docbrown/app/assets/javascripts/initializers/initializePodcastPlayback.js

/**
 * This script hunts for podcast's "Record" for both the podcast_episde's
 * show page and an article page containing podcast liquid tag. It handles
 * playback and makes sure the record will spin when the podcast is currently
 * playing. The high level functions are the following
 *
 * - spinPodcastRecord();
 * - findAndApplyOnclickToRecords();
 */

function initializePodcastPlayback() {

  function getById(name) {
    return document.getElementById(name);
  }

  function getByClass(name) {
    return document.getElementsByClassName(name);
  }

  function audioExistAndIsPlaying() {
    return getById("audio") && !getById("audio").paused;
  }

  function recordExist() {
    return getById(`record-${window.activeEpisode}`)
  }

  function spinPodcastRecord(customMessage) {
    if (audioExistAndIsPlaying() && recordExist()) {
      getById(`record-${window.activeEpisode}`).classList.add("playing");
      changeStatusMessage(customMessage ? customMessage : 'playing');
    }
  }

  function stopRotatingActivePodcastIfExist() {
    if (window.activeEpisode && getById(`record-${window.activeEpisode}`)) {
      getById(`record-${window.activeEpisode}`).classList.remove('playing');
      window.activeEpisode = undefined;
    }
  }

  function findRecords() {
    var podcastPageRecords = getByClass('record-wrapper');
    var podcastLiquidTagrecords = getByClass('podcastliquidtag__record');
    if (podcastPageRecords.length > 0) {
      return podcastPageRecords;
    } else {
      return podcastLiquidTagrecords;
    }
  }

  function applyOnclickToPodcastBar(audio) {
    getById('barPlayPause').onclick = function() { playPause(audio) };
    getById('mutebutt').onclick = function() { muteUnmute(audio) };
    getById('volbutt').onclick = function() { muteUnmute(audio) };
    getById('bufferwrapper').onclick = function(e) { goToTime(e,audio) };
    getById('volumeslider').value = audio.volume*100;
    getById('volumeslider').onchange = function(e) { audio.volume = e.target.value/100 };
    getById('speed').onclick = function() { changePlaybackRate(audio) };
    getById('closebutt').onclick = function() { terminatePodcastBar(audio) };
  }

  function podcastBarAlreadyExistAndPlayingTargetEpisode(episodeSlug) {
    return getById('audiocontent').innerHTML.indexOf(`${episodeSlug}`) !== -1
  }

  function updateProgressListener(audio) {
    return function (e) {
      updateProgress(e, audio);
    }
  }

  function loadAndPlayNewPodcast(episodeSlug) {
    getById('audiocontent').innerHTML = getById(`hidden-audio-${episodeSlug}`).innerHTML;
    var audio = getById('audio');
    audio.addEventListener("timeupdate", updateProgressListener(audio), false);
    audio.load();
    playPause(audio);
    applyOnclickToPodcastBar(audio);
  }

  function findAndApplyOnclickToRecords() {
    var records = findRecords();
    Array.prototype.forEach.call(records, function (record) {
      var episodeSlug = record.getAttribute('data-episode');
      var podcastSlug = record.getAttribute('data-podcast');
      record.onclick = function () {
        if (podcastBarAlreadyExistAndPlayingTargetEpisode(episodeSlug)) {
          var audio = getById('audio');
          if (audio) {
            playPause(audio);
          }
        } else {
          stopRotatingActivePodcastIfExist();
          loadAndPlayNewPodcast(episodeSlug);
        }
      }
    })
  }

  function changePlaybackRate(audio) {
    var el = getById('speed');
    var speed = parseFloat(el.getAttribute('data-speed'));
    if (speed == 2) {
      el.setAttribute('data-speed', 0.5);
      el.innerHTML = '0.5x'
      audio.playbackRate = 0.5
    } else {
      el.setAttribute('data-speed', speed+0.5);
      el.innerHTML = speed+0.5+"x"
      audio.playbackRate = speed+0.5
    }
  }

  function changeStatusMessage(message) {
    if(getById(`status-message-${window.activeEpisode}`)) {
      getById(`status-message-${window.activeEpisode}`).innerHTML = message;
    } else if (message === 'loading' && document.querySelector('.status-message')) {
      document.querySelector('.status-message').innerHTML = message;
    } else {

