Resolve mentioned members on demand inside of markdown

Closes #304

DiscordChatExporter.Core/Discord/DiscordClient.cs

@@ -251,16 +251,17 @@ public class DiscordClient
             yield return Role.Parse(roleJson);
     }
 
-    public async ValueTask<Member> GetGuildMemberAsync(
+    public async ValueTask<Member?> TryGetGuildMemberAsync(
         Snowflake guildId,
-        User user,
+        Snowflake memberId,
         CancellationToken cancellationToken = default)
     {
         if (guildId == Guild.DirectMessages.Id)
-            return Member.CreateForUser(user);
+            return null;
 
-        var response = await TryGetJsonResponseAsync($"guilds/{guildId}/members/{user.Id}", cancellationToken);
-        return response?.Pipe(Member.Parse) ?? Member.CreateForUser(user);
+        var response = await TryGetJsonResponseAsync($"guilds/{guildId}/members/{memberId}", cancellationToken);
+
+        return response?.Pipe(Member.Parse);
     }
 
     public async ValueTask<ChannelCategory> GetChannelCategoryAsync(

DiscordChatExporter.Core/Exporting/ChannelExporter.cs

@@ -1,12 +1,9 @@
 using System;
-using System.Collections.Generic;
 using System.Linq;
 using System.Threading;
 using System.Threading.Tasks;
 using DiscordChatExporter.Core.Discord;
-using DiscordChatExporter.Core.Discord.Data;
 using DiscordChatExporter.Core.Exceptions;
-using DiscordChatExporter.Core.Utils.Extensions;
 using Gress;
 
 namespace DiscordChatExporter.Core.Exporting;
@@ -23,21 +20,8 @@ public class ChannelExporter
         CancellationToken cancellationToken = default)
     {
         // Build context
-        var contextMembers = new Dictionary<Snowflake, Member>();
-
-        var contextChannels = (await _discord.GetGuildChannelsAsync(request.Guild.Id, cancellationToken))
-            .ToDictionary(c => c.Id);
-
-        var contextRoles = (await _discord.GetGuildRolesAsync(request.Guild.Id, cancellationToken))
-            .ToDictionary(r => r.Id);
-
-        var context = new ExportContext(
-            _discord,
-            request,
-            contextMembers,
-            contextChannels,
-            contextRoles
-        );
+        var context = new ExportContext(_discord, request);
+        await context.PopulateChannelsAndRolesAsync(cancellationToken);
 
         // Export messages
         await using var messageExporter = new MessageExporter(context);
@@ -49,20 +33,9 @@ public class ChannelExporter
                            progress,
                            cancellationToken))
         {
-            // Resolve members for referenced users
-            foreach (var referencedUser in message.MentionedUsers.Prepend(message.Author))
-            {
-                if (contextMembers.ContainsKey(referencedUser.Id))
-                    continue;
-
-                var member = await _discord.GetGuildMemberAsync(
-                    request.Guild.Id,
-                    referencedUser,
-                    cancellationToken
-                );
-
-                contextMembers[member.Id] = member;
-            }
+            // Resolve members for the author and mentioned users
+            foreach (var user in message.MentionedUsers.Prepend(message.Author))
+                await context.PopulateMemberAsync(user.Id, cancellationToken);
 
             // Export the message
             if (request.MessageFilter.IsMatch(message))

DiscordChatExporter.Core/Exporting/ExportContext.cs

@@ -12,17 +12,48 @@ using DiscordChatExporter.Core.Utils.Extensions;
 
 namespace DiscordChatExporter.Core.Exporting;
 
