var MessageBox = {
  Ok:             0x0001,
  Cancel:         0x0002,
  Yes:            0x0004,
  No:             0x0008,
  DontShowAgain:  0x8000,
  new: func
  {
    return {
      parents: [MessageBox],
      _title: "Message",
      _standard_buttons: MessageBox.Ok,
      _remember_selection: 0
    };
  },
  setTitle: func(title)
  {
    me._title = title;
  },
  setImage: func(img)
  {
    if( img != nil and img.find('/') < 0 )
      me._img = style._dir_icons ~ "/" ~ img ~ ".png";
    else
      me._img = img;
    return me;
  },
  setText: func(text)
  {
    me._text = text;
    return me;
  },
  setStandardButtons: func(mask)
  {
    me._standard_buttons = mask;
    return me;
  },
  exec: func(cb = nil)
  {
    if( me._standard_buttons & me.DontShowAgain )
      if( (var sel = me._loadSelection()) != nil )
      {
        if( cb != nil )
          cb(sel);
        return me;
      }

    var MARGIN = 12; # TODO implement margin in C++ layouting code
    var dlg = canvas.Window.new([300,120], "dialog")
                           .setTitle(me._title);
    var root = dlg.getCanvas(1)
                  .set("background", style.getColor("bg_color"))
                  .createGroup();
    var vbox = VBoxLayout.new();
    dlg.setLayout(vbox);
    vbox.addSpacing(MARGIN);

    var text_box = HBoxLayout.new();
    vbox.addItem(text_box);
    text_box.setSpacing(MARGIN);

    text_box.addSpacing(MARGIN);

    if( me._img != nil )
    {
      text_box.addItem(
        gui.widgets.Label.new(root, style, {})
                         .setFixedSize(48, 48)
                         .setImage(me._img)
      );
    }

    var label_text = gui.widgets.Label.new(root, style, {wordWrap: 1})
                                      .setText(me._text);
    text_box.addItem(label_text, 1);
    text_box.addSpacing(MARGIN);

    vbox.addStretch(1);

    var button_box = HBoxLayout.new();
    vbox.addItem(button_box);

    if( me._standard_buttons & me.DontShowAgain )
    {
      button_box.addSpacing(MARGIN);
      button_box.addItem(
        gui.widgets.CheckBox.new(root, style, {})
                            .setText("Don't show again.")
                            .listen("toggled", func(e) {
                              me._remember_selection = e.detail.checked
                            })
      );
    }

    button_box.addStretch(1);
    foreach(var button; [me.Ok, me.Cancel, me.Yes, me.No])
    {
      if( !(me._standard_buttons & button) )
        continue;

      (func{
        var b_id = button;
        button_box.addItem(
          gui.widgets.Button.new(root, style, {})
                            .setText(me._button_names[button])
                            .listen("clicked", func {
                              dlg.del();
                              if( me._remember_selection and b_id != me.Cancel)
                                me._saveSelection(b_id);
                              if( cb != nil )
                                cb(b_id);
                            })
        );
      })();
    }
    button_box.addSpacing(MARGIN);

    vbox.addSpacing(MARGIN);

    var w = math.max(300, vbox.sizeHint()[0]);
    dlg.setSize(w, math.max(130, vbox.heightForWidth(w)));

    return me;
  },
  show: func(title, text, icon = nil, cb = nil, buttons = nil)
  {
    var msg_box = MessageBox.new();
    msg_box.setTitle(title);
    msg_box.setText(text);

    if( buttons == nil or buttons == MessageBox.DontShowAgain )
      buttons = (buttons or 0) | MessageBox.Ok;
    msg_box.setStandardButtons(buttons);

    if( icon != nil )
      msg_box.setImage(icon);

    return msg_box.exec(cb);
  },
  # Show an error/critical message in a message box
  #
  # @param title
  # @param text
  # @param cb       Dialog close callback
  # @param buttons  Mask indicating the buttons to show
  #                 (default: MessageBox.Ok)
  critical: func(title, text, cb = nil, buttons = nil)
  {
    MessageBox.show(title, text, "dialog-error", cb, buttons);
  },
  # Show a warning message in a message box
  #
  # @param title
  # @param text
  # @param cb       Dialog close callback
  # @param buttons  Mask indicating the buttons to show
  #                 (default: MessageBox.Ok)
  warning:  func(title, text, cb = nil, buttons = nil)
  {
    MessageBox.show(title, text, "dialog-warning", cb, buttons);
  },
  # Show an informative message in a message box
  #
  # @param title
  # @param text
  # @param cb       Dialog close callback
  # @param buttons  Mask indicating the buttons to show
  #                 (default: MessageBox.Ok)
  information: func(title, text, cb = nil, buttons = nil)
  {
    MessageBox.show(title, text, "dialog-info", cb, buttons);
  },
  # Show a question in a message box
  #
  # @param title
  # @param text
  # @param cb       Dialog close callback
  # @param buttons  Mask indicating the buttons to show
  #                 (default: MessageBox.Yes | MessageBox.No)
  question: func(title, text, cb = nil, buttons = nil)
  {
    if( buttons == nil or buttons == MessageBox.DontShowAgain )
      buttons = (buttons or 0) | MessageBox.Yes | MessageBox.No;

    MessageBox.show(title, text, "dialog-question", cb, buttons);
  },
# private:
  _button_names: {},
  _loadSelection: func
  {
    var dlg_id = md5(me._title ~ me._text ~ me._standard_buttons);
    me._save_path = getprop("/sim/fg-home") ~ "/cache/MessageBox-" ~ dlg_id;

    if( io.stat(me._save_path) != nil )
    {
      printlog("info", "Load dialog selection from '" ~ me._save_path ~ "'");
      return int(io.readfile(me._save_path));
    }

    return nil;
  },
  _saveSelection: func(sel)
  {
    printlog("info", "Saving dialog selection to '" ~ me._save_path ~ "'");

    var fh = io.open(me._save_path, "w");
    io.write(fh, '' ~ sel);
    io.close(fh);
  }
};

# Standard button names
MessageBox._button_names[ MessageBox.Ok     ] = "Ok";
MessageBox._button_names[ MessageBox.Cancel ] = "Cancel";
MessageBox._button_names[ MessageBox.Yes    ] = "Yes";
MessageBox._button_names[ MessageBox.No     ] = "No";