# All files / src/controller abr-controller.js

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     /*
     * simple ABR Controller
     *  - compute next level based on last fragment bw heuristics
     *  - implement an abandon rules triggered if we have less than 2 frag buffered and if computed bw shows that we risk buffer stalling
     */

    import Event from '../events';
    import EventHandler from '../event-handler';
    import { BufferHelper } from '../utils/buffer-helper';
    import { ErrorDetails } from '../errors';
    import { logger } from '../utils/logger';
    import EwmaBandWidthEstimator from '../utils/ewma-bandwidth-estimator';

    const { performance } = window;

    class AbrController extends EventHandler {
      constructor (hls) {
        super(hls, Event.FRAG_LOADING,
          Event.FRAG_LOADED,
          Event.FRAG_BUFFERED,
          Event.ERROR);
        this.lastLoadedFragLevel = 0;
        this._nextAutoLevel = -1;
        this.hls = hls;
        this.timer = null;
        this._bwEstimator = null;
        this.onCheck = this._abandonRulesCheck.bind(this);
      }

      destroy () {
        this.clearTimer();
        EventHandler.prototype.destroy.call(this);
      }

      onFragLoading (data) {
        const frag = data.frag;
        Iif (frag.type === 'main') {
          if (!this.timer) {
            this.fragCurrent = frag;
            this.timer = setInterval(this.onCheck, 100);
          }

          // lazy init of BwEstimator, rationale is that we use different params for Live/VoD
          // so we need to wait for stream manifest / playlist type to instantiate it.
          if (!this._bwEstimator) {
            const hls = this.hls;
            const config = hls.config;
            const level = frag.level;
            const isLive = hls.levels[level].details.live;

            let ewmaFast, ewmaSlow;
            if (isLive) {
              ewmaFast = config.abrEwmaFastLive;
              ewmaSlow = config.abrEwmaSlowLive;
            } else {
              ewmaFast = config.abrEwmaFastVoD;
              ewmaSlow = config.abrEwmaSlowVoD;
            }
            this._bwEstimator = new EwmaBandWidthEstimator(hls, ewmaSlow, ewmaFast, config.abrEwmaDefaultEstimate);
          }
        }
      }

      _abandonRulesCheck () {
        /*
          monitor fragment retrieval time...
          we compute expected time of arrival of the complete fragment.
          we compare it to expected time of buffer starvation
        */
        const hls = this.hls;
        const video = hls.media;
        const frag = this.fragCurrent;

        if (!frag) {
          return;
        }

        const loader = frag.loader;
        const minAutoLevel = hls.minAutoLevel;

