Fix #995, Move Category Implementation from IGuildChannel to INestedChannel (#1004)

* Fix #995 ICategoryChannel.CategoryID throws NotSupportedException

* Add tests

* change run mode of TestChannelCategories

* Add throw for GetCategoryAsync

* Add xml doc explaining why exception is thrown

* Add test coverage for text and voice channel categories

* initial implementation of INestedChannel

* more implementation of INestedChannel design

* Add case in RestChannel Create for Category type

* set the CategoryID for RestVoiceChannel

* rewrite channel category tests to work with existing pattern

* remove outdated todo

* Make IVoiceChannel implement INestedChannel

* remove redundant interface implementation

* Add c#7 feature from feedback

* Remove redundant GetCategoryAsync methods from socket entities

* Added configureawait to async methods

* change signature of interface GetCategoryAsync

* Add check for cachemode in rest channel GetCategory

* remove redundant IGuildChannel interface from ITextChannel and IVoiceChannel

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

@@ -1,4 +1,4 @@
-using System;
+using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Text;

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

@@ -1,4 +1,4 @@
-using System;
+using System;
 using System.Collections.Generic;
 using System.Threading.Tasks;
 
@@ -9,10 +9,6 @@ namespace Discord
         /// <summary> Gets the position of this channel in the guild's channel list, relative to others of the same type. </summary>
         int Position { get; }
 
-        /// <summary> Gets the parentid (category) of this channel in the guild's channel list. </summary>
-        ulong? CategoryId { get; }
-        /// <summary> Gets the parent channel (category) of this channel. </summary>
-        Task<ICategoryChannel> GetCategoryAsync();
         /// <summary> Gets the guild this channel is a member of. </summary>
         IGuild Guild { get; }
         /// <summary> Gets the id of the guild this channel is a member of. </summary>
@@ -49,4 +45,4 @@ namespace Discord
         /// <summary> Gets a user in this channel with the provided id.</summary>
         new Task<IGuildUser> GetUserAsync(ulong id, CacheMode mode = CacheMode.AllowDownload, RequestOptions options = null);
     }
-}
+}

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

@@ -0,0 +1,16 @@
+using System.Threading.Tasks;
+
+namespace Discord
+{
+    /// <summary>
+    /// A type of guild channel that can be nested within a category.
+    /// Contains a CategoryId that is set to the parent category, if it is set.
+    /// </summary>
+    public interface INestedChannel : IGuildChannel
+    {
+        /// <summary> Gets the parentid (category) of this channel in the guild's channel list. </summary>
+        ulong? CategoryId { get; }
+        /// <summary> Gets the parent channel (category) of this channel, if it is set. If unset, returns null.</summary>
+        Task<ICategoryChannel> GetCategoryAsync(CacheMode mode = CacheMode.AllowDownload, RequestOptions options = null);
+    }
+}

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

@@ -1,11 +1,11 @@
-using System;
+using System;
 using System.Collections.Generic;
 using System.IO;
 using System.Threading.Tasks;
 
 namespace Discord
 {
-    public interface ITextChannel : IMessageChannel, IMentionable, IGuildChannel
+    public interface ITextChannel : IMessageChannel, IMentionable, INestedChannel
     {
         /// <summary> Checks if the channel is NSFW. </summary>
         bool IsNsfw { get; }
@@ -28,4 +28,4 @@ namespace Discord
         /// <summary> Gets the webhooks for this text channel. </summary>
         Task<IReadOnlyCollection<IWebhook>> GetWebhooksAsync(RequestOptions options = null);
     }
-}
+}

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

@@ -1,9 +1,9 @@
-using System;
+using System;
 using System.Threading.Tasks;
 
 namespace Discord
 {
-    public interface IVoiceChannel : IGuildChannel, IAudioChannel
+    public interface IVoiceChannel : INestedChannel, IAudioChannel
     {
         /// <summary> Gets the bitrate, in bits per second, clients in this voice channel are requested to use. </summary>
         int Bitrate { get; }
@@ -13,4 +13,4 @@ namespace Discord
         /// <summary> Modifies this voice channel. </summary>
         Task ModifyAsync(Action<VoiceChannelProperties> func, RequestOptions options = null);
     }
-}
+}