Add message editing command

Signed-off-by: Ske <voltasalt@gmail.com>

PluralKit.Bot/CommandSystem/ContextArgumentsExt.cs

@@ -1,8 +1,11 @@
 using System;
 using System.Collections.Generic;
 using System.Linq;
+using System.Text.RegularExpressions;
 using System.Threading.Tasks;
 
+using Myriad.Types;
+
 using PluralKit.Core;
 
 namespace PluralKit.Bot
@@ -68,6 +71,27 @@ namespace PluralKit.Bot
             return matched;
         }
 
+        public static ulong? MatchMessage(this Context ctx, bool parseRawMessageId)
+        {
+            if (ctx.Message.Type == Message.MessageType.Reply && ctx.Message.MessageReference != null)
+                return ctx.Message.MessageReference.MessageId;
+
+            var word = ctx.PeekArgument();
+            if (word == null)
+                return null;
+
+            if (parseRawMessageId && ulong.TryParse(word, out var mid))
+                return mid;
+            
+            var match = Regex.Match(word, "https://(?:\\w+.)?discord(?:app)?.com/channels/\\d+/\\d+/(\\d+)");
+            if (!match.Success)
+                return null;
+            
+            var messageId = ulong.Parse(match.Groups[1].Value);
+            ctx.PopArgument();
+            return messageId;
+        }
+
         public static async Task<List<PKMember>> ParseMemberList(this Context ctx, SystemId? restrictToSystem)
         {
             var members = new List<PKMember>();