// Copyright 2019-2026 The NATS Authors
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
// Mirrors server/memstore_test.go

using System.Text;
using Shouldly;
using ZB.MOM.NatsNet.Server;

namespace ZB.MOM.NatsNet.Server.Tests.JetStream;

/// <summary>
/// Unit tests for the in-memory JetStream message store.
/// Mirrors server/memstore_test.go.
/// </summary>
public class JetStreamMemoryStoreTests
{
    // -----------------------------------------------------------------------
    // Helpers
    // -----------------------------------------------------------------------

    private static JetStreamMemStore NewMemStore(StreamConfig? cfg = null)
    {
        cfg ??= new StreamConfig { Storage = StorageType.MemoryStorage, Name = "test" };
        return JetStreamMemStore.NewMemStore(cfg);
    }

    private static byte[] Bytes(string s) => Encoding.UTF8.GetBytes(s);

    /// <summary>Computes the expected stored-message size: subj.len + hdr.len + msg.len + 16.</summary>
    private static ulong MsgSize(string subj, byte[]? hdr, byte[]? msg)
        => (ulong)(subj.Length + (hdr?.Length ?? 0) + (msg?.Length ?? 0) + 16);

    [Fact]
    public void NewMemStore_FactoryMethod_InitializesFirstSequence()
    {
        var method = typeof(JetStreamMemStore).GetMethod(
            "NewMemStore",
            System.Reflection.BindingFlags.Static | System.Reflection.BindingFlags.Public | System.Reflection.BindingFlags.NonPublic);
        method.ShouldNotBeNull();

        var cfg = new StreamConfig
        {
            Name = "factory-init",
            Storage = StorageType.MemoryStorage,
            FirstSeq = 1000,
        };

        var created = method!.Invoke(null, new object?[] { cfg });
        created.ShouldBeOfType<JetStreamMemStore>();

        var ms = (JetStreamMemStore)created!;
        var state = ms.State();
        state.FirstSeq.ShouldBe(1000UL);
        state.LastSeq.ShouldBe(999UL);
        ms.Stop();
    }

    [Fact]
    public void MemStoreSubjectDeleteMarkers_ShouldSucceed()
    {
        var fs = NewMemStore(new StreamConfig
        {
            Name = "zzz",
            Subjects = ["test"],
            Storage = StorageType.MemoryStorage,
            MaxAge = TimeSpan.FromSeconds(1),
            AllowMsgTTL = true,
            SubjectDeleteMarkerTTL = TimeSpan.FromSeconds(1),
        });

        var (seq, _) = fs.StoreMsg("test", null, Bytes("x"), 0);
        seq.ShouldBe(1UL);

        var (removed, err) = fs.RemoveMsg(seq);
        removed.ShouldBeTrue();
        err.ShouldBeNull();
        fs.State().Msgs.ShouldBe(0UL);

        fs.Stop();
    }

    [Fact]
    public void AllLastSeqsLocked_MatchesPublicAllLastSeqsOrdering()
    {
        var cfg = new StreamConfig
        {
            Name = "locked-all-last-seqs",
            Subjects = new[] { "*.*" },
            MaxMsgsPer = 50,
            Storage = StorageType.MemoryStorage,
        };
        var ms = NewMemStore(cfg);

        var subjs = new[] { "foo.foo", "foo.bar", "foo.baz", "bar.foo", "bar.bar", "bar.baz" };
        var msg = Bytes("abc");
        var rng = new Random(11);

        for (var i = 0; i < 1_000; i++)
        {
            var subj = subjs[rng.Next(subjs.Length)];
            ms.StoreMsg(subj, null, msg, 0);
        }

        var method = typeof(JetStreamMemStore).GetMethod(
            "AllLastSeqsLocked",
            System.Reflection.BindingFlags.Instance | System.Reflection.BindingFlags.NonPublic);
        method.ShouldNotBeNull();

        var result = method!.Invoke(ms, Array.Empty<object>());
        result.ShouldNotBeNull();
        var (lockedSeqs, lockedErr) = ((ValueTuple<ulong[], Exception?>)result!);

        var (publicSeqs, publicErr) = ms.AllLastSeqs();

        lockedErr.ShouldBeNull();
        publicErr.ShouldBeNull();
        lockedSeqs.SequenceEqual(publicSeqs).ShouldBeTrue();

        ms.Stop();
    }

    // -----------------------------------------------------------------------
    // TestMemStoreBasics (T:2023)
    // -----------------------------------------------------------------------

