// Copyright 2012-2026 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/store_test.go (MemStore permutation only; file store permutations deferred).

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

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

/// <summary>
/// Unit tests for IStreamStore contract, exercised against JetStreamMemStore.
/// Mirrors server/store_test.go (memory permutations only).
/// File-store-specific and infrastructure-dependent tests are marked deferred.
/// </summary>
public class StorageEngineTests
{
    // -----------------------------------------------------------------------
    // Helpers
    // -----------------------------------------------------------------------

    private static JetStreamMemStore NewMemStore(StreamConfig cfg)
    {
        cfg.Storage = StorageType.MemoryStorage;
        return JetStreamMemStore.NewMemStore(cfg);
    }

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

    // -----------------------------------------------------------------------
    // TestStoreDeleteSlice (T:2943)
    // -----------------------------------------------------------------------

    [Fact] // T:2943
    public void StoreDeleteSlice_ShouldSucceed()
    {
        // Reference: golang/nats-server/server/store_test.go:TestStoreDeleteSlice line 147
        var ds = new DeleteSlice(new ulong[] { 2 });
        var deletes = new List<ulong>();
        ds.Range(seq => { deletes.Add(seq); return true; });
        deletes.Count.ShouldBe(1);
        deletes[0].ShouldBe(2UL);

        var (first, last, num) = ds.GetState();
        first.ShouldBe(2UL);
        last.ShouldBe(2UL);
        num.ShouldBe(1UL);
    }

    // -----------------------------------------------------------------------
    // TestStoreDeleteRange (T:2944)
    // -----------------------------------------------------------------------

    [Fact] // T:2944
    public void StoreDeleteRange_ShouldSucceed()
    {
        // Reference: golang/nats-server/server/store_test.go:TestStoreDeleteRange line 163
        var dr = new DeleteRange { First = 2, Num = 1 };
        var deletes = new List<ulong>();
        dr.Range(seq => { deletes.Add(seq); return true; });
        deletes.Count.ShouldBe(1);
        deletes[0].ShouldBe(2UL);

        var (first, last, num) = dr.GetState();
        first.ShouldBe(2UL);
        last.ShouldBe(2UL);
        num.ShouldBe(1UL);
    }

    // -----------------------------------------------------------------------
    // TestStoreSubjectStateConsistency (T:2945) — MemStore permutation only
    // -----------------------------------------------------------------------

    [Fact] // T:2945
    public void StoreSubjectStateConsistency_ShouldSucceed()
    {
        // Reference: golang/nats-server/server/store_test.go:TestStoreSubjectStateConsistency line 179
        var fs = NewMemStore(new StreamConfig { Name = "TEST", Subjects = new[] { "foo" } });

        SimpleState GetSubjectState()
        {
            var ss = fs.SubjectsState("foo");
            ss.TryGetValue("foo", out var result);
            return result ?? new SimpleState();
        }

        var smp = new StoreMsg();

        ulong ExpectFirstSeq()
        {
            var (sm, _, err) = fs.LoadNextMsg("foo", false, 0, smp).Sm?.Seq is ulong s
                ? (smp, s, (Exception?)null)
                : (null, 0UL, StoreErrors.ErrStoreMsgNotFound);
            var (smr, skip) = fs.LoadNextMsg("foo", false, 0, smp);
            smr.ShouldNotBeNull();
            return skip;
        }

        ulong ExpectLastSeq()
        {
            var sm = fs.LoadLastMsg("foo", smp);
            sm.ShouldNotBeNull();
            return sm!.Seq;
        }

        // Publish 4 messages
        for (var i = 0; i < 4; i++)
            fs.StoreMsg("foo", null, null, 0);

        var ss = GetSubjectState();
        ss.Msgs.ShouldBe(4UL);
        ss.First.ShouldBe(1UL);
        ss.Last.ShouldBe(4UL);

        // Verify first/last via LoadNextMsg / LoadLastMsg
        var (firstSm, firstSeq) = fs.LoadNextMsg("foo", false, 0, smp);
        firstSm.ShouldNotBeNull();
        firstSeq.ShouldBe(1UL);
        var lastSm = fs.LoadLastMsg("foo", smp);
        lastSm!.Seq.ShouldBe(4UL);

        // Remove first message
        var (removed, _) = fs.RemoveMsg(1);
        removed.ShouldBeTrue();

        ss = GetSubjectState();
        ss.Msgs.ShouldBe(3UL);
        ss.First.ShouldBe(2UL);
        ss.Last.ShouldBe(4UL);

