iprisakaru/onair

Coding interview purpose

We in On Air Entertainment like to see how developers writing a code, that's why we base our interviews mostly on practical parts and code than on theoretical. It is expected that candidate will have a live coding interview and only some theoretical questions are expected as an addition to what is written. Interview purpose is to demonstrate how a candidate can solve a task & how fluent candidate is with technologies used by On Air Entertainment.

NOTE: Coding task is sent to the candidate in advance, so the candidate can be prepared about expectations. It isn't prohibited to write a part or full solution for the practical task before the interview. It isn't expected that full solution will be written in result.

If you started with a solution, then please publish your solution as a private repository in GitHub and grant access to OnAirEntertainment user before the interview.

Technologies to use

Solution can be based (but not limited) on the following technologies:

• Scala
• Akka Actors
• Circe, Spray, Jackson or other alternative can be used for serialization
• Akka HTTP or fs2 / sttp can be used for websockets Other options:
• Cats Effect
• ZIO or Tagless Final

Coding task

Create an application for a Lucky Numbers game.

Game will include following minimal functionality:

• a method / service that generates a random number from 0 to 999999
• a method / service that accepts number of players, e.g. 5 and generates a random number for each player & a bot player
• a method / service that for each player & bot player constructs a game result with the following rules:
  • counts occurrences of each digit in given number, e.g. for number 447974 there are 4 - 3 times, 7 - 2 times, 9 - one time
  • calculates result for each digit by formula 10^(times-1) * digit, e.g. in number 447974 it will be 10 * 10 * 4 for 4, 10 * 7 for 7, 9 for 9
  • summarizes all digit result, e.g. for number 447974 it will be 10 * 10 * 4 + 10 * 7 + 9 = 479
• a method / service that calculates winning list:
  • all results that are below bot player aren't included into result list
  • all winners should be sorted by position

NOTE: Bot player or computer player plays against other players.

Additional functionality

NOTE: can be touched or covered during an interview

Create a websocket for managing game logic.

Following functionality should be covered by websocket:

• play message to websocket

{
  "message_type": "request.play",
  "players": 3
}

• results message from websocket

{
  "message_type": "response.results",
  "results": [
      {
        "position": 1, 
        "player": "1",
        "number": 966337, 
        "result": 106
      },
      {
        "position": 2, 
        "player": "3",
        "number": 964373, 
        "result": 56
      },
      {
        "position": 3, 
        "player": "2",
        "number": 4283, 
        "result": 17
      }
  ]
}

• ping / pong functionality (latency check)

{
  "id": 5,
  "message_type": "request.ping",
  "timestamp": 1234560
}

{
  "message_type": "response.pong",
  "request_id": 5,
  "request_at": 1234560,
  "timestamp": 1234567
}

Alternatively (but it isn't recommended) websocket can be replaced with RESTful API with results & ping requests.

Solution for a review

You can use your own scaffolding for a project if it looks easier for you. Please provide a short readme on how to launch and test application. Please publish your solution as a private repository in GitHub and grant access to OnAirEntertainment user.