unread indicator uses sortId

- removed timestamp parameter. This wasn't totally obvious, previously we were tracking two pieces of state

1. `unreadIndicator.firstUnseenTimestamp`:
    the first unseen timestamp for a conversation that exists in the database
2. `unreadIndicator.timestamp`:
    the timestamp of the first interaction *after* the unread indicator that fits in the loading window

We don't actually need to track `2` because it was only used in a comparison like:

   viewItem.interaction.timestampForSorting >= unreadIndicator.timestamp

But by definition, unreadIndicator.firstUnseenTimestamp is always less than or
equal to unreadIndicator.timestamp. Put into terms of the `sortId` corallary,
the sortId of the first unseen interaction in the database is always less than
or equal to the sortId of the first unseen interaction that fits in the loading
window.

In other words, there's no situation where

   viewItem.interaction.sortId >= unreadIndicator.firstUnseenSortId

Signal/src/ViewControllers/ConversationView/ConversationViewController.m

@@ -4958,20 +4958,15 @@ typedef enum : NSUInteger {
             && !((id<OWSReadTracking>)viewItem.interaction).wasRead);
         if (isItemUnread && !unreadIndicator && !hasPlacedUnreadIndicator && !self.hasClearedUnreadMessagesIndicator) {
 
-            unreadIndicator =
+            unreadIndicator = [[OWSUnreadIndicator alloc] initWithFirstUnseenSortId:viewItem.interaction.sortId
-                [[OWSUnreadIndicator alloc] initUnreadIndicatorWithTimestamp:viewItem.interaction.timestamp
                                                               hasMoreUnseenMessages:NO
                                                missingUnseenSafetyNumberChangeCount:0
-                                                     unreadIndicatorPosition:0
+                                                            unreadIndicatorPosition:0];
-                                             firstUnseenInteractionTimestamp:viewItem.interaction.timestamp];
         }
 
         // Place the unread indicator onto the first appropriate view item,
         // if any.
-        // MJK FIXME - use sortId
+        if (unreadIndicator && viewItem.interaction.sortId >= unreadIndicator.firstUnseenSortId) {
-        // I'm not sure why we need a comparison here, vs. an equality. Maybe if the first unread
-        // message is deleted, we'd need to be sure everything still works.
-        if (unreadIndicator && viewItem.interaction.timestampForLegacySorting >= unreadIndicator.timestamp) {
             viewItem.unreadIndicator = unreadIndicator;
             unreadIndicator = nil;
             hasPlacedUnreadIndicator = YES;

SignalMessaging/utils/OWSUnreadIndicator.h

@@ -6,14 +6,11 @@ NS_ASSUME_NONNULL_BEGIN
 
 @interface OWSUnreadIndicator : NSObject
 
-// MJK FIXME - do we need this timestamp column?
-@property (nonatomic, readonly) uint64_t timestamp;
-
 @property (nonatomic, readonly) BOOL hasMoreUnseenMessages;
 
 @property (nonatomic, readonly) NSUInteger missingUnseenSafetyNumberChangeCount;
 
-// The timestamp of the oldest unseen message.
+// The sortId of the oldest unseen message.
 //
 // Once we enter messages view, we mark all messages read, so we need
 // a snapshot of what the first unread message was when we entered the
@@ -21,7 +18,7 @@ NS_ASSUME_NONNULL_BEGIN
 // repeatedly. The unread indicator should continue to show up until
 // it has been cleared, at which point hideUnreadMessagesIndicator is
 // YES in ensureDynamicInteractionsForThread:...
-@property (nonatomic, readonly) uint64_t firstUnseenInteractionTimestamp;
+@property (nonatomic, readonly) uint64_t firstUnseenSortId;
 
 // The index of the unseen indicator, counting from the _end_ of the conversation
 // history.
@@ -33,11 +30,10 @@ NS_ASSUME_NONNULL_BEGIN
 
 - (instancetype)init NS_UNAVAILABLE;
 
