chamilo / chamilo-lms

        // Check in advance whether the user has already been registered on the platform.

        $sql = "SELECT status FROM " . $user_table . " WHERE user_id = $user_id ";

        if (Database::num_rows(Database::query($sql)) == 0) {

            if ($debug) {

                error_log('The user has not been registered to the platform');

            }

            return false; // The user has not been registered to the platform.

        }

        // Check whether the user has already been subscribed to this course.

        $sql = "SELECT * FROM $course_user_table

                    user_id = $user_id AND

                    relation_type <> " . COURSE_RELATION_TYPE_RRHH . " AND

                    c_id = $courseId";

        if (Database::num_rows(Database::query($sql)) > 0) {

            if ($debug) {

                error_log('The user has been already subscribed to the course');

            }

            return false; // The user has been subscribed to the course.

        }

        if (!api_is_course_admin()) {

            // Check in advance whether subscription is allowed or not for this course.

            // Check in advance whether subscription is allowed or not for this course.

            $sql = "SELECT code, visibility FROM $course_table

                    WHERE id = $courseId AND subscribe = '" . SUBSCRIBE_NOT_ALLOWED . "'";

            if (Database::num_rows(Database::query($sql)) > 0) {

                if ($debug) {

                    error_log('Subscription is not allowed for this course');

                }

                return false; // Subscription is not allowed for this course.

            }

        }

        // Ok, subscribe the user.