+ entity class LatestReplierRevision that has composite PK `TakenAt…

…, Uid` like type 4 of https://en.wikipedia.org/wiki/Slowly_changing_dimension

* now will insert `LatestReplierRevision` entity to store changed uid that might caused by two user swapped their (display)name
* fix exception thrown by `.First()` when no user is matching with the latest replier of parent thread
@ `ThreadLatestReplierSaver.SaveFromUser()`
@ c#/crawler

* rename variables with type `IEnumerable<IGrouping<,>>` to conform naming convention `pluralNoun+GroupBy` like `sKeyBy` for `IDictionary<,>`
@ c#

c#/crawler/src/Db/CrawlerDbContext.cs

@@ -16,6 +16,7 @@ public class CrawlerDbContext(ILogger<CrawlerDbContext> logger, Fid fid = 0)
     public Fid Fid { get; } = fid;
     public DbSet<User> Users => Set<User>();
     public DbSet<LatestReplier> LatestRepliers => Set<LatestReplier>();
+    public DbSet<LatestReplierRevision> LatestReplierRevisions => Set<LatestReplierRevision>();
     public DbSet<AuthorExpGradeRevision> AuthorExpGradeRevisions => Set<AuthorExpGradeRevision>();
     public DbSet<ForumModeratorRevision> ForumModeratorRevisions => Set<ForumModeratorRevision>();
     public DbSet<ThreadPost> Threads => Set<ThreadPost>();
@@ -72,6 +73,8 @@ protected override void OnModelCreating(ModelBuilder b)
         b.Entity<LatestReplier>().Property(e => e.DisplayName).HasConversion<byte[]>();
         b.Entity<LatestReplier>().HasOne<ThreadPost>().WithOne(e => e.LatestReplier)
             .HasForeignKey<ThreadPost>(e => e.LatestReplierId);
+        b.Entity<LatestReplierRevision>().ToTable("tbmcr_user_latestReplier").HasKey(e => new {e.TakenAt, e.Uid});
+        b.Entity<LatestReplierRevision>().Property(e => e.DisplayName).HasConversion<byte[]>();
         b.Entity<ThreadPost>().ToTable($"tbmc_f{Fid}_thread");
         b.Entity<ThreadMissingFirstReply>().ToTable("tbmc_thread_missingFirstReply");
         b.Entity<ReplyPost>().ToTable($"tbmc_f{Fid}_reply");

c#/crawler/src/Db/Revision/LatestReplierRevision.cs

@@ -0,0 +1,11 @@
+// ReSharper disable PropertyCanBeMadeInitOnly.Global
+namespace tbm.Crawler.Db.Revision;
+
+public class LatestReplierRevision
+{
+    public uint TakenAt { get; set; }
+    public uint Id { get; set; }
+    public long Uid { get; set; }
+    public string? Name { get; set; }
+    public string? DisplayName { get; set; }
+}

c#/crawler/src/Tieba/Crawl/Saver/Related/ThreadLatestReplierSaver.cs

@@ -40,16 +40,29 @@ public Action SaveFromUser(CrawlerDbContext db, Tid tid, IEnumerable<User> users
         // possible race: two user swapped their name or displayName
         // within the timespan of crawling threads and crawling its (sub)replies
         // so the one later crawled is not the original latest replier of thread
-        var user = users
+        var matchedUsers = users
             .Where(u => u.Name == threadLatestReplier.Name
                         && u.DisplayName == threadLatestReplier.DisplayName)
             .DistinctBy(u => u.Uid).ToList();
-        if (user.Count > 1)
-            Helper.LogDifferentValuesSharingTheSameKeyInEntities(logger, user,
+        if (matchedUsers.Count == 0) return () => { };
+        if (matchedUsers.Count > 1)
+            Helper.LogDifferentValuesSharingTheSameKeyInEntities(logger, matchedUsers,
                 $"{nameof(User.Name)} and {nameof(User.DisplayName)}",
                 u => u.Uid, u => (u.Name, u.DisplayName));
 
-        threadLatestReplier.Uid = user.First().Uid;
+        var user = matchedUsers[0];
+        if (threadLatestReplier.Uid == user.Uid) return () => { };
+        if (threadLatestReplier.Uid != null)
+            _ = db.LatestReplierRevisions.Add(new()
+            {
+                TakenAt = threadLatestReplier.UpdatedAt ?? threadLatestReplier.CreatedAt,
+                Id = threadLatestReplier.Id,
+                Uid = threadLatestReplier.Uid.Value,
+                Name = threadLatestReplier.Name,
+                DisplayName = threadLatestReplier.DisplayName
+            });
+
+        threadLatestReplier.Uid = user.Uid;
         _ = _saverLocks.Value.Acquire([UniqueLatestReplier.FromLatestReplier(threadLatestReplier)]);
         return _saverLocks.Value.Dispose;
     }

c#/crawler/src/Worker/RetryCrawlWorker.cs

@@ -60,18 +60,18 @@ private async Task RetryThreadLate(
         CancellationToken stoppingToken = default)
     {
         await using var threadLateFacade = threadLateCrawlFacadeFactory();
-        foreach (var tidGroupByFid in failureCountWithPagesKeyByLockId
+        foreach (var tidsGroupByFid in failureCountWithPagesKeyByLockId
                      .Keys.GroupBy(lockId => lockId.Fid, lockId => lockId.Tid))
         {
-            var fid = tidGroupByFid.Key;
+            var fid = tidsGroupByFid.Key;
             FailureCount FailureCountSelector(Tid tid) =>
 
                 // it should always contain only one page which is 1
                 failureCountWithPagesKeyByLockId[new(fid, tid)].Single().Value;
-            var failureCountsKeyByTid = tidGroupByFid
+            var failureCountsKeyByTid = tidsGroupByFid
                 .Cast<Tid>().ToDictionary(tid => tid, FailureCountSelector);
             logger.LogTrace("Retrying previous failed thread late crawl with fid={}, threadsId={}",
-                fid, SharedHelper.UnescapedJsonSerialize(tidGroupByFid));
+                fid, SharedHelper.UnescapedJsonSerialize(tidsGroupByFid));
             await threadLateFacade.Value(fid).CrawlThenSave(failureCountsKeyByTid, stoppingToken);
         }
     }

c#/imagePipeline/src/Ocr/JointRecognizer.cs

@@ -88,8 +88,8 @@ public IReadOnlyDictionary<ImageKey, string> GetRecognizedTextLines
                 })
                 .OrderBy(t => t.alignedY).ThenBy(t => t.X)
                 .GroupBy(t => t.alignedY, t => t.result)
-                .Select(groupByLine =>
-                    string.Join('\n', groupByLine.Select(result => result.Text.Trim())));
+                .Select(resultsGroupByLine =>
+                    string.Join('\n', resultsGroupByLine.Select(result => result.Text.Trim())));
 
             // https://unicode.org/reports/tr15/
             return string.Join('\n', resultTextLines).Normalize(NormalizationForm.FormKC);