Add sender annotations

src/transcript/message-list-model.vala

@@ -9,8 +9,16 @@ public class MessageListModel : Object, ListModel
         owned get { return _messages.read_only_view; }
     }
 
+    public bool is_group_chat {
+        get {
+            return participants.size > 2;
+        }
+    }
+
     public string conversation_guid { get; private set; }
+
     private SortedSet<Message> _messages;
+    private HashSet<string> participants = new HashSet<string>();
     
     public MessageListModel(string conversation_guid) {
         _messages = new TreeSet<Message>((a, b) => {
@@ -29,6 +37,7 @@ public class MessageListModel : Object, ListModel
             // Clear existing set
             uint old_count = _messages.size;
             _messages.clear();
+            participants.clear();
             
             // Notify of removal
             if (old_count > 0) {
@@ -41,6 +50,8 @@ public class MessageListModel : Object, ListModel
             for (int i = 0; i < messages.length; i++) {
                 var message = messages[i];
                 _messages.add(message);
+                participants.add(message.sender);
+
                 position++;
             }