Remote PointsServer

To start your Phoenix server:

• Run mix setup to install and setup dependencies
• This seed the database with one million users.
• Start Phoenix endpoint with mix phx.server or inside IEx with iex -S mix phx.server

Now you can visit localhost:4000 from your browser.

GET / Endpoint

There is a single enpoint that under the hood just calls PointsServer.fetch(). It will just return whatever the GenServer did. The format of the JSON payload is as follows:

{
  "timestamp":"2023-03-11T23:15:34.353848Z",
  "users":[
    {"id":4376232,"points":94},
    {"id":4376234,"points":73}
  ]
}

PointsServer

A supervised GenServer registered under its own name.

Used to return at most 2 users from the database that have more points than a random value that the GenServer keeps in its state.

It also periodically randomizes that value and the points for all users in the database.

For details and options check its source code

Implementation

I started by writing an integration test. Once I understand the specifications of the feature/task, I always try to go outside-in.

When you run this test it keeps telling you what's the next step: adding the endpoint to the router, create the controller, implement the action, etc. Then I had to implenent the GenServer, which AFAIK is nothing special.

How to test that the GenServer refreshes?

I decided to add the option to pass the refreshing interval because:

• It's better not to hardcode this kind of thing (providing a default is fine)
• Allows me to set a very quick interval and be able to test the refresh behaviour in a test using assert_receive.

Refreshing points

I decided to run a raw SQL update to randomize all users at once. It seemed the most straightforward way and also it's the most performant AFAIK.