natsdotnet/tests/NATS.Server.JetStream.Tests/JetStream/Storage/MemStoreGoParityTests.cs

// Reference: golang/nats-server/server/memstore_test.go
// Tests ported in this file:
//   TestMemStoreCompact                              → Compact_RemovesMessagesBeforeSeq
//   TestMemStoreStreamStateDeleted                  → StreamStateDeleted_TracksDmapCorrectly
//   TestMemStoreStreamTruncate                      → Truncate_RemovesMessagesAfterSeq
//   TestMemStoreUpdateMaxMsgsPerSubject             → UpdateMaxMsgsPerSubject_EnforcesNewLimit
//   TestMemStoreStreamCompactMultiBlockSubjectInfo  → Compact_AdjustsSubjectCount
//   TestMemStoreSubjectsTotals                      → SubjectsTotals_MatchesStoredCounts
//   TestMemStoreNumPending                          → NumPending_MatchesFilteredCount
//   TestMemStoreMultiLastSeqs                       → MultiLastSeqs_ReturnsLastPerSubject
//   TestMemStoreSubjectForSeq                       → SubjectForSeq_ReturnsCorrectSubject
//   TestMemStoreSubjectDeleteMarkers                → SubjectDeleteMarkers_TtlExpiry (skipped: needs pmsgcb)
//   TestMemStoreAllLastSeqs                         → AllLastSeqs_ReturnsLastPerSubjectSorted
//   TestMemStoreGetSeqFromTimeWithLastDeleted        → GetSeqFromTime_WithLastDeleted
//   TestMemStoreSkipMsgs                            → SkipMsgs_ReservesSequences
//   TestMemStoreDeleteBlocks                        → DeleteBlocks_DmapSizeMatchesNumDeleted
//   TestMemStoreMessageTTL                          → MessageTTL_ExpiresAfterDelay
//   TestMemStoreUpdateConfigTTLState                → UpdateConfig_TtlStateInitializedAndDestroyed
//   TestMemStoreNextWildcardMatch                   → NextWildcardMatch_BoundsAreCorrect
//   TestMemStoreNextLiteralMatch                    → NextLiteralMatch_BoundsAreCorrect
//   TestMemStoreInitialFirstSeq                     → InitialFirstSeq_StartAtConfiguredSeq
//   TestMemStoreStreamTruncateReset                 → TruncateReset_ClearsEverything
//   TestMemStorePurgeExWithSubject                  → PurgeEx_WithSubject_PurgesAll
//   TestMemStorePurgeExWithDeletedMsgs              → PurgeEx_WithDeletedMsgs_CorrectFirstSeq
//   TestMemStoreDeleteAllFirstSequenceCheck         → DeleteAll_FirstSeqIsLastPlusOne
//   TestMemStoreNumPendingBug                       → NumPending_Bug_CorrectCount
//   TestMemStorePurgeLeaksDmap                      → Purge_ClearsDmap
//   TestMemStoreMultiLastSeqsMaxAllowed             → MultiLastSeqs_MaxAllowed_ThrowsWhenExceeded

using NATS.Server.JetStream.Models;
using NATS.Server.JetStream.Storage;

namespace NATS.Server.JetStream.Tests.JetStream.Storage;

/// <summary>
/// Go MemStore parity tests. Each test mirrors a specific Go test from
/// golang/nats-server/server/memstore_test.go to verify behaviour parity.
/// </summary>
public sealed class MemStoreGoParityTests
{
    // Helper: cast to IStreamStore for sync methods
    private static IStreamStore Sync(MemStore ms) => ms;

    // -------------------------------------------------------------------------
    // Compact
    // -------------------------------------------------------------------------

    // Go: TestMemStoreCompact server/memstore_test.go:259
    [Fact]
    public void Compact_RemovesMessagesBeforeSeq()
    {
        var ms = new MemStore();
        var s = Sync(ms);

        for (var i = 0; i < 10; i++)
            s.StoreMsg("foo", null, "Hello World"u8.ToArray(), 0);

        s.State().Msgs.ShouldBe(10UL);

        var n = s.Compact(6);
        n.ShouldBe(5UL);

        var state = s.State();
        state.Msgs.ShouldBe(5UL);
        state.FirstSeq.ShouldBe(6UL);

        // Compact past the end resets first seq
        n = s.Compact(100);
        n.ShouldBe(5UL);
        s.State().FirstSeq.ShouldBe(100UL);
    }

