Fix Discord merging webhook messages with same username

Closes #33.

PluralKit.Bot/Handlers/MessageDeleted.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Linq;
 using System.Threading.Tasks;
 
 using Myriad.Gateway;
@@ -17,11 +18,13 @@ namespace PluralKit.Bot
         private readonly IDatabase _db;
         private readonly ModelRepository _repo;
         private readonly ILogger _logger;
+        private readonly LastMessageCacheService _lastMessage;
 
-        public MessageDeleted(ILogger logger, IDatabase db, ModelRepository repo)
+        public MessageDeleted(ILogger logger, IDatabase db, ModelRepository repo, LastMessageCacheService lastMessage)
         {
             _db = db;
             _repo = repo;
+            _lastMessage = lastMessage;
             _logger = logger.ForContext<MessageDeleted>();
         }
         
@@ -36,6 +39,8 @@ namespace PluralKit.Bot
                 await _db.Execute(c => _repo.DeleteMessage(c, evt.Id));
             }
 
+            _lastMessage.HandleMessageDeletion(evt.ChannelId, evt.Id);
+
             // Fork a task to delete the message after a short delay
             // to allow for lookups to happen for a little while after deletion
             _ = Inner();
@@ -54,6 +59,7 @@ namespace PluralKit.Bot
                 await _db.Execute(c => _repo.DeleteMessagesBulk(c, evt.Ids));
             }
             
+            _lastMessage.HandleMessageDeletion(evt.ChannelId, evt.Ids.ToList());
             _ = Inner();
             return Task.CompletedTask;
         }

PluralKit.Bot/Proxy/ProxyService.cs

@@ -33,10 +33,11 @@ namespace PluralKit.Bot
         private readonly ProxyMatcher _matcher;
         private readonly IMetrics _metrics;
         private readonly IDiscordCache _cache;
+        private readonly LastMessageCacheService _lastMessage;
         private readonly DiscordApiClient _rest;
 
-        public ProxyService(LogChannelService logChannel, ILogger logger,
+        public ProxyService(LogChannelService logChannel, ILogger logger, WebhookExecutorService webhookExecutor, IDatabase db,
-                            WebhookExecutorService webhookExecutor, IDatabase db, ProxyMatcher matcher, IMetrics metrics, ModelRepository repo, IDiscordCache cache, DiscordApiClient rest)
+            ProxyMatcher matcher, IMetrics metrics, ModelRepository repo, IDiscordCache cache, DiscordApiClient rest, LastMessageCacheService lastMessage)
         {
             _logChannel = logChannel;
             _webhookExecutor = webhookExecutor;
@@ -45,6 +46,7 @@ namespace PluralKit.Bot
             _metrics = metrics;
             _repo = repo;
             _cache = cache;
+            _lastMessage = lastMessage;
             _rest = rest;
             _logger = logger.ForContext<ProxyService>();
         }
@@ -142,7 +144,7 @@ namespace PluralKit.Bot
                 GuildId = trigger.GuildId!.Value,
                 ChannelId = rootChannel.Id,
                 ThreadId = threadId,
-                Name = match.Member.ProxyName(ctx),
+                Name = await FixSameName(messageChannel.Id, ctx, match.Member),
                 AvatarUrl = AvatarUtils.TryRewriteCdnUrl(match.Member.ProxyAvatar(ctx)),
                 Content = content,
                 Attachments = trigger.Attachments,
@@ -230,6 +232,49 @@ namespace PluralKit.Bot
             };
         }
 
