PortsManager.elm

-- Ports.Manager --


type alias Manager msg =
    { threads : Dict String (Decoder msg)
    , seed : Random.Seed
    , errCtor : Error -> msg
    }


type Error 
    = IdDecoderFailed String
    | ThreadDoesNotExist
    | MsgDecoderFailed String


init : Random.Seed -> (String -> msg) -> Manager msg
init seed errCtor =
    { threads = Dict.empty
    , seed = seed
    , errCtor = errCtor
    }

type alias Request a msg =
    { decoder : Decoder a 
    , msgCtor : a -> msg
    , outgoingMsg : (String, Encode.Value)
    }


request : Decoder a -> (a -> msg)-> (String, Encode.Value) -> Request
request =
    Request


jsonRequest : (Decode.Value -> msg) ->  (String, Encode.Value) -> Request
jsonRequest =
    Request Decode.value


map : (a -> b) -> Request a -> Request b
map ctor request =
    { request | msgCtor = ctor << request.msgCtor }


update : Request a msg -> Manager msg -> (Manager msg, Cmd msg)
update request manager =
    let
        (id, newSeed) =
           Random.step idGenerator manager.seed 
    in
    ( { manager 
        | threads = 
            Dict.set
                id 
                (Decode.map request.msgCtor request.decoder) 
                manager.threads
        , seed = newSeed
    }
    , encode id (manager.bundler request.jsMsg)
    )


encode : String -> (String, Encode.Value) -> Encode.Value
encode id (type, payload) =
    [ ("id", Encode.string id) 
    , ("type", Encode.string type)
    , ("payload", payload)
    ] 
        |> Encode.object



decode : Manager msg -> Decode.Value -> msg
decode manager json =
    case Decode.decodeValue (Decode.field "id" Decode.string) json of
        Ok id ->
            case Dict.get id manager.threads of
                Just decoder ->
                    case Decode.decodeValue decoder json of
                        Ok msg ->
                            msg

                        Err err ->
                            err 
                                |> MsgDecoderFailed
                                |> manager.errCtor

                Nothing ->
                    manager.errCtor ThreadDoesNotExist

        Err err ->
            err
                |> IdDecoderFailed
                |> manager.errCtor