/*
 *  Copyright (c) 2017 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 "webrtc/modules/audio_processing/aec3/erle_estimator.h"

#include <algorithm>

#include "webrtc/rtc_base/safe_minmax.h"

namespace webrtc {

namespace {

constexpr float kMinErle = 1.f;
constexpr float kMaxLfErle = 8.f;
constexpr float kMaxHfErle = 1.5f;

}  // namespace

ErleEstimator::ErleEstimator() {
  erle_.fill(kMinErle);
  hold_counters_.fill(0);
}

ErleEstimator::~ErleEstimator() = default;

void ErleEstimator::Update(
    const std::array<float, kFftLengthBy2Plus1>& render_spectrum,
    const std::array<float, kFftLengthBy2Plus1>& capture_spectrum,
    const std::array<float, kFftLengthBy2Plus1>& subtractor_spectrum) {
  const auto& X2 = render_spectrum;
  const auto& Y2 = capture_spectrum;
  const auto& E2 = subtractor_spectrum;

  // Corresponds of WGN of power -46 dBFS.
  constexpr float kX2Min = 44015068.0f;

  // Update the estimates in a clamped minimum statistics manner.
  auto erle_update = [&](size_t start, size_t stop, float max_erle) {
    for (size_t k = start; k < stop; ++k) {
      if (X2[k] > kX2Min && E2[k] > 0.f) {
        const float new_erle = Y2[k] / E2[k];
        if (new_erle > erle_[k]) {
          hold_counters_[k - 1] = 100;
          erle_[k] += 0.1f * (new_erle - erle_[k]);
          erle_[k] = rtc::SafeClamp(erle_[k], kMinErle, max_erle);
        }
      }
    }
  };
  erle_update(1, kFftLengthBy2 / 2, kMaxLfErle);
  erle_update(kFftLengthBy2 / 2, kFftLengthBy2, kMaxHfErle);

  std::for_each(hold_counters_.begin(), hold_counters_.end(),
                [](int& a) { --a; });
  std::transform(hold_counters_.begin(), hold_counters_.end(),
                 erle_.begin() + 1, erle_.begin() + 1, [](int a, float b) {
                   return a > 0 ? b : std::max(kMinErle, 0.97f * b);
                 });

  erle_[0] = erle_[1];
  erle_[kFftLengthBy2] = erle_[kFftLengthBy2 - 1];
}

}  // namespace webrtc