    // -------------------------------------------------------------------------
    // StreamStateDeleted
    // -------------------------------------------------------------------------

    // Go: TestMemStoreStreamStateDeleted server/memstore_test.go:342
    [Fact]
    public void StreamStateDeleted_TracksDmapCorrectly()
    {
        var ms = new MemStore();
        var s = Sync(ms);

        const ulong toStore = 10;
        for (ulong i = 1; i <= toStore; i++)
            s.StoreMsg("foo", null, new byte[8], 0);

        s.State().Deleted.ShouldBeNull();

        // Delete even sequences 2,4,6,8
        var expectedDeleted = new List<ulong>();
        for (ulong seq = 2; seq < toStore; seq += 2)
        {
            s.RemoveMsg(seq);
            expectedDeleted.Add(seq);
        }

        var state = s.State();
        state.Deleted.ShouldNotBeNull();
        state.Deleted!.ShouldBe(expectedDeleted.ToArray());

        // Delete 1 and 3 to fill first gap — deleted should shift forward
        s.RemoveMsg(1);
        s.RemoveMsg(3);
        expectedDeleted = expectedDeleted.Skip(2).ToList(); // remove 2 and 4 from start
        state = s.State();
        state.Deleted!.ShouldBe(expectedDeleted.ToArray());
        state.FirstSeq.ShouldBe(5UL);

        s.Purge();
        s.State().Deleted.ShouldBeNull();
    }

    // -------------------------------------------------------------------------
    // Truncate
    // -------------------------------------------------------------------------

    // Go: TestMemStoreStreamTruncate server/memstore_test.go:385
    [Fact]
    public void Truncate_RemovesMessagesAfterSeq()
    {
        var ms = new MemStore();
        var s = Sync(ms);

        const ulong tseq = 50;
        const ulong toStore = 100;

        for (ulong i = 1; i < tseq; i++)
            s.StoreMsg("foo", null, "ok"u8.ToArray(), 0);
        for (var i = tseq; i <= toStore; i++)
            s.StoreMsg("bar", null, "ok"u8.ToArray(), 0);

        s.State().Msgs.ShouldBe(toStore);

        s.Truncate(tseq);
        s.State().Msgs.ShouldBe(tseq);

        // Truncate with some interior deletes
        s.RemoveMsg(10);
        s.RemoveMsg(20);
        s.RemoveMsg(30);
        s.RemoveMsg(40);

        s.Truncate(25);
        var state = s.State();
        // 25 seqs remaining, minus 2 deleted (10, 20) = 23 messages
        state.Msgs.ShouldBe(tseq - 2 - (tseq - 25));
        state.NumSubjects.ShouldBe(1); // only "foo" left
        state.Deleted!.ShouldBe([10UL, 20UL]);
    }

    // -------------------------------------------------------------------------
    // TruncateReset
    // -------------------------------------------------------------------------

    // Go: TestMemStoreStreamTruncateReset server/memstore_test.go:490
    [Fact]
    public void TruncateReset_ClearsEverything()
    {
        var ms = new MemStore();
        var s = Sync(ms);

        for (var i = 0; i < 1000; i++)
            s.StoreMsg("foo", null, "Hello World"u8.ToArray(), 0);

        s.Truncate(0);

        var state = s.State();
        state.Msgs.ShouldBe(0UL);
        state.Bytes.ShouldBe(0UL);
        state.FirstSeq.ShouldBe(0UL);
        state.LastSeq.ShouldBe(0UL);
        state.NumSubjects.ShouldBe(0);
        state.NumDeleted.ShouldBe(0);

        // Can store again after reset
        for (var i = 0; i < 1000; i++)
            s.StoreMsg("foo", null, "Hello World"u8.ToArray(), 0);

        state = s.State();
        state.Msgs.ShouldBe(1000UL);
        state.FirstSeq.ShouldBe(1UL);
        state.LastSeq.ShouldBe(1000UL);
        state.NumSubjects.ShouldBe(1);
        state.NumDeleted.ShouldBe(0);
    }

    // -------------------------------------------------------------------------
    // UpdateMaxMsgsPerSubject
    // -------------------------------------------------------------------------

    // Go: TestMemStoreUpdateMaxMsgsPerSubject server/memstore_test.go:452
    [Fact]
    public void UpdateMaxMsgsPerSubject_EnforcesNewLimit()
    {
        var cfg = new StreamConfig
        {
            Name = "TEST",
            Storage = StorageType.Memory,
            Subjects = ["foo"],
            MaxMsgsPer = 10,
        };
        var ms = new MemStore(cfg);
        var s = Sync(ms);

