/**
 * Level Helper class, providing methods dealing with playlist sliding and drift
*/

import {logger} from '../utils/logger';

export function updatePTS(fragments,fromIdx, toIdx) {
  var fragFrom = fragments[fromIdx], fragTo = fragments[toIdx], fragToPTS = fragTo.startPTS;
  // if we know startPTS[toIdx]
  if (!isNaN(fragToPTS)) {
    // update fragment duration.
    // it helps to fix drifts between playlist reported duration and fragment real duration
    if (toIdx > fromIdx) {
      fragFrom.duration = fragToPTS - fragFrom.start;
      if (fragFrom.duration < 0) {
        logger.warn(`negative duration computed for frag ${fragFrom.sn},level ${fragFrom.level}, there should be some duration drift between playlist and fragment!`);
      }
    } else {
      fragTo.duration = fragFrom.start - fragToPTS;
      if (fragTo.duration < 0) {
        logger.warn(`negative duration computed for frag ${fragTo.sn},level ${fragTo.level}, there should be some duration drift between playlist and fragment!`);
      }
    }
  } else {
    // we dont know startPTS[toIdx]
    if (toIdx > fromIdx) {
      fragTo.start = fragFrom.start + fragFrom.duration;
    } else {
      fragTo.start = Math.max(fragFrom.start - fragTo.duration, 0);
    }
  }
}

export function updateFragPTSDTS(details,frag,startPTS,endPTS,startDTS,endDTS) {
  // update frag PTS/DTS
  if (!isNaN(frag.startPTS)) {
    // delta PTS between audio and video
    let deltaPTS = Math.abs(frag.startPTS - startPTS);
    if (isNaN(frag.deltaPTS)) {
      frag.deltaPTS = deltaPTS;
    } else {
      frag.deltaPTS = Math.max(deltaPTS, frag.deltaPTS);
    }
    startPTS = Math.min(startPTS, frag.startPTS);
    endPTS = Math.max(endPTS, frag.endPTS);
    startDTS = Math.min(startDTS, frag.startDTS);
    endDTS = Math.max(endDTS, frag.endDTS);
  }

  const drift = startPTS - frag.start;
  frag.start = frag.startPTS = startPTS;
  frag.endPTS = endPTS;
  frag.startDTS = startDTS;
  frag.endDTS = endDTS;
  frag.duration = endPTS - startPTS;

  const sn = frag.sn;
  // exit if sn out of range
  if (!details || sn < details.startSN || sn > details.endSN) {
    return 0;
  }
  var fragIdx, fragments, i;
  fragIdx = sn - details.startSN;
  fragments = details.fragments;
  // update frag reference in fragments array
  // rationale is that fragments array might not contain this frag object.
  // this will happpen if playlist has been refreshed between frag loading and call to updateFragPTSDTS()
  // if we don't update frag, we won't be able to propagate PTS info on the playlist
  // resulting in invalid sliding computation
  fragments[fragIdx] = frag;
  // adjust fragment PTS/duration from seqnum-1 to frag 0
  for (i = fragIdx; i > 0; i--) {
    updatePTS(fragments, i, i - 1);
  }

  // adjust fragment PTS/duration from seqnum to last frag
  for (i = fragIdx; i < fragments.length - 1; i++) {
    updatePTS(fragments, i, i + 1);
  }
  details.PTSKnown = true;
  //logger.log(`                                            frag start/end:${startPTS.toFixed(3)}/${endPTS.toFixed(3)}`);

  return drift;
}

export function mergeDetails(oldDetails,newDetails) {
    var start = Math.max(oldDetails.startSN,newDetails.startSN)-newDetails.startSN,
        end = Math.min(oldDetails.endSN,newDetails.endSN)-newDetails.startSN,
        delta = newDetails.startSN - oldDetails.startSN,
        oldfragments = oldDetails.fragments,
        newfragments = newDetails.fragments,
        ccOffset =0,
        PTSFrag;

    // check if old/new playlists have fragments in common
    if ( end < start) {
      newDetails.PTSKnown = false;
      return;
    }
    // loop through overlapping SN and update startPTS , cc, and duration if any found
    for(var i = start ; i <= end ; i++) {
      var oldFrag = oldfragments[delta+i],
          newFrag = newfragments[i];
      if (newFrag && oldFrag) {
        ccOffset = oldFrag.cc - newFrag.cc;
        if (!isNaN(oldFrag.startPTS)) {
          newFrag.start = newFrag.startPTS = oldFrag.startPTS;
          newFrag.endPTS = oldFrag.endPTS;
          newFrag.duration = oldFrag.duration;
          newFrag.backtracked = oldFrag.backtracked;
          newFrag.dropped = oldFrag.dropped;
          PTSFrag = newFrag;
        }
      }
    }

    if(ccOffset) {
      logger.log(`discontinuity sliding from playlist, take drift into account`);
      for(i = 0 ; i < newfragments.length ; i++) {
        newfragments[i].cc += ccOffset;
      }
    }

    // if at least one fragment contains PTS info, recompute PTS information for all fragments
    if(PTSFrag) {
      updateFragPTSDTS(newDetails,PTSFrag,PTSFrag.startPTS,PTSFrag.endPTS,PTSFrag.startDTS,PTSFrag.endDTS);
    } else {
      // ensure that delta is within oldfragments range
      // also adjust sliding in case delta is 0 (we could have old=[50-60] and new=old=[50-61])
      // in that case we also need to adjust start offset of all fragments
      if (delta >= 0 && delta < oldfragments.length) {
        // adjust start by sliding offset
        var sliding = oldfragments[delta].start;
        for(i = 0 ; i < newfragments.length ; i++) {
          newfragments[i].start += sliding;
        }
      }
    }
    // if we are here, it means we have fragments overlapping between
    // old and new level. reliable PTS info is thus relying on old level
    newDetails.PTSKnown = oldDetails.PTSKnown;
  }
