Function for working out notif trigger permission

And make pushprocessor use this function

src/models/room-state.js

@@ -393,6 +393,37 @@ RoomState.prototype._maySendEventOfType = function(eventType, userId, state) {
     return member.powerLevel >= required_level;
 };
 
+/**
+ * Returns true if the given user ID has permission to trigger notification
+ * of type `notifLevelKey`
+ * @param {string} notifLevelKey The level of notification to test (eg. 'room')
+ * @param {string} userId The user ID of the user to test permission for
+ * @return {boolean} true if the given user ID has permission to trigger a
+ *                        notification of this type.
+ */
+RoomState.prototype.mayTriggerNotifOfType = function(notifLevelKey, userId) {
+    const member = this.getMember(userId);
+    if (!member || member.membership == 'leave') {
+        return false;
+    }
+
+    const powerLevelsEvent = this.getStateEvents('m.room.power_levels', '');
+
+    if (!powerLevelsEvent || !powerLevelsEvent.getContent()) {
+        return false;
+    }
+
+    let notifLevel = 50;
+    if (
+        powerLevelsEvent.getContent().notifications &&
+        powerLevelsEvent.getContent().notifications[notifLevelKey]
+    ) {
+        notifLevel = powerLevelsEvent.getContent().notifications[notifLevelKey];
+    }
+
+    return member.powerLevel >= notifLevel;
+};
+
 /**
  * The RoomState class.
  */

src/pushprocessor.js

@@ -145,28 +145,10 @@ function PushProcessor(client) {
             return false;
         }
 
-        const powerLevels = room.currentState.getStateEvents('m.room.power_levels', '');
-        if (!powerLevels || !powerLevels.getContent()) {
-            return false;
-        }
-
-        let notifLevel = 50;
-        if (
-            powerLevels.getContent().notifications &&
-            powerLevels.getContent().notifications[notifLevelKey]
-        ) {
-            notifLevel = powerLevels.getContent().notifications[notifLevelKey];
-        }
-
-        // This cannot be assumed to always be set for state events
-        // (in particular it is never set for the room creation event
-        // because it preceeds the join event of the sender).
-        // In these cases, this condition cannot match.
-        if (ev.sender === null) {
-            return false;
-        }
-
-        return ev.sender.powerLevel >= notifLevel;
+        // Note that this should not be the current state of the room but the state at
+        // the point the event is in the DAG. Unfortunately the js-sdk does not store
+        // this.
+        return room.currentState.mayTriggerNotifOfType(notifLevelKey, ev.getSender());
     };
 
     const eventFulfillsRoomMemberCountCondition = function(cond, ev) {