/**
   * Returns the cached recent messages history.
   *
   * @return
   * @throws IOException
   */
  private History getHistory() throws IOException {
    synchronized (historyID) {
      HistoryService historyService =
          MessageHistoryActivator.getMessageHistoryService().getHistoryService();

      if (history == null) {
        history = historyService.createHistory(historyID, recordStructure);

        // lets check the version if not our version, re-create
        // history (delete it)
        HistoryReader reader = history.getReader();
        boolean delete = false;
        QueryResultSet<HistoryRecord> res = reader.findLast(1);
        if (res != null && res.hasNext()) {
          HistoryRecord hr = res.next();
          if (hr.getPropertyValues().length >= 4) {
            if (!hr.getPropertyValues()[3].equals(RECENT_MSGS_VER)) delete = true;
          } else delete = true;
        }

        if (delete) {
          // delete it
          try {
            historyService.purgeLocallyStoredHistory(historyID);

            history = historyService.createHistory(historyID, recordStructure);
          } catch (IOException ex) {
            logger.error("Cannot delete recent_messages history", ex);
          }
        }
      }

      return history;
    }
  }
  /**
   * Searches for contact ids in history of recent messages.
   *
   * @param provider
   * @param after
   * @return
   */
  List<String> getRecentContactIDs(String provider, Date after) {
    List<String> res = new ArrayList<String>();

    try {
      History history = getHistory();

      if (history != null) {
        Iterator<HistoryRecord> recs = history.getReader().findLast(NUMBER_OF_MSGS_IN_HISTORY);
        SimpleDateFormat sdf = new SimpleDateFormat(HistoryService.DATE_FORMAT);

        while (recs.hasNext()) {
          HistoryRecord hr = recs.next();

          String contact = null;
          String recordProvider = null;
          Date timestamp = null;

          for (int i = 0; i < hr.getPropertyNames().length; i++) {
            String propName = hr.getPropertyNames()[i];

            if (propName.equals(STRUCTURE_NAMES[0])) recordProvider = hr.getPropertyValues()[i];
            else if (propName.equals(STRUCTURE_NAMES[1])) contact = hr.getPropertyValues()[i];
            else if (propName.equals(STRUCTURE_NAMES[2])) {
              try {
                timestamp = sdf.parse(hr.getPropertyValues()[i]);
              } catch (ParseException e) {
                timestamp = new Date(Long.parseLong(hr.getPropertyValues()[i]));
              }
            }
          }

          if (recordProvider == null || contact == null) continue;

          if (after != null && timestamp != null && timestamp.before(after)) continue;

          if (recordProvider.equals(provider)) res.add(contact);
        }
      }
    } catch (IOException ex) {
      logger.error("cannot create recent_messages history", ex);
    }

    return res;
  }