Export reaction users in JSON format (#1107)

DiscordChatExporter.Core/Discord/DiscordClient.cs

@@ -484,4 +484,46 @@ public class DiscordClient
             }
         }
     }
+
+    public async IAsyncEnumerable<User> GetMessageReactionsAsync(
+        Snowflake channelId,
+        Snowflake messageId,
+        Emoji emoji,
+        [EnumeratorCancellation] CancellationToken cancellationToken = default)
+    {
+
+        var reactionName = Uri.EscapeDataString(
+            emoji.Id is not null
+                // Custom emoji
+                ? emoji.Name + ':' + emoji.Id
+                // Standard emoji
+                : emoji.Name
+        );
+
+        var currentAfter = Snowflake.Zero;
+
+        while (true)
+        {
+            var url = new UrlBuilder()
+                .SetPath($"channels/{channelId}/messages/{messageId}/reactions/{reactionName}")
+                .SetQueryParameter("limit", "100")
+                .SetQueryParameter("after", currentAfter.ToString())
+                .Build();
+
+            var response = await GetJsonResponseAsync(url, cancellationToken);
+
+            var users = response.EnumerateArray().Select(User.Parse).ToArray();
+            if (!users.Any())
+                yield break;
+            foreach (var user in users)
+            {
+                yield return user;
+                currentAfter = user.Id;
+            }
+            // Each batch can contain up to 100 users.
+            // If we got fewer, then it's definitely the last batch.
+            if (users.Length < 100)
+                yield break;
+        }
+    }
 }

DiscordChatExporter.Core/Exporting/JsonMessageWriter.cs

@@ -360,6 +360,37 @@ internal class JsonMessageWriter : MessageWriter
 
             _writer.WriteNumber("count", reaction.Count);
 
+            _writer.WriteStartArray("users");
+            var users = await Context.Discord.GetMessageReactionsAsync(Context.Request.Channel.Id, message.Id, reaction.Emoji, cancellationToken);
+            foreach (var user in users) {
+
+                // write limited user information without color and roles,
+                // because if we would write the full user information,
+                // we would have to fetch the guild member information for each user
+                // which would be a lot of requests
+
+                 _writer.WriteStartObject();
+
+                _writer.WriteString("id", user.Id.ToString());
+                _writer.WriteString("name", user.Name);
+                _writer.WriteString("discriminator", user.DiscriminatorFormatted);
+                _writer.WriteString("nickname", Context.TryGetMember(user.Id)?.DisplayName ?? user.DisplayName);
+                _writer.WriteBoolean("isBot", user.IsBot);
+
+                _writer.WriteString(
+                    "avatarUrl",
+                    await Context.ResolveAssetUrlAsync(
+                        Context.TryGetMember(user.Id)?.AvatarUrl ?? user.AvatarUrl,
+                        cancellationToken
+                    )
+                );
+
+                _writer.WriteEndObject();
+                await _writer.FlushAsync(cancellationToken);
+            }
+
+            _writer.WriteEndArray();
+
             _writer.WriteEndObject();
         }