Challenge

This repository is a possible solution for this challenge.

The aim is to simulate an online marketplace, which allows for promotions and total spending discounts.

Assumptions

I assumed that a CMS of some type would allow the marketing department to easily create promotions and discounts. It was assumed for this exercise that this data would be made available as a valid json endpoint, modelled in this application as a static string for demonstration purposes.

Sample promotion_rules

{
    "version" : 1,
    "total_discount_threshold": 60.00,
    "total_discount_percentage": 10.00,
    "products": [
        {
            "id":"001",
            "name":"Lavender heart",
            "price":9.25,
            "discount_threshold":2,
            "discount_price": 8.50
        },
                {
            "id":"002",
            "name":"Personalised cufflinks",
            "price":45.00,
            "discount_threshold":0.0,
            "discount_price": 0.0
        },
                {
            "id":"003",
            "name":"Kids T-shirt ",
            "price":19.95,
            "discount_threshold":0.0,
            "discount_price": 0.0
        }
    ]
}

Approach

As specified, the application assumes the promotional rules are used to initialise the checkout object. Items are 'scanned' from a basket and added to a view model called 'Order'. This collates the scanned products and records the number of unique items. If the rules specify a discount level has been reached, the order total takes into account a products' discount price. On completion the checkout object returns the order total, while taking into account any percentage discount specified in the rules json.

How to run this application

If you have a local install of Docker, you can use the supplied Dockerfile to run a local copy of the project without needing to install Rust.

for example:

docker build . -t discounter

This will build the project and also run its test suite.

docker run discounter

Will run the application, with the test data specified in the challenge document

Output

Test data
-----------
Basket: ["001", "002", "003"]
£66.78
Basket: ["001", "003", "001"]
£36.95
Basket: ["001", "002", "001", "003"]
£73.76

Once more for luck, randomise the last basket order

Basket: ["001", "001", "002", "003"]
£73.76 which is equal to £73.76

nb: the final test randomises the scanning order as mentioned in the challenge.

Rust notes

I took the words 'challenge' and 'modern language' literally and ended up with this my first Rust application. The 'checkout' functionality is developed as a testable library. With a local install of Rust one can run the library tests with...

cd shop
cargo test

This will output...

running 4 tests
test tests::total_is_correct_without_discounts ... ok
test tests::read_in_rules ... ok
test tests::check_total_order_applies_discount ... ok
test tests::scan_works_correctly ... ok

test result: ok. 4 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out