/*
 *  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 "modules/remote_bitrate_estimator/test/estimators/congestion_window.h"

#include <algorithm>

#include "modules/remote_bitrate_estimator/test/estimators/bbr.h"

namespace webrtc {
namespace testing {
namespace bwe {
namespace {
// kStartingCongestionWindowBytes is used to set congestion window when
// bandwidth delay product is equal to zero, so that we don't set window to zero
// as well. Chosen randomly by me, because this value shouldn't make any
// significant difference, as bandwidth delay product is more than zero almost
// every time.
const int kStartingCongestionWindowBytes = 6000;
}  // namespace

CongestionWindow::CongestionWindow() : data_inflight_bytes_(0) {}

CongestionWindow::~CongestionWindow() {}

int CongestionWindow::GetCongestionWindow(BbrBweSender::Mode mode,
                                          int64_t bandwidth_estimate_bps,
                                          absl::optional<int64_t> min_rtt_ms,
                                          float gain) {
  return GetTargetCongestionWindow(bandwidth_estimate_bps, min_rtt_ms, gain);
}

void CongestionWindow::PacketSent(size_t sent_packet_size_bytes) {
  data_inflight_bytes_ += sent_packet_size_bytes;
}

void CongestionWindow::AckReceived(size_t received_packet_size_bytes) {
  RTC_DCHECK_GE(data_inflight_bytes_ >= received_packet_size_bytes, true);
  data_inflight_bytes_ -= received_packet_size_bytes;
}

int CongestionWindow::GetTargetCongestionWindow(
    int64_t bandwidth_estimate_bps,
    absl::optional<int64_t> min_rtt_ms,
    float gain) {
  // If we have no rtt sample yet, return the starting congestion window size.
  if (!min_rtt_ms)
    return gain * kStartingCongestionWindowBytes;
  int bdp = *min_rtt_ms * bandwidth_estimate_bps / 8000;
  int congestion_window = bdp * gain;
  // Congestion window could be zero in rare cases, when either no bandwidth
  // estimate is available, or path's min_rtt value is zero.
  if (!congestion_window)
    congestion_window = gain * kStartingCongestionWindowBytes;
  return congestion_window;
}
}  // namespace bwe
}  // namespace testing
}  // namespace webrtc