sclass JForwardingLibDownloader is Swingable {
  transient SingleComponentPanel scp;
  
  settable S libraryName;
  
  // snippet ID of library required for this platform
  settable LS libIDs;

  settable S sizeInformation; // how big is the library?
  
  event addingLibraries(Cl<S> libIDs);
  
  bool supported() { ret nempty(libIDs()); }
  
  selfType forward(IF0<JComponent> forward) {
    this.forward = forward;
    this;
  }
  
  swappable JComponent forward() {
    ret vstackWithSpacing(flattenToList(
      jcenteredlabel(libraryName() + " enabled"),
      map(file -> jcenteredline(jFilePathLabel(file).visualize()),
        libFiles()),
      jbutton("Delete " + libraryName(), rThread {
        if (!swingConfirm("Really?")) ret;
        deleteFilesVerbose(libFiles());
        scp.setComponent(makeComponent());
      })));
  }
  
  L<File> libFiles() {
    ret map DiskSnippetCache_getLibrary(libIDs());
  }
  
  bool libDownloaded() {
    ret filesExist(libFiles());
  }
  
  bool hasLib() {
    bool has = currentProgramHasLibraries(libFiles());
    ret has;
  }
  
  void addLib() {
    if (supported()) {
      addingLibraries(libIDs());
      if (addLibraries(libIDs()))
        print(libraryName() + " loaded: " + libIDs());
    }
  }
  
  cachedVisualize {
    if (scp == null)
      scp = singleComponentPanel(makeComponent());
    ret scp;
  }
  
  JComponent makeComponent() {
    if (!supported())
      ret jcenteredlabel(libraryName() + " is not yet supported on your platform");
      
    if (libDownloaded()) {
      addLib();
      ret forward();
    } else
      ret jfullcenter(centerAndEastWithMargin(
        jcenteredlabel("Download " + libraryName() + " for " + platformName() + appendBracketed(sizeInformation()) + "?"),
        jbuttonWithDisable("OK", r addLibWithProgressBar)));
  }
  
  void addLibWithProgressBar {
    scp.setComponent(jcenteredlabel("Downloading " + libraryName() + "..."));
    try {
      addLib();
      scp.setComponent(forward());
    } catch print e {
      scp.setComponent(jErrorView(e));
    }
  }
  
  selfType libID(S libID) { ret libIDs(llNonNulls(libID)); }
  selfType libIDs(S... libIDs) { ret libIDs(asList(libIDs)); }
  
  void loadLibsIfDownloaded() {
    if (supported() && libDownloaded())
      addLib();
  }
}

Began life as a copy of #1034410