-- (instancetype)initUnreadIndicatorWithTimestamp:(uint64_t)timestamp
+- (instancetype)initWithFirstUnseenSortId:(uint64_t)firstUnseenSortId
                     hasMoreUnseenMessages:(BOOL)hasMoreUnseenMessages
      missingUnseenSafetyNumberChangeCount:(NSUInteger)missingUnseenSafetyNumberChangeCount
-                         unreadIndicatorPosition:(NSInteger)unreadIndicatorPosition
+                  unreadIndicatorPosition:(NSInteger)unreadIndicatorPosition NS_DESIGNATED_INITIALIZER;
-                 firstUnseenInteractionTimestamp:(uint64_t)firstUnseenInteractionTimestamp NS_DESIGNATED_INITIALIZER;
 
 @end
 

SignalMessaging/utils/OWSUnreadIndicator.m

@@ -8,11 +8,10 @@ NS_ASSUME_NONNULL_BEGIN
 
 @implementation OWSUnreadIndicator
 
-- (instancetype)initUnreadIndicatorWithTimestamp:(uint64_t)timestamp
+- (instancetype)initWithFirstUnseenSortId:(uint64_t)firstUnseenSortId
                     hasMoreUnseenMessages:(BOOL)hasMoreUnseenMessages
      missingUnseenSafetyNumberChangeCount:(NSUInteger)missingUnseenSafetyNumberChangeCount
                   unreadIndicatorPosition:(NSInteger)unreadIndicatorPosition
-                 firstUnseenInteractionTimestamp:(uint64_t)firstUnseenInteractionTimestamp
 {
     self = [super init];
 
@@ -20,11 +19,10 @@ NS_ASSUME_NONNULL_BEGIN
         return self;
     }
 
-    _timestamp = timestamp;
+    _firstUnseenSortId = firstUnseenSortId;
     _hasMoreUnseenMessages = hasMoreUnseenMessages;
     _missingUnseenSafetyNumberChangeCount = missingUnseenSafetyNumberChangeCount;
     _unreadIndicatorPosition = unreadIndicatorPosition;
-    _firstUnseenInteractionTimestamp = firstUnseenInteractionTimestamp;
 
     return self;
 }
@@ -40,7 +38,8 @@ NS_ASSUME_NONNULL_BEGIN
     }
 
     OWSUnreadIndicator *other = object;
-    return (self.timestamp == other.timestamp && self.hasMoreUnseenMessages == other.hasMoreUnseenMessages
+    return (self.firstUnseenSortId == other.firstUnseenSortId
+        && self.hasMoreUnseenMessages == other.hasMoreUnseenMessages
         && self.missingUnseenSafetyNumberChangeCount == other.missingUnseenSafetyNumberChangeCount
         && self.unreadIndicatorPosition == other.unreadIndicatorPosition);
 }

SignalMessaging/utils/ThreadUtil.m

@@ -363,15 +363,14 @@ NS_ASSUME_NONNULL_BEGIN
         // have been marked as read.
         //
         // IFF this variable is non-null, there are unseen messages in the thread.
-        NSNumber *_Nullable firstUnseenInteractionTimestamp = nil;
+        NSNumber *_Nullable firstUnseenSortId = nil;
         if (lastUnreadIndicator) {
-            firstUnseenInteractionTimestamp = @(lastUnreadIndicator.firstUnseenInteractionTimestamp);
+            firstUnseenSortId = @(lastUnreadIndicator.firstUnseenSortId);
         } else {
             TSInteraction *_Nullable firstUnseenInteraction =
                 [[TSDatabaseView unseenDatabaseViewExtension:transaction] firstObjectInGroup:thread.uniqueId];
             if (firstUnseenInteraction) {
-                // MJK FIXME - use sortId
+                firstUnseenSortId = @(firstUnseenInteraction.sortId);
-                firstUnseenInteractionTimestamp = @(firstUnseenInteraction.timestampForLegacySorting);
             }
         }
 
@@ -532,7 +531,7 @@ NS_ASSUME_NONNULL_BEGIN
                blockingSafetyNumberChanges:blockingSafetyNumberChanges
             nonBlockingSafetyNumberChanges:nonBlockingSafetyNumberChanges
                hideUnreadMessagesIndicator:hideUnreadMessagesIndicator
-            firstUnseenInteractionTimestamp:firstUnseenInteractionTimestamp];
+                         firstUnseenSortId:firstUnseenSortId];
 
