feat: respect Discord permissions in pk;message and pk;edit

PluralKit.Bot/CommandSystem/ContextChecksExt.cs

@@ -1,7 +1,9 @@
 using System.Linq;
+using System.Threading.Tasks;
 
 using Autofac;
 
+using Myriad.Extensions;
 using Myriad.Types;
 
 using PluralKit.Core;
@@ -57,6 +59,28 @@ namespace PluralKit.Bot
             return ctx;
         }
 
+        public static async Task<bool> CheckPermissionsInGuildChannel(this Context ctx, Channel channel, PermissionSet neededPerms)
+        {
+            var guild = ctx.Cache.GetGuild(channel.GuildId.Value);
+            if (guild == null)
+                return false;
+
+            var guildMember = ctx.Member;
+
+            if (ctx.Guild?.Id != channel.GuildId)
+            {
+                guildMember = await ctx.Rest.GetGuildMember(channel.GuildId.Value, ctx.Author.Id);
+                if (guildMember == null)
+                    return false;
+            }
+
+            var userPermissions = PermissionExtensions.PermissionsFor(guild, channel, ctx.Author.Id, guildMember);
+            if ((userPermissions & neededPerms) == 0)
+                return false;
+
+            return true;
+        }
+
         public static bool CheckBotAdmin(this Context ctx)
         {
             var botConfig = ctx.Services.Resolve<BotConfig>();