    [Fact] // T:2023
    public void MemStoreBasics_ShouldSucceed()
    {
        // Reference: golang/nats-server/server/memstore_test.go:TestMemStoreBasics line 32
        var ms = NewMemStore(new StreamConfig { Storage = StorageType.MemoryStorage });
        ms.Stop();

        ms = NewMemStore(new StreamConfig { Storage = StorageType.MemoryStorage });
        var subj = "foo";
        var msg = Bytes("Hello World");
        var now = DateTimeOffset.UtcNow.ToUnixTimeMilliseconds() * 1_000_000L;

        var (seq, ts) = ms.StoreMsg(subj, null, msg, 0);
        seq.ShouldBe(1UL);
        ts.ShouldBeGreaterThanOrEqualTo(now);

        var state = ms.State();
        state.Msgs.ShouldBe(1UL);

        var expectedSize = MsgSize(subj, null, msg);
        state.Bytes.ShouldBe(expectedSize);

        var sm = ms.LoadMsg(1, null);
        sm.ShouldNotBeNull();
        sm!.Subject.ShouldBe(subj);
        sm.Msg.ShouldBe(msg);

        ms.Stop();
    }

    // -----------------------------------------------------------------------
    // TestMemStoreMsgLimit (T:2024)
    // -----------------------------------------------------------------------

    [Fact] // T:2024
    public void MemStoreMsgLimit_ShouldSucceed()
    {
        // Reference: golang/nats-server/server/memstore_test.go:TestMemStoreMsgLimit line 67
        var ms = NewMemStore(new StreamConfig { Storage = StorageType.MemoryStorage, MaxMsgs = 10 });

        var subj = "foo";
        var msg = Bytes("Hello World");
        for (var i = 0; i < 10; i++)
            ms.StoreMsg(subj, null, msg, 0);

        var state = ms.State();
        state.Msgs.ShouldBe(10UL);

        // Adding one more should still keep 10 (oldest evicted)
        ms.StoreMsg(subj, null, msg, 0);
        state = ms.State();
        state.Msgs.ShouldBe(10UL);
        state.LastSeq.ShouldBe(11UL);
        state.FirstSeq.ShouldBe(2UL);

        // Seq 1 should not be loadable
        Should.Throw<Exception>(() => ms.LoadMsg(1, null));

        ms.Stop();
    }

    // -----------------------------------------------------------------------
    // TestMemStoreBytesLimit (T:2025)
    // -----------------------------------------------------------------------

    [Fact] // T:2025
    public void MemStoreBytesLimit_ShouldSucceed()
    {
        // Reference: golang/nats-server/server/memstore_test.go:TestMemStoreBytesLimit line 99
        var subj = "foo";
        var msg = new byte[512];
        var storedMsgSize = MsgSize(subj, null, msg);

        var toStore = 1024UL;
        var maxBytes = storedMsgSize * toStore;

        var ms = NewMemStore(new StreamConfig { Storage = StorageType.MemoryStorage, MaxBytes = (long)maxBytes });

        for (var i = 0UL; i < toStore; i++)
            ms.StoreMsg(subj, null, msg, 0);

        var state = ms.State();
        state.Msgs.ShouldBe(toStore);
        state.Bytes.ShouldBe(storedMsgSize * toStore);

        // Now send 10 more and check that bytes limit enforced
        for (var i = 0; i < 10; i++)
            ms.StoreMsg(subj, null, msg, 0);

        state = ms.State();
        state.Msgs.ShouldBe(toStore);
        state.Bytes.ShouldBe(storedMsgSize * toStore);
        state.FirstSeq.ShouldBe(11UL);
        state.LastSeq.ShouldBe(toStore + 10UL);

        ms.Stop();
    }

    // -----------------------------------------------------------------------
    // TestMemStoreBytesLimitWithDiscardNew (T:2026)
    // -----------------------------------------------------------------------

    [Fact] // T:2026
    public void MemStoreBytesLimitWithDiscardNew_ShouldSucceed()
    {
        // Reference: golang/nats-server/server/memstore_test.go:TestMemStoreBytesLimitWithDiscardNew line 143
        var subj = "tiny";
        var msg = new byte[7];
        var storedMsgSize = MsgSize(subj, null, msg);
        var toStore = 3UL;
        var maxBytes = 100;

        var ms = NewMemStore(new StreamConfig
        {
            Storage = StorageType.MemoryStorage,
            MaxBytes = maxBytes,
            Discard = DiscardPolicy.DiscardNew
        });

        // Send 10 messages; first toStore succeed, the rest hit ErrMaxBytes
        for (var i = 0; i < 10; i++)
        {
            var (seq, _) = ms.StoreMsg(subj, null, msg, 0);
            if (i < (int)toStore)
                seq.ShouldNotBe(0UL); // success
            // After toStore, StoreMsg returns (0, 0) on error
        }

        var state = ms.State();
        state.Msgs.ShouldBe(toStore);
        state.Bytes.ShouldBe(storedMsgSize * toStore);

        ms.Stop();
    }

    // -----------------------------------------------------------------------
    // TestMemStoreAgeLimit (T:2027)
    // -----------------------------------------------------------------------

    [Fact] // T:2027
    public async Task MemStoreAgeLimit_ShouldSucceed()
    {
        // Reference: golang/nats-server/server/memstore_test.go:TestMemStoreAgeLimit line 174
        var maxAge = TimeSpan.FromMilliseconds(100);
        var ms = NewMemStore(new StreamConfig { Storage = StorageType.MemoryStorage, MaxAge = maxAge });

        var subj = "foo";
        var msg = Bytes("Hello World");
        for (var i = 0; i < 100; i++)
            ms.StoreMsg(subj, null, msg, 0);

        var state = ms.State();
        state.Msgs.ShouldBe(100UL);

