How to add Next and Previous links to a blog post with Perch

next_previous_links.php

<?php 
// get the post data, put it into $post variable
$post = perch_blog_custom(array(
  'filter'        => 'postSlug',
  'match'         => 'eq',
  'value'         => perch_get('s'),
  'skip-template' => true,
  'return-html'   => true,
  'template'      => 'blog/post.html',
));

// get the post date and put into variable
$date  = $post[0]['postDateTime'];

// Generate the Previous Link

// This is the post_prev.html template
// <div class="blog-nav"><p>Previous: 
// <a href="/news/amp/<perch:blog id="postSlug" />" class="prev"><perch:blog id="postTitle" /></a></p>

$prev = perch_blog_custom(array(
  'count'=>1,
  'filter'=>'postDateTime',
  'match'=>'lt',
  'sort'=>'postDateTime',
  'sort-order'=>'DESC',
  'value'=>$date2,
  'template'=>'blog/post_prev.html'
    ), true); // stores Prev link in a variable to use later

// Generate the Next Link

// This is the post_next.html template
// <p>Next: <a href="/news/amp/<perch:blog id="postSlug" />" class="next"><perch:blog id="postTitle" /></a></p>
// </div>
          
$next = perch_blog_custom(array(
  'count'=>1,
  'filter'=>'postDateTime',
  'match'=>'gt',
  'sort'=>'postDateTime',
  'sort-order'=>'ASC',
  'value'=>$date2,
  'template'=>'blog/post_next.html'
  ), true); // stores Next link in a variable to use later
 
echo $html; // the post

// Previous and next post navigation
  if (empty($prev)){
          echo '<div class="blog-nav">';
    } else {
          echo $prev;
    }
  if (empty($next)){
      echo '</div>';
    } else {
          echo $next;
  }
?>