Conceptual solution for a supermarket checkout

The aim of this project is to demonstrate Production Ready Good Quality code in implementing a supermarket checkout that calculates the total price of a number of items.

In a normal supermarket, things are identified using Stock Keeping Units, or SKUs. In our store, we’ll use individual letters of the alphabet (A, B, C, and so on). Our goods are priced individually. In addition, some items are multipriced: buy n of them, and they’ll cost you y pounds. For example, item ‘A’ might cost 50 pounds individually, but this week we have a special offer: buy three ‘A’s and they’ll cost you 130. There can also be multiple offers for the same item. The test data is as follows:

For item A the price calculation combines the offers on the basis of the price defined for the largest quantity. E.g. for 14 A the price is calculated as (180 * 2) + 160 = 520.

The ReceiptItemPriceCalculator class calculates the basket item price on the basis of the above logic. It also calculates the offer text on the basis of the price applied. When more than 1 offer applies, the offer text becomes "multiple offers applied". The CheckoutService class composes the receipt on the basis of the items in the basket and also calculates the total.

The BasketItemsController can be used to add 1 item at a time to the basket.
The BasketController can be used to create, checkout and reopen a basket.
The ItemsController can be used to retrieve the items inventory.

The solution is a RESTful web-api based on ASP.NET Core (.Net Core 3.1), Entity Framework Core and SqlServer (localdb). There are unit tests based on xUnit which test the main logic with several input scenarios. The database is seeded with demo data upon start-up.

The solution uses JWT authentication with Microsoft.AspNetCore.Identity. Two roles have been defined: "Pos" and "Admin" and one user on each role ("pos1" and "superadmin"). The Checkout.Server controllers authorise users in role "Pos". The "register" methods in the Checkout.Identity controller authorise users in role "Admin".

To test the solution, run the multiple startup projects in Visual Studio as configured and use PostMan (or any REST client). A PostMan collection and environment is supplied for this:
SupermarketCheckout.postman_collection.json
env.postman_environment.json