        (firstSm, firstSeq) = fs.LoadNextMsg("foo", false, 0, smp);
        firstSm.ShouldNotBeNull();
        firstSeq.ShouldBe(2UL);
        lastSm = fs.LoadLastMsg("foo", smp);
        lastSm!.Seq.ShouldBe(4UL);

        // Remove last message
        (removed, _) = fs.RemoveMsg(4);
        removed.ShouldBeTrue();

        ss = GetSubjectState();
        ss.Msgs.ShouldBe(2UL);
        ss.First.ShouldBe(2UL);
        ss.Last.ShouldBe(3UL);

        (firstSm, firstSeq) = fs.LoadNextMsg("foo", false, 0, smp);
        firstSm.ShouldNotBeNull();
        firstSeq.ShouldBe(2UL);
        lastSm = fs.LoadLastMsg("foo", smp);
        lastSm!.Seq.ShouldBe(3UL);

        // Remove seq 2
        (removed, _) = fs.RemoveMsg(2);
        removed.ShouldBeTrue();

        ss = GetSubjectState();
        ss.Msgs.ShouldBe(1UL);
        ss.First.ShouldBe(3UL);
        ss.Last.ShouldBe(3UL);

        (firstSm, firstSeq) = fs.LoadNextMsg("foo", false, 0, smp);
        firstSm.ShouldNotBeNull();
        firstSeq.ShouldBe(3UL);
        lastSm = fs.LoadLastMsg("foo", smp);
        lastSm!.Seq.ShouldBe(3UL);

        // Publish 3 more
        for (var i = 0; i < 3; i++)
            fs.StoreMsg("foo", null, null, 0);

        ss = GetSubjectState();
        ss.Msgs.ShouldBe(4UL);
        ss.First.ShouldBe(3UL);
        ss.Last.ShouldBe(7UL);

        // Remove seq 7 and seq 3
        (removed, _) = fs.RemoveMsg(7);
        removed.ShouldBeTrue();
        (removed, _) = fs.RemoveMsg(3);
        removed.ShouldBeTrue();

        // Remove seq 5 (the now-first)
        (removed, _) = fs.RemoveMsg(5);
        removed.ShouldBeTrue();

        ss = GetSubjectState();
        ss.Msgs.ShouldBe(1UL);
        ss.First.ShouldBe(6UL);
        ss.Last.ShouldBe(6UL);

        (firstSm, firstSeq) = fs.LoadNextMsg("foo", false, 0, smp);
        firstSm.ShouldNotBeNull();
        firstSeq.ShouldBe(6UL);
        lastSm = fs.LoadLastMsg("foo", smp);
        lastSm!.Seq.ShouldBe(6UL);

        // Store + immediately remove seq 8, then store seq 9
        fs.StoreMsg("foo", null, null, 0);
        (removed, _) = fs.RemoveMsg(8);
        removed.ShouldBeTrue();
        fs.StoreMsg("foo", null, null, 0);

        ss = GetSubjectState();
        ss.Msgs.ShouldBe(2UL);
        ss.First.ShouldBe(6UL);
        ss.Last.ShouldBe(9UL);

        (firstSm, firstSeq) = fs.LoadNextMsg("foo", false, 0, smp);
        firstSm.ShouldNotBeNull();
        firstSeq.ShouldBe(6UL);
        lastSm = fs.LoadLastMsg("foo", smp);
        lastSm!.Seq.ShouldBe(9UL);

        fs.Stop();
    }

    // -----------------------------------------------------------------------
    // TestStoreMaxMsgsPerUpdateBug (T:2947) — MemStore permutation only
    // -----------------------------------------------------------------------

    [Fact] // T:2947
    public void StoreMaxMsgsPerUpdateBug_ShouldSucceed()
    {
        // Reference: golang/nats-server/server/store_test.go:TestStoreMaxMsgsPerUpdateBug line 405
        var cfg = new StreamConfig
        {
            Name = "TEST",
            Subjects = new[] { "foo" },
            MaxMsgsPer = 0,
        };
        var fs = NewMemStore(cfg);

        for (var i = 0; i < 5; i++)
            fs.StoreMsg("foo", null, null, 0);

        var ss = fs.State();
        ss.Msgs.ShouldBe(5UL);
        ss.FirstSeq.ShouldBe(1UL);
        ss.LastSeq.ShouldBe(5UL);

        // Update max messages per-subject from 0 (infinite) to 1
        cfg.MaxMsgsPer = 1;
        fs.UpdateConfig(cfg);

