Changing tax rate on certain cart items in Woocommerce

Question

I am inserting a control in the Wocommerce cart which, based on certain properties of the user and the inserted item, modifies the tax rate for that specific item.

The code I'm using, inside a plugin, is the following:

add_action('woocommerce_before_calculate_totals', 'switch_product_tax_class_in_cart', 10, 1);
/**
 * @param $cart
 */
function switch_product_tax_class_in_cart($cart)
{
    foreach ($cart->get_cart() as $cart_item) {
        if (isUserAgevolabile() && get_field('product_agevolabile', $cart_item['product_id'])) {
            $cart_item['data']->set_tax_class('iva-4');
        }
    }

}

Unfortunately, this doesn't work.

I've also made a test using the function set_price() but this works properly.

Moreover, I already change the tax class in the product listings/product pages in this way, and it works:

add_filter('woocommerce_product_get_tax_class', 'switch_product_tax_class', 1, 2);
add_filter('woocommerce_product_variation_get_tax_class', 'switch_product_tax_class', 1, 2);

/**
 * @param $tax_class
 * @param $product
 * @return mixed
 */
function switch_product_tax_class($tax_class, $product)
{

    if (!is_cart() && isUserAgevolabile() && get_field('product_agevolabile')) {
        return 'iva-4';
    }

    return $tax_class;
}

Answer 1

I've solved the problem by editing the second part of the code in this way:

add_filter('woocommerce_product_get_tax_class', 'switch_product_tax_class', 1, 2);
add_filter('woocommerce_product_variation_get_tax_class', 'switch_product_tax_class', 1, 2);

/**
 * @param $tax_class
 * @param $product
 * @return mixed
 */
function switch_product_tax_class($tax_class, $product)
{

    if (!is_cart() && isUserAgevolabile() && get_field('product_agevolabile')) {
        return 'iva-4';
    }

    if (is_cart() || is_checkout()) {
        $product_id = $product->get_parent_id() ?: $product->get_id();

        if (isUserAgevolabile() && get_field('product_agevolabile', $product_id)) {
            return 'iva-4';
        }
    }

    return $tax_class;
}

The first part (attached to the action woocommerce_before_calculate_totals) is no more required.