more implementation of INestedChannel design

src/Discord.Net.Core/Entities/Channels/INestedChannel.cs

@@ -1,7 +1,3 @@
-using System;
-using System.Collections.Generic;
-using System.Linq;
-using System.Text;
 using System.Threading.Tasks;
 
 namespace Discord

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

@@ -313,6 +313,16 @@ namespace Discord.Rest
             return models.Select(x => RestWebhook.Create(client, channel, x))
                 .ToImmutableArray();
         }
+        // Categories
+        public static async Task<ICategoryChannel> GetCategoryAsync(INestedChannel channel, BaseDiscordClient client, RequestOptions options)
+        {
+            // if no category id specified, return null
+            if (!channel.CategoryId.HasValue)
+                return null;
+            // CategoryId will contain a value here
+            var model = await client.ApiClient.GetChannelAsync(channel.CategoryId.Value, options).ConfigureAwait(false);
+            return RestCategoryChannel.Create(client, model) as ICategoryChannel;
+        }
 
         //Helpers
         private static IUser GetAuthor(BaseDiscordClient client, IGuild guild, UserModel model, ulong? webhookId)

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

@@ -32,7 +32,7 @@ namespace Discord.Rest
         internal override void Update(Model model)
         {
             base.Update(model);
-
+            CategoryId = model.CategoryId;
             Topic = model.Topic.Value;
             _nsfw = model.Nsfw.GetValueOrDefault();
         }
@@ -47,7 +47,7 @@ namespace Discord.Rest
             => ChannelHelper.GetUserAsync(this, Guild, Discord, id, options);
         public IAsyncEnumerable<IReadOnlyCollection<RestGuildUser>> GetUsersAsync(RequestOptions options = null)
             => ChannelHelper.GetUsersAsync(this, Guild, Discord, null, null, options);
-
+        
         public Task<RestMessage> GetMessageAsync(ulong id, RequestOptions options = null)
             => ChannelHelper.GetMessageAsync(this, Discord, id, options);
         public IAsyncEnumerable<IReadOnlyCollection<RestMessage>> GetMessagesAsync(int limit = DiscordConfig.MaxMessagesPerBatch, RequestOptions options = null)
@@ -84,6 +84,9 @@ namespace Discord.Rest
             => ChannelHelper.GetWebhookAsync(this, Discord, id, options);
         public Task<IReadOnlyCollection<RestWebhook>> GetWebhooksAsync(RequestOptions options = null)
             => ChannelHelper.GetWebhooksAsync(this, Discord, options);
+    
+        public Task<ICategoryChannel> GetCategoryAsync(RequestOptions options = null)
+            => ChannelHelper.GetCategoryAsync(this, Discord, options);
 
         private string DebuggerDisplay => $"{Name} ({Id}, Text)";
 
@@ -110,6 +113,7 @@ namespace Discord.Rest
             else
                 return AsyncEnumerable.Empty<IReadOnlyCollection<IMessage>>();
         }
+        
         IAsyncEnumerable<IReadOnlyCollection<IMessage>> IMessageChannel.GetMessagesAsync(ulong fromMessageId, Direction dir, int limit, CacheMode mode, RequestOptions options)
         {
             if (mode == CacheMode.AllowDownload)

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

@@ -39,6 +39,9 @@ namespace Discord.Rest
             Update(model);
         }
 
+        public Task<ICategoryChannel> GetCategoryAsync(RequestOptions options = null)
+            => ChannelHelper.GetCategoryAsync(this, Discord, options);
+
         private string DebuggerDisplay => $"{Name} ({Id}, Voice)";
 
         //IAudioChannel

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

@@ -20,7 +20,7 @@ namespace Discord.WebSocket
                ChannelPermission.ViewChannel)).ToImmutableArray();
 
         public IReadOnlyCollection<SocketGuildChannel> Channels
-            => Guild.Channels.Where(x => x.CategoryId == Id).ToImmutableArray();
+            => Guild.Channels.Where(x => x is INestedChannel && (x as INestedChannel).CategoryId == Id).ToImmutableArray();
 
         internal SocketCategoryChannel(DiscordSocketClient discord, ulong id, SocketGuild guild)
             : base(discord, id, guild)
@@ -51,19 +51,6 @@ namespace Discord.WebSocket
         internal new SocketCategoryChannel Clone() => MemberwiseClone() as SocketCategoryChannel;
 
         // IGuildChannel
-
-        /// <summary>
-        /// Throws a NotSupportedException because Channel Categories cannot be the child of another Channel Category.
-        /// </summary>
-        /// <exception cref="NotSupportedException">A NotSupportedException is always thrown because Channel Categories do not support being nested.</exception>
-        ulong? IGuildChannel.CategoryId
-            => throw new NotSupportedException();
-        /// <summary>
-        /// Throws a NotSupportedException because Channel Categories cannot be the child of another Channel Category.
-        /// </summary>
-        /// <exception cref="NotSupportedException">A NotSupportedException is always thrown because Channel Categories do not support being nested.</exception>
-        Task<ICategoryChannel> IGuildChannel.GetCategoryAsync()
-            => throw new NotSupportedException();
         IAsyncEnumerable<IReadOnlyCollection<IGuildUser>> IGuildChannel.GetUsersAsync(CacheMode mode, RequestOptions options)
             => ImmutableArray.Create<IReadOnlyCollection<IGuildUser>>(Users).ToAsyncEnumerable();
         Task<IGuildUser> IGuildChannel.GetUserAsync(ulong id, CacheMode mode, RequestOptions options)