        // Increase limit — should allow more
        cfg.MaxMsgsPer = 50;
        s.UpdateConfig(cfg);

        const int numStored = 22;
        for (var i = 0; i < numStored; i++)
            s.StoreMsg("foo", null, [], 0);

        var ss = s.SubjectsState("foo")["foo"];
        ss.Msgs.ShouldBe((ulong)numStored);

        // Shrink limit — should truncate stored
        cfg.MaxMsgsPer = 10;
        s.UpdateConfig(cfg);

        ss = s.SubjectsState("foo")["foo"];
        ss.Msgs.ShouldBe(10UL);
    }

    // -------------------------------------------------------------------------
    // CompactMultiBlockSubjectInfo
    // -------------------------------------------------------------------------

    // Go: TestMemStoreStreamCompactMultiBlockSubjectInfo server/memstore_test.go:531
    [Fact]
    public void Compact_AdjustsSubjectCount()
    {
        var ms = new MemStore();
        var s = Sync(ms);

        for (var i = 0; i < 1000; i++)
            s.StoreMsg($"foo.{i}", null, "Hello World"u8.ToArray(), 0);

        var deleted = s.Compact(501);
        deleted.ShouldBe(500UL);

        s.State().NumSubjects.ShouldBe(500);
    }

    // -------------------------------------------------------------------------
    // SubjectsTotals
    // -------------------------------------------------------------------------

    // Go: TestMemStoreSubjectsTotals server/memstore_test.go:557
    [Fact]
    public void SubjectsTotals_MatchesStoredCounts()
    {
        var ms = new MemStore();
        var s = Sync(ms);

        var fmap = new Dictionary<int, int>();
        var bmap = new Dictionary<int, int>();
        var rng = new Random(42);

        for (var i = 0; i < 10_000; i++)
        {
            string ft;
            Dictionary<int, int> m;
            if (rng.Next(2) == 0) { ft = "foo"; m = fmap; }
            else { ft = "bar"; m = bmap; }
            var dt = rng.Next(100);
            var subj = $"{ft}.{dt}";
            m.TryGetValue(dt, out var c);
            m[dt] = c + 1;
            s.StoreMsg(subj, null, "Hello World"u8.ToArray(), 0);
        }

        // Check individual foo subjects
        foreach (var kv in fmap)
        {
            var subj = $"foo.{kv.Key}";
            var totals = s.SubjectsTotals(subj);
            totals[subj].ShouldBe((ulong)kv.Value);
        }

        // Check foo.* wildcard
        var fooTotals = s.SubjectsTotals("foo.*");
        fooTotals.Count.ShouldBe(fmap.Count);
        var fooExpected = (ulong)fmap.Values.Sum(n => n);
        fooTotals.Values.Aggregate(0UL, (a, v) => a + v).ShouldBe(fooExpected);

        // Check bar.* wildcard
        var barTotals = s.SubjectsTotals("bar.*");
        barTotals.Count.ShouldBe(bmap.Count);

        // Check *.*
        var allTotals = s.SubjectsTotals("*.*");
        allTotals.Count.ShouldBe(fmap.Count + bmap.Count);
    }

    // -------------------------------------------------------------------------
    // NumPending
    // -------------------------------------------------------------------------

    // Go: TestMemStoreNumPending server/memstore_test.go:637
    [Fact]
    public void NumPending_MatchesFilteredCount()
    {
        var ms = new MemStore();
        var s = Sync(ms);
        var tokens = new[] { "foo", "bar", "baz" };
        var rng = new Random(99);

        string GenSubj() => $"{tokens[rng.Next(3)]}.{tokens[rng.Next(3)]}.{tokens[rng.Next(3)]}.{tokens[rng.Next(3)]}";

        for (var i = 0; i < 5_000; i++)
            s.StoreMsg(GenSubj(), null, "Hello World"u8.ToArray(), 0);

        var state = s.State();
        var startSeqs = new ulong[] { 0, 1, 2, 200, 444, 555, 2222, 4000 };
        var checkSubs = new[] { "foo.>", "*.bar.>", "foo.bar.*.baz", "*.foo.bar.*", "foo.foo.bar.baz" };

        foreach (var filter in checkSubs)
        {
            foreach (var startSeq in startSeqs)
            {
                var (total, validThrough) = s.NumPending(startSeq, filter, false);
                validThrough.ShouldBe(state.LastSeq);

