Php 如何在商业中获得申请的息票金额？

当我的购物车小计为0时，我正在尝试添加特殊折扣。此折扣适用于包括运费在内的购物车总额

function add_discount_line( $cart ) {
    global $woocommerce;

    if($woocommerce->cart->get_applied_coupons() && $cart->subtotal==0){

  $discount = 2; // here I want the amount of applied coupon
 $cart->add_fee( __( 'Special Discount', 'woocommerce' ) , -$discount );
}
}
add_action( 'woocommerce_cart_calculate_fees', 'add_discount_line' );

$折扣=2；//如何在这里获得申请优惠券的折扣金额。

我得到的解决方案

add_action( 'woocommerce_cart_calculate_fees', 'add_discount_line' );
function add_discount_line( $cart ) {

    if($cart->get_applied_coupons() && $cart->subtotal==0):
    $getDetails = ( new WC_Coupon($cart->get_applied_coupons()));
    $discount  =  $getDetails->amount;

     $cart->add_fee( __( 'Special Discount', 'woocommerce' ) , -$discount );
    endif;
}