Paginate reactions - solved #1007 (#1022)

* Cleaned up and refactored slightly

* Resolves #971

* Adds support for default avatars and resolves #971

* Amendment

* Final amendment

* Paginating reactions

* Amendments based on feedback

* Further amendment based on review

* Final(?) amendment

* Removes default limit and after user id

* Removes fromUserId; cleans up model creation; replaces function with individual parameters

src/Discord.Net.Core/DiscordConfig.cs

@@ -1,4 +1,4 @@
-using System.Reflection;
+using System.Reflection;
 
 namespace Discord
 {
@@ -20,6 +20,7 @@ namespace Discord
         public const int MaxMessagesPerBatch = 100;
         public const int MaxUsersPerBatch = 1000;
         public const int MaxGuildsPerBatch = 100;
+        public const int MaxUserReactionsPerBatch = 100;
         public const int MaxAuditLogEntriesPerBatch = 100;
 
         /// <summary> Gets or sets how a request should act in the case of an error, by default. </summary>

src/Discord.Net.Core/Entities/Messages/IUserMessage.cs

@@ -1,4 +1,4 @@
-using System;
+using System;
 using System.Collections.Generic;
 using System.Threading.Tasks;
 
@@ -23,7 +23,7 @@ namespace Discord
         /// <summary> Removes all reactions from this message. </summary>
         Task RemoveAllReactionsAsync(RequestOptions options = null);
         /// <summary>  Gets all users that reacted to a message with a given emote </summary>
-        Task<IReadOnlyCollection<IUser>> GetReactionUsersAsync(IEmote emoji, int limit = 100, ulong? afterUserId = null, RequestOptions options = null);
+        IAsyncEnumerable<IReadOnlyCollection<IUser>> GetReactionUsersAsync(IEmote emoji, int limit, RequestOptions options = null);
 
         /// <summary> Transforms this message's text into a human readable form by resolving its tags. </summary>
         string Resolve(

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

@@ -1,4 +1,4 @@
-namespace Discord.API.Rest
+namespace Discord.API.Rest
 {
     internal class GetReactionUsersParams
     {

src/Discord.Net.Rest/DiscordRestApiClient.cs

@@ -618,11 +618,11 @@ namespace Discord.API
             Preconditions.NotNullOrWhitespace(emoji, nameof(emoji));
             Preconditions.NotNull(args, nameof(args));
             Preconditions.GreaterThan(args.Limit, 0, nameof(args.Limit));
-            Preconditions.AtMost(args.Limit, DiscordConfig.MaxUsersPerBatch, nameof(args.Limit));
+            Preconditions.AtMost(args.Limit, DiscordConfig.MaxUserReactionsPerBatch, nameof(args.Limit));
             Preconditions.GreaterThan(args.AfterUserId, 0, nameof(args.AfterUserId));
             options = RequestOptions.CreateOrClone(options);
 
-            int limit = args.Limit.GetValueOrDefault(int.MaxValue);
+            int limit = args.Limit.GetValueOrDefault(DiscordConfig.MaxUserReactionsPerBatch);
             ulong afterUserId = args.AfterUserId.GetValueOrDefault(0);
 
             var ids = new BucketIds(channelId: channelId);

src/Discord.Net.Rest/Entities/Messages/MessageHelper.cs

@@ -46,13 +46,38 @@ namespace Discord.Rest
             await client.ApiClient.RemoveAllReactionsAsync(msg.Channel.Id, msg.Id, options);
         }
 
-        public static async Task<IReadOnlyCollection<IUser>> GetReactionUsersAsync(IMessage msg, IEmote emote,
-            Action<GetReactionUsersParams> func, BaseDiscordClient client, RequestOptions options)
+        public static IAsyncEnumerable<IReadOnlyCollection<IUser>> GetReactionUsersAsync(IMessage msg, IEmote emote,
+            int? limit, BaseDiscordClient client, RequestOptions options)
         {
-            var args = new GetReactionUsersParams();
-            func(args);
-            string emoji = (emote is Emote e ? $"{e.Name}:{e.Id}" : emote.Name);
-            return (await client.ApiClient.GetReactionUsersAsync(msg.Channel.Id, msg.Id, emoji, args, options).ConfigureAwait(false)).Select(u => RestUser.Create(client, u)).ToImmutableArray();
+            Preconditions.NotNull(emote, nameof(emote));
+            var emoji = (emote is Emote e ? $"{e.Name}:{e.Id}" : emote.Name);
+
+            return new PagedAsyncEnumerable<IUser>(
+                DiscordConfig.MaxUserReactionsPerBatch,
+                async (info, ct) =>
+                {
+                    var args = new GetReactionUsersParams
+                    {
+                        Limit = info.PageSize
+                    };
+
+                    if (info.Position != null)
+                        args.AfterUserId = info.Position.Value;
+
+                    var models = await client.ApiClient.GetReactionUsersAsync(msg.Channel.Id, msg.Id, emoji, args, options).ConfigureAwait(false);
+                    return models.Select(x => RestUser.Create(client, x)).ToImmutableArray();
+                },
+                nextPage: (info, lastPage) =>
+                {
+                    if (lastPage.Count != DiscordConfig.MaxUsersPerBatch)
+                        return false;
+
+                    info.Position = lastPage.Max(x => x.Id);
+                    return true;
+                },
+                count: limit
+            );
+
         }
 
         public static async Task PinAsync(IMessage msg, BaseDiscordClient client,

src/Discord.Net.Rest/Entities/Messages/RestUserMessage.cs

@@ -136,8 +136,8 @@ namespace Discord.Rest
             => MessageHelper.RemoveReactionAsync(this, user, emote, Discord, options);
         public Task RemoveAllReactionsAsync(RequestOptions options = null)
             => MessageHelper.RemoveAllReactionsAsync(this, Discord, options);
-        public Task<IReadOnlyCollection<IUser>> GetReactionUsersAsync(IEmote emote, int limit = 100, ulong? afterUserId = null, RequestOptions options = null)
-            => MessageHelper.GetReactionUsersAsync(this, emote, x => { x.Limit = limit; x.AfterUserId = afterUserId ?? Optional.Create<ulong>(); }, Discord, options);
+        public IAsyncEnumerable<IReadOnlyCollection<IUser>> GetReactionUsersAsync(IEmote emote, int limit, RequestOptions options = null)
+            => MessageHelper.GetReactionUsersAsync(this, emote, limit, Discord, options);
 
 
         public Task PinAsync(RequestOptions options = null)

src/Discord.Net.WebSocket/Entities/Messages/SocketUserMessage.cs

@@ -130,8 +130,8 @@ namespace Discord.WebSocket
             => MessageHelper.RemoveReactionAsync(this, user, emote, Discord, options);
         public Task RemoveAllReactionsAsync(RequestOptions options = null)
             => MessageHelper.RemoveAllReactionsAsync(this, Discord, options);
-        public Task<IReadOnlyCollection<IUser>> GetReactionUsersAsync(IEmote emote, int limit = 100, ulong? afterUserId = null, RequestOptions options = null)
-            => MessageHelper.GetReactionUsersAsync(this, emote, x => { x.Limit = limit; x.AfterUserId = afterUserId ?? Optional.Create<ulong>(); }, Discord, options);
+        public IAsyncEnumerable<IReadOnlyCollection<IUser>> GetReactionUsersAsync(IEmote emote, int limit, RequestOptions options = null)
+            => MessageHelper.GetReactionUsersAsync(this, emote, limit, Discord, options);
 
         public Task PinAsync(RequestOptions options = null)
             => MessageHelper.PinAsync(this, Discord, options);