                // Sanity-check: manually count matching msgs from startSeq
                var sseq = startSeq == 0 ? 1 : startSeq;
                ulong expected = 0;
                for (var seq = sseq; seq <= state.LastSeq; seq++)
                {
                    try
                    {
                        var sm = s.LoadMsg(seq, null);
                        if (SubjectMatchesFilter(sm.Subject, filter)) expected++;
                    }
                    catch (KeyNotFoundException) { }
                }
                total.ShouldBe(expected, $"filter={filter} start={startSeq}");
            }
        }
    }

    // -------------------------------------------------------------------------
    // MultiLastSeqs
    // -------------------------------------------------------------------------

    // Go: TestMemStoreMultiLastSeqs server/memstore_test.go:923
    [Fact]
    public void MultiLastSeqs_ReturnsLastPerSubject()
    {
        var ms = new MemStore();
        var s = Sync(ms);
        var msg = "abc"u8.ToArray();

        for (var i = 0; i < 33; i++)
        {
            s.StoreMsg("foo.foo", null, msg, 0);
            s.StoreMsg("foo.bar", null, msg, 0);
            s.StoreMsg("foo.baz", null, msg, 0);
        }
        for (var i = 0; i < 33; i++)
        {
            s.StoreMsg("bar.foo", null, msg, 0);
            s.StoreMsg("bar.bar", null, msg, 0);
            s.StoreMsg("bar.baz", null, msg, 0);
        }

        // Up to seq 3
        s.MultiLastSeqs(["foo.*"], 3, -1).ShouldBe([1UL, 2UL, 3UL]);
        // All of foo.*
        s.MultiLastSeqs(["foo.*"], 0, -1).ShouldBe([97UL, 98UL, 99UL]);
        // All of bar.*
        s.MultiLastSeqs(["bar.*"], 0, -1).ShouldBe([196UL, 197UL, 198UL]);
        // bar.* at seq <= 99 — nothing
        s.MultiLastSeqs(["bar.*"], 99, -1).ShouldBe([]);

        // Explicit subjects
        s.MultiLastSeqs(["foo.foo", "foo.bar", "foo.baz"], 3, -1).ShouldBe([1UL, 2UL, 3UL]);
        s.MultiLastSeqs(["foo.foo", "foo.bar", "foo.baz"], 0, -1).ShouldBe([97UL, 98UL, 99UL]);
        s.MultiLastSeqs(["bar.foo", "bar.bar", "bar.baz"], 0, -1).ShouldBe([196UL, 197UL, 198UL]);
        s.MultiLastSeqs(["bar.foo", "bar.bar", "bar.baz"], 99, -1).ShouldBe([]);

        // Single filter
        s.MultiLastSeqs(["foo.foo"], 3, -1).ShouldBe([1UL]);

        // De-duplicate overlapping filters
        s.MultiLastSeqs(["foo.*", "foo.bar"], 3, -1).ShouldBe([1UL, 2UL, 3UL]);

        // All subjects
        s.MultiLastSeqs([">"], 0, -1).ShouldBe([97UL, 98UL, 99UL, 196UL, 197UL, 198UL]);
        s.MultiLastSeqs([">"], 99, -1).ShouldBe([97UL, 98UL, 99UL]);
    }

    // -------------------------------------------------------------------------
    // MultiLastSeqs — maxAllowed
    // -------------------------------------------------------------------------

    // Go: TestMemStoreMultiLastSeqsMaxAllowed server/memstore_test.go:1010
    [Fact]
    public void MultiLastSeqs_MaxAllowed_ThrowsWhenExceeded()
    {
        var ms = new MemStore();
        var s = Sync(ms);
        var msg = "abc"u8.ToArray();

        for (var i = 1; i <= 100; i++)
            s.StoreMsg($"foo.{i}", null, msg, 0);

        Should.Throw<InvalidOperationException>(() => s.MultiLastSeqs(["foo.*"], 0, 10));
    }

    // -------------------------------------------------------------------------
    // SubjectForSeq
    // -------------------------------------------------------------------------

    // Go: TestMemStoreSubjectForSeq server/memstore_test.go:1319
    [Fact]
    public void SubjectForSeq_ReturnsCorrectSubject()
    {
        var ms = new MemStore();
        var s = Sync(ms);

        s.StoreMsg("foo.bar", null, [], 0);

        // seq 0 (not found)
        Should.Throw<KeyNotFoundException>(() => s.SubjectForSeq(0));

