sclass JFileDropTarget extends MetaWithChangeListeners is Swingable {
  settable S msg = "Drop file here";
  
  // currently dropped file
  settableWithVar File file;
  
  // file can also be null
  event fileSelected(File file);
  
  SingleComponentPanel scp = scp();
  
  *() {
    varFile().onChange(file -> {
      updateComponent();
      fileSelected(file);
    });
  }
  
  cachedVisualize {
    if (!scp.hasComponent())
      scp.setComponent(makeComponent());
    ret jHandleFileDrop(l1 setFile, scp);
  }
  
  void updateComponent {
    scp.setComponent(makeComponent());
  }

  JComponent makeComponent() {
    var file = file();
    ret file == null
      ? noFileComponent()
      : componentForFile(file);
  }
  
  JComponent noFileComponent() {
    ret jcenteredlabel(msg);
  }
  
  swappable JComponent componentForFile(File file) {
    ret jfullcenter(jFilePathLabel(file).visualize());
  }
}