function llms_can_user_complete_lesson( $user_id, $lesson ) {

	if ( ! $lesson instanceof LLMS_Lesson ) {
		$lesson = llms_get_post( $lesson );
	}

	if ( ! $lesson || ! is_a( $lesson, 'LLMS_Lesson' ) ) {
		$allowed = false;
	} elseif ( current_user_can( 'edit_post', $lesson->get( 'id' ) ) ) {
		// Instructors / admins able to edit the lesson are always allowed.
		$allowed = true;
	} else {
		// The student must be enrolled in the lesson's parent course and the lesson must be available.
		$allowed = ( $user_id && llms_is_user_enrolled( $user_id, $lesson->get( 'parent_course' ) ) && $lesson->is_available() );
	}

	/**
	 * Filter whether a user is authorized to mark a lesson complete or incomplete.
	 *
	 * @since 10.0.7
	 *
	 * @param bool             $allowed Whether or not the user is authorized.
	 * @param int              $user_id WP User ID of the student.
	 * @param LLMS_Lesson|bool $lesson  LLMS_Lesson instance, or `false` for an invalid lesson.
	 */
	return apply_filters( 'llms_can_user_complete_lesson', $allowed, $user_id, $lesson );
}