GCal: Better Callback management

- when callback of an old channel is received this channel is canceled automatically

eventplanner_gcal/google_sync.py

@@ -332,3 +332,36 @@ def stopAllGCalSubscriptions( service=None ):
     for dbChannel in GCalPushChannel.objects.all():
         print("Stopping %s expiry at %d " % ( dbChannel.id, dbChannel.expiration ) )
         GCalPushChannel.stop( service, dbChannel.toGChannel() )
+
+
+def checkIfGoogleCallbackIsValid( token, channelID, resourceID, service=None ):
+    if service is None: service = getServiceObject()
+
+    allChannels = GCalPushChannel.objects.all()
+    if len(allChannels) == 0:
+        return False # no known subscriptions -> callback has to be from an old channel
+
+    if len(allChannels) > 1:
+        logger.warning( "Multiple GCal subscriptions! This is strange and probably an error. "
+                        "All channels are closed and one new is created. ")
+        stopAllGCalSubscriptions( service )
+        checkGCalSubscription()
+        allChannels = GCalPushChannel.objects.all()
+
+    assert( len(allChannels) == 1 )
+
+    theChannel = allChannels[0]
+
+    if channelID != theChannel.id or resourceID != theChannel.resource_id or token != theChannel.token:
+        logger.warning( "Got GCal Response from an unexpected Channel"
+                        "Got      (%s,%s,%s) "
+                        "expected (%s,%s,%s) "
+                        "Old Channel is stopped."
+                        % ( channelID, resourceID,token, theChannel.id, theChannel.resource_id, theChannel.token ))
+
+        channelToStop = GCalPushChannel( id = channelID, resource_id = resourceID, token = token )
+        GCalPushChannel.stop( service, channelToStop.toGChannel() )
+
+        return False
+
+    return True