Introduce ConversationSnapshot.

Signal/src/ViewControllers/ConversationView/ConversationViewController.m

@@ -450,11 +450,11 @@ typedef enum : NSUInteger {
     NSString *_Nullable recipientId = notification.userInfo[kNSNotificationKey_ProfileRecipientId];
     NSData *_Nullable groupId = notification.userInfo[kNSNotificationKey_ProfileGroupId];
     if (recipientId.length > 0 && [self.thread.recipientIdentifiers containsObject:recipientId]) {
-        [self.conversationViewModel ensureDynamicInteractions];
+        [self.conversationViewModel ensureDynamicInteractionsAndUpdateIfNecessary:YES];
     } else if (groupId.length > 0 && self.thread.isGroupThread) {
         TSGroupThread *groupThread = (TSGroupThread *)self.thread;
         if ([groupThread.groupModel.groupId isEqualToData:groupId]) {
-            [self.conversationViewModel ensureDynamicInteractions];
+            [self.conversationViewModel ensureDynamicInteractionsAndUpdateIfNecessary:YES];
             [self ensureBannerState];
         }
     }
@@ -868,6 +868,7 @@ typedef enum : NSUInteger {
     // Avoid layout corrupt issues and out-of-date message subtitles.
     self.lastReloadDate = [NSDate new];
     [self.conversationViewModel viewDidResetContentAndLayout];
+    [self tryToUpdateConversationSnapshot];
     [self.collectionView.collectionViewLayout invalidateLayout];
     [self.collectionView reloadData];
 
@@ -2437,7 +2438,7 @@ typedef enum : NSUInteger {
 
 - (void)contactsViewHelperDidUpdateContacts
 {
-    [self.conversationViewModel ensureDynamicInteractions];
+    [self.conversationViewModel ensureDynamicInteractionsAndUpdateIfNecessary:YES];
 }
 
 - (void)createConversationScrollButtons
@@ -2475,7 +2476,7 @@ typedef enum : NSUInteger {
     _hasUnreadMessages = hasUnreadMessages;
 
     self.scrollDownButton.hasUnreadMessages = hasUnreadMessages;
-    [self.conversationViewModel ensureDynamicInteractions];
+    [self.conversationViewModel ensureDynamicInteractionsAndUpdateIfNecessary:YES];
 }
 
 - (void)scrollDownButtonTapped
@@ -2620,7 +2621,7 @@ typedef enum : NSUInteger {
     [self showApprovalDialogForAttachment:attachment];
 
     [ThreadUtil addThreadToProfileWhitelistIfEmptyContactThread:self.thread];
-    [self.conversationViewModel ensureDynamicInteractions];
+    [self.conversationViewModel ensureDynamicInteractionsAndUpdateIfNecessary:YES];
 }
 
 - (void)messageWasSent:(TSOutgoingMessage *)message
@@ -2980,7 +2981,7 @@ typedef enum : NSUInteger {
             [self messageWasSent:message];
 
             if (didAddToProfileWhitelist) {
-                [self.conversationViewModel ensureDynamicInteractions];
+                [self.conversationViewModel ensureDynamicInteractionsAndUpdateIfNecessary:YES];
             }
         }];
 }
@@ -3626,7 +3627,7 @@ typedef enum : NSUInteger {
         [self messageWasSent:message];
 
         if (didAddToProfileWhitelist) {
-            [self.conversationViewModel ensureDynamicInteractions];
+            [self.conversationViewModel ensureDynamicInteractionsAndUpdateIfNecessary:YES];
         }
     });
 }
@@ -4029,7 +4030,7 @@ typedef enum : NSUInteger {
 
     [self clearDraft];
     if (didAddToProfileWhitelist) {
-        [self.conversationViewModel ensureDynamicInteractions];
+        [self.conversationViewModel ensureDynamicInteractionsAndUpdateIfNecessary:YES];
     }
 }
 
@@ -4927,6 +4928,15 @@ typedef enum : NSUInteger {
 
 #pragma mark - Conversation Snapshot
 
+- (void)tryToUpdateConversationSnapshot
+{
+    if (!self.isObservingVMUpdates) {
+        return;
+    }
+
+    [self updateConversationSnapshot];
+}
+
 - (void)updateConversationSnapshot
 {
     ConversationSnapshot *conversationSnapshot = [ConversationSnapshot new];

Signal/src/ViewControllers/ConversationView/ConversationViewModel.h

@@ -93,7 +93,7 @@ typedef NS_ENUM(NSUInteger, ConversationUpdateItemType) {
           focusMessageIdOnOpen:(nullable NSString *)focusMessageIdOnOpen
                       delegate:(id<ConversationViewModelDelegate>)delegate NS_DESIGNATED_INITIALIZER;
 
-- (void)ensureDynamicInteractions;
+- (void)ensureDynamicInteractionsAndUpdateIfNecessary:(BOOL)updateIfNecessary;
 
