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 (buy two of the same product, get one 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 server and client that communicate over the network.

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

The server must support concurrent invocations of those operations: any of them may be invoked at any time, while other operations are still being performed, even for the same basket.

At this stage, the service shouldn't use any external databases of any kind, but it should be possible to add one easily in the future.

Implement a checkout service and its client 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.
• Focus on solving the business problem (less boilerplate!)
• Have a clear structure.
• Be easy to grow with new functionality.
• Don't include binaries, and use a dependency management tool.

Bonus Points For:

• Be written in Go (let us know if this is your first time!)
• Unit/Functional tests
• Dealing with money as integers
• Formatting money output
• Useful comments
• Documentation
• Docker images / CI
• Commit messages (include .git in zip)
• Thread-safety
• Clear scalability