Add local chat echo support

osu.Game/Online/Chat/Channel.cs

@@ -3,6 +3,7 @@
 
 using System;
 using System.Collections.Generic;
+using System.Diagnostics;
 using System.Linq;
 using Newtonsoft.Json;
 using osu.Framework.Configuration;
@@ -26,6 +27,8 @@ namespace osu.Game.Online.Chat
 
         public readonly SortedList<Message> Messages = new SortedList<Message>(Comparer<Message>.Default);
 
+        private readonly List<LocalEchoMessage> pendingMessages = new List<LocalEchoMessage>();
+
         public Bindable<bool> Joined = new Bindable<bool>();
 
         public bool ReadOnly => Name != "#lazer";
@@ -38,12 +41,23 @@ namespace osu.Game.Online.Chat
         }
 
         public event Action<IEnumerable<Message>> NewMessagesArrived;
+        public event Action<LocalEchoMessage, Message> PendingMessageResolved;
+        public event Action<Message> MessageRemoved;
+
+        public void AddLocalEcho(LocalEchoMessage message)
+        {
+            pendingMessages.Add(message);
+            Messages.Add(message);
+
+            NewMessagesArrived?.Invoke(new[] { message });
+        }
 
         public void AddNewMessages(params Message[] messages)
         {
             messages = messages.Except(Messages).ToArray();
 
-            Messages.AddRange(messages);
+            foreach (Message message in messages)
+                Messages.Add(message);
 
             purgeOldMessages();
 
@@ -52,11 +66,42 @@ namespace osu.Game.Online.Chat
 
         private void purgeOldMessages()
         {
-            int messageCount = Messages.Count;
+            // never purge local echos
+            int messageCount = Messages.Count - pendingMessages.Count;
             if (messageCount > MAX_HISTORY)
                 Messages.RemoveRange(0, messageCount - MAX_HISTORY);
         }
 
+        /// <summary>
+        /// Replace or remove a message from the channel.
+        /// </summary>
+        /// <param name="echo">The local echo message (client-side).</param>
+        /// <param name="final">The response message, or null if the message became invalid.</param>
+        public void ReplaceMessage(LocalEchoMessage echo, Message final)
+        {
+            if (!pendingMessages.Remove(echo))
+                Trace.Fail("Attempted to remove echo that wasn't present");
+
+            Messages.Remove(echo);
+
+            if (final == null)
+            {
+                MessageRemoved?.Invoke(echo);
+                return;
+            }
+
+            if (Messages.Contains(final))
+            {
+                // message already inserted, so let's throw away this update.
+                // we may want to handle this better in the future, but for the time being api requests are single-threaded so order is assumed.
+                MessageRemoved?.Invoke(echo);
+                return;
+            }
+
+            Messages.Add(final);
+            PendingMessageResolved?.Invoke(echo, final);
+        }
+
         public override string ToString() => Name;
     }
 }

osu.Game/Online/Chat/LocalEchoMessage.cs

@@ -0,0 +1,12 @@
+// Copyright (c) 2007-2017 ppy Pty Ltd <contact@ppy.sh>.
+// Licensed under the MIT Licence - https://raw.githubusercontent.com/ppy/osu/master/LICENCE
+
+namespace osu.Game.Online.Chat
+{
+    public class LocalEchoMessage : Message
+    {
+        public LocalEchoMessage() : base(null)
+        {
+        }
+    }
+}

osu.Game/Online/Chat/Message.cs

@@ -11,7 +11,7 @@ namespace osu.Game.Online.Chat
     public class Message : IComparable<Message>, IEquatable<Message>
     {
         [JsonProperty(@"message_id")]
-        public readonly long Id;
+        public readonly long? Id;
 
         //todo: this should be inside sender.
         [JsonProperty(@"sender_id")]
@@ -37,14 +37,23 @@ namespace osu.Game.Online.Chat
         {
         }
 
-        public Message(long id)
+        public Message(long? id)
         {
             Id = id;
         }
 
-        public int CompareTo(Message other) => Id.CompareTo(other.Id);
+        public int CompareTo(Message other)
+        {
 
-        public bool Equals(Message other) => Id == other?.Id;
+            if (!Id.HasValue)
+                return other.Id.HasValue ? 1 : Timestamp.CompareTo(other.Timestamp);
+            if (!other.Id.HasValue)
+                return -1;
+
+            return Id.Value.CompareTo(other.Id.Value);
+        }
+
+        public virtual bool Equals(Message other) => Id == other?.Id;
 
         public override int GetHashCode() => Id.GetHashCode();
     }