controller.php

<?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   mod_cardbox
 * @copyright 2019 RWTH Aachen (see README.md)
 * @author    Anna Heynkes
 * @license   http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
 */
defined('MOODLE_INTERNAL') || die();
define ('ENABLE_AUTOCORRECT', 0);
define ('DISABLE_AUTOCORRECT', 1);



require_once($CFG->dirroot.'/mod/cardbox/locallib.php');

if (!isset($action)) {
    $action = required_param('action', PARAM_ALPHA);
}

/* *********************************************** Add a new flashcard *********************************************** */

if ($action === 'addflashcard') {

    require_capability('mod/cardbox:submitcard', $context);
    require_once('card_form.php');
    $PAGE->set_url('/mod/cardbox/view.php', array('id' => $cm->id, 'action' => 'addflashcard'));
    $returnurl = new moodle_url('/mod/cardbox/view.php', array('id' => $cmid, 'action' => 'practice'));
    $actionurl = new moodle_url('/mod/cardbox/view.php', array('id' => $cmid, 'action' => 'addflashcard'));

    $stringman = get_string_manager();
    $strings = $stringman->load_component_strings('cardbox', 'en'); // Method gets the strings of the language files.
    $PAGE->requires->strings_for_js(array_keys($strings), 'cardbox'); // Method to use the language-strings in javascript.
    $PAGE->requires->js(new moodle_url("/mod/cardbox/js/addcard.js?ver=00001"));
    $params = array($cmid, 1, null); // true means: the user checks their own results.
    $PAGE->requires->js_init_call('addCard', $params, true);

    // Contextual data to pass on to the card form.
    if (empty($entry)) {
        $entry = new stdClass();
        $entry->id = $cmid;
        $entry->course = $cm->course;
        $entry->action = $action;
    }

    $options = array('subdirs' => 0, 'maxbytes' => 0, 'areamaxbytes' => 10485760, 'maxfiles' => 3,
                          'accepted_types' => array('bmp', 'gif', 'jpeg', 'jpg', 'png', 'svg'), 'return_types' => 1 | 2);
    $component = 'mod_cardbox';
    $filearea = 'content';

    $customdata = array('cardboxid' => $cardbox->id, 'cmid' => $cmid, 'allowautocorrection' => $cardbox->autocorrection);
    $mform = new mod_cardbox_card_form(null, $customdata);
    $mform->set_data($entry);

    if ($mform->is_cancelled()) {