woocommerce_thank_you_data_layer.php

<?php
/**
 * Render dataLayer on a WooCommerce thank you page.
 * This file should be added at the end of Theme Functions (functions.php)
 *
 * Official Class descriptions:
 * https://docs.woocommerce.com/wc-apidocs/class-WC_Abstract_Order.html
 * https://docs.woocommerce.com/wc-apidocs/class-WC_Order.html
 * https://docs.woocommerce.com/wc-apidocs/class-WC_Order_Item.html
 * https://docs.woocommerce.com/wc-apidocs/class-WC_Abstract_Legacy_Order.html
 *
 * Useful links:
 * https://docs.woocommerce.com/document/custom-tracking-code-for-the-thanks-page/
 * https://stackoverflow.com/questions/39401393/how-to-get-woocommerce-order-details/44708344#44708344
 * https://stackoverflow.com/questions/39831875/enhanced-ecommerce-datalayer-woocommerce
 *
 * There are some uncertainties around the implementation.
 * Sometimes $order items appear as an associative array, sometimes as object.
 * The final version should be determined at debugging stage.
 * Also, certain methods are deprecated but yet still appear in "fresh" blog posts.
 *
 * PLEASE NOTE:
 * Below script was not tested at all and the only purpose of it is to
 * demonstrate how the final JS dataLayer object could be renedered on
 * WooCommerce thank you page. Certain adjustment may be needed.
 * Please reference above documentation.
 *
 * IMPORTANT: The top "<?php" should be removed
 * when pasting this entire script into functions.php.
 */

add_action('woocommerce_thankyou', 'woocommerce_thankyou_push_data_layer');
function woocommerce_thankyou_push_data_layer($order_id) {
  // Lets grab the order
  $order = wc_get_order($order_id);
  ?>

  <script>
    window.dataLayer = window.dataLayer || [];
    var nsala_order_info = {
      'event': 'purchase',
      'transactionId': '<?php echo $order->get_order_number(); ?>',
      'transactionAffiliation': '<?php echo get_bloginfo('name'); ?>',
      'transactionTotal': <?php echo number_format($order->get_total(), 2, ".", ""); ?>,
      'transactionTax': <?php echo number_format($order->get_total_tax(), 2, ".", ""); ?>,
      'transactionShipping': <?php echo number_format($order->calculate_shipping(), 2, ".", ""); ?>,
      'transactionProducts': []
    };

  <?php
  $line_items = $order->get_items();

  foreach ($line_items as $item) {
    // get_product_from_item() seems to be deprecated
    // (https://docs.woocommerce.com/wc-apidocs/class-WC_Abstract_Legacy_Order.html#_get_product_from_item)
    // but let's hope still works as it may be the only way to get SKU and categories:
    $product = $order->get_product_from_item($item);
    ?>

    nsala_order_info['transactionProducts'].push({
      'sku': '<?php echo $product->get_sku(); ?>',
      'name': '<?php echo $item->get_name(); ?>',
      'category': '<?php echo strip_tags($product->get_categories(', ', '', '')); ?>',
      'price': <?php echo number_format($order->get_line_total($item), 2, ".", ""); ?>,
      'quantity': <?php echo $item->get_quantity(); ?>
    });

  <?php
	}
  ?>
    dataLayer.push(nsala_order_info);
  </script>
<?php
}