sclass CollapsibleLeftPanel is Swingable {
  S sidePanelName;
  JComponent sideComponent;
  JSplitPane splitPane;
  bool collapsed;
  SingleComponentPanel scp = singleComponentPanel();
  
  *(S *sidePanelName, JComponent *sideComponent, JComponent mainComponent,
    bool *collapsed) {
    splitPane = jhsplit(0.25, wrappedSideComponent(), null);
    updateScp();
  }
  
  void setCollapsed(bool collapsed) swing {
    if (this.collapsed != collapsed) {
      this.collapsed = collapsed;
      updateScp();
    }
  }
  
  void expand { setCollapsed(true); }
  void collapse { setCollapsed(false); }
  
  void updateScp {
    if (collapsed)
      scp.set(westAndCenterWithMargin(
        vstack(expandButton()), mainComponent));
    else {
      splitPane.setRightComponent(mainComponent);
      scp.set(splitPane);
    }
  }
  
  JButton expandButton() {
    ret jimageButton(#1103075, "Expand " + sidePanelName, r expand);
  }
  
  JButton collapseButton() {
    ret jimageButton(#1103076, "Collapse " + sidePanelName, r collapse);
  }
  
  JComponent wrappedSideComponent() {
    //ret jSection(sidePanelName, sideComponent);
    ret northAndCenterWithMargin(
      westAndCenterWithMargin(collapseButton, jlabel(sidePanelName))
    );
  }
  
  visual scp;
}