Engine.debugName("sip_qual_routing");
Message.trackName("sip_qual_routing");

// list of servers used to route a call, all considered to be down initially
sip_servers = {
    "192.168.168.139" : false,
    "192.168.168.241" : false,
    "192.168.168.1" : false,
};

avail_srv = []; // list of servers that are available
idx = 0;

function onXsipQualify(msg)
{
    if(sip_servers[msg.server] == undefined)
	return;
    sip_servers[msg.server] = msg.available;
    // rebuild the list of available servers
    avail_srv = [];
    for (var s in sip_servers) {
	if (sip_servers[s])
	    avail_srv.push(s);
    }
    Engine.debug(Engine.DebugInfo,"Available SIP servers:",avail_srv.join());
    return false; // let others to handle the message too
}

function onRoute(msg)
{
    if (msg.called.startsWith("123")) {
	if (!avail_srv.length) // no available servers
	    return false;
	msg.retValue("sip/sip:" + msg.called + "@" + avail_srv[idx++ % avail_srv.length]);
	return true;
    }
    return false;
}

Message.install(onXsipQualify,"xsip.qualify",50);
Message.install(onRoute,"call.route",50);