Instructions for the assignment

1. Clone this repository on your machine.
2. Use your IDE of choice to complete the assignment.
3. When you are done with the solution and have pushed it to the repo, you can notify us that it was completed.

Assignment Details

We will be using a simple shopping cart, similar to what you would see on any e-commerce website, as the domain for this problem.

We respect your time and understand that asking you to give up an hour or so of your personal time for the interview process is a big ask. However, we want to make the process as simple and stress-free as possible, by allowing you to complete the first stage of the process in the comfort of your own home. We will also be using your submission in further stages of the process should you be successful.

What we are looking for

Test Coverage: The solution should be developed “test-first”, should have good unit tests, and common paths should be covered. Your tests should also be self-contained and not rely on external systems to be available to run.

Simplicity: We value simplicity as an architectural virtue and a development practice. Solutions should reflect the difficulty of the assigned task, and should not be overly complex. Layers of abstraction, patterns, or architectural features that aren’t called for should not be included.

Self-explanatory code: The solution you produce must speak for itself. Multiple paragraphs explaining the solution are a sign that it isn’t straightforward enough to understand purely by reading code, and are not appropriate.

An understanding of functional programming: The solution should demonstrate the use of functional programming concepts, in particular, the use of immutable data structures, referential transparency, and the use of monads in dealing with effects.

The Problem Statement

Create a shopping cart package (e.g. com.siriusxm.example.cart) that facilitates 2 basic capabilities:

1. Add multiple products to the cart. A product has a name and price. You should be able to specify how many of each product is being added to the cart and provide a means to observe the resulting state.
2. Calculate the totals
   1. Cart subtotal (sum of price for all items)
   2. Tax payable, charged at 12.5% on the subtotal
   3. Total payable (subtotal + tax)

Pricing data for each product should be retrieved via an HTTP call. You can find example pricing data for a set of sample products at the URI’s below. You should assume that the product name (lowercase) matches the file name. Use whatever libraries you like to get and parse the JSON. For example OKHttp (https://square.github.io/okhttp/) is a simple client for Java.

Valid Product Information URLs

• https://raw.githubusercontent.com/mattjanks16/shopping-cart-test-data/main/cheerios.json
• https://raw.githubusercontent.com/mattjanks16/shopping-cart-test-data/main/cornflakes.json
• https://raw.githubusercontent.com/mattjanks16/shopping-cart-test-data/main/frosties.json
• https://raw.githubusercontent.com/mattjanks16/shopping-cart-test-data/main/shreddies.json
• https://raw.githubusercontent.com/mattjanks16/shopping-cart-test-data/main/weetabix.json

Sample based on the data

The below is a sample with the correct values you can use to confirm your calculations

  Add 2 × cornflakes @ 2.52 each
  Add 1 × weetabix @ 9.98 each
  Subtotal = 15.02
  Tax = 1.88
  Total = 16.90

FAQ

What other functionality is required?

No other capabilities are required. This is not a trick question and there is no single correct answer. We prefer simple, well tested solutions over clever solutions. The complexity of your solution should reflect that of the problem. Use whatever external libraries or packages you wish.

Should I include an app?

Please do not write a web, desktop, command line or any other kind of app. Your code needs only to be driven by tests and can extend IOApp.

Must I use Cats?

We often use Cats in our projects, so we've provided all the boilerplate and dependencies in this template project. However, we are more interested in your use of functional programming techniques than the use of a library, so feel free to deviate from what we provide here.

What about ambiguity?

If there is any ambiguity please add this in a section added to the bottom of the README and make a choice yourself to resolve the ambiguity.

How should rounding be handled?

Prices should be rounded up where required.

Is there a time limit for completing the exercise?

There is no time limit for how long the exercise should take for you to complete, but we find most people complete the exercise in around 90 mins.

Internal Reference

Please do not remove this section, it helps us a lot to have this information available.

Template: scala-sbt

Notes/ambiguities

Here are some of the notes I have taken during the implementation. They would usually go into the description of a PR or a different discussion with teammates:

1. I chose the verb-centric approach to naming so that the code is more feature-centric. This is not a common approach so should be used if the project is already using it or the team agrees this is needed.
2. FetchTestPrices uses raw Exceptions when a product price is not defined. Is it enough and readable for tests?
3. I used IO explicitly in signatures instead of F to make things simpler.
4. What happens if we are adding multiple products with the same name? For now, I implemented a "combining" algorithm based on my experience with shopping carts.
5. The API doesn't return a failed IO when quantity is negative. It is supported as a side effect of adding multiple products with the same name.
6. There should be some error handling added, like custom ProductDoesntExist, maybe in IO[Either] or a bifunctor IO. For now, it throws DeserializationException which is too low-level.