Mark guild optional in invite & general invite improvement (#1094)

* Mark guild as optional for invite

* Mark partial InviteMetadata members as Optional<T>

* Some of them aren't sent when requesting through the general GET invite endpoint

* Remove GetInviteParams

* It was kinda stupid in the first place, might as well always get the count instead of having to ask the user whether they want the two fields filled or not.

* Add ChannelType property

* Add vanity invite support

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

@@ -0,0 +1,11 @@
+namespace Discord
+{
+    public enum ChannelType
+    {
+        Text = 0,
+        DM = 1,
+        Voice = 2,
+        Group = 3,
+        Category = 4
+    }
+}

src/Discord.Net.Core/Entities/Guilds/IGuild.cs

@@ -120,6 +120,15 @@ namespace Discord
 
         /// <summary> Gets a collection of all invites to this guild. </summary>
         Task<IReadOnlyCollection<IInviteMetadata>> GetInvitesAsync(RequestOptions options = null);
+        /// <summary>
+        ///     Gets the vanity invite URL of this guild.
+        /// </summary>
+        /// <param name="options">The options to be used when sending the request.</param>
+        /// <returns>
+        ///     An awaitable <see cref="Task"/> containing the partial metadata of the vanity invite found within
+        ///     this guild.
+        /// </returns>
+        Task<IInviteMetadata> GetVanityInviteAsync(RequestOptions options = null);
 
         /// <summary> Gets the role in this guild with the provided id, or null if not found. </summary>
         IRole GetRole(ulong id);

src/Discord.Net.Core/Entities/Invites/IInvite.cs

@@ -1,5 +1,3 @@
-using System.Threading.Tasks;
-
 namespace Discord
 {
     public interface IInvite : IEntity<string>, IDeletable
@@ -11,6 +9,8 @@ namespace Discord
 
         /// <summary> Gets the channel this invite is linked to. </summary>
         IChannel Channel { get; }
+        /// <summary> Gets the type of the channel this invite is linked to. </summary>
+        ChannelType ChannelType { get; }
         /// <summary> Gets the id of the channel this invite is linked to. </summary>
         ulong ChannelId { get; }
         /// <summary> Gets the name of the channel this invite is linked to. </summary>
@@ -19,7 +19,7 @@ namespace Discord
         /// <summary> Gets the guild this invite is linked to. </summary>
         IGuild Guild { get; }
         /// <summary> Gets the id of the guild this invite is linked to. </summary>
-        ulong GuildId { get; }
+        ulong? GuildId { get; }
         /// <summary> Gets the name of the guild this invite is linked to. </summary>
         string GuildName { get; }
         /// <summary> Gets the approximated count of online members in the guild. </summary>

src/Discord.Net.Core/Entities/Invites/IInviteMetadata.cs

@@ -1,4 +1,4 @@
-using System;
+using System;
 
 namespace Discord
 {
@@ -15,8 +15,8 @@ namespace Discord
         /// <summary> Gets the max amount of times this invite may be used, or null if there is no limit. </summary>
         int? MaxUses { get; }
         /// <summary> Gets the amount of times this invite has been used. </summary>
-        int Uses { get; }
+        int? Uses { get; }
         /// <summary> Gets when this invite was created. </summary>
-        DateTimeOffset CreatedAt { get; }
+        DateTimeOffset? CreatedAt { get; }
     }
-}
+}