structure MoveMode =
struct
  open AppType
  open InputMessage

  fun makeBlankYAxis length =
    Vector.tabulate (length, fn _ => {r = 0, g = 0, b = 0, a = 0})

  fun moveImageUp (model: app_type) =
    let
      val {squares, ...} = model

      val squares =
        Vector.mapi
          (fn (idx, yAxis) =>
             if idx + 1 < Vector.length squares then
               Vector.sub (squares, idx + 1)
             else
               makeBlankYAxis (Vector.length yAxis)) squares

      val model = AppWith.squares (model, squares)
    in
      (model, [])
    end

  fun update (model, inputMsg) =
    case inputMsg of
      ARROW_UP => moveImageUp model
    (*
    | ARROW_LEFT => moveImageLeft model
    | ARROW_RIGHT => moveImageRight model
    | ARROW_DOWN => moveImageDown model
    *)
    | _ => (model, [])
end