WooCommerce - Show delivery time based on stoc

<?php
  // WooCommerce - Show delivery time based on in or out of stock
  // usage: [delivery in_stock="2" no_stock="10-12"]
  // works only on product pages
  // code goes in functions.php for your child theme
  add_shortcode('delivery', 'delivery');
  function delivery( $atts ) {
    global $product;
    $stock = $product->stock;
    if ($stock) {
      $days = $atts['in_stock'];
      echo '<p class="delivery">In stock: Ships within '.$days.' days</p>';
    } else {
      $days = $atts['no_stock'];
      echo '<p class="delivery">Out of stock: Ships within '.$days.' days</p>';
    }
  }