    }
  }

  function applyOnbeforeUnloadWarning() {
    var message = 'You are currently playing a podcast. Are you sure you want to leave?'
    window.onclick = function(event) {
      if (event.target.tagName === 'A' && !event.target.href.includes('https://dev.to')) {
        event.preventDefault();
        if (window.confirm(message)) { window.location = event.target.href; }
      }
    }
    window.onbeforeunload = function () {
      return message;
    };
  }

  function startPodcastBar() {
    getById('barPlayPause').classList.add("playing");
    getById('progressBar').classList.add("playing");
    getById('animated-bars').classList.add("playing");
  }

  function startAudioPlayback(audio) {
    audio.play().then(function () {
      spinPodcastRecord();
      startPodcastBar();
      applyOnbeforeUnloadWarning();
    }, function () {
      // Handle any pause() failures.
    }).catch(function (error) {
      audio.play();
      setTimeout(function() {
        spinPodcastRecord('loading');
        startPodcastBar();
        applyOnbeforeUnloadWarning();
      }, 300);
    })
  }

  function removeOnbeforeUnloadWarning() {
    window.onbeforeunload = function(){
      return null;
    };
  }

  function pausePodcastBar() {
    getById('barPlayPause').classList.remove("playing");
    getById('animated-bars').classList.remove("playing");
  }

  function pauseAudioPlayback(audio) {
    audio.pause();
    stopRotatingActivePodcastIfExist();
    pausePodcastBar();
    removeOnbeforeUnloadWarning();
  }

  function playPause(audio) {
    changeStatusMessage('loading');
    window.activeEpisode = audio.getAttribute('data-episode');
    window.activePodcast = audio.getAttribute('data-podcast');
    if (audio.paused) {
      ga('send', 'event', 'click', 'play podcast', `${window.activePodcast} ${window.activeEpisode}`, null);
      startAudioPlayback(audio);
    } else {
      ga('send', 'event', 'click', 'pause podcast', `${window.activePodcast} ${window.activeEpisode}`, null);
      pauseAudioPlayback(audio);
    }
  }

  function muteUnmute(audio) {
    if (audio.muted) {
      audio.muted = false;
      getById('mutebutt').classList.add("hidden");
      getById('volumeindicator').classList.add("showing");
      getById('mutebutt').classList.remove("showing");
      getById('volumeindicator').classList.remove("hidden");
    } else {
      audio.muted = true;
      getById('mutebutt').classList.add("showing");
      getById('volumeindicator').classList.add("hidden");
      getById('mutebutt').classList.remove("hidden");
      getById('volumeindicator').classList.remove("showing");
    }
  }

  function updateProgress(e,audio) {
     var progress = getById("progress");
     var buffer = getById("buffer");
     var time = getById("time");
     var value = 0;
     var bufferValue = 0;
     if (audio.currentTime > 0) {
       value = Math.floor((100.0 / audio.duration) * audio.currentTime);
       bufferValue = (audio.buffered.end(audio.buffered.length-1)/ audio.duration)*100;
     }
      progress.style.width = value + "%";
      buffer.style.width = bufferValue + "%";
      time.innerHTML = readableDuration(audio.currentTime)+" / "+readableDuration(audio.duration);
  }

  function goToTime(e, audio) {
    var progress = getById("progress");
    if(e.clientX > 128) {
      var percent = (e.clientX-128)/(window.innerWidth-133);
      var duration = audio.duration;
      audio.currentTime = duration*percent; // jumps to 29th secs
      time.innerHTML = readableDuration(audio.currentTime)+" / "+readableDuration(audio.duration);
      progress.style.width = (percent*100.0) + "%";
    }
  }

  function readableDuration(seconds) {
    var sec = Math.floor( seconds );
    var min = Math.floor( sec / 60 );
    min = min >= 10 ? min : '0' + min;
    sec = Math.floor( sec % 60 );
    sec = sec >= 10 ? sec : '0' + sec;
    return min + ':' + sec;
  }

  function terminatePodcastBar(audio) {
    event.stopPropagation();
    audio.removeEventListener("timeupdate", updateProgressListener, false);
    getById('audiocontent').innerHTML = '';
    stopRotatingActivePodcastIfExist();
    removeOnbeforeUnloadWarning();
  }

  spinPodcastRecord();
  findAndApplyOnclickToRecords();
}