Display navigation to next/previous lesson within a single course with Paid Memberships Pro and the PMPro Courses Add On

my_pmpro_courses_lesson_nav.php

<?php
/**
 * Display navigation to next/previous lesson within a single course.
 */
function my_pmpro_courses_lesson_nav( $course_id ) {
	global $post;

	// Fetch all lessons associated with the course in the correct order.
	$lessons = pmpro_courses_get_lessons( $course_id );

	// Check if lessons are available.
	if ( empty( $lessons ) ) {
		return;
	}

	// Build an array of lesson IDs.
	$lesson_ids = wp_list_pluck( $lessons, 'ID' );

	// Find the current lesson's position.
	$current_index = array_search( $post->ID, $lesson_ids );

	// Determine previous and next lesson IDs.
	$previous_id = $current_index > 0 ? $lesson_ids[ $current_index - 1 ] : false;
	$next_id     = $current_index < count( $lesson_ids ) - 1 ? $lesson_ids[ $current_index + 1 ] : false;

	// Only display navigation if there's a previous or next lesson.
	if ( ! $previous_id && ! $next_id ) {
		return;
	}

	// Output HTML for navigation.
	?>
	<nav class="navigation page-navigation" role="navigation">
		<span class="screen-reader-text"><?php esc_html_e( 'Lesson navigation', 'pmpro-courses' ); ?></span>
		<div class="nav-links">
			<?php if ( $previous_id ) : ?>
				<div class="nav-previous">
					Previous Lesson:
					<a href="<?php echo esc_url( get_permalink( $previous_id ) ); ?>" rel="prev">
						<?php echo esc_html( get_the_title( $previous_id ) ); ?>
					</a>
				</div>
			<?php endif; ?>
			<?php if ( $next_id ) : ?>
				<div class="nav-next">
					Next Lesson:
					<a href="<?php echo esc_url( get_permalink( $next_id ) ); ?>" rel="next">
						<?php echo esc_html( get_the_title( $next_id ) ); ?>
					</a>
				</div>
			<?php endif; ?>
		</div><!-- .nav-links -->
	</nav><!-- .lesson-navigation -->
	<?php
}