BigLoadingState.elm

module BigLoadingState exposing (update)


type Model
    = Loading LoadingModel
    | Loaded LoadedModel


type alias LoadingModel =
    { name : Maybe String
    , age : Maybe Int
    }

type alias LoadedModel =
    { name : String
    , age : Int
    }


type Msg
    = ReceivedAge (Result Error Int)
    | ReceivedName (Result Error String)


update : Msg -> Model -> Model
update msg model =
    case model of
        Loading loadingModel ->
            let
                newLoadingModel =
                    updateLoading msg loadingModel 
            in
            case checkIfLoaded newLoadingModel of
                Just loadedModel ->
                    Loaded loadedModel
            
                Nothing ->
                    Loading newLoadingModel

        Loaded loadedModel ->
            Loaded loadedModel


updateLoading : Msg -> LoadingModel -> (LoadingModel, Cmd Msg)
updateLoading msg loadingModel =
    case msg of
        ReceivedAge (Ok age) ->
            { loadingModel | age = Just age }

        ReceivedName (Ok name) ->
            { loadingModel | name = Just name }


checkIfLoaded : LoadingModel -> Maybe LoadedModel
checkIfLoaded loadingModel =
    Just LoadedModel
        |> andMap loadingModel.age
        |> andMap loadingModel.name


andMap : Maybe a -> Maybe (a -> b) -> Maybe b
andMap maybeA maybeF =
    case (maybeA, maybeF) of
        (Just a, Just f) ->
            Just (f a)

        _ ->
            Nothing