public function get_thumb_url($image_url, $orig_width, $orig_height, $thumb_width = 75, $force = false) {
        global $OUTPUT;

        if (!$force && $orig_width <= $thumb_width && $orig_height <= $thumb_width) {
            return $image_url;
        } else {
            $thumb_url = '';
            $commons_main_dir = 'https://upload.wikimedia.org/wikipedia/commons/';
            if ($image_url) {
                $short_path = str_replace($commons_main_dir, '', $image_url);
                $extension = strtolower(pathinfo($short_path, PATHINFO_EXTENSION));
                if (strcmp($extension, 'gif') == 0) {  //no thumb for gifs
                    return $OUTPUT->image_url(file_extension_icon('.gif', $thumb_width))->out(false);
                }
                $dir_parts = explode('/', $short_path);
                $file_name = end($dir_parts);
                if ($orig_height > $orig_width) {
                    $thumb_width = round($thumb_width * $orig_width/$orig_height);
                }
                $thumb_url = $commons_main_dir . 'thumb/' . implode('/', $dir_parts) . '/'. $thumb_width .'px-' . $file_name;
                if (strcmp($extension, 'svg') == 0) {  //png thumb for svg-s
                    $thumb_url .= '.png';
                }
            }
            return $thumb_url;
        }
    }