Game of Movement

This project is a Game of Three implementation. It does not provide a web interface. Thus, the player must use an HTTP API client, like Postman, curl, or the Swagger UI, available at the URL http://localhost:8080/swagger-ui/, if you are using de default configuration. The solution tries to be as simple as possible, what brings on a few problems, described in section Known issues.

The main technologies used in this game are:

Java 11;
Spring Boot;
Spring for Apache Kafka;
Apache Kafka;
JUnit;
Lombok.

API documentation

The game is composed by the following endpoints. In the next section, we can see a complete example of how to play a game.

POST /v1/players/{playerId}/ready: say that the player is ready;
POST /v1/players/{playerId}/{value}: send a new value;
GET /v1/players: query the game state;
POST /v1/players/restart: restart the game.

The image below shows the Swagger UI of the application, available at http://localhost:8080/swagger-ui/.

How to play

Before playing, both players (1 and 2) must be ready, achieved by using the endpoint POST /v1/players/{playerId}/ready. After that, each player can send a value, which is validated by the application. If the sent value is invalid, the player must choose a different number.

To check the current status you can use GET http://localhost:8080/v1/players.

Let's see an example:

GET http://localhost:8080/v1/players
POST http://localhost:8080/v1/players/1/ready
POST http://localhost:8080/v1/players/2/ready
POST http://localhost:8080/v1/players/1/56
GET http://localhost:8080/v1/players
POST http://localhost:8080/v1/players/2/1
POST http://localhost:8080/v1/players/1/-1
POST http://localhost:8080/v1/players/2/0
POST http://localhost:8080/v1/players/1/1
GET http://localhost:8080/v1/players

The status of movement #1 is WAITING_PLAYERS until both players are ready.

{
    "lastPlayerId": null,
    "currentValue": null,
    "message": null,
    "status": "WAITING_PLAYERS"
}

The resulting body of movement #4 is the following:

{
    "lastPlayerId": 1,
    "currentValue": 56,
    "message": "First play with value [56].",
    "status": "STARTED"
}

{
    "lastPlayerId": 1,
    "currentValue": 1,
    "message": "Player 1 is the winner.",
    "status": "FINISHED"
}

Error messages

For each rule, the application has an expected error messages:

Invalid player (#x). It is the other's player turn.
Invalid input. Valid values are -1, 0, 1.
The value [x] is invalid. The resulting operation is not divisible by 3. Try another value.
The game does not have a winner.
We are waiting for the players to join the game.

Configurations

The main application properties can be configured externally, for example, in the application.properties file we can see these properties:

server.port=${port:8080};
spring.kafka.bootstrap-servers=${bootstrap-servers:localhost:9092};
spring.kafka.consumer.group-id=${group-id:game-player-group};
spring.kafka.consumer.client-id=${client-id:game-client};
game.topic=${game-topic:game-topic}
ready.topic=${ready-topic:ready-topic}

If you want the customize one of them just pass the correct parameter name. For example -Dport=8080.

Known issues

The application uses Apache Kafka as a message consumer, thus, there are synchronization issues. Unfortunately, it was not possible to fix them yet. Maybe we need a more complex solution with different topics and concurrency control. Other improvements could be using design patterns to implement the rules, like Decorator.

Running the app

The application uses Apache Kafka and provides a docker-compose.yml to run it. This image is provided by Bitnami. The Kafka cluster must be running before the application.

To run the Kafka image use the command:

docker-compose up

The application can use Docker to run. To build the app use the commands:

mvn package -DskipTests
docker build -t game/game-of-movement .
docker run --name game-of-movement --network host --rm game/game-of-movement

Author

Marco Reis

Software Engineer

e-mail: ma@marcoreis.net

masreis / game-of-movement-java-api