        // if loader has been destroyed or loading has been aborted, stop timer and return
        if (!loader || (loader.stats && loader.stats.aborted)) {
          logger.warn('frag loader destroy or aborted, disarm abandonRules');
          this.clearTimer();
          // reset forced auto level value so that next level will be selected
          this._nextAutoLevel = -1;
          return;
        }
        let stats = loader.stats;
        /* only monitor frag retrieval time if
        (video not paused OR first fragment being loaded(ready state === HAVE_NOTHING = 0)) AND autoswitching enabled AND not lowest level (=> means that we have several levels) */
        if (video && stats && ((!video.paused && (video.playbackRate !== 0)) || !video.readyState) && frag.autoLevel && frag.level) {
          let requestDelay = performance.now() - stats.trequest,
            playbackRate = Math.abs(video.playbackRate);
          // monitor fragment load progress after half of expected fragment duration,to stabilize bitrate
          if (requestDelay > (500 * frag.duration / playbackRate)) {
            let levels = hls.levels,
              loadRate = Math.max(1, stats.bw ? stats.bw / 8 : stats.loaded * 1000 / requestDelay), // byte/s; at least 1 byte/s to avoid division by zero
              // compute expected fragment length using frag duration and level bitrate. also ensure that expected len is gte than already loaded size
              level = levels[frag.level],
              levelBitrate = level.realBitrate ? Math.max(level.realBitrate, level.bitrate) : level.bitrate,
              expectedLen = stats.total ? stats.total : Math.max(stats.loaded, Math.round(frag.duration * levelBitrate / 8)),
              pos = video.currentTime,
              fragLoadedDelay = (expectedLen - stats.loaded) / loadRate,
              bufferStarvationDelay = (BufferHelper.bufferInfo(video, pos, hls.config.maxBufferHole).end - pos) / playbackRate;
            // consider emergency switch down only if we have less than 2 frag buffered AND
            // time to finish loading current fragment is bigger than buffer starvation delay
            // ie if we risk buffer starvation if bw does not increase quickly
            if ((bufferStarvationDelay < (2 * frag.duration / playbackRate)) && (fragLoadedDelay > bufferStarvationDelay)) {
              let fragLevelNextLoadedDelay, nextLoadLevel;
              // lets iterate through lower level and try to find the biggest one that could avoid rebuffering
              // we start from current level - 1 and we step down , until we find a matching level
              for (nextLoadLevel = frag.level - 1; nextLoadLevel > minAutoLevel; nextLoadLevel--) {
                // compute time to load next fragment at lower level
                // 0.8 : consider only 80% of current bw to be conservative
                // 8 = bits per byte (bps/Bps)
                let levelNextBitrate = levels[nextLoadLevel].realBitrate ? Math.max(levels[nextLoadLevel].realBitrate, levels[nextLoadLevel].bitrate) : levels[nextLoadLevel].bitrate;
                fragLevelNextLoadedDelay = frag.duration * levelNextBitrate / (8 * 0.8 * loadRate);
                if (fragLevelNextLoadedDelay < bufferStarvationDelay) {
                  // we found a lower level that be rebuffering free with current estimated bw !
                  break;
                }
              }
              // only emergency switch down if it takes less time to load new fragment at lowest level instead
              // of finishing loading current one ...
              if (fragLevelNextLoadedDelay < fragLoadedDelay) {
                logger.warn(`loading too slow, abort fragment loading and switch to level ${nextLoadLevel}:fragLoadedDelay[${nextLoadLevel}]<fragLoadedDelay[${frag.level - 1}];bufferStarvationDelay:${fragLevelNextLoadedDelay.toFixed(1)}<${fragLoadedDelay.toFixed(1)}:${bufferStarvationDelay.toFixed(1)}`);
                // force next load level in auto mode
                hls.nextLoadLevel = nextLoadLevel;
                // update bw estimate for this fragment before cancelling load (this will help reducing the bw)
                this._bwEstimator.sample(requestDelay, stats.loaded);
                // abort fragment loading
                loader.abort();
                // stop abandon rules timer
                this.clearTimer();
                hls.trigger(Event.FRAG_LOAD_EMERGENCY_ABORTED, { frag: frag, stats: stats });
              }
            }
          }
        }
      }

      onFragLoaded (data) {
        const frag = data.frag;
        if (frag.type === 'main' && Number.isFinite(frag.sn)) {
          // stop monitoring bw once frag loaded
          this.clearTimer();
          // store level id after successful fragment load
          this.lastLoadedFragLevel = frag.level;
          // reset forced auto level value so that next level will be selected
          this._nextAutoLevel = -1;

          // compute level average bitrate
          Iif (this.hls.config.abrMaxWithRealBitrate) {
            const level = this.hls.levels[frag.level];
            let loadedBytes = (level.loaded ? level.loaded.bytes : 0) + data.stats.loaded;
            let loadedDuration = (level.loaded ? level.loaded.duration : 0) + data.frag.duration;
            level.loaded = { bytes: loadedBytes, duration: loadedDuration };
            level.realBitrate = Math.round(8 * loadedBytes / loadedDuration);
          }
          // if fragment has been loaded to perform a bitrate test,
          Iif (data.frag.bitrateTest) {
            let stats = data.stats;
            stats.tparsed = stats.tbuffered = stats.tload;
            this.onFragBuffered(data);
          }
        }
      }

