception, shouldn't happen if prechecks executed
        if (array_key_exists('errors', $problems)) {
            throw new restore_dbops_exception('restore_problems_processing_roles', null, implode(', ', $problems['errors']));
        }
    }

    /**
     * Load the needed users.xml file to backup_ids table for future reference
     *
     * @param string $restoreid Restore id
     * @param string $usersfile File path
     * @param \core\progress\base $progress Progress tracker
     */
    public static function load_users_to_tempids($restoreid, $usersfile,
            \core\progress\base $progress = null) {

        if (!file_exists($usersfile)) { // Shouldn't happen ever, but...
            throw new backup_helper_exception('missing_users_xml_file', $usersfile);
        }

        // Set up progress tracking (indeterminate).
        if (!$progress) {
            $progress = new \core\progress\none();
        }
        $progress->start_progress('Loading users into temporary table');

        // Let's parse, custom processor will do its work, sending info to DB
        $xmlparser = new progressive_parser();
        $xmlparser->set_file($usersfile);
        $xmlprocessor = new restore_users_parser_processor($restoreid);
        $xmlparser->set_processor($xmlprocessor);
        $xmlparser->set_progress($progress);
        $xmlparser->process();

        // Finish progress.
        $progress->end_progress();
    }

    /**
     * Load the needed questions.xml file to backup_ids table for future reference
     */
    public static function load_categories_and_questions_to_tempids($restoreid, $questionsfile) {

        if (!file_exists($questionsfile)) { // Shouldn't happen ever, but...
            throw new backup_helper_exception('missing_questions_xml_file', $questionsfile);
        }
        // Let's parse, custom processor will do its work, sending info to DB
        $xmlparser = new progressive_parser();
        $xmlparser->set_file($questionsfile);
        $xmlprocessor = new restore_questions_parser_processor($restoreid);
        $xmlparser->set_processor($xmlprocessor);
        $xmlparser->process();
    }

    /**
     * Check all the included categories and questions, deciding the action to perform
     * for each one (mapping / creation) and returning one array of problems in case
     * something is wrong.
     *
     * There are some basic rules that the method below will always try to enforce:
     *
     * Rule1: Targets will be, always, calculated for *whole* question banks (a.k.a. contexid source),
     *     so, given 2 question categories belonging to the same bank, their target bank will be
     *     always the same. If not, we can be incurring into "fragmentation", leading to random/cloze
     *     problems (qtypes having "child" questions).
     *
     * Rule2: The 'moodle/question:managecategory' and 'moodle/question:add' capabilities will be
     *     checked before creating any category/question respectively and, if the cap is not allowed
     *     into upper contexts (system, coursecat)) but in lower ones (course), the *whole* question bank
     *     will be created there.
     *
     * Rule3: Coursecat question banks not existing in the target site will be created as course
     *     (lower ctx) question banks, never as "guessed" coursecat question banks base on depth or so.
     *
     * Rule4: System question banks will be created at system context if user has perms to do so. Else they
     *     will created as course (lower ctx) question banks (similary to rule3). In other words, course ctx
     *     if always a fallback for system and coursecat question banks.
     *
     * Also, there are some notes to clarify the scope of this method:
     *
     * Note1: This method won't create any question category nor question at all. It simply will calculate
     *     which actions (create/map) must be performed for each element and where, validating that all those
     *     actions are doable by the user executing the restore operation. Any problem found will be
     *     returned in the problems array, causing the restore process to stop with error.
     *
     * Note2: To decide if one question bank (all its question categories and questions) is going to be remapped,
     *     then all the categories and questions must exist in the same target bank. If able to do so, missing
     *     qcats and qs will be created (rule2). But if, at the end, something is missing, the whole question bank
     *     will be recreated at course ctx (rule1), no matter if that duplicates some categories/questions.
     *
     * Note3: We'll be using the newitemid column in the temp_ids table to store the action to be performed
     *     with each question category and question. newitemid = 0 means the qcat/q needs to be created and
     *     any other value means the qcat/q is mapped. Also, for qcats, parentitemid will contain the target
     *     context where the categories have to be created (but for module contexts where we'll keep the old
     *     one until the activity is created)
     *
     * Note4: All these "actions" will be "executed" later by {@link restore_create_categories_and_questions}
     */
    public static function precheck_categories_and_questions($restoreid, $courseid, $userid, $samesite) {

