Php 只收取WooCommerce中最高的运费

我正在try 获得与简单和可变产品的每个行项目相关联的发货类别，然后找出哪种产品的成本最高，并收取仅扣除其余发货成本的费用.这是给WooCommerce的.

我所做的是-

1. 添加了两个分区
2. 增加了两个装运类别
3. 为方法中的两个类添加了价格
4. 将"按类"设置为计算方法
5. 在产品变体中设置发货类别

编辑:到目前为止添加的代码.

add_filter('woocommerce_package_rates', 'custom_shipping_method_by_class', 10, 2);

function custom_shipping_method_by_class($rates, $package)
{
    $class_costs = array();

    foreach ($package['contents'] as $item) {
        $product_id = $item['product_id'];
        $product = wc_get_product($product_id);

        if ($product instanceof WC_Product_Variable) {
            foreach ($product->get_visible_children() as $variation_id) {
                $term = wp_get_post_terms($variation_id, 'product_shipping_class');

                if (!empty($term)) {
                    $term = reset($term);
                    $class_costs[$term->term_id] = max($class_costs[$term->term_id] ?? 0, $rates["{$term->term_id}:$variation_id"]->cost);

                    var_dump($class_costs); // I get 0 here although I the variation has the shipping class set and the class has an amount set too.
                }
            }
        } else {
            $term = wp_get_post_terms($product_id, 'product_shipping_class');

            if (!empty($term)) {
                $term = reset($term);
                $class_costs[$term->term_id] = max($class_costs[$term->term_id] ?? 0, $rates["{$term->term_id}:$product_id"]->cost);
            }
        }
    }

    foreach ($rates as $rate_key => $rate) {
        list($class_id, $product_id) = explode(':', $rate_key);

        if (!array_key_exists($class_id, $class_costs) || $class_costs[$class_id] !== $rate->cost) {
            unset($rates[$rate_key]);
        }
    }

    return $rates;
}