      onFragBuffered (data) {
        const stats = data.stats;
        const frag = data.frag;
        // only update stats on first frag buffering
        // if same frag is loaded multiple times, it might be in browser cache, and loaded quickly
        // and leading to wrong bw estimation
        // on bitrate test, also only update stats once (if tload = tbuffered == on FRAG_LOADED)
        Iif (stats.aborted !== true && frag.type === 'main' && Number.isFinite(frag.sn) && ((!frag.bitrateTest || stats.tload === stats.tbuffered))) {
          // use tparsed-trequest instead of tbuffered-trequest to compute fragLoadingProcessing; rationale is that  buffer appending only happens once media is attached
          // in case we use config.startFragPrefetch while media is not attached yet, fragment might be parsed while media not attached yet, but it will only be buffered on media attached
          // as a consequence it could happen really late in the process. meaning that appending duration might appears huge ... leading to underestimated throughput estimation
          let fragLoadingProcessingMs = stats.tparsed - stats.trequest;
          logger.log(`latency/loading/parsing/append/kbps:${Math.round(stats.tfirst - stats.trequest)}/${Math.round(stats.tload - stats.tfirst)}/${Math.round(stats.tparsed - stats.tload)}/${Math.round(stats.tbuffered - stats.tparsed)}/${Math.round(8 * stats.loaded / (stats.tbuffered - stats.trequest))}`);
          this._bwEstimator.sample(fragLoadingProcessingMs, stats.loaded);
          stats.bwEstimate = this._bwEstimator.getEstimate();
          // if fragment has been loaded to perform a bitrate test, (hls.startLevel = -1), store bitrate test delay duration
          if (frag.bitrateTest) {
            this.bitrateTestDelay = fragLoadingProcessingMs / 1000;
          } else {
            this.bitrateTestDelay = 0;
          }
        }
      }

      onError (data) {
        // stop timer in case of frag loading error
        switch (data.details) {
        case ErrorDetails.FRAG_LOAD_ERROR:
        case ErrorDetails.FRAG_LOAD_TIMEOUT:
          this.clearTimer();
          break;
        default:
          break;
        }
      }

      clearTimer () {
        clearInterval(this.timer);
        this.timer = null;
      }

      // return next auto level
      get nextAutoLevel () {
        const forcedAutoLevel = this._nextAutoLevel;
        const bwEstimator = this._bwEstimator;
        // in case next auto level has been forced, and bw not available or not reliable, return forced value
        Iif (forcedAutoLevel !== -1 && (!bwEstimator || !bwEstimator.canEstimate())) {
          return forcedAutoLevel;
        }

        // compute next level using ABR logic
        let nextABRAutoLevel = this._nextABRAutoLevel;
        // if forced auto level has been defined, use it to cap ABR computed quality level
        Iif (forcedAutoLevel !== -1) {
          nextABRAutoLevel = Math.min(forcedAutoLevel, nextABRAutoLevel);
        }

        return nextABRAutoLevel;
      }
      get _nextABRAutoLevel () {
        let hls = this.hls, maxAutoLevel = hls.maxAutoLevel, levels = hls.levels, config = hls.config, minAutoLevel = hls.minAutoLevel;
        const video = hls.media,
          currentLevel = this.lastLoadedFragLevel,
          currentFragDuration = this.fragCurrent ? this.fragCurrent.duration : 0,
          pos = (video ? video.currentTime : 0),
          // playbackRate is the absolute value of the playback rate; if video.playbackRate is 0, we use 1 to load as
          // if we're playing back at the normal rate.
          playbackRate = ((video && (video.playbackRate !== 0)) ? Math.abs(video.playbackRate) : 1.0),
          avgbw = this._bwEstimator ? this._bwEstimator.getEstimate() : config.abrEwmaDefaultEstimate,
          // bufferStarvationDelay is the wall-clock time left until the playback buffer is exhausted.
          bufferStarvationDelay = (BufferHelper.bufferInfo(video, pos, config.maxBufferHole).end - pos) / playbackRate;