        $problems = array();

        // TODO: Check all qs, looking their qtypes are restorable

        // Precheck all qcats and qs looking for target contexts / warnings / errors
        list($syserr, $syswarn) = self::prechek_precheck_qbanks_by_level($restoreid, $courseid, $userid, $samesite, CONTEXT_SYSTEM);
        list($caterr, $catwarn) = self::prechek_precheck_qbanks_by_level($restoreid, $courseid, $userid, $samesite, CONTEXT_COURSECAT);
        list($couerr, $couwarn) = self::prechek_precheck_qbanks_by_level($restoreid, $courseid, $userid, $samesite, CONTEXT_COURSE);
        list($moderr, $modwarn) = self::prechek_precheck_qbanks_by_level($restoreid, $courseid, $userid, $samesite, CONTEXT_MODULE);

        // Acummulate and handle errors and warnings
        $errors   = array_merge($syserr, $caterr, $couerr, $moderr);
        $warnings = array_merge($syswarn, $catwarn, $couwarn, $modwarn);
        if (!empty($errors)) {
            $problems['errors'] = $errors;
        }
        if (!empty($warnings)) {
            $problems['warnings'] = $warnings;
        }
        return $problems;
    }

    /**
     * This function will process all the question banks present in restore
     * at some contextlevel (from CONTEXT_SYSTEM to CONTEXT_MODULE), finding
     * the target contexts where each bank will be restored and returning
     * warnings/errors as needed.
     *
     * Some contextlevels (system, coursecat), will delegate process to
     * course level if any problem is found (lack of permissions, non-matching
     * target context...). Other contextlevels (course, module) will
     * cause return error if some problem is found.
     *
     * At the end, if no errors were found, all the categories in backup_temp_ids
     * will be pointing (parentitemid) to the target context where they must be
     * created later in the restore process.
     *
     * Note: at the time these prechecks are executed, activities haven't been
     * created yet so, for CONTEXT_MODULE banks, we keep the old contextid
     * in the parentitemid field. Once the activity (and its context) has been
     * created, we'll update that context in the required qcats
     *
     * Caller {@link precheck_categories_and_questions} will, simply, execute
     * this function for all the contextlevels, acting as a simple controller
     * of warnings and errors.
     *
     * The function returns 2 arrays, one containing errors and another containing
     * warnings. Both empty if no errors/warnings are found.
     *
     * @param int $restoreid The restore ID
     * @param int $courseid The ID of the course
     * @param int $userid The id of the user doing the restore
     * @param bool $samesite True if restore is to same site
     * @param int $contextlevel (CONTEXT_SYSTEM, etc.)
     * @return array A separate list of all error and warnings detected
     */
    public static function prechek_precheck_qbanks_by_level($restoreid, $courseid, $userid, $samesite, $contextlevel) {
        global $DB;

        // To return any errors and warnings found
        $errors   = array();
        $warnings = array();

        // Specify which fallbacks must be performed
        $fallbacks = array(
            CONTEXT_SYSTEM => CONTEXT_COURSE,
            CONTEXT_COURSECAT => CONTEXT_COURSE);

        $rc = restore_controller_dbops::load_controller($restoreid);
        $restoreinfo = $rc->get_info();
        $rc->destroy(); // Always need to destroy.
        $backuprelease = $restoreinfo->backup_release; // The major version: 2.9, 3.0, 3.10...
        preg_match('/(\d{8})/', $restoreinfo->moodle_release, $matches);
        $backupbuild = (int)$matches[1];
        $after35 = false;
        if (version_compare($backuprelease, '3.5', '>=') && $backupbuild > 20180205) {
            $after35 = true;
        }

        // For any contextlevel, follow this process logic:
        //
        // 0) Iterate over each context (qbank)
        // 1) Iterate over each qcat in the context, matching by stamp for the found target context
        //     2a) No match, check if user can create qcat and q
        //         3a) User can, mark the qcat and all dependent qs to be created in that target context
        //         3b) User cannot, check if we are in some contextlevel with fallback
        //             4a) There is fallback, move ALL the qcats to fallback, warn. End qcat loop
        //             4b) No fallback, error. End qcat loop.
        //     2b) Match, mark qcat to be mapped and iterate over each q, matching by stamp and version
        //         5a) No match, check if user can add q
        //             6a) User can, mark the q to be created
        //             6b) User cannot, check if we are in some contextlevel with fallback
        //                 7a) There is fallback, move ALL the qcats to fallback, warn. End qcat loop
        //                 7b) No fallback, error. End qcat loop
        //         5b) Random question, must always create new.
        //         5c) Match, mark q to be mapped
        // 8) Check if backup is from Moodle >= 3.5 and error if more than one top-level category in the context.