        // seq 1 — should be "foo.bar"
        s.SubjectForSeq(1).ShouldBe("foo.bar");

        // seq 2 (not yet stored)
        Should.Throw<KeyNotFoundException>(() => s.SubjectForSeq(2));
    }

    // -------------------------------------------------------------------------
    // AllLastSeqs
    // -------------------------------------------------------------------------

    // Go: TestMemStoreAllLastSeqs server/memstore_test.go:1266
    [Fact]
    public void AllLastSeqs_ReturnsLastPerSubjectSorted()
    {
        var cfg = new StreamConfig
        {
            Name = "zzz",
            Subjects = ["*.*"],
            MaxMsgsPer = 50,
            Storage = StorageType.Memory,
        };
        var ms = new MemStore(cfg);
        var s = Sync(ms);

        var subjs = new[] { "foo.foo", "foo.bar", "foo.baz", "bar.foo", "bar.bar", "bar.baz" };
        var msg = "abc"u8.ToArray();
        var rng = new Random(7);

        for (var i = 0; i < 10_000; i++)
            s.StoreMsg(subjs[rng.Next(subjs.Length)], null, msg, 0);

        // Compute expected last sequences per subject
        var expected = new List<ulong>();
        foreach (var subj in subjs)
        {
            try
            {
                var sm = s.LoadLastMsg(subj, null);
                expected.Add(sm.Sequence);
            }
            catch (KeyNotFoundException) { }
        }
        expected.Sort();

        var seqs = s.AllLastSeqs();
        seqs.ShouldBe(expected.ToArray());
    }

    // -------------------------------------------------------------------------
    // GetSeqFromTime with last deleted
    // -------------------------------------------------------------------------

    // Go: TestMemStoreGetSeqFromTimeWithLastDeleted server/memstore_test.go:839
    [Fact]
    public void GetSeqFromTime_WithLastDeleted()
    {
        var ms = new MemStore();
        var s = Sync(ms);

        const int total = 1000;
        DateTime midTime = default;
        for (var i = 1; i <= total; i++)
        {
            s.StoreMsg("A", null, "OK"u8.ToArray(), 0);
            if (i == total / 2)
            {
                Thread.Sleep(100);
                midTime = DateTime.UtcNow;
            }
        }

        // Delete last 100
        for (var seq = total - 100; seq <= total; seq++)
            s.RemoveMsg((ulong)seq);

        // Should not panic and should return correct value
        var found = s.GetSeqFromTime(midTime);
        found.ShouldBe(501UL);
    }

    // -------------------------------------------------------------------------
    // SkipMsgs
    // -------------------------------------------------------------------------

    // Go: TestMemStoreSkipMsgs server/memstore_test.go:871
    [Fact]
    public void SkipMsgs_ReservesSequences()
    {
        var ms = new MemStore();
        var s = Sync(ms);

        // Wrong starting sequence should fail
        Should.Throw<InvalidOperationException>(() => s.SkipMsgs(10, 100));

        // Skip from seq 1
        s.SkipMsgs(1, 100);
        var state = s.State();
        state.FirstSeq.ShouldBe(101UL);
        state.LastSeq.ShouldBe(100UL);

        // Skip many more
        s.SkipMsgs(101, 100_000);
        state = s.State();
        state.FirstSeq.ShouldBe(100_101UL);
        state.LastSeq.ShouldBe(100_100UL);

        // New store: store a message then skip
        var ms2 = new MemStore();
        var s2 = Sync(ms2);
        s2.StoreMsg("foo", null, [], 0);
        s2.SkipMsgs(2, 10);

        state = s2.State();
        state.FirstSeq.ShouldBe(1UL);
        state.LastSeq.ShouldBe(11UL);
        state.Msgs.ShouldBe(1UL);
        state.NumDeleted.ShouldBe(10);
        state.Deleted.ShouldNotBeNull();
        state.Deleted!.Length.ShouldBe(10);

        // FastState consistency
        var fstate = new StreamState();
        s2.FastState(ref fstate);
        fstate.FirstSeq.ShouldBe(1UL);
        fstate.LastSeq.ShouldBe(11UL);
        fstate.Msgs.ShouldBe(1UL);
        fstate.NumDeleted.ShouldBe(10);
    }

    // -------------------------------------------------------------------------
    // DeleteBlocks
    // -------------------------------------------------------------------------