        // Wait for messages to expire
        await Task.Delay(TimeSpan.FromMilliseconds(500));

        // Check messages expired
        var deadline = DateTime.UtcNow.AddSeconds(2);
        while (DateTime.UtcNow < deadline)
        {
            state = ms.State();
            if (state.Msgs == 0 && state.Bytes == 0) break;
            await Task.Delay(10);
        }

        state = ms.State();
        state.Msgs.ShouldBe(0UL);
        state.Bytes.ShouldBe(0UL);

        // Now add some more and make sure that timer will fire again
        for (var i = 0; i < 100; i++)
            ms.StoreMsg(subj, null, msg, 0);

        state = ms.State();
        state.Msgs.ShouldBe(100UL);

        await Task.Delay(TimeSpan.FromMilliseconds(500));

        deadline = DateTime.UtcNow.AddSeconds(2);
        while (DateTime.UtcNow < deadline)
        {
            state = ms.State();
            if (state.Msgs == 0 && state.Bytes == 0) break;
            await Task.Delay(10);
        }

        state = ms.State();
        state.Msgs.ShouldBe(0UL);
        state.Bytes.ShouldBe(0UL);

        ms.Stop();
    }

    // -----------------------------------------------------------------------
    // TestMemStoreTimeStamps (T:2028)
    // -----------------------------------------------------------------------

    [Fact] // T:2028
    public async Task MemStoreTimeStamps_ShouldSucceed()
    {
        // Reference: golang/nats-server/server/memstore_test.go:TestMemStoreTimeStamps line 216
        var ms = NewMemStore(new StreamConfig { Storage = StorageType.MemoryStorage });

        var last = DateTimeOffset.UtcNow.ToUnixTimeMilliseconds() * 1_000_000L;
        var subj = "foo";
        var msg = Bytes("Hello World");

        for (var i = 0; i < 10; i++)
        {
            await Task.Delay(5); // small delay to ensure distinct timestamps
            ms.StoreMsg(subj, null, msg, 0);
        }

        var smv = new StoreMsg();
        for (var seq = 1UL; seq <= 10UL; seq++)
        {
            var sm = ms.LoadMsg(seq, smv);
            sm.ShouldNotBeNull();
            sm!.Ts.ShouldBeGreaterThan(last);
            last = sm.Ts;
        }

        ms.Stop();
    }

    // -----------------------------------------------------------------------
    // TestMemStorePurge (T:2029)
    // -----------------------------------------------------------------------

    [Fact] // T:2029
    public void MemStorePurge_ShouldSucceed()
    {
        // Reference: golang/nats-server/server/memstore_test.go:TestMemStorePurge line 241
        var ms = NewMemStore(new StreamConfig { Storage = StorageType.MemoryStorage });

        var subj = "foo";
        var msg = Bytes("Hello World");
        for (var i = 0; i < 10; i++)
            ms.StoreMsg(subj, null, msg, 0);

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

        ms.Purge();

        ms.State().Msgs.ShouldBe(0UL);

        ms.Stop();
    }

    // -----------------------------------------------------------------------
    // TestMemStoreCompact (T:2030)
    // -----------------------------------------------------------------------

    [Fact] // T:2030
    public void MemStoreCompact_ShouldSucceed()
    {
        // Reference: golang/nats-server/server/memstore_test.go:TestMemStoreCompact line 259
        var ms = NewMemStore(new StreamConfig { Storage = StorageType.MemoryStorage });

        var subj = "foo";
        var msg = Bytes("Hello World");
        for (var i = 0; i < 10; i++)
            ms.StoreMsg(subj, null, msg, 0);

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

        var (n, err) = ms.Compact(6);
        err.ShouldBeNull();
        n.ShouldBe(5UL);

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

        // Compact past end should purge
        (n, err) = ms.Compact(100);
        err.ShouldBeNull();
        n.ShouldBe(5UL);

        state = ms.State();
        state.FirstSeq.ShouldBe(100UL);

        ms.Stop();
    }

    // -----------------------------------------------------------------------
    // TestMemStoreEraseMsg (T:2031)
    // -----------------------------------------------------------------------

    [Fact] // T:2031
    public void MemStoreEraseMsg_ShouldSucceed()
    {
        // Reference: golang/nats-server/server/memstore_test.go:TestMemStoreEraseMsg line 298
        var ms = NewMemStore(new StreamConfig { Storage = StorageType.MemoryStorage });

        var subj = "foo";
        var msg = Bytes("Hello World");
        ms.StoreMsg(subj, null, msg, 0);

        var sm = ms.LoadMsg(1, null);
        sm.ShouldNotBeNull();
        sm!.Msg.ShouldBe(msg);

        var (removed, _) = ms.EraseMsg(1);
        removed.ShouldBeTrue();

        ms.Stop();
    }

    // -----------------------------------------------------------------------
    // TestMemStoreMsgHeaders (T:2032)
    // -----------------------------------------------------------------------

