sclass CustomToolTip {
  JComponent target;
  JWindow window;
  bool debug;

  swappable JComponent makeContent() { null; }
  
  *(IF0<JComponent> *makeContent) {}
  
  // run in Swing thread
  void move {
    if (window == null) ret;
    if (debug) print("CustomToolTip move");
    var mouse = mouseLocationOnScreen();
    window.setLocation(mouse.x+10, mouse.y+10);
  }
  
  // run in Swing thread
  void showOrMove {
    if (window != null)
      ret with move();

    window = new JWindow;
    window.pack();

    thread "Make tool tip content" {
      var content = makeContent();
      if (content == null) ret;
      swing {
        setWindowContents(window, content);
        move();
        window.pack();
        showWindow(window);
      }
    }
  }
  
  void hide swing {
    disposeWindow(window);
    window = null;
  }
  
  void installOn(JComponent target) {
    this.target = target;
    
    addMouseAdapter(target, new MouseAdapter {
      @Override public void mouseEntered(MouseEvent e) { showOrMove(); }
      
      @Override public void mouseExited(MouseEvent e) { hide(); }
      
      @Override public void mouseMoved(MouseEvent e) { showOrMove(); }
      
      @Override public void mousePressed(MouseEvent e) { hide(); }
    });
  }
}