/**
   * Resolves a reference to a local element identified by address and identifier, where {@code
   * linkBase} identifies a document, including the current document, and {@code linkRef} is the id
   * of the desired element.
   *
   * <p>If {@code linkBase} refers to a local COLLADA file and {@code linkRef} is non-null, the
   * return value is the element identified by {@code linkRef}. If {@code linkRef} is null, the
   * return value is a parsed {@link ColladaRoot} for the COLLADA file identified by {@code
   * linkBase}. Otherwise, {@code linkBase} is returned.
   *
   * @param linkBase the address of the document containing the requested element.
   * @param linkRef the element's identifier.
   * @return the requested element, or null if the element is not found.
   * @throws IllegalArgumentException if the address is null.
   */
  protected Object resolveLocalReference(String linkBase, String linkRef) {
    if (linkBase == null) {
      String message = Logging.getMessage("nullValue.DocumentSourceIsNull");
      Logging.logger().severe(message);
      throw new IllegalArgumentException(message);
    }

    try {
      File file = new File(linkBase);

      if (!file.exists()) return null;

      // Determine whether the file is a COLLADA document. If not, just return the file path.
      if (!WWIO.isContentType(file, ColladaConstants.COLLADA_MIME_TYPE))
        return file.toURI().toString();

      // Attempt to open and parse the COLLADA file.
      ColladaRoot refRoot = ColladaRoot.createAndParse(file);
      // An exception is thrown if parsing fails, so no need to check for null.

      // Add the parsed file to the session cache so it doesn't have to be parsed again.
      WorldWind.getSessionCache().put(linkBase, refRoot);

      // Now check the newly opened COLLADA file for the referenced item, if a reference was
      // specified.
      if (linkRef != null) return refRoot.getItemByID(linkRef);
      else return refRoot;
    } catch (Exception e) {
      String message =
          Logging.getMessage("generic.UnableToResolveReference", linkBase + "/" + linkRef);
      Logging.logger().warning(message);
      return null;
    }
  }
  /**
   * Resolves a reference to a remote element identified by address and identifier, where {@code
   * linkBase} identifies a remote document, and {@code linkRef} is the id of the desired element.
   * This method retrieves resources asynchronously using the {@link
   * gov.nasa.worldwind.cache.FileStore}.
   *
   * <p>The return value is null if the file is not yet available in the FileStore. If {@code
   * linkBase} refers to a COLLADA file and {@code linkRef} is non-null, the return value is the
   * element identified by {@code linkRef}. If {@code linkBase} refers to a COLLADA file and {@code
   * linkRef} is null, the return value is a parsed {@link ColladaRoot} for the COLLADA file
   * identified by {@code linkBase}. Otherwise the return value is a {@link URL} to the file in the
   * file cache.
   *
   * @param linkBase the address of the document containing the requested element.
   * @param linkRef the element's identifier.
   * @return URL to the requested file, parsed ColladaRoot, or COLLADA element. Returns null if the
   *     document is not yet available in the FileStore.
   * @throws IllegalArgumentException if the {@code linkBase} is null.
   */
  public Object resolveRemoteReference(String linkBase, String linkRef) {
    if (linkBase == null) {
      String message = Logging.getMessage("nullValue.DocumentSourceIsNull");
      Logging.logger().severe(message);
      throw new IllegalArgumentException(message);
    }

    try {
      // See if it's in the cache. If not, requestFile will start another thread to retrieve it and
      // return null.
      URL url = WorldWind.getDataFileStore().requestFile(linkBase);
      if (url == null) return null;

      // It's in the cache. If it's a COLLADA file try to parse it so we can search for the
      // specified reference.
      // If it's not COLLADA, just return the url for the cached file.
      String contentType = WorldWind.getDataFileStore().getContentType(linkBase);
      if (contentType == null) {
        String suffix = WWIO.getSuffix(linkBase.split(";")[0]); // strip of trailing garbage
        if (!WWUtil.isEmpty(suffix)) contentType = WWIO.makeMimeTypeForSuffix(suffix);
      }

      if (!this.canParseContentType(contentType)) return url;

      // If the file is a COLLADA document, attempt to open it. We can't open it as a File with
      // createAndParse
      // because the ColladaRoot that will be created needs to have the remote address in order to
      // resolve any
      // relative references within it.
      ColladaRoot refRoot = this.parseCachedColladaFile(url, linkBase);

      // Add the parsed file to the session cache so it doesn't have to be parsed again.
      WorldWind.getSessionCache().put(linkBase, refRoot);

      // Now check the newly opened COLLADA file for the referenced item, if a reference was
      // specified.
      if (linkRef != null) return refRoot.getItemByID(linkRef);
      else return refRoot;
    } catch (Exception e) {
      String message =
          Logging.getMessage("generic.UnableToResolveReference", linkBase + "/" + linkRef);
      Logging.logger().warning(message);
      return null;
    }
  }