Rubenz navigation for portfolio Items of the same category

<?php

/**
 * Get the term names of taxonomy
 *
 * @param string $post_id
 * @param string $taxonomy
 * @return void
 */
function arts_get_taxonomy_term_names( $post_id, $taxonomy ) {
  $items = get_the_terms( $post_id, $taxonomy );
  $arr   = [];

  if ( is_array( $items ) ) {
    foreach ( $items as $item ) {

      $temp = array(
        'slug' => $item->slug,
        'name' => $item->name,
      );

      // don't add the same item multiple times
      if ( ! in_array( $arr, $temp ) ) {
        array_push( $arr, $temp );
      }
    }
  }

  return $arr;
}

$next_post  = get_previous_post( true, '', 'arts_portfolio_category' );
$prev_post  = get_next_post( true, '', 'arts_portfolio_category' );
$current_id = get_the_ID();
$next_link;
$next_title;
$next_img;
$prev_link;
$prev_title;
$prev_img;
$attr_link                          = '';
$class_link                         = 'col';
$class_link_prev                    = '';
$prev_label                         = get_theme_mod( 'portfolio_nav_prev_title', esc_html__( 'Prev', 'rubenz' ) );
$next_label                         = get_theme_mod( 'portfolio_nav_next_title', esc_html__( 'Next', 'rubenz' ) );
$enable_portfolio_loop              = get_theme_mod( 'enable_portfolio_loop', true );
$enable_portfolio_next_first_mobile = get_theme_mod( 'enable_portfolio_next_first_mobile', false );

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

$args  = 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)
    ),
  ),
);
$posts = get_posts( $args );

$first_post = current( $posts );
$last_post  = end( $posts );

if ( $next_post ) {

  $next_link  = get_permalink( $next_post );
  $next_title = $next_post->post_title;
  $next_img   = get_post_thumbnail_id( $next_post->ID );
}

if ( ! $next_post && $enable_portfolio_loop ) {

  $next_post  = $first_post;
  $next_link  = get_permalink( $next_post );
  $next_title = $next_post->post_title;
  $next_img   = get_post_thumbnail_id( $next_post->ID );

}

if ( $prev_post ) {

  $prev_link  = get_permalink( $prev_post );
  $prev_title = $prev_post->post_title;
  $prev_img   = get_post_thumbnail_id( $prev_post->ID );

}

if ( ! $prev_post && $enable_portfolio_loop ) {

  $prev_post  = $last_post;
  $prev_link  = get_permalink( $prev_post );
  $prev_title = $prev_post->post_title;
  $prev_img   = get_post_thumbnail_id( $prev_post->ID );

}

if ( $next_post && $prev_post ) {
  $class_link = 'col-md-6';
}

if ( $enable_portfolio_next_first_mobile ) {
  $class_link_prev = 'order-md-0 order-2';
}

?>

<?php if ( $next_post || $prev_post ) : ?>
  <!-- section NAV PROJECTS -->
  <section class="section section-nav-projects container-fluid no-gutters">
    <div class="row no-gutters h-100">
      <?php if ( $prev_post ) : ?>
        <?php
        if ( $prev_img ) {
          $attr_link = 'data-pjax-link=navProjects';
        }
        ?>
        <a class="section-nav-projects__inner section-nav-projects__inner_prev <?php echo esc_attr( $class_link ); ?> <?php echo esc_attr( $class_link_prev ); ?>" href="<?php echo esc_url( $prev_link ); ?>" <?php echo esc_attr( $attr_link ); ?> data-post-id="<?php echo esc_attr( $prev_post->ID ); ?>">
          <?php if ( ! empty( $prev_label ) ) : ?>
            <div class="section-nav-projects__label section-nav-projects__label_prev"><?php echo esc_html( $prev_label ); ?></div>
          <?php endif; ?>
          <div class="section-nav-projects__arrow"><i class="material-icons">keyboard_arrow_left</i></div>
          <h3><?php echo esc_html( $prev_title ); ?></h3>
        </a>
      <?php endif; ?>
      <?php if ( $next_post ) : ?>
        <?php
        if ( $next_img ) {
          $attr_link = 'data-pjax-link=navProjects';
        }
        ?>
        <a class="section-nav-projects__inner section-nav-projects__inner_next <?php echo esc_attr( $class_link ); ?>" href="<?php echo esc_url( $next_link ); ?>" <?php echo esc_attr( $attr_link ); ?> data-post-id="<?php echo esc_attr( $next_post->ID ); ?>">
          <?php if ( ! empty( $next_label ) ) : ?>
            <div class="section-nav-projects__label section-nav-projects__label_next"><?php echo esc_html( $next_label ); ?></div>
          <?php endif; ?>
          <h3><?php echo esc_html( $next_title ); ?></h3>
          <div class="section-nav-projects__arrow"><i class="material-icons">keyboard_arrow_right</i></div>
        </a>
      <?php endif; ?>
    </div>
    <div class="section-nav-projects__backgrounds">
      <?php if ( $prev_post && ! empty( $prev_img ) ) : ?>
        <?php
          arts_the_lazy_image(
            array(
              'id'        => $prev_img,
              'class'     => array(
                'image' => array( 'section-nav-projects__background', 'section-nav-projects__background_prev' ),
              ),
              'attribute' => array(
                'image' => array( 'data-background-for=' . $prev_post->ID ),
              ),
            )
          );
        ?>
      <?php endif; ?>
      <?php if ( $next_post && ! empty( $next_img ) ) : ?>
        <?php
          arts_the_lazy_image(
            array(
              'id'        => $next_img,
              'class'     => array(
                'image' => array( 'section-nav-projects__background', 'section-nav-projects__background_next' ),
              ),
              'attribute' => array(
                'image' => array( 'data-background-for=' . $next_post->ID ),
              ),
            )
          );
        ?>
      <?php endif; ?>
      <div class="overlay overlay_dark section-nav-projects__overlay"></div>
    </div>
  </section>
  <!-- - section NAV PROJECTS -->
<?php endif; ?>