index.js

var audioPlayer = function() {
  "use strict";

  var _currentTrack = null;
  var _elements = {
    audio: document.getElementById("audio"),
    playerButtons: {
      largeToggleBtn: document.querySelector(".large-toggle-btn"),
      nextTrackBtn: document.querySelector(".next-track-btn"),
      previousTrackBtn: document.querySelector(".previous-track-btn"),
      smallToggleBtn: document.getElementsByClassName("small-toggle-btn")
    },
    progressBar: document.querySelector(".progress-box"),
    playListRows: document.getElementsByClassName("play-list-row"),
    trackInfoBox: document.querySelector(".track-info-box")
  };
  var _playAHead = false;
  var _progressCounter = 0;
  var _progressBarIndicator = _elements.progressBar.children[0].children[0].children[1];
  var _trackLoaded = false;

  var _bufferProgress = function(audio) {
    var bufferedTime = (audio.buffered.end(0) * 100) / audio.duration;
    var progressBuffer = _elements.progressBar.children[0].children[0].children[0];

    progressBuffer.style.width = bufferedTime + "%";
  };


  var _getXY = function(e) {
    var containerX = _elements.progressBar.offsetLeft;
    var containerY = _elements.progressBar.offsetTop;

    var coords = {
      x: null,
      y: null
    };

    var isTouchSuopported = "ontouchstart" in window;

  if (e.offsetX || e.offsetX === 0) {
      coords.x = e.offsetX;
      coords.y = e.offsetY;

      return coords;
    }
  };

  var _handleProgressIndicatorClick = function(e) {
    var progressBar = document.querySelector(".progress-box");
    var xCoords = _getXY(e).x;

    return (xCoords - progressBar.offsetLeft) / progressBar.children[0].offsetWidth;
  };

  var initPlayer = function() {

    if (_currentTrack === 1 || _currentTrack === null) {
      _elements.playerButtons.previousTrackBtn.disabled = true;
    }

    for (var i = 0; i < _elements.playListRows.length; i++) {
      var smallToggleBtn = _elements.playerButtons.smallToggleBtn[i];
      var playListLink = _elements.playListRows[i].children[2].children[0];

      playListLink.addEventListener("click", function(e) {
        e.preventDefault();
        var selectedTrack = parseInt(this.parentNode.parentNode.getAttribute("data-track-row"));

        if (selectedTrack !== _currentTrack) {
          _resetPlayStatus();
          _currentTrack = null;
          _trackLoaded = false;
        }

        if (_trackLoaded === false) {
          _currentTrack = parseInt(selectedTrack);
          _setTrack();
        } else {
          _playBack(this);
        }
      }, false);

      //Small toggle button clicked.
      smallToggleBtn.addEventListener("click", function(e) {
        e.preventDefault();
        var selectedTrack = parseInt(this.parentNode.getAttribute("data-track-row"));

        if (selectedTrack !== _currentTrack) {
          _resetPlayStatus();
          _currentTrack = null;
          _trackLoaded = false;
        }

        if (_trackLoaded === false) {
          _currentTrack = parseInt(selectedTrack);
          _setTrack();
        } else {
          _playBack(this);
        }

      }, false);
    }

    //Audio time has changed so update it.
    _elements.audio.addEventListener("timeupdate", _trackTimeChanged, false);

    //Audio track has ended playing.
    _elements.audio.addEventListener("ended", function(e) {
      _trackHasEnded();
    }, false);

    
    //Large toggle button clicked.
    _elements.playerButtons.largeToggleBtn.addEventListener("click", function(e) {
      if (_trackLoaded === false) {
        _currentTrack = parseInt(1);
        _setTrack()
      } else {
        _playBack();
      }
    }, false);

    //Next track button clicked.
    _elements.playerButtons.nextTrackBtn.addEventListener("click", function(e) {
      if (this.disabled !== true) {
        _currentTrack++;
        _trackLoaded = false;
        _resetPlayStatus();
        _setTrack();
      }
    }, false);

    //Previous track button clicked.
    _elements.playerButtons.previousTrackBtn.addEventListener("click", function(e) {
      if (this.disabled !== true) {
        _currentTrack--;
        _trackLoaded = false;
        _resetPlayStatus();
        _setTrack();
      }
    }, false);

    //User is moving progress indicator.
    _progressBarIndicator.addEventListener("mousedown", _mouseDown, false);

    //User stops moving progress indicator.
    window.addEventListener("mouseup", _mouseUp, false);
  };


  /**
    Handles the mouseup event by a user.
   **/
  var _mouseUp = function(e) {
    if (_playAHead === true) {
      var duration = parseFloat(audio.duration);
      var progressIndicatorClick = parseFloat(_handleProgressIndicatorClick(e));
      window.removeEventListener("mousemove", _moveProgressIndicator, true);

      audio.currentTime = duration * progressIndicatorClick;
      audio.addEventListener("timeupdate", _trackTimeChanged, false);
      _playAHead = false;
    }
  };

  /**
   Moves the progress indicator to a new point in the audio.
   **/
  var _moveProgressIndicator = function(e) {
    var newPosition = 0;
    var progressBarOffsetLeft = _elements.progressBar.offsetLeft;
    var progressBarWidth = 0;
    var progressBarIndicator = _elements.progressBar.children[0].children[0].children[1];
    var progressBarIndicatorWidth = _progressBarIndicator.offsetWidth;
    var xCoords = _getXY(e).x;

    progressBarWidth = _elements.progressBar.children[0].offsetWidth - progressBarIndicatorWidth;
    newPosition = xCoords - progressBarOffsetLeft;

    if ((newPosition >= 1) && (newPosition <= progressBarWidth)) {
      progressBarIndicator.style.left = newPosition + ".px";
    }
    if (newPosition < 0) {
      progressBarIndicator.style.left = "0";
    }
    if (newPosition > progressBarWidth) {
      progressBarIndicator.style.left = progressBarWidth + "px";
    }
  };

