Lana has come to conclusion that users are very likely to buy awesome Lana merchandising from a physical store that sells the following 3 products:

Code         | Name              |  Price
-----------------------------------------------
PEN          | Lana Pen          |   5.00€
TSHIRT       | Lana T-Shirt      |  20.00€
MUG          | Lana Coffee Mug   |   7.50€

Various departments have insisted on the following discounts:

• The sales department thinks a buy 2 get 1 free promotion will work best (for each two of the same product, get the second free), and would like this to only apply to PEN items.

• The CFO insists that the best way to increase sales is with discounts on bulk purchases (buying x or more of a product, the price of that product is reduced), and requests that if you buy 3 or more TSHIRT items, the price per unit should be reduced by 25%.

Your task is to implement a simple checkout HTTP API.

We'd expect the server to expose the following independent operations:

• Create a new checkout basket
• Add a product to a basket
• Get the total amount in a basket
• Remove the basket

Implement a checkout service that fulfills these requirements.

Examples:

Items: PEN, TSHIRT, MUG
Total: 32.50€

Items: PEN, TSHIRT, PEN
Total: 25.00€

Items: TSHIRT, TSHIRT, TSHIRT, PEN, TSHIRT
Total: 65.00€

Items: PEN, TSHIRT, PEN, PEN, MUG, TSHIRT, TSHIRT
Total: 62.50€

The solution should:

• Build and execute in a Unix operating system using Docker
• Create a CI pipeline to release the application

Bonus Points For:

• Focus on solving the business problem (less boilerplate!)
• Don't include binaries, and use a dependency management tool
• Have a clear structure
• Unit/Functional tests
• Useful comments
• Documentation
• Commit messages (include .git in zip, avoid big bulk changes)
• Enable monitoring on the application
• Curl examples to test the endpoints