function Messaging(screen) {
  var ws = new WebSocket('ws://' + window.location.hostname + '/play/');
  var keepAlivePeriod = 20000;
  var routes = {callbacks: [], children: {}};

  return {
    addEventListener: addEventListener,
    send: send,
    start: start
  }

  function get(obj, path, write) {
    write = write || false;
    if(path.length < 1) {
      return obj;
    } else {
      if(obj.children[path[0]] == undefined && write) {
        obj.children[path[0]] = {callbacks: [], children: {}};
      }
      if(obj.children[path[0]] != undefined) {
        return get(obj.children[path[0]], path.slice(1), write);
      } else {
        return null;
      }
    }
  }

  function addEventListener(path, callback) {
    var route = get(routes, path, true);
    route.callbacks.push(callback);
  }

  function messageListener(event) {
    var o = JSON.parse(event.data);
    var path = [];
    var tmp = o;
    while(tmp != undefined && tmp.tag != undefined) {
      path.push(tmp.tag);
      tmp = tmp.message;
    }
    var route = get(routes, path);
    if(route != undefined && route.callbacks != undefined) {
      route.callbacks.forEach(function(f) {f(o);});
    } else {
      debug.textContent = event.data;
    }
  };

  function start() {
    ping();
    addEventListener(["Pong"], ping);
    ws.addEventListener('message', messageListener);
  }

  function send(o) {
    ws.send(JSON.stringify(o));
  }

  function ping() {
    setTimeout(function() {send({tag: "Ping"});}, keepAlivePeriod);
  }
}