docs: private static Map<Integer, LinkedList<MetadataCache>> gatherCandidateAttachmentGroups() {
          Map<Integer,LinkedList<MetadataCache>> candidateGroups = new TreeMap<Integer, LinkedList<MetadataCache>>();
          final Iterator<File> iterator = MetadataFinder.getInstance().getAutoAttachCacheFiles().iterator();
          while (iterator.hasNext()) {
              final File file = iterator.next();
              try {
                  final MetadataCache candidate = new MetadataCache(file);
                  if (candidateGroups.get(candidate.sourcePlaylist) == null) {
                      candidateGroups.put(candidate.sourcePlaylist, new LinkedList<MetadataCache>());
                  }
                  candidateGroups.get(candidate.sourcePlaylist).add(candidate);
              } catch (Exception e) {
                  logger.error("Unable to open metadata cache file " + file + ", discarding", e);
                  iterator.remove();
              }
          }
          return candidateGroups;
      }