        // Only one message should remain
        ss = fs.State();
        ss.Msgs.ShouldBe(1UL);
        ss.FirstSeq.ShouldBe(5UL);
        ss.LastSeq.ShouldBe(5UL);

        // Update to invalid value (< -1) — should clamp to -1
        cfg.MaxMsgsPer = -2;
        fs.UpdateConfig(cfg);
        cfg.MaxMsgsPer.ShouldBe(-1L);

        fs.Stop();
    }

    // -----------------------------------------------------------------------
    // TestStoreCompactCleansUpDmap (T:2948) — MemStore permutation only
    // -----------------------------------------------------------------------

    [Fact] // T:2948
    public void StoreCompactCleansUpDmap_ShouldSucceed()
    {
        // Reference: golang/nats-server/server/store_test.go:TestStoreCompactCleansUpDmap line 449
        // We run for compact sequences 2, 3, 4
        for (var cseq = 2UL; cseq <= 4UL; cseq++)
        {
            var cfg = new StreamConfig
            {
                Name = "TEST",
                Subjects = new[] { "foo" },
                MaxMsgsPer = 0,
            };
            var fs = NewMemStore(cfg);

            // Publish 3 messages; no interior deletes
            for (var i = 0; i < 3; i++)
                fs.StoreMsg("foo", null, null, 0);

            // Remove one message in the middle = interior delete
            var (removed, _) = fs.RemoveMsg(2);
            removed.ShouldBeTrue();

            // The dmap should have 1 entry (seq 2) — verify via State().NumDeleted
            var state = fs.State();
            state.NumDeleted.ShouldBe(1);

            // Compact — must clean up the interior delete
            var (_, err) = fs.Compact(cseq);
            err.ShouldBeNull();

            // After compaction, no deleted entries in the range
            state = fs.State();
            state.NumDeleted.ShouldBe(0);

            // Validate first/last sequence
            var expectedFirst = Math.Max(3UL, cseq);
            state.FirstSeq.ShouldBe(expectedFirst);
            state.LastSeq.ShouldBe(3UL);

            fs.Stop();
        }
    }

    // -----------------------------------------------------------------------
    // TestStoreTruncateCleansUpDmap (T:2949) — MemStore permutation only
    // -----------------------------------------------------------------------

    [Fact] // T:2949
    public void StoreTruncateCleansUpDmap_ShouldSucceed()
    {
        // Reference: golang/nats-server/server/store_test.go:TestStoreTruncateCleansUpDmap line 500
        // We run for truncate sequences 0 and 1
        for (var tseq = 0UL; tseq <= 1UL; tseq++)
        {
            var cfg = new StreamConfig
            {
                Name = "TEST",
                Subjects = new[] { "foo" },
                MaxMsgsPer = 0,
            };
            var fs = NewMemStore(cfg);

            // Publish 3 messages
            for (var i = 0; i < 3; i++)
                fs.StoreMsg("foo", null, null, 0);

            // Remove middle message = interior delete
            var (removed, _) = fs.RemoveMsg(2);
            removed.ShouldBeTrue();

            var state = fs.State();
            state.NumDeleted.ShouldBe(1);

            // Truncate
            fs.Truncate(tseq);

            state = fs.State();
            state.NumDeleted.ShouldBe(0);

            // Validate first/last sequence
            var expectedFirst = Math.Min(1UL, tseq);
            state.FirstSeq.ShouldBe(expectedFirst);
            state.LastSeq.ShouldBe(tseq);

            fs.Stop();
        }
    }

    // -----------------------------------------------------------------------
    // TestStorePurgeExZero (T:2950) — MemStore permutation only
    // -----------------------------------------------------------------------

    [Fact] // T:2950
    public void StorePurgeExZero_ShouldSucceed()
    {
        // Reference: golang/nats-server/server/store_test.go:TestStorePurgeExZero line 552
        var fs = NewMemStore(new StreamConfig { Name = "TEST", Subjects = new[] { "foo" } });

        // Simple purge all
        var (_, err) = fs.Purge();
        err.ShouldBeNull();

        var ss = fs.State();
        ss.FirstSeq.ShouldBe(1UL);
        ss.LastSeq.ShouldBe(0UL);

