Make clock/calendar aware of system timezone changes. Fixes #21

Related to nodejs/node#4022

app/clock.js

@@ -1,5 +1,6 @@
 const Electron = require('electron'); // eslint-disable-line
 const Moment = require('moment');
+const ResetDateCache = require('reset-date-cache');
 
 class Clock {
     /**
@@ -16,6 +17,12 @@ class Clock {
 
         // Start the clock
         this.start();
+
+        // System timezone was changed during runtime…
+        Electron.systemPreferences.subscribeNotification(
+            'NSSystemTimeZoneDidChangeDistributedNotification',
+            () => this.onTimeZoneChange()
+        );
     }
 
     /**
@@ -53,9 +60,36 @@ class Clock {
      * Sets the callback function which will be called on each tick.
      *
      * @param {function} callback Tick function to call.
+     * @return {Clock}
      */
     onTick(callback) {
         this.onTickHandler = callback;
+
+        return this;
+    }
+
+    /**
+     * System timezone was changed during runtime.
+     *
+     * @return {Clock}
+     */
+    onTimeZoneChange() {
+        // Need to use a timeout since resetting the date cache right after the
+        // system event has occured didn’t work properly/consistently.
+        // Unfortunately I have no idea what’s the actual problem over here.
+        setTimeout(() => {
+            // Reset v8’s date cache…
+            // @see https://github.com/nodejs/node/issues/4022
+            // @see https://github.com/nodejs/node/issues/3449
+            ResetDateCache();
+
+            // Notifiy all webContents about the timezone change
+            (Electron.webContents.getAllWebContents() || []).forEach(
+                webContent => webContent.send('clock.timezone.changed')
+            );
+        }, 1000);
+
+        return this;
     }
 
     /**

app/components/calendar/calendar-view/index.js

@@ -28,6 +28,9 @@ class CalendarView extends BaseElement {
 
         document.addEventListener('keydown', e => this.onKeyDown(e));
 
+        // When the system timezone was changed…
+        Electron.ipcRenderer.on('clock.timezone.changed', () => this.update());
+
         // Redraw calendar every minute to avoid displaying old/wrong states
         setInterval(() => this.update(), 1000 * 60);