<?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/>.

declare(strict_types=1);

namespace mod_scorm\cache;

use core_cache\data_source_interface;
use core_cache\definition;

/**
 * Cache data source for the scorm elements.
 *
 * @package   mod_scorm
 * @copyright 2023 Catalyst IT Ltd
 * @author    Dan Marsden <dan@danmarsden.com>
 * @license   http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
 */
class elements implements data_source_interface {

    /** @var elements the singleton instance of this class. */
    protected static $instance = null;

    /**
     * Returns an instance of the data source class that the cache can use for loading data using the other methods
     * specified by this interface.
     *
     * @param definition $definition
     * @return object
     */
    public static function get_instance_for_cache(definition $definition): elements {
        if (is_null(self::$instance)) {
            self::$instance = new elements();
        }
        return self::$instance;
    }

    /**
     * Loads the data for the key provided ready formatted for caching.
     *
     * @param string|int $key The key to load.
     * @return string What ever data should be returned, or null if it can't be loaded.
     * @throws \coding_exception
     */
    public function load_for_cache($key): ?string {
        global $DB;

        $element = $DB->get_field('scorm_element', 'id', ['element' => $key]);
        // Return null instead of false, because false will not be cached.
        return $element ?: null;
    }

    /**
     * Loads several keys for the cache.
     *
     * @param array $keys An array of keys each of which will be string|int.
     * @return array An array of matching data items.
     */
    public function load_many_for_cache(array $keys): array {
        global $DB;
        list ($elementsql, $params) = $DB->get_in_or_equal($keys);
        $sql = "SELECT element, id
                  FROM {scorm_element}
                 WHERE element ".$elementsql;
        return $DB->get_records_sql_menu($sql, $params);
    }
}