-internal record ExportContext(
-    DiscordClient Discord,
-    ExportRequest Request,
-    IReadOnlyDictionary<Snowflake, Member> Members,
-    IReadOnlyDictionary<Snowflake, Channel> Channels,
-    IReadOnlyDictionary<Snowflake, Role> Roles)
+internal class ExportContext
 {
-    private readonly ExportAssetDownloader _assetDownloader = new(
-        Request.OutputAssetsDirPath,
-        Request.ShouldReuseAssets
-    );
+    private readonly Dictionary<Snowflake, Member?> _members = new();
+    private readonly Dictionary<Snowflake, Channel> _channels = new();
+    private readonly Dictionary<Snowflake, Role> _roles = new();
+    private readonly ExportAssetDownloader _assetDownloader;
+
+    public DiscordClient Discord { get; }
+    public ExportRequest Request { get; }
+
+    public ExportContext(DiscordClient discord,
+        ExportRequest request)
+    {
+        Discord = discord;
+        Request = request;
+
+        _assetDownloader = new ExportAssetDownloader(
+            request.OutputAssetsDirPath,
+            request.ShouldReuseAssets
+        );
+    }
+
+    public async ValueTask PopulateChannelsAndRolesAsync(CancellationToken cancellationToken = default)
+    {
+        await foreach (var channel in Discord.GetGuildChannelsAsync(Request.Guild.Id, cancellationToken))
+            _channels[channel.Id] = channel;
+
+        await foreach (var role in Discord.GetGuildRolesAsync(Request.Guild.Id, cancellationToken))
+            _roles[role.Id] = role;
+    }
+
+    // Because members are not pulled in bulk, we need to populate them on demand
+    public async ValueTask PopulateMemberAsync(Snowflake id, CancellationToken cancellationToken = default)
+    {
+        if (_members.ContainsKey(id))
+            return;
+
+        var member = await Discord.TryGetGuildMemberAsync(Request.Guild.Id, id, cancellationToken);
+
+        // Store the result even if it's null, to avoid re-fetching non-existing members
+        _members[id] = member;
+    }
 
     public string FormatDate(DateTimeOffset instant) => Request.DateFormat switch
     {
@@ -31,11 +62,11 @@ internal record ExportContext(
         var format => instant.ToLocalString(format)
     };
 
-    public Member? TryGetMember(Snowflake id) => Members.GetValueOrDefault(id);
+    public Member? TryGetMember(Snowflake id) => _members.GetValueOrDefault(id);
 
-    public Channel? TryGetChannel(Snowflake id) => Channels.GetValueOrDefault(id);
+    public Channel? TryGetChannel(Snowflake id) => _channels.GetValueOrDefault(id);
 
-    public Role? TryGetRole(Snowflake id) => Roles.GetValueOrDefault(id);
+    public Role? TryGetRole(Snowflake id) => _roles.GetValueOrDefault(id);
 
     public Color? TryGetUserColor(Snowflake id)
     {

DiscordChatExporter.Core/Exporting/HtmlMarkdownVisitor.cs

@@ -195,6 +195,12 @@ internal partial class HtmlMarkdownVisitor : MarkdownVisitor
         }
         else if (mention.Kind == MentionKind.User)
         {
+            // User mentions are not always included in the message object,
+            // which means they need to be populated on demand.
+            // https://github.com/Tyrrrz/DiscordChatExporter/issues/304
+            if (mention.TargetId is not null)
+                await _context.PopulateMemberAsync(mention.TargetId.Value, cancellationToken);
+
             var member = mention.TargetId?.Pipe(_context.TryGetMember);
             var fullName = member?.User.FullName ?? "Unknown";
             var nick = member?.Nick ?? "Unknown";

DiscordChatExporter.Core/Exporting/PlainTextMarkdownVisitor.cs

@@ -53,6 +53,12 @@ internal partial class PlainTextMarkdownVisitor : MarkdownVisitor
         }
         else if (mention.Kind == MentionKind.User)
         {
+            // User mentions are not always included in the message object,
+            // which means they need to be populated on demand.
+            // https://github.com/Tyrrrz/DiscordChatExporter/issues/304
+            if (mention.TargetId is not null)
+                await _context.PopulateMemberAsync(mention.TargetId.Value, cancellationToken);
+
             var member = mention.TargetId?.Pipe(_context.TryGetMember);
             var name = member?.User.Name ?? "Unknown";