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

@@ -1,4 +1,4 @@
-using Discord.Rest;
+using Discord.Rest;
 using System;
 using System.Collections.Generic;
 using System.Collections.Immutable;
@@ -16,10 +16,7 @@ namespace Discord.WebSocket
 
         public SocketGuild Guild { get; }
         public string Name { get; private set; }
-        public int Position { get; private set; }
-        public ulong? CategoryId { get; private set; }
-        public ICategoryChannel Category 
-            => CategoryId.HasValue ? Guild.GetChannel(CategoryId.Value) as ICategoryChannel : null;
+        public int Position { get; private set; }        
 
         public IReadOnlyCollection<Overwrite> PermissionOverwrites => _overwrites;
         public new virtual IReadOnlyCollection<SocketGuildUser> Users => ImmutableArray.Create<SocketGuildUser>();
@@ -48,8 +45,7 @@ namespace Discord.WebSocket
         {
             Name = model.Name.Value;
             Position = model.Position.Value;
-            CategoryId = model.CategoryId;
-
+            
             var overwrites = model.PermissionOverwrites.Value;
             var newOverwrites = ImmutableArray.CreateBuilder<Overwrite>(overwrites.Length);
             for (int i = 0; i < overwrites.Length; i++)
@@ -135,9 +131,6 @@ namespace Discord.WebSocket
         IGuild IGuildChannel.Guild => Guild;
         ulong IGuildChannel.GuildId => Guild.Id;
 
-        Task<ICategoryChannel> IGuildChannel.GetCategoryAsync()
-            => Task.FromResult(Category);
-
         async Task<IReadOnlyCollection<IInviteMetadata>> IGuildChannel.GetInvitesAsync(RequestOptions options)
             => await GetInvitesAsync(options).ConfigureAwait(false);
         async Task<IInviteMetadata> IGuildChannel.CreateInviteAsync(int? maxAge, int? maxUses, bool isTemporary, bool isUnique, RequestOptions options)

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

@@ -45,7 +45,7 @@ namespace Discord.WebSocket
         internal override void Update(ClientState state, Model model)
         {
             base.Update(state, model);
-
+            CategoryId = model.CategoryId;
             Topic = model.Topic.Value;
             _nsfw = model.Nsfw.GetValueOrDefault();
         }
@@ -124,6 +124,10 @@ namespace Discord.WebSocket
         public Task<IReadOnlyCollection<RestWebhook>> GetWebhooksAsync(RequestOptions options = null)
             => ChannelHelper.GetWebhooksAsync(this, Discord, options);
 
+        // Categories
+        public Task<ICategoryChannel> GetCategoryAsync(RequestOptions options = null)
+            => ChannelHelper.GetCategoryAsync(this, Discord, options);
+
         private string DebuggerDisplay => $"{Name} ({Id}, Text)";
         internal new SocketTextChannel Clone() => MemberwiseClone() as SocketTextChannel;
 

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

@@ -35,7 +35,7 @@ namespace Discord.WebSocket
         internal override void Update(ClientState state, Model model)
         {
             base.Update(state, model);
-
+            CategoryId = model.CategoryId;
             Bitrate = model.Bitrate.Value;
             UserLimit = model.UserLimit.Value != 0 ? model.UserLimit.Value : (int?)null;
         }
@@ -55,7 +55,10 @@ namespace Discord.WebSocket
                 return user;
             return null;
         }
-        
+
+        public Task<ICategoryChannel> GetCategoryAsync(RequestOptions options = null)
+            => ChannelHelper.GetCategoryAsync(this, Discord, options);
+
         private string DebuggerDisplay => $"{Name} ({Id}, Voice)";
         internal new SocketVoiceChannel Clone() => MemberwiseClone() as SocketVoiceChannel;
 

test/Discord.Net.Tests/Tests.Channels.cs

@@ -156,18 +156,6 @@ namespace Discord
             var cat1 = await guild.CreateCategoryChannelAsync("Cat1");
             var cat2 = await guild.CreateCategoryChannelAsync("Cat2");
 
-            // check that both CategoryID and GetCategoryID throw NotSupportedException
-            // because Categories cannot be nested
-            Assert.Throws<NotSupportedException>(() =>
-            {
-                var x = cat1.CategoryId;
-            });
-
-            Assert.Throws<NotSupportedException>(() =>
-            {
-                var x = cat2.GetCategoryAsync();
-            });
-
             var text1 = await guild.CreateTextChannelAsync("nestedText1");
             var voice1 = await guild.CreateVoiceChannelAsync("nestedVoice1");
             // set the text channel parent to Cat 1
@@ -185,10 +173,17 @@ namespace Discord
 
             // assert that CategoryId works for text channels
             Assert.Equal(text1.CategoryId, cat1.Id);
+            Assert.True(text1 is INestedChannel);
+            Assert.Equal((await (text1 as INestedChannel).GetCategoryAsync()).Id, cat1.Id);
             Assert.Equal((await text1.GetCategoryAsync()).Id, cat1.Id);
+            Assert.Equal(text1.CategoryId, cat1.Id);
+
             // and for voice channels
             Assert.Equal(voice1.CategoryId, cat2.Id);
+            Assert.True(voice1 is INestedChannel);
+            Assert.Equal((await (voice1 as INestedChannel).GetCategoryAsync()).Id, cat2.Id);
             Assert.Equal((await voice1.GetCategoryAsync()).Id, cat2.Id);
+            Assert.Equal(voice1.CategoryId, cat1.Id);
 
             // incomplete test, could use more coverage of other methods
         }