partial use of coupons

functions.php

<?php

add_action('woocommerce_checkout_order_processed', 'handle_partial_coupon_usage', 10, 3);
function handle_partial_coupon_usage($order_id, $posted_data, $order) {
    $applied_coupons = $order->get_coupon_codes();
    
    // Ensure only one coupon is applied
    if (count($applied_coupons) === 1) {
        $coupon_code = current($applied_coupons);
        $coupon = new WC_Coupon($coupon_code);

        $order_total = $order->get_total();
        // Get the total discount applied to the order
        $total_discount = $order->get_total_discount();
        // Calculate the total before discount
        $total_before_discount = $order_total + $total_discount;

        $coupon_amount = $coupon->get_amount();

        // If coupon amount is greater than order total
        if ($coupon_amount > $total_before_discount) {
            // Calculate remaining balance
            $remaining_balance = $coupon_amount - $total_before_discount;
            if ($remaining_balance <= 0) {
                return;
            }

            // Update the existing coupon with the remaining balance
            $coupon->set_amount($remaining_balance);
            $coupon->save();
          
            // Reset the usage count to 0
            $coupon->set_usage_count(0);
            $coupon->save();

            // Add a note to the order about the updated coupon
            $order->add_order_note(sprintf(
                'Coupon %s partially used. Remaining balance updated to €%s.',
                $coupon_code,
                $remaining_balance
            ));

            // Inform the user (this will appear on the thank you page)
            wc_add_notice(sprintf(
                'Vous avez utilisé une partie de votre cagnotte. Le solde restant de votre coupon est maintenant de €%s.',
                $remaining_balance
            ), 'success');
        }
    }
}