    [Fact] // T:2032
    public void MemStoreMsgHeaders_ShouldSucceed()
    {
        // Reference: golang/nats-server/server/memstore_test.go:TestMemStoreMsgHeaders line 317
        var ms = NewMemStore(new StreamConfig { Storage = StorageType.MemoryStorage });

        var subj = "foo";
        var hdr = Bytes("name:derek");
        var msg = Bytes("Hello World");

        // Verify computed size
        var sz = (int)MsgSize(subj, hdr, msg);
        sz.ShouldBe(subj.Length + hdr.Length + msg.Length + 16);

        ms.StoreMsg(subj, hdr, msg, 0);

        var sm = ms.LoadMsg(1, null);
        sm.ShouldNotBeNull();
        sm!.Msg.ShouldBe(msg);
        sm.Hdr.ShouldBe(hdr);

        var (removed, _) = ms.EraseMsg(1);
        removed.ShouldBeTrue();

        ms.Stop();
    }

    // -----------------------------------------------------------------------
    // TestMemStoreStreamStateDeleted (T:2033)
    // -----------------------------------------------------------------------

    [Fact] // T:2033
    public void MemStoreStreamStateDeleted_ShouldSucceed()
    {
        // Reference: golang/nats-server/server/memstore_test.go:TestMemStoreStreamStateDeleted line 342
        var ms = NewMemStore(new StreamConfig { Storage = StorageType.MemoryStorage });

        var subj = "foo";
        var toStore = 10UL;
        for (var i = 1UL; i <= toStore; i++)
        {
            var m = Encoding.UTF8.GetBytes($"[{i:D8}] Hello World!");
            ms.StoreMsg(subj, null, m, 0);
        }

        var state = ms.State();
        state.Deleted.ShouldBeNull();

        // Remove some interior messages (even seqs: 2,4,6,8)
        var expected = new List<ulong>();
        for (var seq = 2UL; seq < toStore; seq += 2)
        {
            ms.RemoveMsg(seq);
            expected.Add(seq);
        }

        state = ms.State();
        state.Deleted.ShouldNotBeNull();
        state.Deleted!.ShouldBe(expected.ToArray());

        // Now fill the gap by deleting 1 and 3
        ms.RemoveMsg(1);
        ms.RemoveMsg(3);
        expected.RemoveRange(0, 2); // remove 2 and 4 (the first two)
        state = ms.State();
        state.Deleted!.ShouldBe(expected.ToArray());
        state.FirstSeq.ShouldBe(5UL);

        ms.Purge();
        state = ms.State();
        (state.Deleted?.Length ?? 0).ShouldBe(0);

        ms.Stop();
    }

    // -----------------------------------------------------------------------
    // TestMemStoreStreamTruncate (T:2034)
    // -----------------------------------------------------------------------

    [Fact] // T:2034
    public void MemStoreStreamTruncate_ShouldSucceed()
    {
        // Reference: golang/nats-server/server/memstore_test.go:TestMemStoreStreamTruncate line 385
        var ms = NewMemStore(new StreamConfig { Storage = StorageType.MemoryStorage });

        var tseq = 50UL;
        var toStore = 100UL;

        for (var i = 1UL; i < tseq; i++)
            ms.StoreMsg("foo", null, Bytes("ok"), 0);
        for (var i = tseq; i <= toStore; i++)
            ms.StoreMsg("bar", null, Bytes("ok"), 0);

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

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

        // Now test with interior deletes
        ms.RemoveMsg(10);
        ms.RemoveMsg(20);
        ms.RemoveMsg(30);
        ms.RemoveMsg(40);

        tseq = 25UL;
        ms.Truncate(tseq);

        var state = ms.State();
        state.Msgs.ShouldBe(tseq - 2); // 10 and 20 deleted
        state.NumSubjects.ShouldBe(1);
        state.Deleted.ShouldBe(new ulong[] { 10, 20 });

        ms.Stop();
    }

    // -----------------------------------------------------------------------
    // TestMemStorePurgeExWithSubject (T:2035)
    // -----------------------------------------------------------------------

    [Fact] // T:2035
    public void MemStorePurgeExWithSubject_ShouldSucceed()
    {
        // Reference: golang/nats-server/server/memstore_test.go:TestMemStorePurgeExWithSubject line 437
        var ms = NewMemStore(new StreamConfig { Storage = StorageType.MemoryStorage });

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

        // Purge all with subject "foo"
        ms.PurgeEx("foo", 1, 0);
        ms.State().Msgs.ShouldBe(0UL);

        ms.Stop();
    }

    // -----------------------------------------------------------------------
    // TestMemStoreUpdateMaxMsgsPerSubject (T:2036)
    // -----------------------------------------------------------------------

