re-add core logic

Signed-off-by: Michael Telatynski <7t3chguy@gmail.com>

src/shouldHideEvent.js

@@ -0,0 +1,48 @@
+/*
+ Copyright 2017 Michael Telatynski <7t3chguy@gmail.com>
+
+ Licensed under the Apache License, Version 2.0 (the "License");
+ you may not use this file except in compliance with the License.
+ You may obtain a copy of the License at
+
+ http://www.apache.org/licenses/LICENSE-2.0
+
+ Unless required by applicable law or agreed to in writing, software
+ distributed under the License is distributed on an "AS IS" BASIS,
+ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ See the License for the specific language governing permissions and
+ limitations under the License.
+ */
+
+function _isLeaveOrJoin(ev) {
+    const isMemberEvent = ev.getType() === 'm.room.member' && ev.getStateKey() !== undefined;
+    if (!isMemberEvent) {
+        return false; // bail early: all the checks below concern member events only
+    }
+
+    // TODO: These checks are done to make sure we're dealing with membership transitions not avatar changes / dupe joins
+    //       These checks are also being done in TextForEvent and should really reside in the JS SDK as a helper function
+    const membership = ev.getContent().membership;
+    const prevMembership = ev.getPrevContent().membership;
+    if (membership === prevMembership && membership === 'join') {
+        // join -> join : This happens when display names change / avatars are set / genuine dupe joins with no changes.
+        //                Find out which we're dealing with.
+        if (ev.getPrevContent().displayname !== ev.getContent().displayname) {
+            return false; // display name changed
+        }
+        if (ev.getPrevContent().avatar_url !== ev.getContent().avatar_url) {
+            return false; // avatar url changed
+        }
+        // dupe join event, fall through to hide rules
+    }
+
+    // this only applies to joins/leaves not invites/kicks/bans
+    return membership === 'join' || (membership === 'leave' && ev.getStateKey() === ev.getSender());
+}
+
+export default function(ev, syncedSettings) {
+    // Hide redacted events
+    if (syncedSettings['hideRedactions'] && ev.isRedacted()) return true;
+    if (syncedSettings['hideJoinLeaves'] && _isLeaveOrJoin(ev)) return true;
+    return false;
+}