        // Get all the contexts (question banks) in restore for the given contextlevel
        $contexts = self::restore_get_question_banks($restoreid, $contextlevel);

        // 0) Iterate over each context (qbank)
        foreach ($contexts as $contextid => $contextlevel) {
            // Init some perms
            $canmanagecategory = false;
            $canadd            = false;
            // Top-level category counter.
            $topcats = 0;
            // get categories in context (bank)
            $categories = self::restore_get_question_categories($restoreid, $contextid);
            // cache permissions if $targetcontext is found
            if ($targetcontext = self::restore_find_best_target_context($categories, $courseid, $contextlevel)) {
                $canmanagecategory = has_capability('moodle/question:managecategory', $targetcontext, $userid);
                $canadd            = has_capability('moodle/question:add', $targetcontext, $userid);
            }
            // 1) Iterate over each qcat in the context, matching by stamp for the found target context
            foreach ($categories as $category) {
                if ($category->parent == 0) {
                    $topcats++;
                }

                $matchcat = false;
                if ($targetcontext) {
                    $matchcat = $DB->get_record('question_categories', array(
                                    'contextid' => $targetcontext->id,
                                    'stamp' => $category->stamp));
                }
                // 2a) No match, check if user can create qcat and q
                if (!$matchcat) {
                    // 3a) User can, mark the qcat and all dependent qs to be created in that target context
                    if ($canmanagecategory && $canadd) {
                        // Set parentitemid to targetcontext, BUT for CONTEXT_MODULE categories, where
                        // we keep the source contextid unmodified (for easier matching later when the
                        // activities are created)
                        $parentitemid = $targetcontext->id;
                        if ($contextlevel == CONTEXT_MODULE) {
                            $parentitemid = null; // null means "not modify" a.k.a. leave original contextid
                        }
                        self::set_backup_ids_record($restoreid, 'question_category', $category->id, 0, $parentitemid);
                        // Nothing else to mark, newitemid = 0 means create

                    // 3b) User cannot, check if we are in some contextlevel with fallback
                    } else {
                        // 4a) There is fallback, move ALL the qcats to fallback, warn. End qcat loop
                        if (array_key_exists($contextlevel, $fallbacks)) {
                            foreach ($categories as $movedcat) {
                                $movedcat->contextlevel = $fallbacks[$contextlevel];
                                self::set_backup_ids_record($restoreid, 'question_category', $movedcat->id, 0, $contextid, $movedcat);
                                // Warn about the performed fallback
                                $warnings[] = get_string('qcategory2coursefallback', 'backup', $movedcat);
                            }

                        // 4b) No fallback, error. End qcat loop.
                        } else {
                            $errors[] = get_string('qcategorycannotberestored', 'backup', $category);
                        }
                        break; // out from qcat loop (both 4a and 4b), we have decided about ALL categories in context (bank)
                    }

                // 2b) Match, mark qcat to be mapped and iterate over each q, matching by stamp and version
                } else {
                    self::set_backup_ids_record($restoreid, 'question_category', $category->id, $matchcat->id, $targetcontext->id);
                    $questions = self::restore_get_questions($restoreid, $category->id);

                    // Collect all the questions for this category into memory so we only talk to the DB once.
                    $questioncache = $DB->get_records_sql_menu("SELECT ".$DB->sql_concat('stamp', "' '", 'version').", id
                                                                  FROM {question}
                                                                 WHERE category = ?", array($matchcat->id));

                    foreach ($questions as $question) {
                        if (isset($questioncache[$question->stamp." ".$question->version])) {
                            $matchqid = $questioncache[$question->stamp." ".$question->version];
                        } else {
                            $matchqid = false;
                        }
                        // 5a) No match, check if user can add q
                        if (!$matchqid) {
                            // 6a) User can, mark the q to be created
                            if ($canadd) {
                                // Nothing to mark, newitemid means create

