apollo/services/recorder.js

const AggregateTracker = require("./trackers/aggregate-tracker");
const Session = require("../models/session");

class Recorder {
  #sessions = null;
  #trackers = null;
  #originalTrackers = [];
  #scrobblers = [];
  #config = null;
  #logger = null;

  constructor(sessions, trackers, scrobblers, config, logger) {
    this.#sessions = sessions;
    this.#trackers = new AggregateTracker('aggregate', trackers);
    this.#originalTrackers = trackers;
    this.#scrobblers = scrobblers;
    this.#config = config;
    this.#logger = logger;
  }

  async record() {
    const now = Date.now();
    const media = await this.#trackers.poll();
    const contexts = media.map(m => this.#fetchContext(m));

    // Find sessions that ended and that are deemable of a scrobble.
    const sessionIds = this.#sessions.getSessionIds();
    const stopped = sessionIds.filter(sessionId => !contexts.some(context => sessionId == context.session.id))
      .map(sessionId => this.#sessions.get(sessionId))
      .map(session => this.#fetchContext(session.playing));
    const contextEnded = stopped.filter(context => this.#canScrobble(context.session, null, context.session.playing));

    for (let context of contextEnded)
      context.session.playDuration = now - (context.session.lastScrobbleTimestamp || context.session.started) - context.session.pauseDuration;

    // Find ongoing sessions that have moved on to the next song.
    const finishedPlaying = contexts.filter(context => this.#listen(context, now));

    // Scrobble
    const scrobbling = finishedPlaying.concat(contextEnded);
    for (let context of scrobbling) {
      await this.#scrobble(context);

      if (context.session.playing == null)
        continue;

      context.session.playDuration = context.extraDuration;
      context.session.pauseDuration = 0;
    }

    // Remove dead sessions.
    for (let context of stopped) {
      this.#sessions.remove(context.session.id);
    }
  }

  #fetchContext(media) {
    const tracker = this.#originalTrackers.find(t => t.provider == media.provider && t.name == media.source);
    let session = this.#sessions.get(media.session);
    if (session == null) {
      session = new Session(media.session);
      this.#sessions.add(session);
    }

    return { session, media, tracker, extraDuration: 0 }
  }

  #listen(context, timestamp) {
    const session = context.session;
    const current = context.media;
    const previous = context.session.playing;
    session.playing = current;

    if (!previous) {
      this.#logger.info(current, "A new session has started.");
      session.lastUpdateTimestamp = timestamp;
      return false;
    }

    const updated = current.progress != previous.progress || current.id != previous.id || current.state != previous.state;
    if (!updated)
      return false;

    const timeDiff = timestamp - session.lastUpdateTimestamp;
    const progressDiff = Math.max(0, Math.min(current.progress - previous.progress, timeDiff));
    session.playDuration += progressDiff;
    session.pauseDuration += timeDiff - progressDiff;
    
    const canScrobble = this.#canScrobble(session, current, previous);
    if (canScrobble || current.id != previous.id) {
      context.extraDuration = Math.min(current.progress, timeDiff - (previous.duration - previous.progress));
      session.lastScrobbleTimestamp = timestamp;
    }

    session.lastUpdateTimestamp = timestamp;
    return canScrobble;
  }

  #canScrobble(session, current, previous) {
    if (previous == null)
      return false;

    const scrobbleDuration = this.#config.minimum.duration || 240;
    const scrobblePercent = this.#config.minimum.percent || 50;

    const newPlayback = current == null || current.progress < previous.progress;
    const canBeScrobbled = session.playDuration > scrobbleDuration * 1000 || session.playDuration / previous.duration > scrobblePercent / 100.0;

    return newPlayback && canBeScrobbled;
  }

  async #scrobble(context) {
    this.#logger.info(context, "Scrobble");

    for (var scrobblerName of context.tracker.scrobblerNames) {
      const scrobbler = this.#scrobblers.find(s => s.name == scrobblerName);
      if (scrobbler == null) {
        this.#logger.error(`Cannot find scrobbler by name of '${scrobblerName}'.`);
        continue;
      }

      try {
        await scrobbler.scrobble(context.media, Date.now() - Math.min(context.media.duration, context.session.playDuration));
      } catch (ex) {
        this.#logger.error(ex, "Could not send to maloja.");
      }
    }
  }
}

module.exports = Recorder;