function spliceOne(list, index) {
  for (var i = index, k = i + 1, n = list.length; k < n; i += 1, k += 1)
    list[i] = list[k];
  list.pop();
}

function Manager(interval, streamInterval, kaCountMax) {
  var streams = this._streams = [];
  this._timer = undefined;
  this._timerInterval = interval;
  this._timerfn = function() {
    var now = Date.now();
    for (var i = 0, len = streams.length, s, last; i < len; ++i) {
      s = streams[i];
      last = s._kalast;
      if (last && (now - last) >= streamInterval) {
        if (++s._kacnt > kaCountMax) {
          var err = new Error('Keepalive timeout');
          err.level = 'client-timeout';
          s.emit('error', err);
          s.disconnect();
          spliceOne(streams, i);
          --i;
          len = streams.length;
        } else {
          s._kalast = now;
          // XXX: if the server ever starts sending real global requests to the
          //      client, we will need to add a dummy callback here to keep the
          //      correct reply order
          s.ping();
        }
      }
    }
  };
}

Manager.prototype.start = function() {
  if (this._timer)
    this.stop();
  this._timer = setInterval(this._timerfn, this._timerInterval);
};

Manager.prototype.stop = function() {
  if (this._timer) {
    clearInterval(this._timer);
    this._timer = undefined;
  }
};

Manager.prototype.add = function(stream) {
  var streams = this._streams,
      self = this;

  stream.once('end', function() {
    self.remove(stream);
  }).on('packet', resetKA);

  streams[streams.length] = stream;

  resetKA();

  if (!this._timer)
    this.start();

  function resetKA() {
    stream._kalast = Date.now();
    stream._kacnt = 0;
  }
};

Manager.prototype.remove = function(stream) {
  var streams = this._streams,
      index = streams.indexOf(stream);
  if (index > -1)
    spliceOne(streams, index);
  if (!streams.length)
    this.stop();
};

module.exports = Manager;