                             // 6b) User cannot, check if we are in some contextlevel with fallback
                            } else {
                                // 7a) There is fallback, move ALL the qcats to fallback, warn. End qcat loo
                                if (array_key_exists($contextlevel, $fallbacks)) {
                                    foreach ($categories as $movedcat) {
                                        $movedcat->contextlevel = $fallbacks[$contextlevel];
                                        self::set_backup_ids_record($restoreid, 'question_category', $movedcat->id, 0, $contextid, $movedcat);
                                        // Warn about the performed fallback
                                        $warnings[] = get_string('question2coursefallback', 'backup', $movedcat);
                                    }

                                // 7b) No fallback, error. End qcat loop
                                } else {
                                    $errors[] = get_string('questioncannotberestored', 'backup', $question);
                                }
                                break 2; // out from qcat loop (both 7a and 7b), we have decided about ALL categories in context (bank)
                            }

                        // 5b) Random questions must always be newly created.
                        } else if ($question->qtype == 'random') {
                            // Nothing to mark, newitemid means create

                        // 5c) Match, mark q to be mapped.
                        } else {
                            self::set_backup_ids_record($restoreid, 'question', $question->id, $matchqid);
                        }
                    }
                }
            }

            // 8) Check if backup is made on Moodle >= 3.5 and there are more than one top-level category in the context.
            if ($after35 && $topcats > 1) {
                $errors[] = get_string('restoremultipletopcats', 'question', $contextid);
            }

        }

        return array($errors, $warnings);
    }

    /**
     * Return one array of contextid => contextlevel pairs
     * of question banks to be checked for one given restore operation
     * ordered from CONTEXT_SYSTEM downto CONTEXT_MODULE
     * If contextlevel is specified, then only banks corresponding to
     * that level are returned
     */
    public static function restore_get_question_banks($restoreid, $contextlevel = null) {
        global $DB;

        $results = array();
        $qcats = $DB->get_recordset_sql("SELECT itemid, parentitemid AS contextid, info
                                         FROM {backup_ids_temp}
                                       WHERE backupid = ?
                                         AND itemname = 'question_category'", array($restoreid));
        foreach ($qcats as $qcat) {
            // If this qcat context haven't been acummulated yet, do that
            if (!isset($results[$qcat->contextid])) {
                $info = backup_controller_dbops::decode_backup_temp_info($qcat->info);
                // Filter by contextlevel if necessary
                if (is_null($contextlevel) || $contextlevel == $info->contextlevel) {
                    $results[$qcat->contextid] = $info->contextlevel;
                }
            }
        }
        $qcats->close();
        // Sort by value (contextlevel from CONTEXT_SYSTEM downto CONTEXT_MODULE)
        asort($results);
        return $results;
    }

    /**
     * Return one array of question_category records for
     * a given restore operation and one restore context (question bank)
     */
    public static function restore_get_question_categories($restoreid, $contextid) {
        global $DB;

        $results = array();
        $qcats = $DB->get_recordset_sql("SELECT itemid, info
                                         FROM {backup_ids_temp}
                                        WHERE backupid = ?
                                          AND itemname = 'question_category'
                                          AND parentitemid = ?", array($restoreid, $contextid));
        foreach ($qcats as $qcat) {
            $results[$qcat->itemid] = backup_controller_dbops::decode_backup_temp_info($qcat->info);
        }
        $qcats->close();

        return $results;
    }

    /**
     * Calculates the best context found to restore one collection of qcats,
     * al them belonging to the same context (question bank), returning the
     * target context found (object) or false
     */
    public static function restore_find_best_target_context($categories, $courseid, $contextlevel) {
        global $DB;

        $targetcontext = false;

        // Depending of $contextlevel, we perform different actions
        switch ($contextlevel) {
             // For system is easy, the best context is the system context
             case CONTEXT_SYSTEM:
                 $targetcontext = context_system::instance();
                 break;

