add custom discount (order level like coupon discount) before tax calculation

Question

I have already used the event sales_order_place_after

$quote->setSubtotal(0);
                    $quote->setBaseSubtotal(0);

                    $quote->setSubtotalWithDiscount(0);
                    $quote->setBaseSubtotalWithDiscount(0);

                    $quote->setGrandTotal(0);
                    $quote->setBaseGrandTotal(0);


                    $canAddItems = $quote->isVirtual() ? ('billing') : ('shipping');
                    foreach ($quote->getAllAddresses() as $address) {

                        $address->setSubtotal(0);
                        $address->setBaseSubtotal(0);

                        $address->setGrandTotal(0);
                        $address->setBaseGrandTotal(0);

                        $address->collectTotals();

                        $quote->setSubtotal((float) $quote->getSubtotal() + $address->getSubtotal());
                        $quote->setBaseSubtotal((float) $quote->getBaseSubtotal() + $address->getBaseSubtotal());

                        $quote->setSubtotalWithDiscount(
                                (float) $quote->getSubtotalWithDiscount() + $address->getSubtotalWithDiscount()
                        );
                        $quote->setBaseSubtotalWithDiscount(
                                (float) $quote->getBaseSubtotalWithDiscount() + $address->getBaseSubtotalWithDiscount()
                        );

                        $quote->setGrandTotal((float) $quote->getGrandTotal() + $address->getGrandTotal());
                        $quote->setBaseGrandTotal((float) $quote->getBaseGrandTotal() + $address->getBaseGrandTotal());

                        $quote->save();

                        $quote->setGrandTotal($quote->getBaseSubtotal() - $discountAmount)
                                ->setBaseGrandTotal($quote->getBaseSubtotal() - $discountAmount)
                                ->setSubtotalWithDiscount($quote->getBaseSubtotal() - $discountAmount)
                                ->setBaseSubtotalWithDiscount($quote->getBaseSubtotal() - $discountAmount)
                                ->save();


                        if ($address->getAddressType() == $canAddItems) {
                            //echo $address->setDiscountAmount; exit;
                            $address->setSubtotalWithDiscount((float) $address->getSubtotalWithDiscount() - $discountAmount);
                            $address->setGrandTotal((float) $address->getGrandTotal() - $discountAmount);
                            $address->setBaseSubtotalWithDiscount((float) $address->getBaseSubtotalWithDiscount() - $discountAmount);
                            $address->setBaseGrandTotal((float) $address->getBaseGrandTotal() - $discountAmount);
                            if ($address->getDiscountDescription()) {
                                $address->setDiscountAmount(-($address->getDiscountAmount() - $discountAmount));
                                $address->setDiscountDescription($address->getDiscountDescription() . ', Company Discount');
                                $address->setBaseDiscountAmount(-($address->getBaseDiscountAmount() - $discountAmount));
                            } else {
                                $address->setDiscountAmount(-($discountAmount));
                                $address->setDiscountDescription('Company Discount');
                                $address->setBaseDiscountAmount(-($discountAmount));
                            }
                            $address->save();
                        }//end: if
                    } //end: foreach
                    //echo $quote->getGrandTotal();

                    foreach ($quote->getAllItems() as $item) {
                        //We apply discount amount based on the ratio between the GrandTotal and the RowTotal
                        $rat = $item->getPrice() / $total;
                        $ratdisc = $discountAmount * $rat;
                        $item->setDiscountAmount($item->getDiscountAmount() + $ratdisc * $item->getQty());
                        $item->setBaseDiscountAmount($item->getBaseDiscountAmount() + $ratdisc * $item->getQty())->save();
                    }

Now, the problem I'm facing is, Tax setting is, Apply Tax After Discount, but Tax is calculated before this custom discount.

Answer 1

I'm not sure to understand well your problem but you are starting from a quote to do a discount based on the address informations.

It can be better to wait that you have a real order and at this moment all the address informations will be filled, that might not be the case at the quote state.

If you do the same behaviour starting on the order you ll probably have your discount well calculated and then the taxes that will apply on this amount.

Keep me in touch if it is better.