+        private async Task<string> FixSameName(ulong channel_id, MessageContext ctx, ProxyMember member)
+        {
+            var proxyName = member.ProxyName(ctx);
+
+            Message? lastMessage = null;
+
+            var lastMessageId = _lastMessage.GetLastMessage(channel_id)?.Previous;
+            if (lastMessageId == null)
+                // cache is out of date or channel is empty.
+                return proxyName;
+
+            lastMessage = await _rest.GetMessage(channel_id, lastMessageId.Value);
+
+            if (lastMessage == null)
+                // we don't have enough information to figure out if we need to fix the name, so bail here.
+                return proxyName;
+
+            await using var conn = await _db.Obtain();
+            var message = await _repo.GetMessage(conn, lastMessage.Id);
+
+            if (lastMessage.Author.Username == proxyName)
+            {
+                // last message wasn't proxied by us, but somehow has the same name
+                // it's probably from a different webhook (Tupperbox?) but let's fix it anyway!
+                if (message == null)
+                    return FixSameNameInner(proxyName);
+
+                // last message was proxied by a different member
+                if (message.Member.Id != member.Id)
+                    return FixSameNameInner(proxyName);
+            }
+
+            // if we fixed the name last message and it's the same member proxying, we want to fix it again
+            if (lastMessage.Author.Username == FixSameNameInner(proxyName) && message?.Member.Id == member.Id)
+                return FixSameNameInner(proxyName);
+
+            // No issues found, current proxy name is fine.
+            return proxyName;
+        }
+
+        private string FixSameNameInner(string name)
+            => $"{name}\u17b5";
+
         private async Task HandleProxyExecutedActions(Shard shard, IPKConnection conn, MessageContext ctx,
                                                       Message triggerMessage, Message proxyMessage,
                                                       ProxyMatch match)

PluralKit.Bot/Services/LastMessageCacheService.cs

@@ -1,6 +1,7 @@
 #nullable enable
 using System.Collections.Concurrent;
 using System.Collections.Generic;
+using System.Linq;
 
 using Myriad.Types;
 
@@ -13,14 +14,58 @@ namespace PluralKit.Bot
 
         public void AddMessage(Message msg)
         {
-            _cache[msg.ChannelId] = new CachedMessage(msg.Id, msg.ReferencedMessage.Value?.Id);
+            var previous = GetLastMessage(msg.ChannelId);
+            _cache[msg.ChannelId] = new CachedMessage(msg.Id, msg.ReferencedMessage.Value?.Id, previous?.Id);
         }
 
         public CachedMessage? GetLastMessage(ulong channel)
         {
             return _cache.TryGetValue(channel, out var message) ? message : null;
         }
+
+        public void HandleMessageDeletion(ulong channel, ulong message)
+        {
+            var storedMessage = GetLastMessage(channel);
+            if (storedMessage == null)
+                return;
+
+            if (message == storedMessage.Id)
+                if (storedMessage.Previous != null)
+                    _cache[channel] = new CachedMessage(storedMessage.Previous.Value, null, null);
+                else
+                    _cache.Remove(channel);
+            else if (message == storedMessage.Previous)
+                _cache[channel] = new CachedMessage(storedMessage.Id, storedMessage.ReferencedMessage, null);
+        }
+
+        public void HandleMessageDeletion(ulong channel, List<ulong> messages)
+        {
+            var storedMessage = GetLastMessage(channel);
+            if (storedMessage == null)
+                return;
+
+            if (!(messages.Contains(storedMessage.Id) || (storedMessage.Previous != null && messages.Contains(storedMessage.Previous.Value))))
+                // none of the deleted messages are relevant to the cache
+                return;
+
+            ulong? newLastMessage = null;
+
+            if (messages.Contains(storedMessage.Id))
+                newLastMessage = storedMessage.Previous;
+
+            if (storedMessage.Previous != null && messages.Contains(storedMessage.Previous.Value))
+                if (newLastMessage == storedMessage.Previous)
+                    newLastMessage = null;
+                else
+                {
+                    _cache[channel] = new CachedMessage(storedMessage.Id, storedMessage.ReferencedMessage, null);
+                    return;
+                }
+
+            if (newLastMessage == null)
+                _cache.Remove(channel);
+        }
     }
 
-    public record CachedMessage(ulong Id, ulong? ReferencedMessage);
+    public record CachedMessage(ulong Id, ulong? ReferencedMessage, ulong? Previous);
 }