[feature] Create option to automatically reconnect after a few seconds

On some erros that display a modal with "Force reconnect" button, allow
Etherpad to automatically reload pad after a few seconds. Amount of
seconds is defined on settings.json.

Still need to create tests for this feature, and implement i18n.

src/static/css/pad.css

@@ -517,6 +517,23 @@ table#otheruserstable {
   display: block;
 }
 
+/* styles for the automatic reconnection timer: */
+#connectivity .visible.with_reconnect_timer button,
+#connectivity .visible.with_reconnect_timer .reconnecttimer * {
+  display: inline-block;
+}
+
+#connectivity .with_reconnect_timer .hidden,
+#connectivity .with_reconnect_timer #defaulttext.hidden,
+#connectivity .with_reconnect_timer button.hidden {
+  display: none;
+}
+
+#connectivity .with_reconnect_timer #cancelreconnect {
+  margin-left: 10px;
+}
+/* end of styles for the automatic reconnection timer */
+
 #reconnect_form button {
   font-size: 12pt;
   padding: 5px;

src/static/js/pad_automatic_reconnect.js

@@ -0,0 +1,135 @@
+
+exports.showCountDownTimerToReconnectOnModal = function($modal) {
+  if (clientVars.automaticReconnectionTimeout && $modal.is('.with_reconnect_timer')) {
+    createCountDownElementsIfNecessary($modal);
+
+    var timer = createTimerForModal($modal);
+
+    $modal.find('#cancelreconnect').one('click', function() {
+      timer.cancel();
+      disableAutomaticReconnection($modal);
+    });
+
+    enableAutomaticReconnection($modal);
+  }
+}
+
+var createCountDownElementsIfNecessary = function($modal) {
+  var elementsDoNotExist = $modal.find('#cancelreconnect').length === 0;
+  if (elementsDoNotExist) {
+    var $defaultMessage = $modal.find('#defaulttext');
+    var $reconnectButton = $modal.find('#forcereconnect');
+
+    // create extra DOM elements, if they don't exist
+    var $reconnectTimerMessage = $('<p class="reconnecttimer"> \
+                                      <span data-l10n-id="pad.modals.reconnecttimer">This window will automatically reconnect in </span> \
+                                      <span class="timetoexpire"></span> \
+                                    </p>');
+    var $cancelReconnect = $('<button id="cancelreconnect" data-l10n-id="pad.modals.cancel">Cancel</button>');
+
+    $reconnectTimerMessage.insertAfter($defaultMessage);
+    $cancelReconnect.insertAfter($reconnectButton);
+  }
+}
+
+var createTimerForModal = function($modal) {
+  var timer = new CountDownTimer(clientVars.automaticReconnectionTimeout);
+
+  timer.onTick(function(minutes, seconds) {
+    updateCountDownTimerMessage($modal, minutes, seconds);
+  }).onExpire(function() {
+    reconnect($modal);
+  }).start();
+
+  return timer;
+}
+
+var disableAutomaticReconnection = function($modal) {
+  toggleAutomaticReconnectionOption($modal, true);
+}
+var enableAutomaticReconnection = function($modal) {
+  toggleAutomaticReconnectionOption($modal, false);
+}
+var toggleAutomaticReconnectionOption = function($modal, disableAutomaticReconnect) {
+  $modal.find('#cancelreconnect, .reconnecttimer').toggleClass('hidden', disableAutomaticReconnect);
+  $modal.find('#defaulttext').toggleClass('hidden', !disableAutomaticReconnect);
+}
+
+var reconnect = function($modal) {
+  $modal.find('#forcereconnect').click();
+}
+
+var updateCountDownTimerMessage = function($modal, minutes, seconds) {
+  minutes = minutes < 10 ? '0' + minutes : minutes;
+  seconds = seconds < 10 ? '0' + seconds : seconds;
+
+  $modal.find('.timetoexpire').text(minutes + ':' + seconds);
+}
+
+// Timer based on http://stackoverflow.com/a/20618517.
+// duration: how many **seconds** until the timer ends
+// granularity (optional): how many **milliseconds** between each 'tick' of timer. Default: 1000ms (1s)
+var CountDownTimer = function(duration, granularity) {
+  this.duration    = duration;
+  this.granularity = granularity || 1000;
+  this.running     = false;
+
+  this.onTickCallbacks    = [];
+  this.onExpireCallbacks = [];
+}
+
+CountDownTimer.prototype.start = function() {
+  if (this.running) {
+    return;
+  }
+  this.running = true;
+  var start = Date.now(),
+      that = this,
+      diff, obj;
+
+  (function timer() {
+    diff = that.duration - Math.floor((Date.now() - start) / 1000);
+
+    if (diff > 0) {
+      that.timeoutId = setTimeout(timer, that.granularity);
+
+      obj = CountDownTimer.parse(diff);
+      that.onTickCallbacks.forEach(function(callback) {
+        callback.call(this, obj.minutes, obj.seconds);
+      }, that);
+    } else {
+      that.running = false;
+
+      that.onExpireCallbacks.forEach(function(callback) {
+        callback.call(this);
+      }, that);
+    }
+  }());
+};
+
+CountDownTimer.prototype.onTick = function(callback) {
+  if (typeof callback === 'function') {
+    this.onTickCallbacks.push(callback);
+  }
+  return this;
+};
+
+CountDownTimer.prototype.onExpire = function(callback) {
+  if (typeof callback === 'function') {
+    this.onExpireCallbacks.push(callback);
+  }
+  return this;
+};
+
+CountDownTimer.prototype.cancel = function() {
+  this.running = false;
+  clearTimeout(this.timeoutId);
+  return this;
+};
+
+CountDownTimer.parse = function(seconds) {
+  return {
+    'minutes': (seconds / 60) | 0,
+    'seconds': (seconds % 60) | 0
+  };
+};

src/static/js/pad_modals.js

@@ -1,5 +1,5 @@
 /**
- * This code is mostly from the old Etherpad. Please help us to comment this code. 
+ * This code is mostly from the old Etherpad. Please help us to comment this code.
  * This helps other people to understand this code better and helps them to improve it.
  * TL;DR COMMENTS ON THIS FILE ARE HIGHLY APPRECIATED
  */
@@ -19,8 +19,9 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
- 
+
 var padeditbar = require('./pad_editbar').padeditbar;
+var automaticReconnect = require('./pad_automatic_reconnect');
 
 var padmodals = (function()
 {
@@ -35,6 +36,9 @@ var padmodals = (function()
       padeditbar.toggleDropDown("none", function() {
         $("#connectivity .visible").removeClass('visible');
         $("#connectivity ."+messageId).addClass('visible');
+
+        automaticReconnect.showCountDownTimerToReconnectOnModal($('#connectivity .' + messageId));
+
         padeditbar.toggleDropDown("connectivity");
       });
     },