/*
 *  Copyright (c) 2018 The WebRTC project authors. All Rights Reserved.
 *
 *  Use of this source code is governed by a BSD-style license
 *  that can be found in the LICENSE file in the root of the source
 *  tree. An additional intellectual property rights grant can be found
 *  in the file PATENTS.  All contributing project authors may
 *  be found in the AUTHORS file in the root of the source tree.
 */

#include <limits>

#include "rtc_base/checks.h"
#include "rtc_base/numerics/safe_conversions.h"
#include "rtc_base/numerics/sample_counter.h"

namespace rtc {

SampleCounter::SampleCounter() = default;
SampleCounter::~SampleCounter() = default;

void SampleCounter::Add(int sample) {
  if (sum_ > 0) {
    RTC_DCHECK_LE(sample, std::numeric_limits<int64_t>::max() - sum_);
  } else {
    RTC_DCHECK_GE(sample, std::numeric_limits<int64_t>::min() - sum_);
  }
  sum_ += sample;
  // Prevent overflow in squaring.
  RTC_DCHECK_GT(sample, std::numeric_limits<int32_t>::min());
  RTC_DCHECK_LE(int64_t{sample} * sample,
                std::numeric_limits<int64_t>::max() - sum_squared_);
  sum_squared_ += int64_t{sample} * sample;
  ++num_samples_;
  if (!max_ || sample > *max_) {
    max_ = sample;
  }
}

void SampleCounter::Add(const SampleCounter& other) {
  if (sum_ > 0) {
    RTC_DCHECK_LE(other.sum_, std::numeric_limits<int64_t>::max() - sum_);
  } else {
    RTC_DCHECK_GE(other.sum_, std::numeric_limits<int64_t>::min() - sum_);
  }
  sum_ += other.sum_;
  RTC_DCHECK_LE(other.sum_squared_,
                std::numeric_limits<int64_t>::max() - sum_squared_);
  sum_squared_ += other.sum_squared_;
  RTC_DCHECK_LE(other.num_samples_,
                std::numeric_limits<int64_t>::max() - num_samples_);
  num_samples_ += other.num_samples_;
  if (other.max_ && (!max_ || *max_ < *other.max_))
    max_ = other.max_;
}

absl::optional<int> SampleCounter::Avg(int64_t min_required_samples) const {
  RTC_DCHECK_GT(min_required_samples, 0);
  if (num_samples_ < min_required_samples)
    return absl::nullopt;
  return rtc::dchecked_cast<int>(sum_ / num_samples_);
}

absl::optional<int64_t> SampleCounter::Variance(
    int64_t min_required_samples) const {
  RTC_DCHECK_GT(min_required_samples, 0);
  if (num_samples_ < min_required_samples)
    return absl::nullopt;
  // E[(x-mean)^2] = E[x^2] - mean^2
  int64_t mean = sum_ / num_samples_;
  return sum_squared_ / num_samples_ - mean * mean;
}

absl::optional<int> SampleCounter::Max() const {
  return max_;
}

void SampleCounter::Reset() {
  *this = {};
}

}  // namespace rtc