signature FILE_THREAD =
sig
  val run: FileMessage.t Mailbox.mbox * InputMessage.t Mailbox.mbox -> unit
end

structure FileThread :> FILE_THREAD =
struct
  open FileMessage
  open InputMessage

  fun loadIO (io, str) =
    case TextIO.inputLine io of
      SOME line => loadIO (io, str ^ line)
    | NONE => str

  fun loadSquares (path, inputMailbox) =
    let
      val io = TextIO.openIn path
      val str = loadIO (io, "")
      val () = TextIO.closeIn io
    in
      case Parser.parse str of
        SOME (canvasWidth, canvasHeight, tree) =>
          Mailbox.send
            ( inputMailbox
            , USE_LAYERS
                { tree = tree
                , canvasWidth = canvasWidth
                , canvasHeight = canvasHeight
                }
            )
      | NONE => ()
    end

  fun saveString (filename, toSaveString) =
    let
      val io = TextIO.openOut filename
      val () = TextIO.output (io, toSaveString)
    in
      TextIO.closeOut io
    end

  fun run (fileMailbox, inputMailbox) =
    let
      val _ =
        case Mailbox.recv fileMailbox of
          SAVE_SQUARES {filepath, output} => saveString (filepath, output)
        | EXPORT_SQUARES {filepath, output} => saveString (filepath, output)
        | EXPORT_COLLISIONS {filepath, output} => saveString (filepath, output)
        | LOAD_SQUARES {filepath} => loadSquares (filepath, inputMailbox)
    in
      run (fileMailbox, inputMailbox)
    end
end