(function initAutoUpgrade () {
  // Prevent click-jacking
  try {
    if (window == window.top || window.chrome && chrome.app && chrome.app.window) {
      document.documentElement.style.display = 'block';
    } else {
      top.location = self.location;
    }
  } catch (e) {console.error('CJ protection', e)};

  window.safeConfirm = function (params, callback) {
    if (typeof params === 'string') {
      params = {message: params};
    }
    var result = false
    try {
      result = confirm(params.message);
    } catch (e) {
      result = true;
    }
    setTimeout(function () {callback(result)}, 10);
  };

  if ((!navigator.serviceWorker && !window.applicationCache) || Config.Modes.packed || !window.addEventListener) {
    return;
  }

  var declined = false;
  function updateFound() {
    if (!declined) {
      safeConfirm({type: 'WEBOGRAM_UPDATED_RELOAD', message: 'A new version of Webogram is downloaded. Launch it?'}, function (result) {
        if (result) {
          window.location.reload();
        } else {
          declined = true;
        }
      });
    }
  }

  if (navigator.serviceWorker) {
    // If available, use a Service Worker to handle offlining.
    navigator.serviceWorker.register('offline-worker.js').then(function(registration) {
      console.log('offline worker registered');
      registration.addEventListener('updatefound', function() {
        var installingWorker = this.installing;

        // Wait for the new service worker to be installed before prompting to update.
        installingWorker.addEventListener('statechange', function() {
          switch (installingWorker.state) {
            case 'installed':
              // Only show the prompt if there is currently a controller so it is not
              // shown on first load.
              if (navigator.serviceWorker.controller) {
                updateFound();
              }
              break;

            case 'redundant':
              console.error('The installing service worker became redundant.');
              break;
          }
        });
      });
    });
  } else {
    // Otherwise, use AppCache.
    var appCache = window.applicationCache,
        updateTimeout = false,
        scheduleUpdate = function (delay) {
          clearTimeout(updateTimeout);
          updateTimeout = setTimeout(function () {
            try {
              appCache.update();
            } catch (ex) {
              console.log('appCache.update: ' + ex);
            }
          }, delay || 300000);
        };

    scheduleUpdate(3000);
    window.addEventListener('load', function () {
      appCache.addEventListener('updateready', function () {
        if (appCache.status == appCache.UPDATEREADY) {
          updateFound();
        }
      }, false);
      appCache.addEventListener('noupdate', function () {scheduleUpdate()}, false);
      appCache.addEventListener('error', function () {scheduleUpdate()}, false);
    });
  }
})();