  /**
   Controls playback of the audio element.
   **/
  var _playBack = function() {
    if (_elements.audio.paused) {
      _elements.audio.play();
      _updatePlayStatus(true);
      document.title = "\u25B6 " + document.title;
    } else {
      _elements.audio.pause();
      _updatePlayStatus(false);
      document.title = document.title.substr(2);
    }
  };

  /**
   Sets the track if it hasn't already been loaded yet.
   **/
  var _setTrack = function() {
    var songURL = _elements.audio.children[_currentTrack - 1].src;

    _elements.audio.setAttribute("src", songURL);
    _elements.audio.load();

    _trackLoaded = true;

    _setTrackTitle(_currentTrack, _elements.playListRows);

    _setActiveItem(_currentTrack, _elements.playListRows);

    _elements.trackInfoBox.style.visibility = "visible";

    _playBack();
  };

  /**
   Sets the activly playing item within the playlist.
   **/
  var _setActiveItem = function(currentTrack, playListRows) {
    for (var i = 0; i < playListRows.length; i++) {
      playListRows[i].children[2].className = "track-title";
    }

    playListRows[currentTrack - 1].children[2].className = "track-title active-track";
  };

  /**
   Sets the text for the currently playing song.
   **/
  var _setTrackTitle = function(currentTrack, playListRows) {
    var trackTitleBox = document.querySelector(".player .info-box .track-info-box .track-title-text");
    var trackTitle = playListRows[currentTrack - 1].children[2].outerText;

    trackTitleBox.innerHTML = null;

    trackTitleBox.innerHTML = trackTitle;

    document.title = trackTitle;
  };

  /**
   Plays the next track when a track has ended playing.
   **/
  var _trackHasEnded = function() {
    parseInt(_currentTrack);
    _currentTrack = (_currentTrack === _elements.playListRows.length) ? 1 : _currentTrack + 1;
    _trackLoaded = false;

    _resetPlayStatus();

    _setTrack();
  };

  /**
 Updates the time for the song being played.
   **/
  var _trackTimeChanged = function() {
    var currentTimeBox = document.querySelector(".player .info-box .track-info-box .audio-time .current-time");
    var currentTime = audio.currentTime;
    var duration = audio.duration;
    var durationBox = document.querySelector(".player .info-box .track-info-box .audio-time .duration");
    var trackCurrentTime = _trackTime(currentTime);
    var trackDuration = _trackTime(duration);

    currentTimeBox.innerHTML = null;
    currentTimeBox.innerHTML = trackCurrentTime;

    durationBox.innerHTML = null;
    durationBox.innerHTML = trackDuration;

    _updateProgressIndicator(audio);
    _bufferProgress(audio);
  };

  /**
   A utility function for converting a time in miliseconds to a readable time of minutes and seconds.
   **/
  var _trackTime = function(seconds) {
    var min = 0;
    var sec = Math.floor(seconds);
    var time = 0;

    min = Math.floor(sec / 60);

    min = min >= 10 ? min : '0' + min;

    sec = Math.floor(sec % 60);

    sec = sec >= 10 ? sec : '0' + sec;

    time = min + ':' + sec;

    return time;
  };

  /**
   * Updates both the large and small toggle buttons accordingly.
   **/
  var _updatePlayStatus = function(audioPlaying) {
    if (audioPlaying) {
      _elements.playerButtons.largeToggleBtn.children[0].className = "large-pause-btn";

      _elements.playerButtons.smallToggleBtn[_currentTrack - 1].children[0].className = "small-pause-btn";
    } else {
      _elements.playerButtons.largeToggleBtn.children[0].className = "large-play-btn";

      _elements.playerButtons.smallToggleBtn[_currentTrack - 1].children[0].className = "small-play-btn";
    }

    //Update next and previous buttons accordingly
    if (_currentTrack === 1) {
      _elements.playerButtons.previousTrackBtn.disabled = true;
      _elements.playerButtons.previousTrackBtn.className = "previous-track-btn disabled";
    } else if (_currentTrack > 1 && _currentTrack !== _elements.playListRows.length) {
      _elements.playerButtons.previousTrackBtn.disabled = false;
      _elements.playerButtons.previousTrackBtn.className = "previous-track-btn";
      _elements.playerButtons.nextTrackBtn.disabled = false;
      _elements.playerButtons.nextTrackBtn.className = "next-track-btn";
    } else if (_currentTrack === _elements.playListRows.length) {
      _elements.playerButtons.nextTrackBtn.disabled = true;
      _elements.playerButtons.nextTrackBtn.className = "next-track-btn disabled";
    }
  };


  /**
   Resets all toggle buttons to be play buttons.
   **/
  var _resetPlayStatus = function() {
    var smallToggleBtn = _elements.playerButtons.smallToggleBtn;

    _elements.playerButtons.largeToggleBtn.children[0].className = "large-play-btn";

    for (var i = 0; i < smallToggleBtn.length; i++) {
      if (smallToggleBtn[i].children[0].className === "small-pause-btn") {
        smallToggleBtn[i].children[0].className = "small-play-btn";
      }
    }
  };

  return {
    initPlayer: initPlayer
  };
};

(function() {
  var player = new audioPlayer();

  player.initPlayer();
})();