    [Fact] // T:2036
    public void MemStoreUpdateMaxMsgsPerSubject_ShouldSucceed()
    {
        // Reference: golang/nats-server/server/memstore_test.go:TestMemStoreUpdateMaxMsgsPerSubject line 452
        var cfg = new StreamConfig
        {
            Name = "TEST",
            Storage = StorageType.MemoryStorage,
            Subjects = new[] { "foo" },
            MaxMsgsPer = 10,
        };
        var ms = NewMemStore(cfg);

        // Increase limit
        cfg.MaxMsgsPer = 50;
        ms.UpdateConfig(cfg);

        var numStored = 22;
        for (var i = 0; i < numStored; i++)
            ms.StoreMsg("foo", null, null, 0);

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

        // Decrease limit to 10 — should trim to 10
        cfg.MaxMsgsPer = 10;
        ms.UpdateConfig(cfg);

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

        ms.Stop();
    }

    // -----------------------------------------------------------------------
    // TestMemStoreStreamTruncateReset (T:2037)
    // -----------------------------------------------------------------------

    [Fact] // T:2037
    public void MemStoreStreamTruncateReset_ShouldSucceed()
    {
        // Reference: golang/nats-server/server/memstore_test.go:TestMemStoreStreamTruncateReset line 490
        var cfg = new StreamConfig
        {
            Name = "TEST",
            Storage = StorageType.MemoryStorage,
            Subjects = new[] { "foo" },
        };
        var ms = NewMemStore(cfg);

        var subj = "foo";
        var msg = Bytes("Hello World");
        for (var i = 0; i < 1000; i++)
            ms.StoreMsg(subj, null, msg, 0);

        // Reset everything via Truncate(0)
        ms.Truncate(0);

        var state = ms.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);

        // Store 1000 more after reset
        for (var i = 0; i < 1000; i++)
            ms.StoreMsg(subj, null, msg, 0);

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

        ms.Stop();
    }

    // -----------------------------------------------------------------------
    // TestMemStoreStreamCompactMultiBlockSubjectInfo (T:2038)
    // -----------------------------------------------------------------------

    [Fact] // T:2038
    public void MemStoreStreamCompactMultiBlockSubjectInfo_ShouldSucceed()
    {
        // Reference: golang/nats-server/server/memstore_test.go:TestMemStoreStreamCompactMultiBlockSubjectInfo line 531
        var cfg = new StreamConfig
        {
            Name = "TEST",
            Storage = StorageType.MemoryStorage,
            Subjects = new[] { "foo.*" },
        };
        var ms = NewMemStore(cfg);

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

        var (deleted, err) = ms.Compact(501);
        err.ShouldBeNull();
        deleted.ShouldBe(500UL);

        var state = ms.State();
        state.NumSubjects.ShouldBe(500);

        ms.Stop();
    }

    // -----------------------------------------------------------------------
    // TestMemStoreSubjectsTotals (T:2039)
    // -----------------------------------------------------------------------

    [Fact] // T:2039
    public void MemStoreSubjectsTotals_ShouldSucceed()
    {
        // Reference: golang/nats-server/server/memstore_test.go:TestMemStoreSubjectsTotals line 557
        var cfg = new StreamConfig
        {
            Name = "TEST",
            Storage = StorageType.MemoryStorage,
            Subjects = new[] { "*.*" },
        };
        var ms = NewMemStore(cfg);

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

        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[dt] = m.GetValueOrDefault(dt) + 1;
            ms.StoreMsg(subj, null, Bytes("Hello World"), 0);
        }

        // Check each individual subject in fmap
        foreach (var (dt, total) in fmap)
        {
            var subj = $"foo.{dt}";
            var m = ms.SubjectsTotals(subj);
            m[subj].ShouldBe((ulong)total);
        }

        // Check fmap wildcard totals
        var st = ms.SubjectsTotals("foo.*");
        st.Count.ShouldBe(fmap.Count);
        var expectedTotal = fmap.Values.Sum();
        var receivedTotal = st.Values.Select(v => (long)v).Sum();
        receivedTotal.ShouldBe(expectedTotal);

        // Check bmap wildcard totals
        st = ms.SubjectsTotals("bar.*");
        st.Count.ShouldBe(bmap.Count);
        expectedTotal = bmap.Values.Sum();
        receivedTotal = st.Values.Select(v => (long)v).Sum();
        receivedTotal.ShouldBe(expectedTotal);

        // All with pwc match
        st = ms.SubjectsTotals("*.*");
        st.Count.ShouldBe(bmap.Count + fmap.Count);

        ms.Stop();
    }

    // -----------------------------------------------------------------------
    // TestMemStoreNumPending (T:2040)
    // -----------------------------------------------------------------------

    [Fact] // T:2040
    public void MemStoreNumPending_ShouldSucceed()
    {
        // Reference: golang/nats-server/server/memstore_test.go:TestMemStoreNumPending line 637
        var cfg = new StreamConfig
        {
            Name = "TEST",
            Storage = StorageType.MemoryStorage,
            Subjects = new[] { "*.*.*.*" },
        };
        var ms = NewMemStore(cfg);

        var tokens = new[] { "foo", "bar", "baz" };
        var rng = new Random(99);
        string GenSubj() =>
            $"{tokens[rng.Next(tokens.Length)]}.{tokens[rng.Next(tokens.Length)]}.{tokens[rng.Next(tokens.Length)]}.{tokens[rng.Next(tokens.Length)]}";

        for (var i = 0; i < 5_000; i++)
        {
            var subj = GenSubj();
            ms.StoreMsg(subj, null, Bytes("Hello World"), 0);
        }

        var state = ms.State();

