Get next post in current URL category Wordpress

single.php

<?php 						
// BASED ON @ https://wordpress.stackexchange.com/questions/149826/display-posts-from-the-same-category-using-next-previous-post-link

$post_id = $post->ID; // current post ID
$cat = get_the_category(); 
$current_cat_id = $cat[0]->cat_ID; // current category ID 
$cat_id = get_queried_object_id();
// GET CAT FROM URL
// this is hacky as hell.
$current_url = home_url( add_query_arg( array(), $wp->request ) );
$u = parse_url($current_url);
$r = array_reverse(explode('/', $u['path'])); // note flipping because base might change. e.g. currently second from first is 2020. That will change. So flip will give you penulimate. 
$l = $r[1];
$cat_slug = $l;

$args = array( 
	'post_type'	=> 'portfolio',
    'tax_query' => array(
        array(
            'taxonomy' => 'category',
            'field' => 'slug',
            'terms' => $cat_slug
        )
     ),
    'posts_per_page' => 999,
    'orderby'	=> 'post_date',
    'order'		=> 'DESC'
);

$posts = get_posts( $args );
// get IDs of posts retrieved from get_posts
$ids = array();
foreach ( $posts as $thepost ) {
    $ids[] = $thepost->ID;
}
// get and echo previous and next post in the same category
$thisindex = array_search( $post_id, $ids );
$goto_previous    = isset( $ids[ $thisindex - 1 ] ) ? $ids[ $thisindex - 1 ] : 0;
$goto_next    = isset( $ids[ $thisindex + 1 ] ) ? $ids[ $thisindex + 1 ] : 0;

if ( $goto_previous ):

	$root = get_post_type_archive_link( 'portfolio' );
    $post_slug = get_post_field( 'post_name', $goto_previous );;
	// $link = get_permalink();
    $link = $root . $cat_slug ."/". $post_slug;

    ?>

    <div class="l-prev ">
    	<a rel="prev" href="<?php echo $link ?>"><?php echo get_the_title($goto_previous); ?></a>
    </div>

<?php
endif; // prev
if ( $goto_next ):
	$root = get_post_type_archive_link( 'portfolio' );
    $post_slug = get_post_field( 'post_name', $goto_next );;
	// $link = get_permalink();
    $link = $root . $cat_slug ."/". $post_slug;
    ?>
    <div class="l-next ">
    	<a rel="next" href="<?php  echo $link ?>"><?php echo get_the_title($goto_next); ?></a>
	</div>

<?php

endif; //next

?>