 - (void)clearUnreadMessagesIndicator;
 

Signal/src/ViewControllers/ConversationView/ConversationViewModel.m

@@ -273,7 +273,7 @@ static const int kYapDatabaseRangeMaxLength = 25000;
 {
     OWSAssertIsOnMainThread();
 
-    [self ensureDynamicInteractions];
+    [self ensureDynamicInteractionsAndUpdateIfNecessary:YES];
 }
 
 - (void)profileWhitelistDidChange:(NSNotification *)notification
@@ -308,7 +308,7 @@ static const int kYapDatabaseRangeMaxLength = 25000;
     self.typingIndicatorsSender = [self.typingIndicators typingRecipientIdForThread:self.thread];
     self.collapseCutoffDate = [NSDate new];
 
-    [self ensureDynamicInteractions];
+    [self ensureDynamicInteractionsAndUpdateIfNecessary:NO];
     [self.primaryStorage updateUIDatabaseConnectionToLatest];
 
     [self createNewMessageMapping];
@@ -464,14 +464,15 @@ static const int kYapDatabaseRangeMaxLength = 25000;
     self.collapseCutoffDate = [NSDate new];
 }
 
-- (void)ensureDynamicInteractions
+- (void)ensureDynamicInteractionsAndUpdateIfNecessary:(BOOL)updateIfNecessary
 {
     OWSAssertIsOnMainThread();
 
     const int currentMaxRangeSize = (int)self.messageMapping.desiredLength;
     const int maxRangeSize = MAX(kConversationInitialMaxRangeSize, currentMaxRangeSize);
 
-    self.dynamicInteractions = [ThreadUtil ensureDynamicInteractionsForThread:self.thread
+    ThreadDynamicInteractions *dynamicInteractions =
+        [ThreadUtil ensureDynamicInteractionsForThread:self.thread
                                        contactsManager:self.contactsManager
                                        blockingManager:self.blockingManager
                                           dbConnection:self.editingDatabaseConnection
@@ -479,6 +480,16 @@ static const int kYapDatabaseRangeMaxLength = 25000;
                                    lastUnreadIndicator:self.dynamicInteractions.unreadIndicator
                                         focusMessageId:self.focusMessageIdOnOpen
                                           maxRangeSize:maxRangeSize];
+    BOOL didChange = ![NSObject isNullableObject:self.dynamicInteractions equalTo:dynamicInteractions];
+    self.dynamicInteractions = dynamicInteractions;
+
+    if (didChange && updateIfNecessary) {
+        if (![self reloadViewItems]) {
+            OWSFailDebug(@"Failed to reload view items.");
+        }
+
+        [self.delegate conversationViewModelDidUpdate:ConversationUpdate.reloadUpdate];
+    }
 }
 
 - (nullable id<ConversationViewItem>)viewItemForUnreadMessagesIndicator
@@ -519,7 +530,7 @@ static const int kYapDatabaseRangeMaxLength = 25000;
     if (self.dynamicInteractions.unreadIndicator) {
         // If we've just cleared the "unread messages" indicator,
         // update the dynamic interactions.
-        [self ensureDynamicInteractions];
+        [self ensureDynamicInteractionsAndUpdateIfNecessary:YES];
     }
 }
 
@@ -962,7 +973,7 @@ static const int kYapDatabaseRangeMaxLength = 25000;
 
     self.collapseCutoffDate = [NSDate new];
 
-    [self ensureDynamicInteractions];
+    [self ensureDynamicInteractionsAndUpdateIfNecessary:NO];
 
     if (![self reloadViewItems]) {
         OWSFailDebug(@"failed to reload view items in resetMapping.");
@@ -1584,7 +1595,7 @@ static const int kYapDatabaseRangeMaxLength = 25000;
 
     self.collapseCutoffDate = [NSDate new];
 
-    [self ensureDynamicInteractions];
+    [self ensureDynamicInteractionsAndUpdateIfNecessary:NO];
 
     if (![self reloadViewItems]) {
         OWSFailDebug(@"failed to reload view items in resetMapping.");

SignalMessaging/utils/ThreadUtil.m

@@ -45,6 +45,21 @@ NS_ASSUME_NONNULL_BEGIN
     self.unreadIndicator = nil;
 }
 
+- (BOOL)isEqual:(id)object
+{
+    if (self == object) {
+        return YES;
+    }
+
+    if (![object isKindOfClass:[ThreadDynamicInteractions class]]) {
+        return NO;
+    }
+
+    ThreadDynamicInteractions *other = (ThreadDynamicInteractions *)object;
+    return ([NSObject isNullableObject:self.focusMessagePosition equalTo:other.focusMessagePosition] &&
+        [NSObject isNullableObject:self.unreadIndicator equalTo:other.unreadIndicator]);
+}
+
 @end
 
 #pragma mark -