#include "CommonTools/Statistics/interface/Accumulator.h"
#include <ostream>

Accumulator::Accumulator() : sum_(0.), sumOfSquares_(0.), weightedSum_(0.), sumOfWeights_(0.), n_(0) {}

void Accumulator::addEntry(double value, double weight) {
  sum_ += value;
  sumOfSquares_ += (value * value);
  weightedSum_ += value * weight;
  sumOfWeights_ += weight;
  ++n_;
}

double Accumulator::mean() const { return sum_ / n_; }

double Accumulator::variance() const {
  double numerator = sumOfSquares_ - sum_ * mean();
  unsigned long denominator = n_ - 1;
  return numerator / denominator;
}

double Accumulator::weightedMean() const { return weightedSum_ / sumOfWeights_; }

std::ostream& operator<<(std::ostream& os, const Accumulator& stat) {
  os << "entries: " << stat.nEntries();
  if (stat.nEntries() > 0) {
    os << "   Mean: " << stat.mean();
  }
  if (stat.nEntries() > 1) {
    os << "   Sigma: " << stat.sigma();
  }
  return os;
}