Todo.elm

update : Msg -> Model -> ( Model, Cmd Msg )
update msg model =
  case msg of
    NoOp ->
      model ! []

    Add ->
      { model
        | uid = model.uid + 1
        , field = ""
        , tasks =
            if String.isEmpty model.field then
              model.tasks
            else
              model.tasks ++ [newTask model.field model.uid]
      }
        ! []

    UpdateField str ->
      { model | field = str }
        ! []

    EditingTask id isEditing ->
      let
        updateTask t =
          if t.id == id then { t | editing = isEditing } else t
      in
        { model | tasks = List.map updateTask model.tasks }
          ! [ focus ("#todo-" ++ toString id) ]

    UpdateTask id task ->
      let
        updateTask t =
          if t.id == id then { t | description = task } else t
      in
        { model | tasks = List.map updateTask model.tasks }
          ! []

    Delete id ->
      { model | tasks = List.filter (\t -> t.id /= id) model.tasks }
        ! []

    DeleteComplete ->
      { model | tasks = List.filter (not << .completed) model.tasks }
        ! []

    Check id isCompleted ->
      let
        updateTask t =
          if t.id == id then { t | completed = isCompleted } else t
      in
        { model | tasks = List.map updateTask model.tasks }
          ! []

    CheckAll isCompleted ->
      let
        updateTask t =
          { t | completed = isCompleted }
      in
        { model | tasks = List.map updateTask model.tasks }
          ! []

    ChangeVisibility visibility ->
      { model | visibility = visibility }
        ! []