readAsText.elm

-- new library function for using a FileReader contains this function:
readAsText : FileRef -> Task Error String

-- new helper to render HTML input with type set to "file" and a built-in decoder for a getting a List of FileRefs out.
-- I think this will be less prone to abuse than exposing the decoder and letting the user create the input herself
fileInput : (List FileRef -> msg) ->  List (Attribute msg) -> List (Html msg) -> Html msg


type Model 
  = Empty
  | Loaded String
  | Failed String
  

type Msg 
  = FilesSelected (List FileRef)
  | ReadSucceeded String
  | ReadFailed String

view : Model -> Html Msg
view model =
  div [] 
    [ fileInput FilesSelected [] []
    , (resultView model)
    ]


resultView : Model -> Html Msg
resultView model =
  case model of 
    Empty ->
      text "Please select a file"
    Loaded content ->
      text content
    Failed message ->
      text message


update : Msg -> Model -> (Model, Cmd Msg)
update msg model =
  case msg of
    FileSelected files ->
      case files of 
        [] ->
          ( model, Cmd.none )
        first :: rest ->
          ( model
          , readChosenFile first
          )
    ReadSucceeded content ->
      ( Loaded content
      , Cmd.none
      )
    ReadFailed message ->
      (Failed message 
      , Cmd.none
      )


readChosenFile : FileRef -> Cmd Msg
readChosenFile fileRef =
  Task.perform ReadFailed ReadSucceeded (FileReader.readAsText fileRef)