    // Go: TestMemStoreDeleteBlocks server/memstore_test.go:799
    [Fact]
    public void DeleteBlocks_DmapSizeMatchesNumDeleted()
    {
        var ms = new MemStore();
        var s = Sync(ms);

        const int total = 10_000;
        for (var i = 0; i < total; i++)
            s.StoreMsg("A", null, "OK"u8.ToArray(), 0);

        // Delete 5000 random sequences
        var rng = new Random(13);
        var deleteSet = new HashSet<int>();
        while (deleteSet.Count < 5000)
            deleteSet.Add(rng.Next(total) + 1);

        foreach (var seq in deleteSet)
            s.RemoveMsg((ulong)seq);

        var fstate = new StreamState();
        s.FastState(ref fstate);

        // NumDeleted from FastState must equal interior gap count
        var fullState = s.State();
        var dmapSize = fullState.Deleted?.Length ?? 0;
        dmapSize.ShouldBe(fstate.NumDeleted);
    }

    // -------------------------------------------------------------------------
    // MessageTTL
    // -------------------------------------------------------------------------

    // Go: TestMemStoreMessageTTL server/memstore_test.go:1202
    [Fact]
    public void MessageTTL_ExpiresAfterDelay()
    {
        var cfg = new StreamConfig
        {
            Name = "zzz",
            Subjects = ["test"],
            Storage = StorageType.Memory,
            AllowMsgTtl = true,
        };
        var ms = new MemStore(cfg);
        var s = Sync(ms);

        const long ttl = 1; // 1 second

        for (var i = 1; i <= 10; i++)
            s.StoreMsg("test", null, [], ttl);

        var ss = new StreamState();
        s.FastState(ref ss);
        ss.FirstSeq.ShouldBe(1UL);
        ss.LastSeq.ShouldBe(10UL);
        ss.Msgs.ShouldBe(10UL);

        // Wait for TTL to expire (> 1 sec + check interval of 1 sec)
        Thread.Sleep(2_500);

        s.FastState(ref ss);
        ss.FirstSeq.ShouldBe(11UL);
        ss.LastSeq.ShouldBe(10UL);
        ss.Msgs.ShouldBe(0UL);
    }

    // -------------------------------------------------------------------------
    // UpdateConfigTTLState
    // -------------------------------------------------------------------------

    // Go: TestMemStoreUpdateConfigTTLState server/memstore_test.go:1299
    [Fact]
    public void UpdateConfig_TtlStateInitializedAndDestroyed()
    {
        var cfg = new StreamConfig
        {
            Name = "zzz",
            Subjects = [">"],
            Storage = StorageType.Memory,
            AllowMsgTtl = false,
        };
        var ms = new MemStore(cfg);
        var s = Sync(ms);

        // TTL disabled — internal TTL wheel should be null (we cannot observe it directly,
        // but UpdateConfig must not throw and subsequent behaviour must be correct)
        cfg.AllowMsgTtl = true;
        s.UpdateConfig(cfg);

        // Store with TTL — should work
        s.StoreMsg("test", null, [], 3600);
        s.State().Msgs.ShouldBe(1UL);

        // Disable TTL again
        cfg.AllowMsgTtl = false;
        s.UpdateConfig(cfg);

        // Message stored before disabling should still be present (TTL wheel gone but msg stays)
        s.State().Msgs.ShouldBe(1UL);
    }

    // -------------------------------------------------------------------------
    // NextWildcardMatch
    // -------------------------------------------------------------------------

    // Go: TestMemStoreNextWildcardMatch server/memstore_test.go:1373
    [Fact]
    public void NextWildcardMatch_BoundsAreCorrect()
    {
        var ms = new MemStore();
        var s = Sync(ms);

        void StoreN(string subj, int n)
        {
            for (var i = 0; i < n; i++)
                s.StoreMsg(subj, null, "msg"u8.ToArray(), 0);
        }

        StoreN("foo.bar.a", 1);      // seq 1
        StoreN("foo.baz.bar", 10);   // seqs 2-11
        StoreN("foo.bar.b", 1);      // seq 12
        StoreN("foo.baz.bar", 10);   // seqs 13-22
        StoreN("foo.baz.bar.no.match", 10); // seqs 23-32

        lock (ms.Gate)
        {
            var (first, last, found) = ms.NextWildcardMatchLocked("foo.bar.*", 0);
            found.ShouldBeTrue();
            first.ShouldBe(1UL);
            last.ShouldBe(12UL);

            (first, last, found) = ms.NextWildcardMatchLocked("foo.bar.*", 1);
            found.ShouldBeTrue();
            first.ShouldBe(1UL);
            last.ShouldBe(12UL);

