WooCommerce - related products by tags and categor

I want to display 8 "related products" in every product page of my site based on tags. But if there are less than 8 results fill the gaps with products in the same Categories.

Here is code that I'm using for showing only tag-related products (functions.php):

//New "Related Products" function for WooCommerce
function get_related_custom( $id, $limit = 5 ) {
global $woocommerce;

// Related products are found from category and tag
$tags_array = array(0);
$cats_array = array(0);

// Get tags
$terms = wp_get_post_terms($id, 'product_tag');
foreach ( $terms as $term ) $tags_array[] = $term->term_id;

// Get categories (removed / commented)
/*
$terms = wp_get_post_terms($id, 'product_cat');
foreach ( $terms as $term ) $cats_array[] = $term->term_id;
 */

// Don't bother if none are set
if ( sizeof($cats_array)==1 && sizeof($tags_array)==1 ) return array();

// Meta query
$meta_query = array();
$meta_query[] = $woocommerce->query->visibility_meta_query();
$meta_query[] = $woocommerce->query->stock_status_meta_query();

// Get the posts
$related_posts = get_posts( apply_filters('woocommerce_product_related_posts', array(
    'orderby'        => 'rand',
    'posts_per_page' => $limit,
    'post_type'      => 'product',
    'fields'         => 'ids',
    'meta_query'     => $meta_query,
    'tax_query'      => array(
        'relation'      => 'OR',
        array(
            'taxonomy'     => 'product_cat',
            'field'        => 'id',
            'terms'        => $cats_array
        ),
        array(
            'taxonomy'     => 'product_tag',
            'field'        => 'id',
            'terms'        => $tags_array
        )
    )
) ) );
$related_posts = array_diff( $related_posts, array( $id ));
return $related_posts;
}
add_action('init','get_related_custom');

Open your functions.php file in wp-content/themes/your-theme-name/ and add this code at the end of the file:

/**
 * Does not filter related products by tag
 */
add_filter( 'woocommerce_product_related_posts_relate_by_tag', '__return_false' );

/**
 * Does not filter related products by category
 */
add_filter( 'woocommerce_product_related_posts_relate_by_category', '__return_false' );