             // For coursecat, we are going to look for stamps in all the
             // course categories between CONTEXT_SYSTEM and CONTEXT_COURSE
             // (i.e. in all the course categories in the path)
             //
             // And only will return one "best" target context if all the
             // matches belong to ONE and ONLY ONE context. If multiple
             // matches are found, that means that there is some annoying
             // qbank "fragmentation" in the categories, so we'll fallback
             // to create the qbank at course level
             case CONTEXT_COURSECAT:
                 // Build the array of stamps we are going to match
                 $stamps = array();
                 foreach ($categories as $category) {
                     $stamps[] = $category->stamp;
                 }
                 $contexts = array();
                 // Build the array of contexts we are going to look
                 $systemctx = context_system::instance();
                 $coursectx = context_course::instance($courseid);
                 $parentctxs = $coursectx->get_parent_context_ids();
                 foreach ($parentctxs as $parentctx) {
                     // Exclude system context
                     if ($parentctx == $systemctx->id) {
                         continue;
                     }
                     $contexts[] = $parentctx;
                 }
                 if (!empty($stamps) && !empty($contexts)) {
                     // Prepare the query
                     list($stamp_sql, $stamp_params) = $DB->get_in_or_equal($stamps);
                     list($context_sql, $context_params) = $DB->get_in_or_equal($contexts);
                     $sql = "SELECT DISTINCT contextid
                               FROM {question_categories}
                              WHERE stamp $stamp_sql
                                AND contextid $context_sql";
                     $params = array_merge($stamp_params, $context_params);
                     $matchingcontexts = $DB->get_records_sql($sql, $params);
                     // Only if ONE and ONLY ONE context is found, use it as valid target
                     if (count($matchingcontexts) == 1) {
                         $targetcontext = context::instance_by_id(reset($matchingcontexts)->contextid);
                     }
                 }
                 break;

             // For course is easy, the best context is the course context
             case CONTEXT_COURSE:
                 $targetcontext = context_course::instance($courseid);
                 break;

             // For module is easy, there is not best context, as far as the
             // activity hasn't been created yet. So we return context course
             // for them, so permission checks and friends will work. Note this
             // case is handled by {@link prechek_precheck_qbanks_by_level}
             // in an special way
             case CONTEXT_MODULE:
                 $targetcontext = context_course::instance($courseid);
                 break;
        }
        return $targetcontext;
    }

    /**
     * Return one array of question records for
     * a given restore operation and one question category
     */
    public static function restore_get_questions($restoreid, $qcatid) {
        global $DB;

        $results = array();
        $qs = $DB->get_recordset_sql("SELECT itemid, info
                                      FROM {backup_ids_temp}
                                     WHERE backupid = ?
                                       AND itemname = 'question'
                                       AND parentitemid = ?", array($restoreid, $qcatid));
        foreach ($qs as $q) {
            $results[$q->itemid] = backup_controller_dbops::decode_backup_temp_info($q->info);
        }
        $qs->close();
        return $results;
    }

    /**
     * Given one component/filearea/context and
     * optionally one source itemname to match itemids
     * put the corresponding files in the pool
     *
     * If you specify a progress reporter, it will get called once per file with
     * indeterminate progress.
     *
     * @param string $basepath the full path to the root of unzipped backup file
     * @param string $restoreid the restore job's identification
     * @param string $component
     * @param string $filearea
     * @param int $oldcontextid
     * @param int $dfltuserid default $file->user if the old one can't be mapped
     * @param string|null $itemname
     * @param int|null $olditemid
     * @param int|null $forcenewcontextid explicit value for the new contextid (skip mapping)
     * @param bool $skipparentitemidctxmatch
     * @param \core\progress\base $progress Optional progress reporter
     * @return array of result object
     */
    public static function send_files_to_pool($basepath, $restoreid, $component, $filearea,
            $oldcontextid, $dfltuserid, $itemname = null, $olditemid = null,
            $forcenewcontextid = null, $skipparentitemidctxmatch = false,
            \core\progress\base $progress = null) {
        global $DB, $CFG;

        $backupinfo = backup_general_helper::get_backup_information(basename($basepath));
        $includesfiles = $backupinfo->include_files;

        $results = array();

        if ($forcenewcontextid) {
            // Some components can have "forced" new contexts (example: questions can end belonging to non-standard context mappings,
            // with questions originally at system/coursecat context in source being restored to course context in target). So we need
            // to be able to force the new contextid
            $newcontextid = $forcenewcontextid;
        } else {
            // Get new context, must exist or this will fail
            $newcontextrecord = self::get_backup_ids_record($restoreid, 'context', $oldcontextid);
            if (!$newcontextrecord || !$newcontextrecord->newitemid) {
                throw new restore_dbops_exception('unknown_context_mapping', $oldcontextid);
            }
            $newcontextid = $newcontextrecord->newitemid;
        }

