// EWMA = ExponentiallyWeightedMovingAverage from
// https://github.com/felixge/node-measured/blob/master/lib/util/ExponentiallyMovingWeightedAverage.js
// used to compute the nbr of time per minute that a variance is hit by a new trace
function EWMA() {
  this._timePeriod = 60000;
  this._tickInterval = 5000;
  this._alpha = 1 - Math.exp(-this._tickInterval / this._timePeriod);
  this._count = 0;
  this._rate = 0;

  var self = this;
  this._interval = setInterval(function () {
    self.tick();
  }, this._tickInterval);
  this._interval.unref();
};

EWMA.prototype.update = function (n) {
  this._count += n || 1;
};

EWMA.prototype.tick = function () {
  var instantRate = this._count / this._tickInterval;
  this._count = 0;

  this._rate += (this._alpha * (instantRate - this._rate));
};

EWMA.prototype.rate = function (timeUnit) {
  return (this._rate || 0) * timeUnit;
};

module.exports = {
  EWMA : EWMA
};