/*
 * SRT - Secure, Reliable, Transport
 * Copyright (c) 2018 Haivision Systems Inc.
 *
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/.
 *
 */

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  and/or other materials provided with the distribution.

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/*****************************************************************************
written by
   Yunhong Gu, last updated 03/12/2011
modified by
   Haivision Systems Inc.
*****************************************************************************/

#include "platform_sys.h"
#include "buffer_tools.h"
#include "packet.h"
#include "logger_defs.h"
#include "utilities.h"

namespace srt {

using namespace std;
using namespace srt_logging;
using namespace sync;

// You can change this value at build config by using "ENFORCE" options.
#if !defined(SRT_MAVG_SAMPLING_RATE)
#define SRT_MAVG_SAMPLING_RATE 40
#endif

bool AvgBufSize::isTimeToUpdate(const time_point& now) const
{
    const int      usMAvgBasePeriod = 1000000; // 1s in microseconds
    const int      us2ms            = 1000;
    const int      msMAvgPeriod     = (usMAvgBasePeriod / SRT_MAVG_SAMPLING_RATE) / us2ms;
    const uint64_t elapsed_ms       = count_milliseconds(now - m_tsLastSamplingTime); // ms since last sampling
    return (elapsed_ms >= msMAvgPeriod);
}

void AvgBufSize::update(const steady_clock::time_point& now, int pkts, int bytes, int timespan_ms)
{
    const uint64_t elapsed_ms       = count_milliseconds(now - m_tsLastSamplingTime); // ms since last sampling
    m_tsLastSamplingTime            = now;
    const uint64_t one_second_in_ms = 1000;
    if (elapsed_ms > one_second_in_ms)
    {
        // No sampling in last 1 sec, initialize average
        m_dCountMAvg      = pkts;
        m_dBytesCountMAvg = bytes;
        m_dTimespanMAvg   = timespan_ms;
        return;
    }

    //
    // weight last average value between -1 sec and last sampling time (LST)
    // and new value between last sampling time and now
    //                                      |elapsed_ms|
    //   +----------------------------------+-------+
    //  -1                                 LST      0(now)
    //
    m_dCountMAvg      = avg_iir_w<1000, double>(m_dCountMAvg, pkts, elapsed_ms);
    m_dBytesCountMAvg = avg_iir_w<1000, double>(m_dBytesCountMAvg, bytes, elapsed_ms);
    m_dTimespanMAvg   = avg_iir_w<1000, double>(m_dTimespanMAvg, timespan_ms, elapsed_ms);
}

CRateEstimator::CRateEstimator(int /*family*/)
    : m_iInRatePktsCount(0)
    , m_iInRateBytesCount(0)
    , m_InRatePeriod(INPUTRATE_FAST_START_US) // 0.5 sec (fast start)
    , m_iInRateBps(INPUTRATE_INITIAL_BYTESPS)
    , m_iFullHeaderSize(CPacket::UDP_HDR_SIZE + CPacket::HDR_SIZE)
{}

void CRateEstimator::setInputRateSmpPeriod(int period)
{
    m_InRatePeriod = (uint64_t)period; //(usec) 0=no input rate calculation
}

void CRateEstimator::updateInputRate(const time_point& time, int pkts, int bytes)
{
    // no input rate calculation
    if (m_InRatePeriod == 0)
        return;

    if (is_zero(m_tsInRateStartTime))
    {
        m_tsInRateStartTime = time;
        return;
    }
    else if (time < m_tsInRateStartTime)
    {
        // Old packets are being submitted for estimation, e.g. during the backup link activation.
        return;
    }

    m_iInRatePktsCount  += pkts;
    m_iInRateBytesCount += bytes;

    // Trigger early update in fast start mode
    const bool early_update = (m_InRatePeriod < INPUTRATE_RUNNING_US) && (m_iInRatePktsCount > INPUTRATE_MAX_PACKETS);

    const uint64_t period_us = count_microseconds(time - m_tsInRateStartTime);
    if (!early_update && period_us <= m_InRatePeriod)
        return;

    // Required Byte/sec rate (payload + headers)
    m_iInRateBytesCount += (m_iInRatePktsCount * m_iFullHeaderSize);
    m_iInRateBps = (int)(((int64_t)m_iInRateBytesCount * 1000000) / period_us);
    HLOGC(bslog.Debug,
        log << "updateInputRate: pkts:" << m_iInRateBytesCount << " bytes:" << m_iInRatePktsCount
        << " rate=" << (m_iInRateBps * 8) / 1000 << "kbps interval=" << period_us);
    m_iInRatePktsCount  = 0;
    m_iInRateBytesCount = 0;
    m_tsInRateStartTime = time;

    setInputRateSmpPeriod(INPUTRATE_RUNNING_US);
}

CSndRateEstimator::CSndRateEstimator(const time_point& tsNow)
    : m_tsFirstSampleTime(tsNow)
    , m_iFirstSampleIdx(0)
    , m_iCurSampleIdx(0)
    , m_iRateBps(0)
{
    