        // Scan one by one for sanity check
        SimpleState SanityCheck(ulong sseq, string filter)
        {
            var ss = new SimpleState();
            var smv = new StoreMsg();
            if (sseq == 0) sseq = 1;
            for (var seq = sseq; seq <= state.LastSeq; seq++)
            {
                try
                {
                    var sm = ms.LoadMsg(seq, smv);
                    if (sm != null && SubjectIsSubsetMatch(sm.Subject, filter))
                    {
                        ss.Msgs++;
                        ss.Last = seq;
                        if (ss.First == 0 || seq < ss.First) ss.First = seq;
                    }
                }
                catch { /* skip deleted */ }
            }
            return ss;
        }

        void Check(ulong sseq, string filter)
        {
            var (np, lvs, err) = ms.NumPending(sseq, filter, false);
            err.ShouldBeNull();
            lvs.ShouldBe(state.LastSeq);
            var ss = ms.FilteredState(sseq, filter);
            var sss = SanityCheck(sseq, filter);
            ss.Msgs.ShouldBe(np);
            ss.Msgs.ShouldBe(sss.Msgs);
        }

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

        foreach (var filter in checkSubs)
        foreach (var start in startSeqs)
            Check(start, filter);

        ms.Stop();
    }

    // -----------------------------------------------------------------------
    // TestMemStoreInitialFirstSeq (T:2041)
    // -----------------------------------------------------------------------

    [Fact] // T:2041
    public void MemStoreInitialFirstSeq_ShouldSucceed()
    {
        // Reference: golang/nats-server/server/memstore_test.go:TestMemStoreInitialFirstSeq line 765
        var cfg = new StreamConfig
        {
            Name = "zzz",
            Storage = StorageType.MemoryStorage,
            FirstSeq = 1000,
        };
        var ms = NewMemStore(cfg);

        var (seq, _, err) = (ms.StoreMsg("A", null, Bytes("OK"), 0).Seq, 0L, (Exception?)null);
        seq.ShouldBe(1000UL);

        var (seq2, _) = ms.StoreMsg("B", null, Bytes("OK"), 0);
        seq2.ShouldBe(1001UL);

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

        ms.Stop();
    }

    // -----------------------------------------------------------------------
    // TestMemStoreGetSeqFromTimeWithLastDeleted (T:2043)
    // -----------------------------------------------------------------------

    [Fact] // T:2043
    public async Task MemStoreGetSeqFromTimeWithLastDeleted_ShouldSucceed()
    {
        // Reference: golang/nats-server/server/memstore_test.go:TestMemStoreGetSeqFromTimeWithLastDeleted line 839
        var cfg = new StreamConfig
        {
            Name = "zzz",
            Subjects = new[] { "*" },
            Storage = StorageType.MemoryStorage,
        };
        var ms = NewMemStore(cfg);

        var total = 100;
        DateTime st = default;
        for (var i = 1; i <= total; i++)
        {
            ms.StoreMsg("A", null, Bytes("OK"), 0);
            if (i == total / 2)
            {
                await Task.Delay(50);
                st = DateTime.UtcNow;
            }
        }

        // Delete last 10
        for (var seq = total - 10; seq <= total; seq++)
            ms.RemoveMsg((ulong)seq);

        // Make sure this does not panic with last sequence no longer accessible
        var gotSeq = ms.GetSeqFromTime(st);
        // Should return around 51 (the halfway point)
        gotSeq.ShouldBeGreaterThanOrEqualTo(49UL);
        gotSeq.ShouldBeLessThanOrEqualTo(53UL);

        ms.Stop();
    }

    // -----------------------------------------------------------------------
    // TestMemStoreSkipMsgs (T:2044)
    // -----------------------------------------------------------------------

    [Fact] // T:2044
    public void MemStoreSkipMsgs_ShouldSucceed()
    {
        // Reference: golang/nats-server/server/memstore_test.go:TestMemStoreSkipMsgs line 871
        var cfg = new StreamConfig
        {
            Name = "zzz",
            Subjects = new[] { "*" },
            Storage = StorageType.MemoryStorage,
        };
        var ms = NewMemStore(cfg);

        // Wrong starting sequence must fail
        Should.Throw<Exception>(() => ms.SkipMsgs(10, 100));

        ms.SkipMsgs(1, 100);

        var state = ms.State();
        state.FirstSeq.ShouldBe(101UL);
        state.LastSeq.ShouldBe(100UL);

        // Now skip a large amount
        ms.SkipMsgs(101, 100_000);
        state = ms.State();
        state.FirstSeq.ShouldBe(100_101UL);
        state.LastSeq.ShouldBe(100_100UL);

