From 2d241623b713fcab4df2a283e83943b83ba60c6b Mon Sep 17 00:00:00 2001
From: Matthew Chen <charlesmchen@gmail.com>
Date: Tue, 21 Nov 2017 18:17:19 -0500
Subject: [PATCH] Improve handling of edge cases around unread indicator
 delimiting deleted message(s).

---
 .../ConversationViewController.m                |  6 ++++++
 Signal/src/util/ThreadUtil.m                    | 17 ++++++++++++++++-
 2 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/Signal/src/ViewControllers/ConversationView/ConversationViewController.m b/Signal/src/ViewControllers/ConversationView/ConversationViewController.m
index 6c7a37bc5..a93d6526a 100644
--- a/Signal/src/ViewControllers/ConversationView/ConversationViewController.m
+++ b/Signal/src/ViewControllers/ConversationView/ConversationViewController.m
@@ -3413,6 +3413,12 @@ typedef NS_ENUM(NSInteger, MessagesRangeSizeMode) {
     if (lastVisibleViewItem) {
         uint64_t lastVisibleTimestamp = lastVisibleViewItem.interaction.timestampForSorting;
         self.lastVisibleTimestamp = MAX(self.lastVisibleTimestamp, lastVisibleTimestamp);
+
+        // If we delete the last unread message (manually or due to disappearing messages)
+        // we may need to clean up an obsolete unread indicator.
+        if (lastVisibleViewItem.interaction.interactionType == OWSInteractionType_UnreadIndicator) {
+            [self ensureDynamicInteractions];
+        }
     }
 
     [self ensureScrollDownButton];
diff --git a/Signal/src/util/ThreadUtil.m b/Signal/src/util/ThreadUtil.m
index 00b6638ee..2ee2e5206 100644
--- a/Signal/src/util/ThreadUtil.m
+++ b/Signal/src/util/ThreadUtil.m
@@ -137,7 +137,7 @@ NS_ASSUME_NONNULL_BEGIN
                                                      dbConnection:(YapDatabaseConnection *)dbConnection
                                       hideUnreadMessagesIndicator:(BOOL)hideUnreadMessagesIndicator
                                   firstUnseenInteractionTimestamp:
-                                      (nullable NSNumber *)firstUnseenInteractionTimestampParameter
+                                      (nullable NSNumber *)firstUnseenInteractionTimestampParam
                                                      maxRangeSize:(int)maxRangeSize
 {
     OWSAssert(thread);
@@ -232,6 +232,21 @@ NS_ASSUME_NONNULL_BEGIN
         // have been marked as read.
         //
         // IFF this variable is non-null, there are unseen messages in the thread.
+        //
+        // Make a local copy of this parameter that we can modify.
+        NSNumber *_Nullable firstUnseenInteractionTimestampParameter = firstUnseenInteractionTimestampParam;
+        if (firstUnseenInteractionTimestampParameter) {
+            // Due to disappearing messages or manual deletion,
+            // firstUnseenInteractionTimestampParameter may refer to an obsolete
+            // interaction in which case we want to discard it.
+            TSInteraction *_Nullable lastInteraction =
+                [[transaction ext:TSMessageDatabaseViewExtensionName] lastObjectInGroup:thread.uniqueId];
+            if (!lastInteraction
+                || lastInteraction.timestampForSorting
+                    < firstUnseenInteractionTimestampParameter.unsignedLongLongValue) {
+                firstUnseenInteractionTimestampParameter = nil;
+            }
+        }
         if (firstUnseenInteractionTimestampParameter) {
             result.firstUnseenInteractionTimestamp = firstUnseenInteractionTimestampParameter;
         } else {