/**
   * Removes from the specified list of candidates providers connected to a registrar that does not
   * match the IP address that we are receiving a request from.
   *
   * @param candidates the list of providers we've like to filter.
   * @param request the request that we are currently dispatching
   */
  private void filterByAddress(List<ProtocolProviderServiceSipImpl> candidates, Request request) {
    Iterator<ProtocolProviderServiceSipImpl> iterPP = candidates.iterator();
    while (iterPP.hasNext()) {
      ProtocolProviderServiceSipImpl candidate = iterPP.next();

      if (candidate.getRegistrarConnection() == null) {
        // RegistrarLess connections are ok
        continue;
      }

      if (!candidate.getRegistrarConnection().isRegistrarless()
          && !candidate.getRegistrarConnection().isRequestFromSameConnection(request)) {
        iterPP.remove();
      }
    }
  }
  /**
   * Find the <tt>ProtocolProviderServiceSipImpl</tt> (one of our "candidate recipient" listeners)
   * which this <tt>request</tt> should be dispatched to. The strategy is to look first at the
   * request URI, and then at the To field to find a matching candidate for dispatching. Note that
   * this method takes a <tt>Request</tt> as param, and not a <tt>ServerTransaction</tt>, because
   * sometimes <tt>RequestEvent</tt>s have no associated <tt>ServerTransaction</tt>.
   *
   * @param request the <tt>Request</tt> to find a recipient for.
   * @return a suitable <tt>ProtocolProviderServiceSipImpl</tt>.
   */
  private ProtocolProviderServiceSipImpl findTargetFor(Request request) {
    if (request == null) {
      logger.error("request shouldn't be null.");
      return null;
    }

    List<ProtocolProviderServiceSipImpl> currentListenersCopy =
        new ArrayList<ProtocolProviderServiceSipImpl>(this.getSipListeners());

    // Let's first narrow down candidate choice by comparing
    // addresses and ports (no point in delivering to a provider with a
    // non matching IP address  since they will reject it anyway).
    filterByAddress(currentListenersCopy, request);

    if (currentListenersCopy.size() == 0) {
      logger.error("no listeners");
      return null;
    }

    URI requestURI = request.getRequestURI();

    if (requestURI.isSipURI()) {
      String requestUser = ((SipURI) requestURI).getUser();

      List<ProtocolProviderServiceSipImpl> candidates =
          new ArrayList<ProtocolProviderServiceSipImpl>();

      // check if the Request-URI username is
      // one of ours usernames
      for (ProtocolProviderServiceSipImpl listener : currentListenersCopy) {
        String ourUserID = listener.getAccountID().getUserID();
        // logger.trace(ourUserID + " *** " + requestUser);
        if (ourUserID.equals(requestUser)) {
          if (logger.isTraceEnabled())
            logger.trace("suitable candidate found: " + listener.getAccountID());
          candidates.add(listener);
        }
      }

      // the perfect match
      // every other case is approximation
      if (candidates.size() == 1) {
        ProtocolProviderServiceSipImpl perfectMatch = candidates.get(0);

        if (logger.isTraceEnabled())
          logger.trace("Will dispatch to \"" + perfectMatch.getAccountID() + "\"");
        return perfectMatch;
      }

      // more than one account match
      if (candidates.size() > 1) {
        // check if a custom param exists in the contact
        // address (set for registrar accounts)
        for (ProtocolProviderServiceSipImpl candidate : candidates) {
          String hostValue =
              ((SipURI) requestURI).getParameter(SipStackSharing.CONTACT_ADDRESS_CUSTOM_PARAM_NAME);
          if (hostValue == null) continue;
          if (hostValue.equals(candidate.getContactAddressCustomParamValue())) {
            if (logger.isTraceEnabled())
              logger.trace(
                  "Will dispatch to \""
                      + candidate.getAccountID()
                      + "\" because "
                      + "\" the custom param was set");
            return candidate;
          }
        }

        // Past this point, our guess is not reliable. We try to find
        // the "least worst" match based on parameters like the To field

        // check if the To header field host part
        // matches any of our SIP hosts
        for (ProtocolProviderServiceSipImpl candidate : candidates) {
          URI fromURI = ((FromHeader) request.getHeader(FromHeader.NAME)).getAddress().getURI();
          if (fromURI.isSipURI() == false) continue;
          SipURI ourURI = (SipURI) candidate.getOurSipAddress((SipURI) fromURI).getURI();
          String ourHost = ourURI.getHost();

          URI toURI = ((ToHeader) request.getHeader(ToHeader.NAME)).getAddress().getURI();
          if (toURI.isSipURI() == false) continue;
          String toHost = ((SipURI) toURI).getHost();

          // logger.trace(toHost + "***" + ourHost);
          if (toHost.equals(ourHost)) {
            if (logger.isTraceEnabled())
              logger.trace(
                  "Will dispatch to \""
                      + candidate.getAccountID()
                      + "\" because "
                      + "host in the To: is the same as in our AOR");
            return candidate;
          }
        }

        // fallback on the first candidate
        ProtocolProviderServiceSipImpl target = candidates.iterator().next();
        logger.info(
            "Will randomly dispatch to \""
                + target.getAccountID()
                + "\" because there is ambiguity on the username from"
                + " the Request-URI");
        if (logger.isTraceEnabled()) logger.trace("\n" + request);
        return target;
      }

      // fallback on any account
      ProtocolProviderServiceSipImpl target = currentListenersCopy.iterator().next();
      if (logger.isDebugEnabled())
        logger.debug(
            "Will randomly dispatch to \""
                + target.getAccountID()
                + "\" because the username in the Request-URI "
                + "is unknown or empty");
      if (logger.isTraceEnabled()) logger.trace("\n" + request);
      return target;
    } else {
      logger.error("Request-URI is not a SIP URI, dropping");
    }
    return null;
  }