        // First, look to see if we can find a level matching with our avg bandwidth AND that could also guarantee no rebuffering at all
        let bestLevel = this._findBestLevel(currentLevel, currentFragDuration, avgbw, minAutoLevel, maxAutoLevel, bufferStarvationDelay, config.abrBandWidthFactor, config.abrBandWidthUpFactor, levels);
        Iif (bestLevel >= 0) {
          return bestLevel;
        } else {
          logger.trace('rebuffering expected to happen, lets try to find a quality level minimizing the rebuffering');
          // not possible to get rid of rebuffering ... let's try to find level that will guarantee less than maxStarvationDelay of rebuffering
          // if no matching level found, logic will return 0
          let maxStarvationDelay = currentFragDuration ? Math.min(currentFragDuration, config.maxStarvationDelay) : config.maxStarvationDelay,
            bwFactor = config.abrBandWidthFactor,
            bwUpFactor = config.abrBandWidthUpFactor;
          Eif (bufferStarvationDelay === 0) {
            // in case buffer is empty, let's check if previous fragment was loaded to perform a bitrate test
            let bitrateTestDelay = this.bitrateTestDelay;
            Iif (bitrateTestDelay) {
              // if it is the case, then we need to adjust our max starvation delay using maxLoadingDelay config value
              // max video loading delay used in  automatic start level selection :
              // in that mode ABR controller will ensure that video loading time (ie the time to fetch the first fragment at lowest quality level +
              // the time to fetch the fragment at the appropriate quality level is less than ```maxLoadingDelay``` )
              // cap maxLoadingDelay and ensure it is not bigger 'than bitrate test' frag duration
              const maxLoadingDelay = currentFragDuration ? Math.min(currentFragDuration, config.maxLoadingDelay) : config.maxLoadingDelay;
              maxStarvationDelay = maxLoadingDelay - bitrateTestDelay;
              logger.trace(`bitrate test took ${Math.round(1000 * bitrateTestDelay)}ms, set first fragment max fetchDuration to ${Math.round(1000 * maxStarvationDelay)} ms`);
              // don't use conservative factor on bitrate test
              bwFactor = bwUpFactor = 1;
            }
          }
          bestLevel = this._findBestLevel(currentLevel, currentFragDuration, avgbw, minAutoLevel, maxAutoLevel, bufferStarvationDelay + maxStarvationDelay, bwFactor, bwUpFactor, levels);
          return Math.max(bestLevel, 0);
        }
      }

      _findBestLevel (currentLevel, currentFragDuration, currentBw, minAutoLevel, maxAutoLevel, maxFetchDuration, bwFactor, bwUpFactor, levels) {
        for (let i = maxAutoLevel; i >= minAutoLevel; i--) {
          let levelInfo = levels[i];

          Iif (!levelInfo) {
            continue;
          }

          let levelDetails = levelInfo.details,
            avgDuration = levelDetails ? levelDetails.totalduration / levelDetails.fragments.length : currentFragDuration,
            live = levelDetails ? levelDetails.live : false,
            adjustedbw;
          // follow algorithm captured from stagefright :
          // https://android.googlesource.com/platform/frameworks/av/+/master/media/libstagefright/httplive/LiveSession.cpp
          // Pick the highest bandwidth stream below or equal to estimated bandwidth.
          // consider only 80% of the available bandwidth, but if we are switching up,
          // be even more conservative (70%) to avoid overestimating and immediately
          // switching back.
          if (i <= currentLevel) {
            adjustedbw = bwFactor * currentBw;
          } else {
            adjustedbw = bwUpFactor * currentBw;
          }

          const bitrate = levels[i].realBitrate ? Math.max(levels[i].realBitrate, levels[i].bitrate) : levels[i].bitrate,
            fetchDuration = bitrate * avgDuration / adjustedbw;

          logger.trace(`level/adjustedbw/bitrate/avgDuration/maxFetchDuration/fetchDuration: ${i}/${Math.round(adjustedbw)}/${bitrate}/${avgDuration}/${maxFetchDuration}/${fetchDuration}`);
          // if adjusted bw is greater than level bitrate AND
          if (adjustedbw > bitrate &&
          // fragment fetchDuration unknown OR live stream OR fragment fetchDuration less than max allowed fetch duration, then this level matches
          // we don't account for max Fetch Duration for live streams, this is to avoid switching down when near the edge of live sliding window ...
          // special case to support startLevel = -1 (bitrateTest) on live streams : in that case we should not exit loop so that _findBestLevel will return -1
            (!fetchDuration || (live && !this.bitrateTestDelay) || fetchDuration < maxFetchDuration)) {
            // as we are looping from highest to lowest, this will return the best achievable quality level
            return i;
          }
        }
        // not enough time budget even with quality level 0 ... rebuffering might happen
        return -1;
      }

      set nextAutoLevel (nextLevel) {
        this._nextAutoLevel = nextLevel;
      }
    }

    export default AbrController;