<script>
function PerfRunner(options) {
  this.unit_ = options.unit || "ms";
  this.iterationsRemaining_ = options.iterations || 10;
  this.results_ = [];
  this.setup_ = options.setup;
  this.logLines_ = [];
}

PerfRunner.prototype.log = function(line) {
  this.logLines_.push(line);
};

PerfRunner.prototype.recordResult = function(result) {
  this.results_.push(result);
};

PerfRunner.prototype.runAsync = function(test) {
  var self = this;
  window.setTimeout(function() {
    if (self.setup_) {
      var setup = self.setup_;
      setup();
    }

    var startTime = Date.now();
    test(function() {
      var endTime = Date.now();

      self.recordResult(endTime - startTime);
      if (--self.iterationsRemaining_ > 0)
        self.runAsync(test);
      else
        self.finish();
    });
  });
};

PerfRunner.prototype.computeStatistics = function() {
  var data = this.results_.slice();

  // Add values from the smallest to the largest to avoid the loss of significance
  data.sort(function(a, b) { return a - b; });

  var middle = Math.floor(data.length / 2);
  var stats = {
    min: data[0],
    max: data[data.length - 1],
    median: data.length % 2 ? data[middle] : (data[middle - 1] + data[middle]) / 2,
  };

  // Compute the mean and variance using Knuth's online algorithm (has good numerical stability).
  var squareSum = 0;
  stats.values = this.results_;
  stats.mean = 0;
  for (var i = 0; i < data.length; ++i) {
      var x = data[i];
      var delta = x - stats.mean;
      var sweep = i + 1.0;
      stats.mean += delta / sweep;
      squareSum += delta * (x - stats.mean);
  }
  stats.variance = data.length <= 1 ? 0 : squareSum / (data.length - 1);
  stats.stdev = Math.sqrt(stats.variance);
  stats.unit = this.unit_;

  return stats;
};

PerfRunner.prototype.logStatistics = function(title) {
  var stats = this.computeStatistics();
  this.log("");
  this.log(title);
  if (stats.values)
    this.log("values " + stats.values.join(", ") + " " + stats.unit);
  this.log("avg " + stats.mean + " " + stats.unit);
  this.log("median " + stats.median + " " + stats.unit);
  this.log("stdev " + stats.stdev + " " + stats.unit);
  this.log("min " + stats.min + " " + stats.unit);
  this.log("max " + stats.max + " " + stats.unit);
};

PerfRunner.prototype.finish = function () {
  this.logStatistics("Time:");
  internals.notifyTestComplete(this.logLines_.join('\n'));
}

module.exports = PerfRunner;
</script>