function llms_post_classes( $classes, $class = array(), $post_id = '' ) {

	if ( ! $post_id ) {
		return $classes;
	}

	$post_type = get_post_type( $post_id );

	// Add enrolled classes.
	if ( 'lesson' === $post_type || 'course' === $post_type || 'llms_membership' === $post_type ) {

		$classes[] = llms_is_user_enrolled( get_current_user_id(), $post_id ) ? 'is-enrolled' : 'not-enrolled';

	}

	// Add completion classes.
	if ( 'lesson' === $post_type || 'course' === $post_type ) {

		if ( get_current_user_id() ) {

			$student   = new LLMS_Student();
			$classes[] = $student->is_complete( $post_id, $post_type ) ? 'is-complete' : 'is-incomplete';

		} else {

			$classes[] = 'is-complete';

		}
	}

	return $classes;

}