function get_related_tag_posts_ids( $post_id, $number = 5 ) {

    $related_ids = false;

    $post_ids = array();

    // get tag ids belonging to $post_id
    $tag_ids = wp_get_post_terms( $post_id, 'industry', array( 'fields' => 'ids' ) );

    if ( $tag_ids ) {
        // get all posts that have the same tags
        $tag_posts = get_posts(
            array(
                'post_type'      => 'projects',
                'posts_per_page' => -1, // return all posts
                'no_found_rows'  => true, // no need for pagination
                'fields'         => 'ids', // only return ids
                'post__not_in'   => array( $post_id ), // exclude $post_id from results
                'tax_query'      => array(
                    array(
                        'taxonomy' => 'industry',
                        'field'    => 'id',
                        'terms'    => $tag_ids,
                        'operator' => 'IN'
                    )
                )
            )
        );

        // loop through posts with the same tags
        if ( $tag_posts ) {
            $score = array();
            $i = 0;
            foreach ( $tag_posts as $tag_post ) {
                // get tags for related post
                $terms = wp_get_post_terms( $tag_post, 'industry', array( 'fields' => 'ids' ) );
                $total_score = 0;

                foreach ( $terms as $term ) {
                    if ( in_array( $term, $tag_ids ) ) {
                        ++$total_score;
                    }
                }

                if ( $total_score > 0 ) {
                    $score[$i]['ID'] = $tag_post;
                    // add number $i for sorting
                    $score[$i]['score'] = array( $total_score, $i );
                }
                ++$i;
            }

            // sort the related posts from high score to low score
            uasort( $score, 'sort_tag_score' );
            // get sorted related post ids
            $related_ids = wp_list_pluck( $score, 'ID' );
            // limit ids
            $related_ids = array_slice( $related_ids, 0, (int) $number );
        }
    }
    return $related_ids;
}


function sort_tag_score( $item1, $item2 ) {
    if ( $item1['score'][0] != $item2['score'][0] ) {
        return $item1['score'][0] < $item2['score'][0] ? 1 : -1;
    } else {
        return $item1['score'][1] < $item2['score'][1] ? -1 : 1; // ASC
    }
}