REST-based order management sample app in Rails. It doesn't need views, we just need a REST API and JSON-only responses are sufficient.

Requirements:

• Users need to be able to maintain a list of products
• Each product has a unique name, and a (net) price
• Users should be able to add/edit orders
• Orders cannot be deleted
• Each order has a customizable order-date (must not be in the past when created) and a VAT (percentage) which should default to 20% but should be configurable (through an app-wide constant)
• Orders can have multiple line items
• Each line item must belong to an order, reference a product and have a quantity > 0
• User should be able to add/edit/delete line items
• Products cannot be deleted if they were previously ordered
• Orders can have the following statuses: DRAFT, PLACED, PAID, CANCELLED
  • Newly created orders must be DRAFT
  • An order's status can be "bumped" order from DRAFT to PLACED, but only if there is at least one line item
  • An order's status can change from DRAFT to CANCELLED, when this happens a short reason must be provided
  • An order's status can change from PLACED to PAID
  • An order's status can change from PLACED to CANCELLED, when this happens a short reason must be provided
  • No other other status changes are permitted, e.g. an order's status can never change back to DRAFT
  • Changes can be made to orders, including adding/editing/deleting line items, while the orders are DRAFTs
  • Changes should not be permitted once the status is either PLACED, PAID or CANCELLED, neither to the order itself nor its line items
• Line items, when retrieved, should expose the product name to the API client
• Orders, when retrieved, should expose a net- and a gross-total (net total + VAT) to the API client
• It's an internal application and there is no authentication/user management/etc required