public static function get_lessons_by_courses($courseids = array()) {
        global $PAGE;

        $warnings = array();
        $returnedlessons = array();

        $params = array(
            'courseids' => $courseids,
        );
        $params = self::validate_parameters(self::get_lessons_by_courses_parameters(), $params);

        $mycourses = array();
        if (empty($params['courseids'])) {
            $mycourses = enrol_get_my_courses();
            $params['courseids'] = array_keys($mycourses);
        }

        // Ensure there are courseids to loop through.
        if (!empty($params['courseids'])) {

            list($courses, $warnings) = external_util::validate_courses($params['courseids'], $mycourses);

            // Get the lessons in this course, this function checks users visibility permissions.
            // We can avoid then additional validate_context calls.
            $lessons = get_all_instances_in_courses("lesson", $courses);
            foreach ($lessons as $lessonrecord) {
                $context = context_module::instance($lessonrecord->coursemodule);

                // Remove fields added by get_all_instances_in_courses.
                unset($lessonrecord->coursemodule, $lessonrecord->section, $lessonrecord->visible, $lessonrecord->groupmode,
                    $lessonrecord->groupingid);

                $lessonrecord = self::get_lesson_summary_for_exporter($lessonrecord);

                $exporter = new lesson_summary_exporter($lessonrecord, array('context' => $context));
                $returnedlessons[] = $exporter->export($PAGE->get_renderer('core'));
            }
        }
        $result = array();
        $result['lessons'] = $returnedlessons;
        $result['warnings'] = $warnings;
        return $result;
    }