(function() {
  'use strict';

  var battery;

  function toTime(sec) {
    sec = parseInt(sec, 10);

    var hours = Math.floor(sec / 3600),
        minutes = Math.floor((sec - (hours * 3600)) / 60),
        seconds = sec - (hours * 3600) - (minutes * 60);

    if (hours < 10) { hours   = '0' + hours; }
    if (minutes < 10) { minutes = '0' + minutes; }
    if (seconds < 10) { seconds = '0' + seconds; }

    return hours + ':' + minutes;
  }

  function readBattery(b) {
    battery = b || battery;

    var percentage = parseFloat((battery.level * 100).toFixed(2)) + '%',
        fully,
        remaining;

    if (battery.charging && battery.chargingTime === Infinity) {
      fully = 'Calculating...';
    } else if (battery.chargingTime !== Infinity) {
      fully = toTime(battery.chargingTime);
    } else {
      fully = '---';
    }

    if (!battery.charging && battery.dischargingTime === Infinity) {
      remaining = 'Calculating...';
    } else if (battery.dischargingTime !== Infinity) {
      remaining = toTime(battery.dischargingTime);
    } else {
      remaining = '---';
    }

    document.styleSheets[0].insertRule('.battery:before{width:' + percentage + '}', 0);
    document.querySelector('.battery-percentage').innerHTML = percentage;
    document.querySelector('.battery-status').innerHTML = battery.charging ? 'Adapter' : 'Battery';
    document.querySelector('.battery-level').innerHTML = percentage;
    document.querySelector('.battery-fully').innerHTML = fully;
    document.querySelector('.battery-remaining').innerHTML = remaining;

  }

  if (navigator.battery) {
    readBattery(navigator.battery);

  } else if (navigator.getBattery) {
    navigator.getBattery().then(readBattery);

  } else {
    document.querySelector('.not-support').removeAttribute('hidden');
  }

  window.onload = function () {
    battery.addEventListener('chargingchange', function() {
      readBattery();
    });

    battery.addEventListener("levelchange", function() {
      readBattery();
    });
  };
}());