}

void CSndRateEstimator::addSample(const time_point& ts, int pkts, size_t bytes)
{
    const int iSampleDeltaIdx = (int) count_milliseconds(ts - m_tsFirstSampleTime) / SAMPLE_DURATION_MS;
    const int delta = NUM_PERIODS - iSampleDeltaIdx;

    // TODO: -delta <= NUM_PERIODS, then just reset the state on the estimator.

    if (iSampleDeltaIdx >= 2 * NUM_PERIODS)
    {
        // Just reset the estimator and start like if new.
        for (int i = 0; i < NUM_PERIODS; ++i)
        {
            const int idx = incSampleIdx(m_iFirstSampleIdx, i);
            m_Samples[idx].reset();

            if (idx == m_iCurSampleIdx)
                break;
        }

        m_iFirstSampleIdx = 0;
        m_iCurSampleIdx = 0;
        m_iRateBps = 0;
        m_tsFirstSampleTime += milliseconds_from(iSampleDeltaIdx * SAMPLE_DURATION_MS);
    }
    else if (iSampleDeltaIdx > NUM_PERIODS)
    {
        // In run-time a constant flow of samples is expected. Once all periods are filled (after 1 second of sampling),
        // the iSampleDeltaIdx should be either (NUM_PERIODS - 1),
        // or NUM_PERIODS. In the later case it means the start of a new sampling period.
        int d = delta;
        while (d < 0)
        {
            m_Samples[m_iFirstSampleIdx].reset();
            m_iFirstSampleIdx = incSampleIdx(m_iFirstSampleIdx);
            m_tsFirstSampleTime += milliseconds_from(SAMPLE_DURATION_MS);
            m_iCurSampleIdx = incSampleIdx(m_iCurSampleIdx);
            ++d;
        }
    }

    // Check if the new sample period has started.
    const int iNewDeltaIdx = (int) count_milliseconds(ts - m_tsFirstSampleTime) / SAMPLE_DURATION_MS;
    if (incSampleIdx(m_iFirstSampleIdx, iNewDeltaIdx) != m_iCurSampleIdx)
    {
        // Now there should be some periods (at most last NUM_PERIODS) ready to be summed,
        // rate estimation updated, after which all the new entry should be added.
        Sample sum;
        int iNumPeriods = 0;
        bool bMetNonEmpty = false;
        for (int i = 0; i < NUM_PERIODS; ++i)
        {
            const int idx = incSampleIdx(m_iFirstSampleIdx, i);
            const Sample& s = m_Samples[idx];
            sum += s;
            if (bMetNonEmpty || !s.empty())
            {
                ++iNumPeriods;
                bMetNonEmpty = true;
            }

            if (idx == m_iCurSampleIdx)
                break;
        }

        if (iNumPeriods == 0)
        {
            m_iRateBps = 0;
        }
        else
        {
            m_iRateBps = (sum.m_iBytesCount + CPacket::HDR_SIZE * sum.m_iPktsCount) * 1000 / (iNumPeriods * SAMPLE_DURATION_MS);
        }

        HLOGC(bslog.Note,
            log << "CSndRateEstimator: new rate estimation :" << (m_iRateBps * 8) / 1000 << " kbps. Based on "
                 << iNumPeriods << " periods, " << sum.m_iPktsCount << " packets, " << sum.m_iBytesCount << " bytes.");

        // Shift one sampling period to start collecting the new one.
        m_iCurSampleIdx = incSampleIdx(m_iCurSampleIdx);
        m_Samples[m_iCurSampleIdx].reset();
        
        // If all NUM_SAMPLES are recorded, the first position has to be shifted as well.
        if (delta <= 0)
        {
            m_iFirstSampleIdx = incSampleIdx(m_iFirstSampleIdx);
            m_tsFirstSampleTime += milliseconds_from(SAMPLE_DURATION_MS);
        }
    }

    m_Samples[m_iCurSampleIdx].m_iBytesCount += (int) bytes;
    m_Samples[m_iCurSampleIdx].m_iPktsCount  += pkts;
}

int CSndRateEstimator::getCurrentRate() const
{
    SRT_ASSERT(m_iCurSampleIdx >= 0 && m_iCurSampleIdx < NUM_PERIODS);
    const Sample& s = m_Samples[m_iCurSampleIdx];
    return (int) avg_iir<16, unsigned long long>(m_iRateBps, (CPacket::HDR_SIZE * s.m_iPktsCount + s.m_iBytesCount) * 1000 / SAMPLE_DURATION_MS);
}

int CSndRateEstimator::incSampleIdx(int val, int inc) const
{
    SRT_ASSERT(inc >= 0 && inc <= NUM_PERIODS);
    val += inc;
    while (val >= NUM_PERIODS)
        val -= NUM_PERIODS;
    return val;
}

}