        // Sometimes it's possible to have not the oldcontextids stored into backup_ids_temp->parentitemid
        // columns (because we have used them to store other information). This happens usually with
        // all the question related backup_ids_temp records. In that case, it's safe to ignore that
        // matching as far as we are always restoring for well known oldcontexts and olditemids
        $parentitemctxmatchsql = ' AND i.parentitemid = f.contextid ';
        if ($skipparentitemidctxmatch) {
            $parentitemctxmatchsql = '';
        }

        // Important: remember how files have been loaded to backup_files_temp
        //   - info: contains the whole original object (times, names...)
        //   (all them being original ids as loaded from xml)

        // itemname = null, we are going to match only by context, no need to use itemid (all them are 0)
        if ($itemname == null) {
            $sql = "SELECT id AS bftid, contextid, component, filearea, itemid, itemid AS newitemid, info
                      FROM {backup_files_temp}
                     WHERE backupid = ?
                       AND contextid = ?
                       AND component = ?
                       AND filearea  = ?";
            $params = array($restoreid, $oldcontextid, $component, $filearea);

        // itemname not null, going to join with backup_ids to perform the old-new mapping of itemids
        } else {
            $sql = "SELECT f.id AS bftid, f.contextid, f.component, f.filearea, f.itemid, i.newitemid, f.info
                      FROM {backup_files_temp} f
                      JOIN {backup_ids_temp} i ON i.backupid = f.backupid
                                              $parentitemctxmatchsql
                                              AND i.itemid = f.itemid
                     WHERE f.backupid = ?
                       AND f.contextid = ?
                       AND f.component = ?
                       AND f.filearea = ?
                       AND i.itemname = ?";
            $params = array($restoreid, $oldcontextid, $component, $filearea, $itemname);
            if ($olditemid !== null) { // Just process ONE olditemid intead of the whole itemname
                $sql .= ' AND i.itemid = ?';
                $params[] = $olditemid;
            }
        }

        $fs = get_file_storage();         // Get moodle file storage
        $basepath = $basepath . '/files/';// Get backup file pool base
        // Report progress before query.
        if ($progress) {
            $progress->progress();
        }
        $rs = $DB->get_recordset_sql($sql, $params);
        foreach ($rs as $rec) {
            // Report progress each time around loop.
            if ($progress) {
                $progress->progress();
            }

            $file = (object)backup_controller_dbops::decode_backup_temp_info($rec->info);

            // ignore root dirs (they are created automatically)
            if ($file->filepath == '/' && $file->filename == '.') {
                continue;
            }

            // set the best possible user
            $mappeduser = self::get_backup_ids_record($restoreid, 'user', $file->userid);
            $mappeduserid = !empty($mappeduser) ? $mappeduser->newitemid : $dfltuserid;

            // dir found (and not root one), let's create it
            if ($file->filename == '.') {
                $fs->create_directory($newcontextid, $component, $filearea, $rec->newitemid, $file->filepath, $mappeduserid);
                continue;
            }

            // The file record to restore.
            $file_record = array(
                'contextid'   => $newcontextid,
                'component'   => $component,
                'filearea'    => $filearea,
                'itemid'      => $rec->newitemid,
                'filepath'    => $file->filepath,
                'filename'    => $file->filename,
                'timecreated' => $file->timecreated,
                'timemodified'=> $file->timemodified,
                'userid'      => $mappeduserid,
                'source'      => $file->source,
                'author'      => $file->author,
                'license'     => $file->license,
                'sortorder'   => $file->sortorder
            );

            if (empty($file->repositoryid)) {
                // If contenthash is empty then gracefully skip adding file.
                if (empty($file->contenthash)) {
                    $result = new stdClass();
                    $result->code = 'file_missing_in_backup';
                    $result->message = sprintf('missing file (%s) contenthash in backup for component %s', $file->filename, $component);
                    $result->level = backup::LOG_WARNING;
                    $results[] = $result;
                    continue;
                }
                // this is a regular file, it must be present in the backup pool
                $backuppath = $basepath . backup_file_manager::get_backup_content_file_location($file->contenthash);

                // Some file types do not include the files as they should already be
                // present. We still need to create entries into the files table.
                if ($includesfiles) {
                    // The file is not found in the backup.
                    if (!file_exists($backuppath)) {
                        $results[] = self::get_missing_file_result($file);
                        continue;
                    }

                    // create the file in the filepool if it does not exist yet
                    if (!$fs->file_exists($newcontextid, $component, $fi…

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