public function complete_course( $course_id = 0 ) {
		if ( $course_id ) {
			$completed_courses                                     = (array) $this->get( 'completed_courses' );
			$completed_courses[ $course_id ]['is_course_complete'] = 1;
			$this->update( 'completed_courses', array_filter( $completed_courses ) );
		}
	}