Customer query on VAT and discounts

[tidygraphic]

We have a customer query which we've been looking at in our private repo around how discounts are made at the checkout; they aren't made on prices excluding VAT and so can cause invoicing discrepancies. Is there anything simple we can do to address this or does this involve breaking/updating core functionality?

I have noticed when we receive orders through the website that when a discount code is applied (5%) its being taken from the full invoice total (including VAT) not from the net price then adding the VAT on top. Although the figures match in the end as some of our customers claim their VAT back the values are incorrect, also when we then invoice though Sage the net values do not match for the customer and they do get a breakdown.

Example (UK VAT @ 20%) -

Product price: £575.00
Promo code: 5% off → £28.75
New price: £546.25
VAT (20%): £109.25
Total payable: £655.50

Our Invoice #5464

Product price: £575.00
Promo code: 5% off → £34.50
New price: £540.50
VAT (20%): £115.00
Total payable: £655.50

Overall we'd like to move them to Cargo but that's a big upgrade and so I wondered if we have anything we can do within Simple Commerce first?

[duncanmcclean]

The easiest approach would probably be to override SC's CouponCalculator class, which will let you change how the amount used to apply discounts.

I haven't tested these steps, but you should be able to do this:

1. Create your own CouponCalculator class:

<?php

namespace App\SimpleCommerce;

use Closure;
use DuncanMcClean\SimpleCommerce\Contracts\Order;
use DuncanMcClean\SimpleCommerce\Coupons\CouponType;

class CouponCalculator
{
    public function handle(Order $order, Closure $next)
    {
        if ($coupon = $order->coupon()) {
            $value = (int) $coupon->value();

            // Double check coupon is still valid
            if (! $coupon->isValid($order)) {
                $order->coupon(null);
                $order->couponTotal(0);

                return $next($order);
            }

            $baseAmount = $order->itemsTotal() + $order->taxTotal(); // TODO: probably remove taxTotal() from the calculation here

            // Otherwise do all the other stuff...
            if ($coupon->type() === CouponType::Percentage) {
                $order->couponTotal(
                    (int) ($value * $baseAmount) / 100
                );
            }

            if ($coupon->type() === CouponType::Fixed) {
                $order->couponTotal(
                    (int) $baseAmount - ($baseAmount - $value)
                );
            }

            $order->couponTotal(
                (int) round($order->couponTotal())
            );
        }

        return $next($order);
    }
}

2. Create a Calculator class and bind it in your AppServiceProvider. It lets you override which classes are used to calculate totals:

<?php

namespace App\SimpleCommerce;

use DuncanMcClean\SimpleCommerce\Contracts\Calculator as Contract;
use DuncanMcClean\SimpleCommerce\Contracts\Order;
use Illuminate\Support\Facades\Pipeline;

class Calculator implements Contract
{
    public static function calculate(Order $order): Order
    {
        return Pipeline::send($order)
            ->through([
                \DuncanMcClean\SimpleCommerce\Orders\Calculator\ResetTotals::class,
                \DuncanMcClean\SimpleCommerce\Orders\Calculator\LineItemCalculator::class,
                L\DuncanMcClean\SimpleCommerce\Orders\Calculator\ineItemTaxCalculator::class,
                \DuncanMcClean\SimpleCommerce\Orders\Calculator\CalculateItemsTotal::class,
                CouponCalculator::class, // this is your class
                \DuncanMcClean\SimpleCommerce\Orders\Calculator\ShippingCalculator::class,
                \DuncanMcClean\SimpleCommerce\Orders\Calculator\ShippingTaxCalculator::class,
                \DuncanMcClean\SimpleCommerce\Orders\Calculator\CalculateGrandTotal::class,
            ])
            ->thenReturn();
    }
}

// app/Providers/AppServiceProvider.php

public function boot(): void
{
    // ...

    $this->app->bind(
        \DuncanMcClean\SimpleCommerce\Contracts\Calculator::class,
        \App\SimpleCommerce\Calculator::class
    );
}

Hopefully that'll work! 😅

[tidygraphic]

Thanks so much - we'll give this a whirl and report back.