/**
  * @param $cart
  * @param $product_id
  *
  * @return array
  */
 public function getExistingProductQuantity(Cart $cart, $product_id)
 {
     if (empty($cart)) {
         return 0;
     }
     $data = $cart->products()->get()->where('id', $product_id)->fetch('pivot')->implode('quantity');
     if (empty($data)) {
         return 0;
     }
     return (int) $data;
 }