Multisite routing for ProcessWire

Multisite.module.php

<?php

// source: https://processwire.com/talk/topic/680-multiple-sites-from-one-install/?p=8778

class Multisite extends WireData implements Module, ConfigurableModule {

  public static function getModuleInfo() {
    return array(
      'title' => 'Multisite',
      'version' => 1,
      'summary' => 'Allows multiple sites with different domains run from single PW-site and database.',
      'singular' => true,
      'autoload' => true,
    );
  }
  
  public function init() {
    $subdomains = explode("\n", strtolower($this->subdomains));
  
    foreach($subdomains as $subdomain) {
      $httpHost = strtolower(wire('config')->httpHost);
      
      if(strpos($httpHost, $subdomain) !== false) {
        $this->subdomain = $subdomain;
        // change path like /about/contact/ to /campaign.com/about/contact/
        $_GET['it'] = "/{$subdomain}/" . ltrim($_GET['it'], '/');
        // hook for path method to make path() and url() methods context aware
        $this->addHookAfter('Page::path', $this, 'modifyPath');
      }
    }
  }

  public function modifyPath($event) {
    $event->return = str_replace("{$this->subdomain}/", '', $event->return);;
  }

  static public function getModuleConfigInputfields(array $data) {
  
    $fields = new InputfieldWrapper();
    $modules = wire('modules');
    
    $field = $modules->get("InputfieldTextarea");
    $field->name = "subdomains";
    $field->label = "Other sites running from same install";
    $field->description = "Add each domain for their own line. Don't add http or https, just simple domain like: www.example.com tai campaign.example.com";
    $field->notes = "IMPORTANT: create homepage for each of these domains right on the root. Name should be exactly same as the domain you use here.";
    $field->attr('value', $data['subdomains']);
    $fields->add($field);
    
    return $fields;
  }
}