Rhye navigation for portfolio Items of the same category

<?php

$portfolio_nav_direction = get_theme_mod( 'portfolio_nav_direction', 'forward' );
$next_post               = $portfolio_nav_direction === 'forward' ? get_previous_post(true, '', 'arts_portfolio_category') : get_next_post(true, '', 'arts_portfolio_category');
$current_id              = get_the_ID();
$next_link;
$next_title;
$next_image_id;
$attrs_link = '';

$portfolio_nav_background               = arts_get_overridden_document_option( 'portfolio_nav_background', 'page_portfolio_nav_settings_overridden', 'bg-light-1' );
$portfolio_nav_theme                    = arts_get_overridden_document_option( 'portfolio_nav_theme', 'page_portfolio_nav_settings_overridden', 'dark' );
$portfolio_nav_divider_enabled          = arts_get_overridden_document_option( 'portfolio_nav_divider_enabled', 'page_portfolio_nav_settings_overridden', true );
$portfolio_nav_image_transition_enabled = get_theme_mod( 'portfolio_nav_image_transition_enabled', true );
$portfolio_nav_scroll_down_enabled      = get_theme_mod( 'portfolio_nav_scroll_down_enabled', true );
$portfolio_nav_scroll_down_label        = get_theme_mod( 'portfolio_nav_scroll_down_label', esc_html__( 'Keep Scrolling', 'rhye' ) );
$portfolio_nav_headings_preset          = get_theme_mod( 'portfolio_nav_headings_preset', 'h1' );
$portfolio_nav_labels_preset            = get_theme_mod( 'portfolio_nav_labels_preset', 'subheading' );
$portfolio_nav_next_label               = get_theme_mod( 'portfolio_nav_next_label', esc_html__( 'Next Project', 'rhye' ) );

$categories = array();
$current_categories = arts_get_taxonomy_term_names( $current_id, 'arts_portfolio_category' );
foreach ( $current_categories as $item ) {
  array_push( $categories, $item['slug']);
}

$posts = get_posts(
  array(
    'post_type'      => 'arts_portfolio_item',
    'posts_per_page' => -1,
    'tax_query' => array(
      array(
        'taxonomy' => 'arts_portfolio_category',
        'field' => 'slug',
        'terms' => $categories, // include only posts of the current categories (slugs)
      )
   )
  )
);