# order Specification

## Purpose
Checkout splitting a cart into per-shop orders, plus order lifecycle and ownership.

## Requirements

### Requirement: Checkout splits by shop
`POST /api/orders/checkout` SHALL create one order per distinct shop in the cart, in a single database transaction: stock decrement, order + item insert with price snapshots, cart clear, and requested coupon redemption. All amounts use the cart's SKU currencies converted into the buyer-chosen display currency at checkout time. The request MAY select at most one owned coupon per generated shop order; the server SHALL validate its ownership, shop, status, validity window, threshold, and converted amount, then persist `coupon_id`, `discount_minor`, and the post-discount `total_minor`. The client SHALL NOT provide a discount amount. This requirement does not define activity prices; a later flash-sale or group-buying change that rewrites checkout SHALL restate these coupon clauses and SHALL reject a coupon on any shop order that applied an activity price.

#### Scenario: two shops → two orders
- **WHEN** the cart contains SKUs from shops A and B
- **THEN** two orders are created, each with only its shop's items, and the cart is empty

#### Scenario: insufficient stock
- **WHEN** any line's qty exceeds SKU stock
- **THEN** the whole checkout returns 409 and no order is created and stock is unchanged

#### Scenario: coupon applies to one matching shop
- **WHEN** the customer selects an eligible coupon issued by shop A for a cart containing shops A and B
- **THEN** only shop A's order records that coupon and its server-calculated discount

### Requirement: Order lifecycle
Status transitions SHALL be: pending_payment → paid → fulfilling → shipped → completed; cancellable only from pending_payment, which MUST restore stock and restore a redeemed coupon to claimed status when the order has one.

#### Scenario: cancel restores stock
- **WHEN** a customer cancels a pending_payment order
- **THEN** stock of each SKU increases by the ordered qty and status is cancelled

#### Scenario: cancel restores coupon
- **WHEN** a customer cancels a pending_payment order with a redeemed coupon
- **THEN** the coupon is detached from the order and becomes claimed

#### Scenario: illegal transition rejected
- **WHEN** cancelling a paid order via the customer endpoint
- **THEN** the API returns 409

### Requirement: Order ownership
Customers SHALL see only their own orders; shop roles only their shop's orders; platform_admin sees all.

#### Scenario: cross-customer read denied
- **WHEN** customer X requests customer Y's order id
- **THEN** the API returns 404