Create CPT with semantic URL structure (i.e. /taxonomy/term/post)

wordpress-semantic-urls.php

<?php
/**
 * Services class file.
 *
 * @package WTF
 */

namespace WTF;

/**
 * Class Services
 */
class Services {

  /**
   * Init class.
   */
  public function init(): void {
    add_filter('init', [$this, 'create_tax']);
    add_filter('init', [$this, 'create_cpt']);
    add_filter('post_type_link', [$this, 'seo_permalinks'], 10, 2);

    add_action('init', [$this, 'rewrite_rules']);

  }

  public function create_tax() {

    register_taxonomy('service_type', ['post', 'services'],
      [
        'label'              => __('Service Types', 'wtf'),
        'public'             => true,
        'show_tagcloud'      => false,
        'show_in_rest'       => true,
        'hierarchical'       => false,
        'show_admin_column'  => true,
        'query_var'          => true
      ]
    );
  }


  public function create_cpt() {

    register_post_type('services',
      [
        'label'             => __('Services', 'wtf'),
        'public'            => true,
        'capability_type'   => 'post',
        'show_in_rest'      => true,
        'hierarchical'      => false,
        'rewrite'           => [
          'slug'       => '/services/%service_types%',
          'with_front' => false,
          'feeds'      => false
        ],
        'query_var'         => true,
        'supports'          => ['title', 'tags', 'editor', 'comments', 'custom-fields', 'thumbnail'],
        'has_archive'       => 'services',
        'taxonomies'        => ['service_type', 'post_tag'],
        'show_in_nav_menus' => true,
        'menu_icon'         => 'dashicons-admin-site',
      ]
    );
  }

  /**
   * Adds some rewrite rules for semantic URLs (archive, taxonomy)
   */
  public function rewrite_rules() {

    add_rewrite_rule(
      'services/([a-z]+)/page/?([0-9]{1,})/?$',
      'index.php?post_type=services&service_type=$matches[1]&paged=$matches[2]',
      'top'
    );

    add_rewrite_rule(
      'services/([a-z]+)/([a-z0-9_-]+)/?$',
      'index.php?post_type=services&service_type=$matches[1]&services=$matches[2]',
      'top'
    );

    add_rewrite_rule(
      'services/([a-z]+)/?$',
      'index.php?post_type=services&service_type=$matches[1]',
      'top'
    );

    add_filter('query_vars', function($vars) {
      $vars[] .= 'service_type';
      $vars[] .= 'service_type-page';

      return $vars;
    });

  }

  /**
   * Adding service types to single service URLs: https://wtf.com/services/%service_type%/%service%/
   *
   * @param $permalink
   * @param $post
   *
   * @return string|string[]
   */
  public function seo_permalinks(
    $permalink, $post
  ) {

    if (strpos($permalink, '%service_types%') === false) {
      return $permalink;
    }

    $terms = get_the_terms($post, 'service_type');

    if ( ! is_wp_error($terms) && ! empty($terms) && is_object($terms[0])) {
      $term_slug = array_pop($terms)->slug;
    } else {
      $term_slug = 'd';
    }

    return str_replace('%service_types%', $term_slug, $permalink);
  }

}