How to Get Previous and Next Lesson IDs

This code snippet retrieves the previous and next lesson IDs based on a users last viewed lesson.  A link is echoed if a previous or next lesson exists within the same course.
<?php

// get the user’s viewed lessons

$user_id = get_current_user_id();
$viewed_lessons = get_user_meta($user_id, 'wpc-lesson-tracking', true);  

// get the last viewed lesson

$last_viewed_id = null;
if(!empty($viewed_lessons)){
	$last_viewed_id = $viewed_lessons[0][‘id’];
}

// get previous and next IDs

$wpc_courses = new WPC_Courses();
$ids = $wpc_courses->get_previous_and_next_lesson_ids($last_viewed_id);

// echo previous lesson link if exists

if($ids['prev_id'] !== false){
	echo '<a href="' . get_permalink($ids['next_id']) . '">Prev</a>';
}

// echo next lesson link if exists

if($ids['next_id'] !== false){
	echo '<a href="' . get_permalink($ids['next_id']) . '">Next</a>';
}

?>