        // New store: add a message then skip
        ms = NewMemStore(cfg);
        ms.StoreMsg("foo", null, null, 0);

        ms.SkipMsgs(2, 10);
        state = ms.State();
        state.FirstSeq.ShouldBe(1UL);
        state.LastSeq.ShouldBe(11UL);
        state.Msgs.ShouldBe(1UL);
        state.NumDeleted.ShouldBe(10);
        state.Deleted!.Length.ShouldBe(10);

        // Check FastState
        state.Deleted = null;
        ms.FastState(state);
        state.FirstSeq.ShouldBe(1UL);
        state.LastSeq.ShouldBe(11UL);
        state.Msgs.ShouldBe(1UL);
        state.NumDeleted.ShouldBe(10);

        ms.Stop();
    }

    // -----------------------------------------------------------------------
    // TestMemStoreMultiLastSeqs (T:2045)
    // -----------------------------------------------------------------------

    [Fact] // T:2045
    public void MemStoreMultiLastSeqs_ShouldSucceed()
    {
        // Reference: golang/nats-server/server/memstore_test.go:TestMemStoreMultiLastSeqs line 923
        var cfg = new StreamConfig
        {
            Name = "zzz",
            Subjects = new[] { "foo.*", "bar.*" },
            Storage = StorageType.MemoryStorage,
        };
        var ms = NewMemStore(cfg);

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

        void CheckResults(ulong[] seqs, ulong[] expected)
        {
            seqs.Length.ShouldBe(expected.Length);
            for (var i = 0; i < seqs.Length; i++)
                seqs[i].ShouldBe(expected[i]);
        }

        // UpTo sequence 3
        var (seqs, err) = ms.MultiLastSeqs(new[] { "foo.*" }, 3, -1);
        err.ShouldBeNull();
        CheckResults(seqs!, new ulong[] { 1, 2, 3 });

        // Up to last sequence of the stream
        (seqs, err) = ms.MultiLastSeqs(new[] { "foo.*" }, 0, -1);
        err.ShouldBeNull();
        CheckResults(seqs!, new ulong[] { 97, 98, 99 });

        // Check for bar.* at the end
        (seqs, err) = ms.MultiLastSeqs(new[] { "bar.*" }, 0, -1);
        err.ShouldBeNull();
        CheckResults(seqs!, new ulong[] { 196, 197, 198 });

        // This should find nothing
        (seqs, err) = ms.MultiLastSeqs(new[] { "bar.*" }, 99, -1);
        err.ShouldBeNull();
        CheckResults(seqs!, Array.Empty<ulong>());

        // Explicit subjects
        (seqs, err) = ms.MultiLastSeqs(new[] { "foo.foo", "foo.bar", "foo.baz" }, 3, -1);
        err.ShouldBeNull();
        CheckResults(seqs!, new ulong[] { 1, 2, 3 });

        (seqs, err) = ms.MultiLastSeqs(new[] { "foo.foo", "foo.bar", "foo.baz" }, 0, -1);
        err.ShouldBeNull();
        CheckResults(seqs!, new ulong[] { 97, 98, 99 });

        (seqs, err) = ms.MultiLastSeqs(new[] { "bar.foo", "bar.bar", "bar.baz" }, 0, -1);
        err.ShouldBeNull();
        CheckResults(seqs!, new ulong[] { 196, 197, 198 });

        (seqs, err) = ms.MultiLastSeqs(new[] { "bar.foo", "bar.bar", "bar.baz" }, 99, -1);
        err.ShouldBeNull();
        CheckResults(seqs!, Array.Empty<ulong>());

        // Single subject
        (seqs, err) = ms.MultiLastSeqs(new[] { "foo.foo" }, 3, -1);
        err.ShouldBeNull();
        CheckResults(seqs!, new ulong[] { 1 });

        // De-duplicate
        (seqs, err) = ms.MultiLastSeqs(new[] { "foo.*", "foo.bar" }, 3, -1);
        err.ShouldBeNull();
        CheckResults(seqs!, new ulong[] { 1, 2, 3 });

        (seqs, err) = ms.MultiLastSeqs(new[] { "bar.>", "bar.bar", "bar.baz" }, 0, -1);
        err.ShouldBeNull();
        CheckResults(seqs!, new ulong[] { 196, 197, 198 });

        // All
        (seqs, err) = ms.MultiLastSeqs(new[] { ">" }, 0, -1);
        err.ShouldBeNull();
        CheckResults(seqs!, new ulong[] { 97, 98, 99, 196, 197, 198 });

        (seqs, err) = ms.MultiLastSeqs(new[] { ">" }, 99, -1);
        err.ShouldBeNull();
        CheckResults(seqs!, new ulong[] { 97, 98, 99 });

        ms.Stop();
    }

    // -----------------------------------------------------------------------
    // TestMemStoreMultiLastSeqsMaxAllowed (T:2046)
    // -----------------------------------------------------------------------

