Add command to check channel permissions for proxying

PluralKit.Bot/Commands/MiscCommands.cs

@@ -1,8 +1,11 @@
+using System.Collections.Generic;
+using System.ComponentModel;
 using System.Linq;
 using System.Threading.Tasks;
 using App.Metrics;
 using Discord;
 using Discord.Commands;
+using Humanizer;
 
 namespace PluralKit.Bot.Commands {
     public class MiscCommands: ModuleBase<PKCommandContext> {
@@ -51,5 +54,79 @@ namespace PluralKit.Bot.Commands {
                 .AddField("Proxy success rate", $"{proxySuccessRate.Percent/100:P1}")
                 .Build());
         }
+
+        [Command("permcheck")]
+        [Summary("permcheck [guild]")]
+        public async Task PermCheckGuild(ulong guildId)
+        {
+            // TODO: will this call break for sharding if you try to request a guild on a different bot instance?
+            var guild = Context.Client.GetGuild(guildId) as IGuild;
+            if (guild == null)
+                throw Errors.GuildNotFound(guildId);
+            
+            var requiredPermissions = new []
+            {
+                ChannelPermission.ViewChannel, // Manage Messages automatically grants Send and Add Reactions, but not Read
+                ChannelPermission.ManageMessages,
+                ChannelPermission.ManageWebhooks
+            };
+
+            // Loop through every channel and group them by sets of permissions missing
+            var permissionsMissing = new Dictionary<ulong, List<ITextChannel>>();
+            foreach (var channel in await guild.GetTextChannelsAsync())
+            {
+                // TODO: do we need to hide channels here to prevent info-leaking?
+                var perms = await channel.PermissionsIn();
+
+                // We use a bitfield so we can set individual permission bits in the loop
+                ulong missingPermissionField = 0;
+                foreach (var requiredPermission in requiredPermissions)
+                    if (!perms.Has(requiredPermission))
+                        missingPermissionField |= (ulong) requiredPermission;
+
+                // If we're not missing any permissions, don't bother adding it to the dict
+                // This means we can check if the dict is empty to see if all channels are proxyable
+                if (missingPermissionField != 0)
+                {
+                    permissionsMissing.TryAdd(missingPermissionField, new List<ITextChannel>());
+                    permissionsMissing[missingPermissionField].Add(channel);
+                }
+            }
+            
+            // Generate the output embed
+            var eb = new EmbedBuilder()
+                .WithTitle($"Permission check for **{guild.Name}**");
+
+            if (permissionsMissing.Count == 0)
+            {
+                eb.WithDescription($"No errors found, all channels proxyable :)").WithColor(Color.Green);
+            }
+            else
+            {
+                foreach (var (missingPermissionField, channels) in permissionsMissing)
+                {
+                    // Each missing permission field can have multiple missing channels
+                    // so we extract them all and generate a comma-separated list
+                    var missingPermissionNames = string.Join(", ", new ChannelPermissions(missingPermissionField)
+                        .ToList()
+                        .Select(perm => perm.Humanize().Transform(To.TitleCase)));
+                    
+                    var channelsList = string.Join("\n", channels
+                        .OrderBy(c => c.Position)
+                        .Select(c => $"#{c.Name}"));
+                    eb.AddField($"Missing *{missingPermissionNames}*", channelsList);
+                    eb.WithColor(Color.Red);
+                }
+            }
+
+            // Send! :)
+            await Context.Channel.SendMessageAsync(embed: eb.Build());
+        }
+
+        [Command("permcheck")]
+        [Summary("permcheck [guild]")]
+        [RequireContext(ContextType.Guild, ErrorMessage =
+            "When running this command in DMs, you must pass a guild ID.")]
+        public Task PermCheckGuild() => PermCheckGuild(Context.Guild.Id);
     }
 }

PluralKit.Bot/Errors.cs

@@ -1,3 +1,4 @@
+using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Net;
@@ -70,5 +71,7 @@ namespace PluralKit.Bot {
         
         public static PKError DurationParseError(string durationStr) => new PKError($"Could not parse '{durationStr.Sanitize()}' as a valid duration. Try a format such as `30d`, `1d3h` or `20m30s`.");
         public static PKError FrontPercentTimeInFuture => new PKError("Cannot get the front percent between now and a time in the future.");
+
+        public static PKError GuildNotFound(ulong guildId) => new PKError($"Guild with ID {guildId} not found.");
     }
 }