gdgpisa / pbg

Project examples to explain Go backend development principles

PokèmonBattleGo

Pokèmon battles powered by Go!

(Note: I know, Pokèmon is spelled with "é" but I'm too lazy to correct it, anyway...)

Architecture

All the main server logic is contained inside the github.com/ar3s3ru/pbg package.

To download the package, use the command:

    go get github.com/ar3s3ru/pbg

Component-based architecture

Since we'd like to abstract from concrete implementation of data storage (hence, usage of one DB instead of another, or just using in-heap memory objects), I choose to structure the whole system as independent components, following the principles behind CBSE, or Component-based software engineering.

After identifying key roles inside the system (at analysis stage), which are:

• Server HTTP (for middlewares registration)
• PokèmonDB
• MoveDB
• TrainerDB
• SessionDB

I proceed with writing interfaces that actually decouples the server logic, such as:

    // Middleware registration
    ServerHTTP interface { ... }

    // Data storage
    PokèmonDBComponent interface { ... }
    MoveDBComponent    interface { ... }
    TrainerDBComponent interface { ... }
    SessionDBComponent interface { ... }

Every DB software-component allows CRUD operations through a component-required interface:

    PokèmonDBInterface interface { ... }
    MoveDBInterface    interface { ... }
    TrainerDBInterface interface { ... }
    SessionDBInterface interface { ... } 

Such interfaces are provided by their own component (following ObjectPool semantic) and can be requested inside an HTTP handler through a Server-level decorator (see ServerAdapter interfaces for reference); the Server will make such interfaces accessible through the fasthttp.RequestCtx object of the HTTP handler.

REST Architecture

The executable server should follow the REST Architecture. As such, models representations at module level and models representations at middleware level should be different.

Meaning:

    // At framework level we could have this interface
    Model interface {
        Name() string
        Dog()  Dog     // Dog is another model interface
    }

    // At module level we could have this model
    mem.Model struct {
        name string
        dog  Dog
    }

    func (m *mem.Model) Name() string { return m.name }
    func (m *mem.Model) Dog() Dog { return m.dog }

    // At middleware level, we would like to implement HATEOAS principle from REST architecture, and thus...
    RESTDog struct {
        Dog             // Embedding
    } 

    RESTModel struct {
        Model
    }

    func (rd *RESTDog) MarshalJSON() ([]byte, error) {
        /**
            Do marshalling here with this structure:

            { 
                "name": <dog name>, 
                "href": "http(s)://server:port/dog/102"  // HATEOAS, state of this dog is available at that link
            }
         */
    }

    func (rm *RESTModel) MarshalJSON() ([]byte, error) {
        // Create temporary RESTDog value that holds the original Dog interface value
        dog := &RESTDog{rm.Dog()}

        // Do marshalling here...
    }

Moreover, we can use a Negotiator-like handler that will output API data with requested encoding/format. For this purpouse, we have an APIResponser interface (look at the documentation for further references).

TODO

Use cases implementated as far are:

• Retrieve Pokèmon and Moves registered and available (permanently) on the server
• Create and setup new Pokèmon trainer profiles

Must still implement:

• Matchmaking mechanisms
• Database migration (considering MongoDB as of today)

Contributing

As a GDG Pisa community project, everyone can contribute as they like. All the code here is open source (duh!), without license (so free to use and modify).

License could be used in further commits, though.

Anyway, feel free to do significant pull request when you like :)

• • Danilo Cianfrone*