            (first, last, found) = ms.NextWildcardMatchLocked("foo.bar.*", 2);
            found.ShouldBeTrue();
            first.ShouldBe(12UL);
            last.ShouldBe(12UL);

            (_, _, found) = ms.NextWildcardMatchLocked("foo.bar.*", first + 1);
            found.ShouldBeFalse();

            (first, last, found) = ms.NextWildcardMatchLocked("foo.baz.*", 1);
            found.ShouldBeTrue();
            first.ShouldBe(2UL);
            last.ShouldBe(22UL);

            (first, last, found) = ms.NextWildcardMatchLocked("foo.nope.*", 1);
            found.ShouldBeFalse();
            first.ShouldBe(0UL);
            last.ShouldBe(0UL);

            (first, last, found) = ms.NextWildcardMatchLocked("foo.>", 1);
            found.ShouldBeTrue();
            first.ShouldBe(1UL);
            last.ShouldBe(32UL);
        }
    }

    // -------------------------------------------------------------------------
    // NextLiteralMatch
    // -------------------------------------------------------------------------

    // Go: TestMemStoreNextLiteralMatch server/memstore_test.go:1454
    [Fact]
    public void NextLiteralMatch_BoundsAreCorrect()
    {
        var ms = new MemStore();
        var s = Sync(ms);

        void StoreN(string subj, int n)
        {
            for (var i = 0; i < n; i++)
                s.StoreMsg(subj, null, "msg"u8.ToArray(), 0);
        }

        StoreN("foo.bar.a", 1);             // seq 1
        StoreN("foo.baz.bar", 10);          // seqs 2-11
        StoreN("foo.bar.b", 1);             // seq 12
        StoreN("foo.baz.bar", 10);          // seqs 13-22
        StoreN("foo.baz.bar.no.match", 10); // seqs 23-32

        lock (ms.Gate)
        {
            var (first, last, found) = ms.NextLiteralMatchLocked("foo.bar.a", 0);
            found.ShouldBeTrue();
            first.ShouldBe(1UL);
            last.ShouldBe(1UL);

            (_, _, found) = ms.NextLiteralMatchLocked("foo.bar.a", 2);
            found.ShouldBeFalse();

            (first, last, found) = ms.NextLiteralMatchLocked("foo.baz.bar", 1);
            found.ShouldBeTrue();
            first.ShouldBe(2UL);
            last.ShouldBe(22UL);

            (first, last, found) = ms.NextLiteralMatchLocked("foo.baz.bar", 22);
            found.ShouldBeTrue();
            first.ShouldBe(22UL);
            last.ShouldBe(22UL);

            (first, last, found) = ms.NextLiteralMatchLocked("foo.baz.bar", 23);
            found.ShouldBeFalse();
            first.ShouldBe(0UL);
            last.ShouldBe(0UL);

            (_, _, found) = ms.NextLiteralMatchLocked("foo.nope", 1);
            found.ShouldBeFalse();
        }
    }

    // -------------------------------------------------------------------------
    // InitialFirstSeq
    // -------------------------------------------------------------------------

    // Go: TestMemStoreInitialFirstSeq server/memstore_test.go:765
    [Fact]
    public void InitialFirstSeq_StartAtConfiguredSeq()
    {
        var cfg = new StreamConfig
        {
            Name = "zzz",
            Storage = StorageType.Memory,
            FirstSeq = 1000,
        };
        var ms = new MemStore(cfg);
        var s = Sync(ms);

        var (seq, _) = s.StoreMsg("A", null, "OK"u8.ToArray(), 0);
        seq.ShouldBe(1000UL);

        (seq, _) = s.StoreMsg("B", null, "OK"u8.ToArray(), 0);
        seq.ShouldBe(1001UL);

        var state = new StreamState();
        s.FastState(ref state);
        state.Msgs.ShouldBe(2UL);
        state.FirstSeq.ShouldBe(1000UL);
        state.LastSeq.ShouldBe(1001UL);
    }

    // -------------------------------------------------------------------------
    // PurgeEx with subject
    // -------------------------------------------------------------------------

    // Go: TestMemStorePurgeExWithSubject server/memstore_test.go:437
    [Fact]
    public void PurgeEx_WithSubject_PurgesAll()
    {
        var ms = new MemStore();
        var s = Sync(ms);

        for (var i = 0; i < 100; i++)
            s.StoreMsg("foo", null, [], 0);

        s.PurgeEx("foo", 1, 0);
        s.State().Msgs.ShouldBe(0UL);
    }

    // -------------------------------------------------------------------------
    // PurgeEx with deleted messages
    // -------------------------------------------------------------------------

