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* remove outdated todo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

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

@@ -1,4 +1,5 @@
 using Discord.Rest;
+using System;
 using System.Linq;
 using System.Threading.Tasks;
 using Xunit;
@@ -15,17 +16,28 @@ namespace Discord
             var text4 = await guild.CreateTextChannelAsync("text4");
             var text5 = await guild.CreateTextChannelAsync("text5");
 
+            // create a channel category
+            var cat1 = await guild.CreateCategoryChannelAsync("cat1");
+
+            if (text1 == null)
+            {
+                // the guild did not have a default channel, so make a new one
+                text1 = await guild.CreateTextChannelAsync("default");
+            }
+
             //Modify #general
             await text1.ModifyAsync(x =>
             {
                 x.Name = "text1";
                 x.Position = 1;
                 x.Topic = "Topic1";
+                x.CategoryId = cat1.Id;
             });
 
             await text2.ModifyAsync(x =>
             {
                 x.Position = 2;
+                x.CategoryId = cat1.Id;
             });
             await text3.ModifyAsync(x =>
             {
@@ -89,10 +101,13 @@ namespace Discord
             var voice2 = await guild.CreateVoiceChannelAsync("voice2");
             var voice3 = await guild.CreateVoiceChannelAsync("voice3");
 
+            var cat2 = await guild.CreateCategoryChannelAsync("cat2");
+
             await voice1.ModifyAsync(x =>
             {
                 x.Bitrate = 96000;
                 x.Position = 1;
+                x.CategoryId = cat2.Id;
             });
             await voice2.ModifyAsync(x =>
             {
@@ -103,6 +118,7 @@ namespace Discord
                 x.Bitrate = 8000;
                 x.Position = 1;
                 x.UserLimit = 16;
+                x.CategoryId = cat2.Id;
             });
 
             CheckVoiceChannels(voice1, voice2, voice3);
@@ -140,5 +156,63 @@ namespace Discord
             Assert.Equal(1, voice3.Position);
             Assert.Equal(16, voice3.UserLimit);
         }
+
+        [Fact]
+        public async Task TestChannelCategories()
+        {
+            // (await _guild.GetVoiceChannelsAsync()).ToArray()
+            var channels = await _guild.GetCategoryChannelsAsync();
+
+            await CheckChannelCategories(channels.ToArray(), (await _guild.GetChannelsAsync()).ToArray());
+        }
+
+        private async Task CheckChannelCategories(RestCategoryChannel[] categories, RestGuildChannel[] allChannels)
+        {
+            // 2 categories
+            Assert.Equal(categories.Length, 2);
+
+            var cat1 = categories.Where(x => x.Name == "cat1").FirstOrDefault();
+            var cat2 = categories.Where(x => x.Name == "cat2").FirstOrDefault();
+
+            Assert.NotNull(cat1);
+            Assert.NotNull(cat2);
+
+            // get text1, text2, ensure they have category id == cat1
+            var text1 = allChannels.Where(x => x.Name == "text1").FirstOrDefault() as RestTextChannel;
+            var text2 = allChannels.Where(x => x.Name == "text2").FirstOrDefault() as RestTextChannel;
+
+            Assert.NotNull(text1);
+            Assert.NotNull(text2);
+
+            // check that CategoryID and .GetCategoryAsync work correctly
+            // for both of the text channels
+            Assert.Equal(text1.CategoryId, cat1.Id);
+            var text1Cat = await text1.GetCategoryAsync();
+            Assert.Equal(text1Cat.Id, cat1.Id);
+            Assert.Equal(text1Cat.Name, cat1.Name);
+
+            Assert.Equal(text2.CategoryId, cat1.Id);
+            var text2Cat = await text2.GetCategoryAsync();
+            Assert.Equal(text2Cat.Id, cat1.Id);
+            Assert.Equal(text2Cat.Name, cat1.Name);
+
+            // do the same for the voice channels
+            var voice1 = allChannels.Where(x => x.Name == "voice1").FirstOrDefault() as RestVoiceChannel;
+            var voice3 = allChannels.Where(x => x.Name == "voice3").FirstOrDefault() as RestVoiceChannel;
+
+            Assert.NotNull(voice1);
+            Assert.NotNull(voice3);
+            
+            Assert.Equal(voice1.CategoryId, cat2.Id);
+            var voice1Cat = await voice1.GetCategoryAsync();
+            Assert.Equal(voice1Cat.Id, cat2.Id);
+            Assert.Equal(voice1Cat.Name, cat2.Name);
+
+            Assert.Equal(voice3.CategoryId, cat2.Id);
+            var voice3Cat = await voice3.GetCategoryAsync();
+            Assert.Equal(voice3Cat.Id, cat2.Id);
+            Assert.Equal(voice3Cat.Name, cat2.Name);
+
+        }
     }
 }