update_categories_form.php

<?php
// This file is part of Exabis Competence Grid
//
// (c) 2019 GTN - Global Training Network GmbH <office@gtn-solutions.com>
//
// Exabis Competence Grid 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.
//
// This script 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 can find the GNU General Public License at <http://www.gnu.org/licenses/>.
//
// This copyright notice MUST APPEAR in all copies of the script!

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

require_once $CFG->libdir . '/formslib.php';

class block_exacomp_update_categories_form extends moodleform {

    private $hideSelectbox = false;

    function definition() {
        global $CFG, $DB;

        $output = block_exacomp_get_renderer();

        $mform = $this->_form; // Don't forget the underscore!

        $descrid = $this->_customdata['descrid'];

        $descrTitle = $DB->get_field(BLOCK_EXACOMP_DB_DESCRIPTORS, 'title', array("id" => $descrid));
        // 	    $mform->addElement('header', 'general', block_exacomp_get_string("example_upload_header", null, $descrTitle));

        if (!$this->_customdata['categories']) {
            $this->hideSelectbox = true;
        }
        $categories = ['0' => ' - - - '] + $this->_customdata['categories'];
        $cselect = $mform->addElement('select', 'catid', block_exacomp_get_string('descriptor_categories'), $categories);
        $cselect->setMultiple(true);
        $cselect->setSelected(array_keys($DB->get_records(BLOCK_EXACOMP_DB_DESCCAT, array("descrid" => $this->_customdata['descrid']), "", "catid")));


        $this->add_action_buttons(true);
    }

    public function display() {
        ob_start();
        parent::display();
        $out = ob_get_contents();
        ob_end_clean();
        $doc = new DOMDocument();
        //        @$doc->loadHTML(utf8_decode($out), LIBXML_HTML_NOIMPLIED | LIBXML_HTML_NODEFDTD);
        @$doc->loadHTML(mb_convert_encoding($out, 'HTML-ENTITIES', 'UTF-8'), LIBXML_HTML_NOIMPLIED | LIBXML_HTML_NODEFDTD);
        $selector = new DOMXPath($doc);
        // Add class to the form.
        foreach ($selector->query('//form') as $f) {
            $f->setAttribute("class", $f->getAttribute('class') . ' category_form');
        }
        // Add "new category" input.
        $newInput = $doc->createDocumentFragment();
        $newInput->appendXML('<br /><span>' . block_exacomp_get_string('descriptor_add_category') . ' <input type="text" class="form-control" name="newcategory" value="" /> </span>');
        $subText = $doc->createDocumentFragment();
        $subText->appendXML('<span class="exacomp_sublabel">' . block_exacomp_get_string('descriptor_categories_description') . '</span>');
        foreach ($selector->query('//select[@name=\'catid[]\']') as $e) {
            if ($this->hideSelectbox) {
                $e->setAttribute("style", "display: none;");
            }
            $e->setAttribute("class", $e->getAttribute('class') . ' exacomp_forpreconfig');
            $e->parentNode->appendChild($newInput);
            $e->parentNode->insertBefore($subText, $e);
        }
        // Add subtext - description.

        // foreach ($selector->query('//select[@name=\'catid[]\']/ancestor::*[contains(@class, \'form-group\')]') as $e) {
        //     $e->parentNode->insertBefore($subText);
        // }
        $output = $doc->saveHTML($doc->documentElement);
        print $output;
    }

}