Add GetChannelType extension method (#2035)

src/Discord.Net.Core/Extensions/ChannelExtensions.cs

@@ -0,0 +1,54 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace Discord
+{
+    public static class ChannelExtensions
+    {
+        /// <summary>
+        ///     Attempts to get the <see cref="ChannelType"/> based off of the channel's interfaces.
+        /// </summary>
+        /// <param name="channel">The channel to get the type of.</param>
+        /// <returns>The <see cref="ChannelType"/> of the channel if found, otherwise <see langword="null"/>.</returns>
+        public static ChannelType? GetChannelType(this IChannel channel)
+        {
+            switch (channel)
+            {
+                case IStageChannel:
+                    return ChannelType.Stage;
+
+                case IThreadChannel thread:
+                    return thread.Type switch
+                    {
+                        ThreadType.NewsThread => ChannelType.NewsThread,
+                        ThreadType.PrivateThread => ChannelType.PrivateThread,
+                        ThreadType.PublicThread => ChannelType.PublicThread,
+                        _ => null,
+                    };
+
+                case ICategoryChannel:
+                    return ChannelType.Category;
+
+                case IDMChannel:
+                    return ChannelType.DM;
+
+                case IGroupChannel:
+                    return ChannelType.Group;
+
+                case INewsChannel:
+                    return ChannelType.News;
+
+                case IVoiceChannel:
+                    return ChannelType.Voice;
+
+                case ITextChannel:
+                    return ChannelType.Text;
+            }
+
+            return null;
+        }
+    }
+}