'use strict';

var _logger = require('../utils/logger');

var LevelHelper = {

  mergeDetails: 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.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) {
      LevelHelper.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;
    return;
  },

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

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

    var 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--) {
      LevelHelper.updatePTS(fragments, i, i - 1);
    }

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

    return drift;
  },

  updatePTS: 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.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.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);
      }
    }
  }
}; /**
    * Level Helper class, providing methods dealing with playlist sliding and drift
   */

module.exports = LevelHelper;