/*
 * 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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  following disclaimer.

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  above copyright notice, this list of conditions
  and the following disclaimer in the documentation
  and/or other materials provided with the distribution.

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  nor the names of its contributors may be used to
  endorse or promote products derived from this
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THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
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*****************************************************************************/

/*****************************************************************************
written by
   Yunhong Gu, last updated 01/22/2011
modified by
   Haivision Systems Inc.
*****************************************************************************/

#include "platform_sys.h"

#include <cmath>
#include <cstring>
#include "common.h"
#include "window.h"
#include <algorithm>

using namespace std;
using namespace srt::sync;

namespace ACKWindowTools
{

void store(Seq* r_aSeq, const size_t size, int& r_iHead, int& r_iTail, int32_t seq, int32_t ack)
{
   r_aSeq[r_iHead].iACKSeqNo = seq;
   r_aSeq[r_iHead].iACK = ack;
   r_aSeq[r_iHead].tsTimeStamp = steady_clock::now();

   r_iHead = (r_iHead + 1) % size;

   // overwrite the oldest ACK since it is not likely to be acknowledged
   if (r_iHead == r_iTail)
      r_iTail = (r_iTail + 1) % size;
}

int acknowledge(Seq* r_aSeq, const size_t size, int& r_iHead, int& r_iTail, int32_t seq, int32_t& r_ack)
{
   if (r_iHead >= r_iTail)
   {
      // Head has not exceeded the physical boundary of the window

      for (int i = r_iTail, n = r_iHead; i < n; ++ i)
      {
         // looking for indentical ACK Seq. No.
         if (seq == r_aSeq[i].iACKSeqNo)
         {
            // return the Data ACK it carried
            r_ack = r_aSeq[i].iACK;

            // calculate RTT
            const int rtt = count_microseconds(steady_clock::now() - r_aSeq[i].tsTimeStamp);

            if (i + 1 == r_iHead)
            {
               r_iTail = r_iHead = 0;
               r_aSeq[0].iACKSeqNo = SRT_SEQNO_NONE;
            }
            else
               r_iTail = (i + 1) % size;

            return rtt;
         }
      }

      // Bad input, the ACK node has been overwritten
      return -1;
   }

   // Head has exceeded the physical window boundary, so it is behind tail
   for (int j = r_iTail, n = r_iHead + size; j < n; ++ j)
   {
      // looking for indentical ACK seq. no.
      if (seq == r_aSeq[j % size].iACKSeqNo)
      {
         // return Data ACK
         j %= size;
         r_ack = r_aSeq[j].iACK;

         // calculate RTT
         const int rtt = count_microseconds(steady_clock::now() - r_aSeq[j].tsTimeStamp);

         if (j == r_iHead)
         {
            r_iTail = r_iHead = 0;
            r_aSeq[0].iACKSeqNo = -1;
         }
         else
            r_iTail = (j + 1) % size;

         return rtt;
      }
   }

   // bad input, the ACK node has been overwritten
   return -1;
}
}

////////////////////////////////////////////////////////////////////////////////

void CPktTimeWindowTools::initializeWindowArrays(int* r_pktWindow, int* r_probeWindow, int* r_bytesWindow, size_t asize, size_t psize)
{
   for (size_t i = 0; i < asize; ++ i)
      r_pktWindow[i] = 1000000;   //1 sec -> 1 pkt/sec

   for (size_t k = 0; k < psize; ++ k)
      r_probeWindow[k] = 1000;    //1 msec -> 1000 pkts/sec

   for (size_t i = 0; i < asize; ++ i)
      r_bytesWindow[i] = CPacket::SRT_MAX_PAYLOAD_SIZE; //based on 1 pkt/sec set in r_pktWindow[i]
}


int CPktTimeWindowTools::getPktRcvSpeed_in(const int* window, int* replica, const int* abytes, size_t asize, int& bytesps)
{
   // get median value, but cannot change the original value order in the window
   std::copy(window, window + asize, replica);
   std::nth_element(replica, replica + (asize / 2), replica + asize);
   //std::sort(replica, replica + asize);
   int median = replica[asize / 2];

   unsigned count = 0;
   int sum = 0;
   int upper = median << 3;
   int lower = median >> 3;

   bytesps = 0;
   unsigned long bytes = 0;
   const int* bp = abytes;
   // median filtering
   const int* p = window;
   for (int i = 0, n = asize; i < n; ++ i)
   {
      if ((*p < upper) && (*p > lower))
      {
         ++ count;  //packet counter
         sum += *p; //usec counter
         bytes += (unsigned long)*bp;   //byte counter
      }
      ++ p;     //advance packet pointer
      ++ bp;    //advance bytes pointer
   }

   // claculate speed, or return 0 if not enough valid value
   if (count > (asize >> 1))
   {
      bytes += (CPacket::SRT_DATA_HDR_SIZE * count); //Add protocol headers to bytes received
      bytesps = (unsigned long)ceil(1000000.0 / (double(sum) / double(bytes)));
      return (int)ceil(1000000.0 / (sum / count));
   }
   else
   {
      bytesps = 0;
      return 0;
   }
}

int CPktTimeWindowTools::getBandwidth_in(const int* window, int* replica, size_t psize)
{
    // This calculation does more-less the following:
    //
    // 1. Having example window:
    //  - 50, 51, 100, 55, 80, 1000, 600, 1500, 1200, 10, 90
    // 2. This window is now sorted, but we only know the value in the middle:
    //  - 10, 50, 51, 55, 80, [[90]], 100, 600, 1000, 1200, 1500
    // 3. Now calculate:
    //   - lower: 90/8 = 11.25
    //   - upper: 90*8 = 720
    // 4. Now calculate the arithmetic median from all these values,
    //    but drop those from outside the <lower, upper> range:
    //  - 10, (11<) [ 50, 51, 55, 80, 90, 100, 600, ] (>720) 1000, 1200, 1500
    // 5. Calculate the median from the extracted range,
    //    NOTE: the median is actually repeated once, so size is +1.
    //
    //    values = { 50, 51, 55, 80, 90, 100, 600 };
    //    sum = 90 + accumulate(values); ==> 1026
    //    median = sum/(1 + values.size()); ==> 147
    //
    // For comparison: the overall arithmetic median from this window == 430
    //
    // 6. Returned value = 1M/median

   // get median value, but cannot change the original value order in the window
   std::copy(window, window + psize - 1, replica);
   std::nth_element(replica, replica + (psize / 2), replica + psize - 1);
   //std::sort(replica, replica + psize); <--- was used for debug, just leave it as a mark
   int median = replica[psize / 2];

   int count = 1;
   int sum = median;
   int upper = median << 3; // median*8
   int lower = median >> 3; // median/8

   // median filtering
   const int* p = window;
   for (int i = 0, n = psize; i < n; ++ i)
   {
      if ((*p < upper) && (*p > lower))
      {
         ++ count;
         sum += *p;
      }
      ++ p;
   }

   return (int)ceil(1000000.0 / (double(sum) / double(count)));
}