nshop/packages/Longyi/Member/src/Services/MemberDiscountService.php

<?php

namespace Longyi\Member\Services;

use Webkul\Checkout\Facades\Cart;

class MemberDiscountService
{
    /**
     * Member discount amount.
     */
    protected const MEMBER_DISCOUNT_AMOUNT = 19.9;

    /**
     * Apply member discount to cart.
     */
    public function apply(): void
    {
        $cart = Cart::getCart();

        if (! $cart) {
            throw new \Exception('Shopping cart not found.');
        }

        if ($cart->vip_plus_amount && $cart->vip_plus_amount > 0) {
            throw new \Exception('Member discount has already been applied.');
        }

        $discountAmount = core()->convertPrice(self::MEMBER_DISCOUNT_AMOUNT);

        $cart->vip_plus_amount = $discountAmount;
        $cart->base_vip_plus_amount = core()->convertToBasePrice($discountAmount);
        $cart->save();
        Cart::collectTotals();
    }

    /**
     * Remove member discount from cart.
     */
    public function remove(): void
    {
        $cart = Cart::getCart();

        if (! $cart || ! $cart->vip_plus_amount || $cart->vip_plus_amount <= 0) {
            return;
        }

        $cart->vip_plus_amount = null;
        $cart->base_vip_plus_amount = null;
        $cart->save();
        Cart::collectTotals();
    }
}