DevShell.elm

main : Program Decode.Value Model_ Msg
main =
    Browser.application
        { init = init_
        , update = update_
        , view = view_
        , subscriptions = subscriptions
        , onUrlRequest = UrlRequested
        , onUrlChange = UrlChanged
        }


type alias Model_ =
    Result Error Model


type Error
    = InitializationError Decode.Error


type alias Model =
    { flags : Flags
    , url : Url
    , navKey : Browser.Navigation.Key
    }


type Msg
    = NoOp


init_ : Decode.Value -> Url -> Browser.Navigation.Key -> ( Model_, Cmd Msg )
init_ flagsJson url key =
    case Decode.decodeValue Flags.decoder flagsJson of
        Ok flags ->
            init flags url key
                |> Tuple.mapFirst Ok

        Err err ->
            ( Err <| InitializationError err
            , Cmd.none
            )


init : Flags -> Url -> Browser.Navigation.Key -> ( Model, Cmd Msg )
init flags url navKey =
    ( { flags = flags
      , url = url
      , navKey = navKey
      }
    , Cmd.none
    )


subscriptions : Model_ -> Sub Msg
subscriptions model_ =
    case model_ of
        Err (InitializationError _) ->
            Sub.none

        Ok model ->
            Sub.none


update_ : Msg -> Model_ -> ( Model_, Cmd Msg )
update_ msg model_ =
    case model_ of
        Err (InitializationError _) ->
            ( model_, Cmd.none )

        Ok model ->
            update msg model
                |> Tuple.mapFirst Ok


update : Msg -> Model -> ( Model, Cmd Msg )
update msg model =
    case msg of
        NoOp ->
            ( model, Cmd.none )


view_ : Model_ -> Browser.Document Msg
view_ model_ =
    { title = "DevShell"
    , body =
        case model_ of
            Err (InitializationError err) ->
                [ Html.text <| "DevShell initialization error: " ++ Decode.errorToString err ]

            Ok model ->
                view model
    }


view : Model -> List (Html Msg)
view model =
    -- happy path, works on Model