From b9557064bf6003a666b8fb6813dd3618fe9e48b4 Mon Sep 17 00:00:00 2001
From: Luke Barnard <lukeb@openmarket.com>
Date: Wed, 12 Apr 2017 14:36:20 +0100
Subject: [PATCH] Simplify is_event_after logic

---
 synapse/handlers/read_marker.py |  5 +++--
 synapse/storage/events.py       | 13 +++----------
 2 files changed, 6 insertions(+), 12 deletions(-)

diff --git a/synapse/handlers/read_marker.py b/synapse/handlers/read_marker.py
index 800240b8a..3f46a16b9 100644
--- a/synapse/handlers/read_marker.py
+++ b/synapse/handlers/read_marker.py
@@ -48,9 +48,10 @@ class ReadMarkerHandler(BaseHandler):
             should_update = True
 
             if existing_read_marker:
+                # Only update if the new marker is ahead in the stream
                 should_update = yield self.store.is_event_after(
-                    existing_read_marker['marker'],
-                    event_id
+                    event_id,
+                    existing_read_marker['marker']
                 )
 
             if should_update:
diff --git a/synapse/storage/events.py b/synapse/storage/events.py
index 702bd64b2..221cb563d 100644
--- a/synapse/storage/events.py
+++ b/synapse/storage/events.py
@@ -2161,18 +2161,11 @@ class EventsStore(SQLBaseStore):
 
     @defer.inlineCallbacks
     def is_event_after(self, event_id1, event_id2):
-        is_after = True
-
+        """Returns True if event_id1 is after event_id2 in the stream
+        """
         to_1, so_1 = yield self._get_event_ordering(event_id1)
         to_2, so_2 = yield self._get_event_ordering(event_id2)
-
-        # Prevent updating if the existing marker is ahead in the stream
-        if to_1 > to_2:
-            is_after = False
-        elif to_1 == to_2 and so_1 >= so_2:
-            is_after = False
-
-        defer.returnValue(is_after)
+        defer.returnValue(to_1 > to_2 and so_1 > so_2)
 
     @defer.inlineCallbacks
     def _get_event_ordering(self, event_id):