msglist: Separate messages after 10-min gap, with a sender row

Fixes: #1773

Author: rajveermalviya

lib/model/message_list.dart

@@ -459,8 +459,10 @@ mixin _MessageSequence {
       if (!messagesSameDay(prevMessageItem.message, message)) {
         items.add(MessageListDateSeparatorItem(message));
         canShareSender = false;
+      } else if (prevMessageItem.message.senderId == message.senderId) {
+        canShareSender = messagesCloseInTime(prevMessage, message);
       } else {
-        canShareSender = prevMessageItem.message.senderId == message.senderId;
+        canShareSender = false;
       }
     }
     final item = buildItem(canShareSender);
@@ -568,6 +570,12 @@ bool messagesSameDay(MessageBase prevMessage, MessageBase message) {
   return true;
 }
 
+@visibleForTesting
+bool messagesCloseInTime(MessageBase prevMessage, MessageBase message) {
+  final diffSeconds = (message.timestamp - prevMessage.timestamp).abs();
+  return diffSeconds <= 10 * 60;
+}
+
 bool _sameDay(DateTime date1, DateTime date2) {
   if (date1.year != date2.year) return false;
   if (date1.month != date2.month) return false;

test/model/message_list_test.dart

@@ -2946,6 +2946,8 @@ void main() {
     // whether the sender should be shown, but the difference between
     // fetchInitial and handleMessageEvent etc. doesn't matter.
 
+    // TODO(#1825) test that messagesCloseInTime gets used
+
     final now = clock.now();
     final t1 = eg.utcTimestamp(now.subtract(Duration(days: 1)));
     final t2 = eg.utcTimestamp(now);
@@ -3118,6 +3120,8 @@ void main() {
       }
     }
   });
+
+  // TODO(#1825) test messagesCloseInTime
 }
 
 MessageListView? _lastModel;
@@ -3244,7 +3248,7 @@ void checkInvariants(MessageListView model) {
         .message.identicalTo(model.outboxMessages[j-model.messages.length]);
     }
     check(model.items[i++]).isA<MessageListMessageBaseItem>()
-      ..showSender.equals(
+      ..showSender.equals( // TODO(#1825) adjust to reflect messagesCloseInTime
         forcedShowSender || allMessages[j].senderId != allMessages[j-1].senderId)
       ..isLastInBlock.equals(
         i == model.items.length || switch (model.items[i]) {