feature: Add INVITE_CREATE and INVITE_DELETE events (#1491)

* Add invite events (create and delete)

* Removed unused using

* Fixing IInviteMetadata properties

* Add two new fields to the gateway event

* Better event summary and remarks

* Change how to assign to target variable

Co-Authored-By: Joe4evr <jii.geugten@gmail.com>

* Applying suggested changes to TargetUserType

* Renaming NotDefined to Undefined

* Fixing xml docs

* Changed the summary style format

Co-authored-by: Joe4evr <jii.geugten@gmail.com>

src/Discord.Net.WebSocket/Entities/Invites/SocketInvite.cs

@@ -0,0 +1,143 @@
+using Discord.Rest;
+using System;
+using System.Diagnostics;
+using System.Threading.Tasks;
+using Model = Discord.API.Gateway.InviteCreateEvent;
+
+namespace Discord.WebSocket
+{
+    [DebuggerDisplay(@"{DebuggerDisplay,nq}")]
+    public class SocketInvite : SocketEntity<string>, IInviteMetadata
+    {
+        private long _createdAtTicks;
+
+        /// <inheritdoc />
+        public ulong ChannelId { get; private set; }
+        /// <summary>
+        ///     Gets the channel where this invite was created.
+        /// </summary>
+        public SocketGuildChannel Channel { get; private set; }
+        /// <inheritdoc />
+        public ulong? GuildId { get; private set; }
+        /// <summary>
+        ///     Gets the guild where this invite was created.
+        /// </summary>
+        public SocketGuild Guild { get; private set; }
+        /// <inheritdoc />
+        ChannelType IInvite.ChannelType
+        {
+            get
+            {
+                switch (Channel)
+                {
+                    case IVoiceChannel voiceChannel: return ChannelType.Voice;
+                    case ICategoryChannel categoryChannel: return ChannelType.Category;
+                    case IDMChannel dmChannel: return ChannelType.DM;
+                    case IGroupChannel groupChannel: return ChannelType.Group;
+                    case SocketNewsChannel socketNewsChannel: return ChannelType.News;
+                    case ITextChannel textChannel: return ChannelType.Text;
+                    default: throw new InvalidOperationException("Invalid channel type.");
+                }
+            }
+        }
+        /// <inheritdoc />
+        string IInvite.ChannelName => Channel.Name;
+        /// <inheritdoc />
+        string IInvite.GuildName => Guild.Name;
+        /// <inheritdoc />
+        int? IInvite.PresenceCount => throw new NotImplementedException();
+        /// <inheritdoc />
+        int? IInvite.MemberCount => throw new NotImplementedException();
+        /// <inheritdoc />
+        bool IInviteMetadata.IsRevoked => throw new NotImplementedException();
+        /// <inheritdoc />
+        public bool IsTemporary { get; private set; }
+        /// <inheritdoc />
+        int? IInviteMetadata.MaxAge { get => MaxAge; }
+        /// <inheritdoc />
+        int? IInviteMetadata.MaxUses { get => MaxUses; }
+        /// <inheritdoc />
+        int? IInviteMetadata.Uses { get => Uses; }
+        /// <summary>
+        ///     Gets the time (in seconds) until the invite expires.
+        /// </summary>
+        public int MaxAge { get; private set; }
+        /// <summary>
+        ///     Gets the max number of uses this invite may have.
+        /// </summary>
+        public int MaxUses { get; private set; }
+        /// <summary>
+        ///     Gets the number of times this invite has been used.
+        /// </summary>
+        public int Uses { get; private set; }
+        /// <summary>
+        ///     Gets the user that created this invite if available.
+        /// </summary>
+        public SocketGuildUser Inviter { get; private set; }
+        /// <inheritdoc />
+        DateTimeOffset? IInviteMetadata.CreatedAt => DateTimeUtils.FromTicks(_createdAtTicks);
+        /// <summary>
+        ///     Gets when this invite was created.
+        /// </summary>
+        public DateTimeOffset CreatedAt => DateTimeUtils.FromTicks(_createdAtTicks);
+        /// <summary>
+        ///     Gets the user targeted by this invite if available.
+        /// </summary>
+        public SocketUser TargetUser { get; private set; }
+        /// <summary>
+        ///     Gets the type of the user targeted by this invite.
+        /// </summary>
+        public TargetUserType TargetUserType { get; private set; }
+
+        /// <inheritdoc />
+        public string Code => Id;
+        /// <inheritdoc />
+        public string Url => $"{DiscordConfig.InviteUrl}{Code}";
+
+        internal SocketInvite(DiscordSocketClient discord, SocketGuild guild, SocketGuildChannel channel, SocketGuildUser inviter, SocketUser target, string id)
+            : base(discord, id)
+        {
+            Guild = guild;
+            Channel = channel;
+            Inviter = inviter;
+            TargetUser = target;
+        }
+        internal static SocketInvite Create(DiscordSocketClient discord, SocketGuild guild, SocketGuildChannel channel, SocketGuildUser inviter, SocketUser target, Model model)
+        {
+            var entity = new SocketInvite(discord, guild, channel, inviter, target, model.Code);
+            entity.Update(model);
+            return entity;
+        }
+        internal void Update(Model model)
+        {
+            ChannelId = model.ChannelId;
+            GuildId = model.GuildId.IsSpecified ? model.GuildId.Value : Guild.Id;
+            IsTemporary = model.Temporary;
+            MaxAge = model.MaxAge;
+            MaxUses = model.MaxUses;
+            Uses = model.Uses;
+            _createdAtTicks = model.CreatedAt.UtcTicks;
+            TargetUserType = model.TargetUserType.IsSpecified ? model.TargetUserType.Value : TargetUserType.Undefined;
+        }
+
+        /// <inheritdoc />
+        public Task DeleteAsync(RequestOptions options = null)
+            => InviteHelper.DeleteAsync(this, Discord, options);
+
+        /// <summary>
+        ///     Gets the URL of the invite.
+        /// </summary>
+        /// <returns>
+        ///     A string that resolves to the Url of the invite.
+        /// </returns>
+        public override string ToString() => Url;
+        private string DebuggerDisplay => $"{Url} ({Guild?.Name} / {Channel.Name})";
+
+        /// <inheritdoc />
+        IGuild IInvite.Guild => Guild;
+        /// <inheritdoc />
+        IChannel IInvite.Channel => Channel;
+        /// <inheritdoc />
+        IUser IInviteMetadata.Inviter => Inviter;
+    }
+}