function format_track(index, title, length, bpm, notes) {
  length = Math.round(length);
  var minutes = Math.floor(length / 60);
  var seconds = length % 60;
  var length = minutes + ":" + ( "0" + seconds ).slice(-2);
  if ( notes == null ) notes = '-';
  entry = $('<div id="track_' + index + '" class="track" onClick="current(' + index + ');">');
  entry.append($('<span class="index">' + index + '</span>'));
  entry.append($('<span class="title" title="' + title + '">' + title.slice(0,65) + '</span>'));
  entry.append($('<span class="length">' + length + '</span>'));
  entry.append($('<span class="clear"></span>'));
  entry.append($('<span class="bpm">' + bpm + ' BPM</span>'));
  entry.append($('<span class="notes" title="' + notes + '">' + notes.slice(0,80) + '</span>'));
  return entry;
}

function init() {
  for (var index in tracklist) {
    track = tracklist[index];
    entry = format_track(track['index'], track['title'], track['length'], track['bpm'], track['notes']);
    $('#tracks').append(entry);
  }
}

/* Track 0 is 'no current track' */
function current(index) {
  if (index < 0 || index > maximum_index)
    return;
  current_index = index;
  $("div.track").removeClass("current");
  $("div#track_" + index).addClass("current");
  scroll_to(index);
}

function running(index) {
  if (index < 0 || index > maximum_index)
    return;
  running_index = index;
  $("div.track").removeClass("running");
  $("div#track_" + index).addClass("running");
}

function scroll_to(index) {
  // Scroll so that this tile is at the top third. If beyond page boundaries, clamp.
  var height = $(document).height();
  var viewport = $(window).height() / 3;
  var target = height * (index / maximum_index) - viewport;

  $('html,body').animate({scrollTop: target}, 250);
}

function next() {
  current(current_index + 1);
}

function prev() {
  current(current_index - 1);
}

function commit() {
  running(current_index);
  commit_update();

  params = {
    url: "/commit",
    type: "POST",
    data: { index: current_index }
  };

  var req = $.ajax(params)
    .done(function(data, textStatus, req) {
      commit_ready();
    })
    .fail(function(req, textStatus, errorThrown) {
      console.log("AjaxFailed:" + textStatus + " - " + errorThrown);
      commit_failed();
    });
}

function commit_ready() {
  var e = $('#commit');
  e.removeClass('update');
  e.removeClass('failed');
  e.html('&#x2713');
}

function commit_update() {
  var e = $('#commit');
  e.removeClass('failed');
  e.addClass('update');
  e.html('&#x2026');
}

function commit_failed() {
  var e = $('#commit');
  e.removeClass('update');
  e.addClass('failed');
  e.html('&#x2717');
}

maximum_index = tracklist.length;
current_index = 0;
running_index = 0;

init();