api: add slow mode

This adds the following property to ITextChannel
- SlowMode (int)

The SlowMode field defines the time in seconds users must wait between
sending messages; if zero, slow-mode is disabled.

Bots are not affected by slow-mode, and as such, no changes need to be
made to the REST client's internal ratelimiting. This is strictly a
read/write cosmetic property for bots.

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

@@ -13,6 +13,9 @@ namespace Discord
         /// <summary> Gets the current topic for this text channel. </summary>
         string Topic { get; }
 
+        ///<summary> Gets the current slow-mode delay for this channel. 0 if disabled. </summary>
+        int SlowMode { get; }
+
         /// <summary> Bulk deletes multiple messages. </summary>
         Task DeleteMessagesAsync(IEnumerable<IMessage> messages, RequestOptions options = null);
         /// <summary> Bulk deletes multiple messages. </summary>

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

@@ -1,4 +1,6 @@
-namespace Discord
+using System;
+
+namespace Discord
 {
     /// <inheritdoc />
     public class TextChannelProperties : GuildChannelProperties
@@ -11,5 +13,15 @@
         /// Should this channel be flagged as NSFW?
         /// </summary>
         public Optional<bool> IsNsfw { get; set; }
+        /// <summary>
+        /// What the slow-mode ratelimit for this channel should be set to; 0 will disable slow-mode.
+        /// </summary>
+        /// <remarks>
+        /// This value must fall within [0, 120]
+        /// 
+        /// Users with <see cref="ChannelPermission.ManageMessages"/> will be exempt from slow-mode.
+        /// </remarks>
+        /// <exception cref="ArgumentOutOfRangeException">Throws ArgummentOutOfRange if the value does not fall within [0, 120]</exception>
+        public Optional<int> SlowMode { get; set; }
     }
 }

src/Discord.Net.Rest/API/Common/Channel.cs

@@ -1,4 +1,4 @@
-#pragma warning disable CS1591
+#pragma warning disable CS1591
 using Newtonsoft.Json;
 using System;
 
@@ -33,6 +33,8 @@ namespace Discord.API
         public Optional<DateTimeOffset?> LastPinTimestamp { get; set; }
         [JsonProperty("nsfw")]
         public Optional<bool> Nsfw { get; set; }
+        [JsonProperty("rate_limit_per_user")]
+        public Optional<int> SlowMode { get; set; }
 
         //VoiceChannel
         [JsonProperty("bitrate")]

src/Discord.Net.Rest/API/Rest/ModifyTextChannelParams.cs

@@ -1,4 +1,4 @@
-#pragma warning disable CS1591
+#pragma warning disable CS1591
 using Newtonsoft.Json;
 
 namespace Discord.API.Rest
@@ -10,5 +10,7 @@ namespace Discord.API.Rest
         public Optional<string> Topic { get; set; }
         [JsonProperty("nsfw")]
         public Optional<bool> IsNsfw { get; set; }
+        [JsonProperty("rate_limit_per_user")]
+        public Optional<int> SlowMode { get; set; }
     }
 }

src/Discord.Net.Rest/DiscordRestApiClient.cs

@@ -356,6 +356,8 @@ namespace Discord.API
             Preconditions.NotNull(args, nameof(args));
             Preconditions.AtLeast(args.Position, 0, nameof(args.Position));
             Preconditions.NotNullOrEmpty(args.Name, nameof(args.Name));
+            Preconditions.AtLeast(args.SlowMode, 0, nameof(args.SlowMode));
+            Preconditions.AtMost(args.SlowMode, 120, nameof(args.SlowMode));
             options = RequestOptions.CreateOrClone(options);
 
             var ids = new BucketIds(channelId: channelId);

src/Discord.Net.Rest/Entities/Channels/ChannelHelper.cs

@@ -45,7 +45,8 @@ namespace Discord.Rest
                 Position = args.Position,
                 CategoryId = args.CategoryId,
                 Topic = args.Topic,
-                IsNsfw = args.IsNsfw
+                IsNsfw = args.IsNsfw,
+                SlowMode = args.SlowMode,
             };
             return await client.ApiClient.ModifyGuildChannelAsync(channel.Id, apiArgs, options).ConfigureAwait(false);
         }

src/Discord.Net.Rest/Entities/Channels/RestTextChannel.cs

@@ -12,6 +12,7 @@ namespace Discord.Rest
     public class RestTextChannel : RestGuildChannel, IRestMessageChannel, ITextChannel
     {
         public string Topic { get; private set; }
+        public int SlowMode { get; private set; } 
         public ulong? CategoryId { get; private set; }
 
         public string Mention => MentionUtils.MentionChannel(Id);
@@ -34,6 +35,7 @@ namespace Discord.Rest
             base.Update(model);
             CategoryId = model.CategoryId;
             Topic = model.Topic.Value;
+            SlowMode = model.SlowMode.Value;
             _nsfw = model.Nsfw.GetValueOrDefault();
         }
 

src/Discord.Net.WebSocket/Entities/Channels/SocketTextChannel.cs

@@ -16,6 +16,7 @@ namespace Discord.WebSocket
         private readonly MessageCache _messages;
 
         public string Topic { get; private set; }
+        public int SlowMode { get; private set; }
         public ulong? CategoryId { get; private set; }
         public ICategoryChannel Category
             => CategoryId.HasValue ? Guild.GetChannel(CategoryId.Value) as ICategoryChannel : null;
@@ -47,6 +48,7 @@ namespace Discord.WebSocket
             base.Update(state, model);
             CategoryId = model.CategoryId;
             Topic = model.Topic.Value;
+            SlowMode = model.SlowMode.GetValueOrDefault(); // some guilds haven't been patched to include this yet?
             _nsfw = model.Nsfw.GetValueOrDefault();
         }