         // Determine the position of the focus message _after_ performing any mutations
         // around dynamic interactions.
@@ -553,7 +552,7 @@ NS_ASSUME_NONNULL_BEGIN
        blockingSafetyNumberChanges:(NSArray<TSInvalidIdentityKeyErrorMessage *> *)blockingSafetyNumberChanges
     nonBlockingSafetyNumberChanges:(NSArray<TSInteraction *> *)nonBlockingSafetyNumberChanges
        hideUnreadMessagesIndicator:(BOOL)hideUnreadMessagesIndicator
-    firstUnseenInteractionTimestamp:(nullable NSNumber *)firstUnseenInteractionTimestamp
+                 firstUnseenSortId:(nullable NSNumber *)firstUnseenSortId
 {
     OWSAssertDebug(dynamicInteractions);
     OWSAssertDebug(thread);
@@ -564,7 +563,7 @@ NS_ASSUME_NONNULL_BEGIN
     if (hideUnreadMessagesIndicator) {
         return;
     }
-    if (!firstUnseenInteractionTimestamp) {
+    if (!firstUnseenSortId) {
         // If there are no unseen interactions, don't show an unread indicator.
         return;
     }
@@ -600,9 +599,7 @@ NS_ASSUME_NONNULL_BEGIN
                           return;
                       }
 
-                      // MJK FIXME - use sortId
+                      if (interaction.sortId < firstUnseenSortId.unsignedLongLongValue) {
-                      if (interaction.timestampForLegacySorting
-                          < firstUnseenInteractionTimestamp.unsignedLongLongValue) {
                           // By default we want the unread indicator to appear just before
                           // the first unread message.
                           *stop = YES;
@@ -634,15 +631,12 @@ NS_ASSUME_NONNULL_BEGIN
     if (hasMoreUnseenMessages) {
         NSMutableSet<NSData *> *missingUnseenSafetyNumberChanges = [NSMutableSet set];
         for (TSInvalidIdentityKeyErrorMessage *safetyNumberChange in blockingSafetyNumberChanges) {
-            // MJK FIXME - use sortId
+            BOOL isUnseen = safetyNumberChange.sortId >= firstUnseenSortId.unsignedLongLongValue;
-            BOOL isUnseen
-                = safetyNumberChange.timestampForLegacySorting >= firstUnseenInteractionTimestamp.unsignedLongLongValue;
             if (!isUnseen) {
                 continue;
             }
-            // MJK FIXME - use sortId
+
-            BOOL isMissing = safetyNumberChange.timestampForLegacySorting
+            BOOL isMissing = safetyNumberChange.sortId < interactionAfterUnreadIndicator.sortId;
-                < interactionAfterUnreadIndicator.timestampForLegacySorting;
             if (!isMissing) {
                 continue;
             }
@@ -667,14 +661,12 @@ NS_ASSUME_NONNULL_BEGIN
         unreadIndicatorPosition++;
     }
 
-    // MJK FIXME - use sortId, or maybe just timestamp, do we even need timestamp?
+    dynamicInteractions.unreadIndicator =
-    dynamicInteractions.unreadIndicator = [[OWSUnreadIndicator alloc]
+        [[OWSUnreadIndicator alloc] initWithFirstUnseenSortId:firstUnseenSortId.unsignedLongLongValue
-            initUnreadIndicatorWithTimestamp:interactionAfterUnreadIndicator.timestampForLegacySorting
                                         hasMoreUnseenMessages:hasMoreUnseenMessages
                          missingUnseenSafetyNumberChangeCount:missingUnseenSafetyNumberChangeCount
-                     unreadIndicatorPosition:unreadIndicatorPosition
+                                      unreadIndicatorPosition:unreadIndicatorPosition];
-             firstUnseenInteractionTimestamp:firstUnseenInteractionTimestamp.unsignedLongLongValue];
+    OWSLogInfo(@"Creating Unread Indicator: %llu", dynamicInteractions.unreadIndicator.firstUnseenSortId);
-    OWSLogInfo(@"Creating Unread Indicator: %llu", dynamicInteractions.unreadIndicator.timestamp);
 }
 
 + (nullable NSNumber *)focusMessagePositionForThread:(TSThread *)thread