How to get the first topic in a lesson in learndash - wordpress

Question

I want to retrieve the first topic in a lesson in learndash and redirect it through it. But for some reason am not sure how to do it.
I checked the API and doesn't see any appropriate filter/hook for it.
Here is my code:
function redirect_to_first_topic() {
// We only want to do this for Topics. But the below code can be adapted to work for Lessons
global $post;
$post_id = $post->ID;
if ( get_post_type( $post_id ) == 'sfwd-lessons' ) {
$progress = learndash_get_course_progress( null, $post_id );
$link = $progress['next'];
$parent_lesson_id = learndash_get_setting( $post, 'topic' );
$parent_lesson = get_post( $parent_lesson_id );
var_dump($parent_lesson);
}
// Always return $link
// return $link;
}
add_action('wp', 'redirect_to_first_topic');
So basically what am doing here is getting the parent which is the lesson.

Answer 1

A bit late, but mb it will help someone else. You can see how to get 1. lesson of a course and go deeper if needed fe. first topic of first lesson and so on :
add_action( 'template_redirect', 'course_overview_redirect' );
function course_overview_redirect() {
global $post;
if ( ! empty( $post ) && $post->post_type == 'sfwd-courses' && ! empty( $post->ID ) ) {
$lessons = learndash_get_course_lessons_list( $post->ID );
if ( ! empty( $lessons ) ) {
$lesson = array_shift( $lessons );
if ( ! empty( $lesson ) ) {
$url = get_permalink( $lesson[ "post" ]->ID );
if ( ! empty( $url ) ) {
wp_redirect( esc_url( $url ) ); // And redirect if needed
exit;
}
}
}
}
}

Answer 2

You can add a button like this;
$args = array(
'posts_per_page' => -1,
'post_type' => 'sfwd-lessons', // you can change here to find topics : 'sfwd-topics'
'suppress_filters' => true,
'fields' => 'ids',
'orderby' => 'menu_order', // ordering by menu_order will show lesson list, in their order in course.
'order' => 'ASC',
// this meta query is used if you want to search a lesson under a course, or if you search for a topic which is in a course but not under a lesson
'meta_query' => array(
array(
'key' => 'course_id',
'value' => $course_id, // this is id of your course
)
// if your topic is under a lesson than you should add lesson meta query
// your meta query should be changed like below
/*
'meta_query' => array(
'relation' => 'AND',
array(
'key' => 'course_id',
'value' => $course_id,
),
array(
'key' => 'lesson_id',
'value' => $lesson_id,
),
),
*/
),
);
$all_lessons = get_posts($args);
$first_lesson = $all_lessons[0]; // taking directly first element of array
$button_html = '' . __( 'Start the course', 'custom-text' ) . '';