commerce_google_tag_manager: Example of an AlterEventData event subscriber

AlterShippingData.php

<?php

use Drupal\commerce_google_tag_manager\Event\AlterEventDataEvent;

class AlterShippingData implements EventSubscriberInterface {

  public static function getSubscribedEvents() {
    return [
      'commerce_gtm_enhanced_ecommerce.alter_event_data' => 'addShipping'
    ];
  }

  public function addShipping(AlterEventDataEvent $event) {
    $data = $event->getEventData();

    // Only alter the "purchase" event.
    if ($data['event'] !== 'purchase') {
      return;
    }

    // Set the shipping cost.
    $shipping_fee = OrderProcessor::SHIPPING_FEE;
    $data['ecommerce']['purchase']['actionField']['shipping'] = $shipping_fee;

    $event->setEventData($data);
  }
}