<?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/>.

namespace core_question;

use core_question\local\bank\question_version_status;

/**
 * This class should provide an API for managing question_references.
 *
 * Unfortunately, question_references were introduced in the DB structure
 * without an nice API. This class is being added later, and is currently
 * terribly incomplete, but hopefully it can be improved in time.
 *
 * @package    core_question
 * @copyright  2023 The Open University
 * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
 */
class question_reference_manager {
    /**
     * Return a list of those questions from the list passed in, which are referenced.
     *
     * A question is referenced if either:
     * - There is a question_reference pointing at exactly that version of that question; or
     * - There is an 'always latest' reference, and the question id is the latest non-draft version
     *   of that question_bank_entry.
     *
     * @param array $questionids a list of question ids to check.
     * @return array a list of the question ids from the input array which are referenced.
     */
    public static function questions_with_references(array $questionids): array {
        global $DB;

        if (empty($questionids)) {
            return [];
        }

        [$qidtest, $params] = $DB->get_in_or_equal($questionids, SQL_PARAMS_NAMED, 'outerqid');
        [$lqidtest, $lparams] = $DB->get_in_or_equal($questionids, SQL_PARAMS_NAMED, 'innerqid');

        return $DB->get_fieldset_sql("
            SELECT qv.questionid

              FROM {question_versions} qv

         -- This is a performant to get the latest non-draft version for each
         -- question_bank_entry that relates to one of our questionids.
         LEFT JOIN (
                       SELECT lqv.questionbankentryid,
                              MAX(lv.version) AS latestusableversion
                         FROM {question_versions} lqv
                         JOIN {question_versions} lv ON lv.questionbankentryid = lqv.questionbankentryid
                        WHERE lqv.questionid $lqidtest
                          AND lv.status <> :draft
                     GROUP BY lqv.questionbankentryid
                   ) latestversions ON latestversions.questionbankentryid = qv.questionbankentryid

              JOIN {question_references} qr ON qr.questionbankentryid = qv.questionbankentryid
                       AND (qr.version = qv.version OR qr.version IS NULL AND qv.version = latestversions.latestusableversion)

             WHERE qv.questionid $qidtest
            ", array_merge($params, $lparams, ['draft' => question_version_status::QUESTION_STATUS_DRAFT]));
    }

> 
}
>     /**
>      * This will transform set reference filter conditions to use the new filter structure.
>      *
>      * Previously filterconditions had questioncategoryid, includesubcategories and tags options.
>      * These have been replaced by the new category and tags filters. This function convers the old
>      * pre-4.3 filter condition structure to the new one.
>      *
>      * @param array $filtercondition Pre-4.3 filter condition.
>      * @return array Post-4.3 filter condition.
>      */
>     public static function convert_legacy_set_reference_filter_condition(array $filtercondition): array {
>         if (!isset($filtercondition['filter'])) {
>             $filtercondition['filter'] = [];
> 
>             // Question category filter.
>             if (isset($filtercondition['questioncategoryid'])) {
>                 $filtercondition['filter']['category'] = [
>                     'jointype' => \qbank_managecategories\category_condition::JOINTYPE_DEFAULT,
>                     'values' => [$filtercondition['questioncategoryid']],
>                     'includesubcategories' => $filtercondition['includingsubcategories'],
>                 ];
>                 unset($filtercondition['questioncategoryid']);
>                 unset($filtercondition['includingsubcategories']);
>             }
> 
>             // Tag filters.
>             if (isset($filtercondition['tags'])) {
>                 // Get the names of the tags in the condition. Find or create corresponding tags,
>                 // and set their ids in the new condition.
>                 $oldtags = array_map(fn($oldtag) => explode(',', $oldtag)[1], $filtercondition['tags']);
>                 $newtags = \core_tag_tag::create_if_missing(1, $oldtags);
>                 $newtagids = array_map(fn($newtag) => $newtag->id, $newtags);
> 
>                 $filtercondition['filter']['qtagids'] = [
>                     'jointype' => \qbank_tagquestion\tag_condition::JOINTYPE_DEFAULT,
>                     'values' => array_values($newtagids),
>                 ];
>                 unset($filtercondition['tags']);
>             }
>             // Add additional default properties to the filtercondition.
>             $filtercondition['tabname'] = 'questions';
>             $filtercondition['qpage'] = 0;
>             $filtercondition['qperpage'] = 100;
>             $filtercondition['jointype'] = \core\output\datafilter::JOINTYPE_ALL;
>         }
>         return $filtercondition;
>     }