The task is to implement the server side of a multiplayer noughts and crosses or tic-tac-toe game. We've provided a skeleton Dropwizard app that defines the API but lacks an implementation. You will need to provide an implementation.
Two players take turns to place a mark in one of the spaces on a 3x3 grid. Each player cannot place a mark where either player has placed one previously. The first player who places three consecutive marks in a horizontal, vertical or diagonal row wins the game. If all of the spaces are taken and no player has succeeded in placing 3 marks in a row then the game is a draw.
Please ensure that your application meets this API. The NoughtsResource and NoughtsTest classes provided should make it clear how to achieve this. Please return appropriate http error codes to enforce both the rules described above and the restrictions described below.
method : POST
url : /game?player1Id=<id of player 1>&player2Id=<id of player 2>
example response body : "<id of the new game>"
The client will provide the ids of the players. Players can create games against multiple different players concurrently but an appropriate error code should be returned if a player tries to create a new game against a player that they currently have an unfinished game against. The response should be a json string containing an id that identifies the new game.
method : PUT
url : /game/<id of the game>
example request body : {"playerId": "<id of player making the move>", "x": <column index to make a mark in>, , "y": <row index to make a mark in>}
example response body : <empty>
The will be the id of a game previously created via a call the Create a game endpoint. The player id will be the id of the player making the move. An error code should be returned if a player makes a move out of turn. Assume that player 1 will always go first.
method : GET
url : /game/<id of the game>
example response body (game in progress) : {"winnerId": null, "gameOver": false}
example response body (win) : {"winnerId": "<id of the winning player>", "gameOver": true}
example response body (draw) : {"winnerId": null, "gameOver": true}
The will be the id of a game previously created via a call the Create a game endpoint. If the game is still in progress the winnerId should be null and gameOver should be false. If a player has won then then the winnerId should be the the id of that player and gameOver should be true. If the game is complete and a draw then the winnerId should be null and gameOver should be true.
For bonus points:
Extend the NoughtsTest class to cover more of the rules and restrictions described above.
Ensure that your application runs efficiently and without error despite serving multiple players playing concurrently. Assume that players will try and break the game by making concurrent requests against the same player.
Store the state of the games in an external data store of your choice. Aim to handle 1000s of concurrent games on a modern mid-range laptop.
Add a leaderboard to the game, allowing clients to get the top 10 player ids and scores. Players should get 1 point per game won and no points for draws.
Please add any assumptions or commentary on your implementation decisions here.
Before start, we need to install and run Mongodb locally
$ brew install mongodb
$ mkdir /data/db
$ mongod
Before running test, we need to wipe out test collections
$ mongo
> use tic_tac_toe
> db.leaderBoard.remove("")
> db.games.remove("")
> exit
$ mvn test
I've chosen mongodb as data storage for TicTacToe game server over relational database such as mysql / postgresql, because mongodb stores data record as json object which gives more flexibility, very mature express query language, and scalability. And we don't need complex relational queries in TicTacToe game, so document database is the best fit for the case.
Of course, they will be outperformed than mongodb. I was thinking to choose one of those key/value store as data storage but we need to de-normalise data structure and more time will be spent on development / maintenance. Unless the application requires super-high performance, I prefer easy development / maintenance with scalable solution than super high performance / complex development / maintenance.
Error response has json body which contains proper error code / message like below
{"error": {"code": 100, "message": "Hello Spaceape, Something goes bad O_o!!!"}}
Java mongodb driver takes care of db connection pooling. Default is set to 10