    [Fact] // T:2046
    public void MemStoreMultiLastSeqsMaxAllowed_ShouldSucceed()
    {
        // Reference: golang/nats-server/server/memstore_test.go:TestMemStoreMultiLastSeqsMaxAllowed line 1010
        var cfg = new StreamConfig
        {
            Name = "zzz",
            Subjects = new[] { "foo.*" },
            Storage = StorageType.MemoryStorage,
        };
        var ms = NewMemStore(cfg);

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

        var (seqs, err) = ms.MultiLastSeqs(new[] { "foo.*" }, 0, 10);
        seqs.ShouldBeNull();
        err.ShouldNotBeNull();
        err!.Message.ShouldContain("too many");

        ms.Stop();
    }

    // -----------------------------------------------------------------------
    // TestMemStorePurgeExWithDeletedMsgs (T:2047)
    // -----------------------------------------------------------------------

    [Fact] // T:2047
    public void MemStorePurgeExWithDeletedMsgs_ShouldSucceed()
    {
        // Reference: golang/nats-server/server/memstore_test.go:TestMemStorePurgeExWithDeletedMsgs line 1031
        var cfg = new StreamConfig
        {
            Name = "zzz",
            Subjects = new[] { "foo" },
            Storage = StorageType.MemoryStorage,
        };
        var ms = NewMemStore(cfg);

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

        ms.RemoveMsg(2);
        ms.RemoveMsg(9); // This was the bug

        var (n, err) = ms.PurgeEx(string.Empty, 9, 0);
        err.ShouldBeNull();
        n.ShouldBe(7UL);

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

        ms.Stop();
    }

    // -----------------------------------------------------------------------
    // TestMemStoreDeleteAllFirstSequenceCheck (T:2048)
    // -----------------------------------------------------------------------

    [Fact] // T:2048
    public void MemStoreDeleteAllFirstSequenceCheck_ShouldSucceed()
    {
        // Reference: golang/nats-server/server/memstore_test.go:TestMemStoreDeleteAllFirstSequenceCheck line 1060
        var cfg = new StreamConfig
        {
            Name = "zzz",
            Subjects = new[] { "foo" },
            Storage = StorageType.MemoryStorage,
        };
        var ms = NewMemStore(cfg);

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

        for (var seq = 1UL; seq <= 10UL; seq++)
            ms.RemoveMsg(seq);

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

        ms.Stop();
    }

    // -----------------------------------------------------------------------
    // TestMemStoreAllLastSeqs (T:2054)
    // -----------------------------------------------------------------------

    [Fact] // T:2054
    public void MemStoreAllLastSeqs_ShouldSucceed()
    {
        // Reference: golang/nats-server/server/memstore_test.go:TestMemStoreAllLastSeqs line 1266
        var cfg = new StreamConfig
        {
            Name = "zzz",
            Subjects = new[] { "*.*" },
            MaxMsgsPer = 50,
            Storage = StorageType.MemoryStorage,
        };
        var ms = NewMemStore(cfg);

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

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

        var expected = new List<ulong>();
        var smv = new StoreMsg();
        foreach (var subj in subjs)
        {
            var sm = ms.LoadLastMsg(subj, smv);
            sm.ShouldNotBeNull();
            expected.Add(sm!.Seq);
        }
        expected.Sort();

        var (seqs, err) = ms.AllLastSeqs();
        err.ShouldBeNull();
        seqs!.SequenceEqual(expected).ShouldBeTrue();

        ms.Stop();
    }

    // -----------------------------------------------------------------------
    // TestMemStoreSubjectForSeq (T:2056)
    // -----------------------------------------------------------------------

    [Fact] // T:2056
    public void MemStoreSubjectForSeq_ShouldSucceed()
    {
        // Reference: golang/nats-server/server/memstore_test.go:TestMemStoreSubjectForSeq line 1319
        var cfg = new StreamConfig
        {
            Name = "foo",
            Subjects = new[] { "foo.>" },
            Storage = StorageType.MemoryStorage,
        };
        var ms = NewMemStore(cfg);

        var (seq, _) = ms.StoreMsg("foo.bar", null, null, 0);
        seq.ShouldBe(1UL);

        var (subj, err) = ms.SubjectForSeq(0);
        err.ShouldNotBeNull();

        (subj, err) = ms.SubjectForSeq(1);
        err.ShouldBeNull();
        subj.ShouldBe("foo.bar");

        (subj, err) = ms.SubjectForSeq(2);
        err.ShouldNotBeNull();

        ms.Stop();
    }

    // -----------------------------------------------------------------------
    // Private helper: subject subset matching (mirrors Go subjectIsSubsetMatch)
    // -----------------------------------------------------------------------

    private static bool SubjectIsSubsetMatch(string subject, string filter)
    {
        var sParts = subject.Split('.');
        var fParts = filter.Split('.');
        var si = 0;
        for (var fi = 0; fi < fParts.Length; fi++)
        {
            if (fParts[fi] == ">")
                return si < sParts.Length;
            if (si >= sParts.Length)
                return false;
            if (fParts[fi] != "*" && fParts[fi] != sParts[si])
                return false;
            si++;
        }
        return si == sParts.Length;
    }
}