Labotopia E-commerce App

The obvious design takes the stock off at checkout and puts it back when the order is cancelled. That assumes someone cancels. A customer who opens the Midtrans page and walks away never triggers anything, and the stock stays gone for good.

So checkout doesn't touch the stock. Each item gets a reservation with an expiry time, one day by default, and the available stock is always the stock minus the reservations still active. When the admin confirms the payment, the stock is taken off and the reservation removed; a cancelled order just removes its reservation. If nobody does anything, the reservation expires and simply stops counting. Releasing the stock depends on the clock, not on a customer remembering to cancel.

At checkout the browser sends only IDs and quantities. The server reads the catalogue again and works out every price, discount and add-on itself, and an add-on only counts if it belongs to the product it was sent with. Whatever the page displayed, the order is charged what the database says.

Vouchers have a usage limit, so claiming one is a single conditional update: add one use, but only while the count is still under the limit. If no row was updated, someone else took the last use and the checkout stops there. The tax rate is saved with each order, so old orders keep the rate that applied when they were placed.

Characterization orders and equipment orders look alike, but they aren't. A characterization order has 11 states, including an unusable sample and results that are redone. An equipment order has 14, including shipping, returns and refunds. Neither needs the other's states.

One generic order would have been two things pretending to be one, with every branch asking which kind it really was. So they are separate all the way down: orders, items, add-ons, status history, reviews, carts and API routes each exist twice. Each order keeps a status history that records who made a change, an admin or the system itself.