feature: Add Direction.Around to GetMessagesAsync (#1526)

* Add Direction.Around to GetMessagesAsync

* Reuse the method

* Reuse GetMany

* Fix limit when getting from cache without message id

* Fix limit when getting from rest without message id

* Change cache return

It will return in a similar way to REST

src/Discord.Net.Rest/Entities/Channels/ChannelHelper.cs

@@ -109,12 +109,19 @@ namespace Discord.Rest
         public static IAsyncEnumerable<IReadOnlyCollection<RestMessage>> GetMessagesAsync(IMessageChannel channel, BaseDiscordClient client,
             ulong? fromMessageId, Direction dir, int limit, RequestOptions options)
         {
-            if (dir == Direction.Around)
-                throw new NotImplementedException(); //TODO: Impl
-
             var guildId = (channel as IGuildChannel)?.GuildId;
             var guild = guildId != null ? (client as IDiscordClient).GetGuildAsync(guildId.Value, CacheMode.CacheOnly).Result : null;
 
+            if (dir == Direction.Around && limit > DiscordConfig.MaxMessagesPerBatch)
+            {
+                int around = limit / 2;
+                if (fromMessageId.HasValue)
+                    return GetMessagesAsync(channel, client, fromMessageId.Value + 1, Direction.Before, around + 1, options) //Need to include the message itself
+                        .Concat(GetMessagesAsync(channel, client, fromMessageId, Direction.After, around, options));
+                else //Shouldn't happen since there's no public overload for ulong? and Direction
+                    return GetMessagesAsync(channel, client, null, Direction.Before, around + 1, options);
+            }
+
             return new PagedAsyncEnumerable<RestMessage>(
                 DiscordConfig.MaxMessagesPerBatch,
                 async (info, ct) =>

src/Discord.Net.WebSocket/Entities/Channels/SocketChannelHelper.cs

@@ -11,23 +11,11 @@ namespace Discord.WebSocket
         public static IAsyncEnumerable<IReadOnlyCollection<IMessage>> GetMessagesAsync(ISocketMessageChannel channel, DiscordSocketClient discord, MessageCache messages,
             ulong? fromMessageId, Direction dir, int limit, CacheMode mode, RequestOptions options)
         {
-            if (dir == Direction.Around)
-                throw new NotImplementedException(); //TODO: Impl
-
-            IReadOnlyCollection<SocketMessage> cachedMessages = null;
-            IAsyncEnumerable<IReadOnlyCollection<IMessage>> result = null;
-            
             if (dir == Direction.After && fromMessageId == null)
                 return AsyncEnumerable.Empty<IReadOnlyCollection<IMessage>>();
 
-            if (dir == Direction.Before || mode == CacheMode.CacheOnly)
-            {
-                if (messages != null) //Cache enabled
-                    cachedMessages = messages.GetMany(fromMessageId, dir, limit);
-                else
-                    cachedMessages = ImmutableArray.Create<SocketMessage>();
-                result = ImmutableArray.Create(cachedMessages).ToAsyncEnumerable<IReadOnlyCollection<IMessage>>();
-            }
+            var cachedMessages = GetCachedMessages(channel, discord, messages, fromMessageId, dir, limit);
+            var result = ImmutableArray.Create(cachedMessages).ToAsyncEnumerable<IReadOnlyCollection<IMessage>>();
 
             if (dir == Direction.Before)
             {
@@ -38,18 +26,35 @@ namespace Discord.WebSocket
                 //Download remaining messages
                 ulong? minId = cachedMessages.Count > 0 ? cachedMessages.Min(x => x.Id) : fromMessageId;
                 var downloadedMessages = ChannelHelper.GetMessagesAsync(channel, discord, minId, dir, limit, options);
-                return result.Concat(downloadedMessages);
+                if (cachedMessages.Count != 0)
+                    return result.Concat(downloadedMessages);
+                else
+                    return downloadedMessages;
             }
-            else
+            else if (dir == Direction.After)
+            {
+                limit -= cachedMessages.Count;
+                if (mode == CacheMode.CacheOnly || limit <= 0)
+                    return result;
+
+                //Download remaining messages
+                ulong maxId = cachedMessages.Count > 0 ? cachedMessages.Max(x => x.Id) : fromMessageId.Value;
+                var downloadedMessages = ChannelHelper.GetMessagesAsync(channel, discord, maxId, dir, limit, options);
+                if (cachedMessages.Count != 0)
+                    return result.Concat(downloadedMessages);
+                else
+                    return downloadedMessages;
+            }
+            else //Direction.Around
             {
-                if (mode == CacheMode.CacheOnly)
+                if (mode == CacheMode.CacheOnly || limit <= cachedMessages.Count)
                     return result;
 
-                //Dont use cache in this case
+                //Cache isn't useful here since Discord will send them anyways
                 return ChannelHelper.GetMessagesAsync(channel, discord, fromMessageId, dir, limit, options);
             }
         }
-        public static IReadOnlyCollection<SocketMessage> GetCachedMessages(SocketChannel channel, DiscordSocketClient discord, MessageCache messages,
+        public static IReadOnlyCollection<SocketMessage> GetCachedMessages(ISocketMessageChannel channel, DiscordSocketClient discord, MessageCache messages,
             ulong? fromMessageId, Direction dir, int limit)
         {
             if (messages != null) //Cache enabled

src/Discord.Net.WebSocket/Entities/Messages/MessageCache.cs

@@ -56,11 +56,23 @@ namespace Discord.WebSocket
                 cachedMessageIds = _orderedMessages;
             else if (dir == Direction.Before)
                 cachedMessageIds = _orderedMessages.Where(x => x < fromMessageId.Value);
-            else
+            else if (dir == Direction.After)
                 cachedMessageIds = _orderedMessages.Where(x => x > fromMessageId.Value);
+            else //Direction.Around
+            {
+                if (!_messages.TryGetValue(fromMessageId.Value, out SocketMessage msg))
+                    return ImmutableArray<SocketMessage>.Empty;
+                int around = limit / 2;
+                var before = GetMany(fromMessageId, Direction.Before, around);
+                var after = GetMany(fromMessageId, Direction.After, around).Reverse();
+
+                return after.Concat(new SocketMessage[] { msg }).Concat(before).ToImmutableArray();
+            }
 
             if (dir == Direction.Before)
                 cachedMessageIds = cachedMessageIds.Reverse();
+            if (dir == Direction.Around) //Only happens if fromMessageId is null, should only get "around" and itself (+1)
+                limit = limit / 2 + 1;
 
             return cachedMessageIds
                 .Select(x =>