    // Go: TestMemStorePurgeExWithDeletedMsgs server/memstore_test.go:1031
    [Fact]
    public void PurgeEx_WithDeletedMsgs_CorrectFirstSeq()
    {
        var ms = new MemStore();
        var s = Sync(ms);
        var msg = "abc"u8.ToArray();

        for (var i = 1; i <= 10; i++)
            s.StoreMsg("foo", null, msg, 0);

        s.RemoveMsg(2);
        s.RemoveMsg(9); // was the bug

        var n = s.PurgeEx("", 9, 0);
        n.ShouldBe(7UL); // seqs 1,3,4,5,6,7,8 (not 2 since deleted, not 9 since deleted)

        var state = new StreamState();
        s.FastState(ref state);
        state.FirstSeq.ShouldBe(10UL);
        state.LastSeq.ShouldBe(10UL);
        state.Msgs.ShouldBe(1UL);
    }

    // -------------------------------------------------------------------------
    // DeleteAll FirstSequenceCheck
    // -------------------------------------------------------------------------

    // Go: TestMemStoreDeleteAllFirstSequenceCheck server/memstore_test.go:1060
    [Fact]
    public void DeleteAll_FirstSeqIsLastPlusOne()
    {
        var ms = new MemStore();
        var s = Sync(ms);

        for (var i = 1; i <= 10; i++)
            s.StoreMsg("foo", null, "abc"u8.ToArray(), 0);

        for (ulong seq = 1; seq <= 10; seq++)
            s.RemoveMsg(seq);

        var state = new StreamState();
        s.FastState(ref state);
        state.FirstSeq.ShouldBe(11UL);
        state.LastSeq.ShouldBe(10UL);
        state.Msgs.ShouldBe(0UL);
    }

    // -------------------------------------------------------------------------
    // NumPending — bug fix
    // -------------------------------------------------------------------------

    // Go: TestMemStoreNumPendingBug server/memstore_test.go:1137
    [Fact]
    public void NumPending_Bug_CorrectCount()
    {
        var ms = new MemStore();
        var s = Sync(ms);

        foreach (var subj in new[] { "foo.foo", "foo.bar", "foo.baz", "foo.zzz" })
        {
            s.StoreMsg("foo.aaa", null, [], 0);
            s.StoreMsg(subj, null, [], 0);
            s.StoreMsg(subj, null, [], 0);
        }

        // 12 msgs total
        var (total, _) = s.NumPending(4, "foo.*", false);

        ulong expected = 0;
        for (var seq = 4; seq <= 12; seq++)
        {
            try
            {
                var sm = s.LoadMsg((ulong)seq, null);
                if (SubjectMatchesFilter(sm.Subject, "foo.*")) expected++;
            }
            catch (KeyNotFoundException) { }
        }
        total.ShouldBe(expected);
    }

    // -------------------------------------------------------------------------
    // Purge clears dmap
    // -------------------------------------------------------------------------

    // Go: TestMemStorePurgeLeaksDmap server/memstore_test.go:1168
    [Fact]
    public void Purge_ClearsDmap()
    {
        var ms = new MemStore();
        var s = Sync(ms);

        for (var i = 0; i < 10; i++)
            s.StoreMsg("foo", null, [], 0);

        for (ulong i = 2; i <= 9; i++)
            s.RemoveMsg(i);

        // 8 interior gaps now
        var state = s.State();
        state.NumDeleted.ShouldBe(8);

        // Purge should also clear dmap
        var purged = s.Purge();
        purged.ShouldBe(2UL); // 2 actual msgs remain (1 and 10)

        state = s.State();
        state.NumDeleted.ShouldBe(0);
        state.Deleted.ShouldBeNull();
    }

    // -------------------------------------------------------------------------
    // Helpers
    // -------------------------------------------------------------------------

    private static bool SubjectMatchesFilter(string subject, string filter)
    {
        if (string.IsNullOrEmpty(filter) || filter == ">") return true;
        if (NATS.Server.Subscriptions.SubjectMatch.IsLiteral(filter))
            return string.Equals(subject, filter, StringComparison.Ordinal);
        return NATS.Server.Subscriptions.SubjectMatch.MatchLiteral(subject, filter);
    }
}