        // PurgeEx(seq=0) must equal Purge()
        (_, err) = fs.PurgeEx(string.Empty, 0, 0);
        err.ShouldBeNull();

        ss = fs.State();
        ss.FirstSeq.ShouldBe(1UL);
        ss.LastSeq.ShouldBe(0UL);

        fs.Stop();
    }

    // -----------------------------------------------------------------------
    // TestStoreGetSeqFromTimeWithInteriorDeletesGap (T:2955) — MemStore permutation only
    // -----------------------------------------------------------------------

    [Fact] // T:2955
    public void StoreGetSeqFromTimeWithInteriorDeletesGap_ShouldSucceed()
    {
        // Reference: golang/nats-server/server/store_test.go:TestStoreGetSeqFromTimeWithInteriorDeletesGap line 874
        // Go: start = ts from StoreMsg at i==1; ts := time.Unix(0, start).UTC()
        // .NET: convert the 100-ns store timestamp directly to DateTime (same precision).
        var fs = NewMemStore(new StreamConfig { Name = "zzz", Subjects = new[] { "foo" } });

        long start = 0;
        for (var i = 0; i < 10; i++)
        {
            var (_, ts) = fs.StoreMsg("foo", null, null, 0);
            if (i == 1)
                start = ts; // exact timestamp of seq 2
        }

        // Create a delete gap at seqs 4-7
        for (var seq = 4UL; seq <= 7UL; seq++)
            fs.RemoveMsg(seq);

        // Convert 100-ns-since-epoch to DateTime (mirrors Go's time.Unix(0, start))
        const long UnixEpochTicks = 621355968000000000L;
        var t = new DateTime(start / 100L + UnixEpochTicks, DateTimeKind.Utc);

        var gotSeq = fs.GetSeqFromTime(t);
        gotSeq.ShouldBe(2UL);

        fs.Stop();
    }

    // -----------------------------------------------------------------------
    // TestStoreGetSeqFromTimeWithTrailingDeletes (T:2956) — MemStore permutation only
    // -----------------------------------------------------------------------

    [Fact] // T:2956
    public void StoreGetSeqFromTimeWithTrailingDeletes_ShouldSucceed()
    {
        // Reference: golang/nats-server/server/store_test.go:TestStoreGetSeqFromTimeWithTrailingDeletes line 900
        // Go: start = ts from StoreMsg at i==1; ts := time.Unix(0, start).UTC()
        // .NET: convert the 100-ns store timestamp directly to DateTime (same precision).
        var fs = NewMemStore(new StreamConfig { Name = "zzz", Subjects = new[] { "foo" } });

        long start = 0;
        for (var i = 0; i < 3; i++)
        {
            var (_, ts) = fs.StoreMsg("foo", null, null, 0);
            if (i == 1)
                start = ts; // exact timestamp of seq 2
        }

        fs.RemoveMsg(3);

        // Convert 100-ns-since-epoch to DateTime (mirrors Go's time.Unix(0, start))
        const long UnixEpochTicks = 621355968000000000L;
        var t = new DateTime(start / 100L + UnixEpochTicks, DateTimeKind.Utc);

        var gotSeq = fs.GetSeqFromTime(t);
        gotSeq.ShouldBe(2UL);

        fs.Stop();
    }

    // -----------------------------------------------------------------------
    // TestFileStoreMultiLastSeqsAndLoadLastMsgWithLazySubjectState (T:2957)
    // MemStore permutation only
    // -----------------------------------------------------------------------

    [Fact] // T:2957
    public void FileStoreMultiLastSeqsAndLoadLastMsgWithLazySubjectState_ShouldSucceed()
    {
        // Reference: golang/nats-server/server/store_test.go:TestFileStoreMultiLastSeqsAndLoadLastMsgWithLazySubjectState line 921
        var fs = NewMemStore(new StreamConfig { Name = "zzz", Subjects = new[] { "foo" } });

        for (var i = 0; i < 3; i++)
            fs.StoreMsg("foo", null, null, 0);

        var (seqs, err) = fs.MultiLastSeqs(new[] { "foo" }, 0, 0);
        err.ShouldBeNull();
        seqs!.Length.ShouldBe(1);
        seqs![0].ShouldBe(3UL);

        var (removed, _) = fs.RemoveMsg(3);
        removed.ShouldBeTrue();

        (seqs, err) = fs.MultiLastSeqs(new[] { "foo" }, 0, 0);
        err.ShouldBeNull();
        seqs!.Length.ShouldBe(1);
        seqs![0].ShouldBe(2UL);

        fs.StoreMsg("foo", null, null, 0);
        var sm = fs.LoadLastMsg("foo", null);
        sm.ShouldNotBeNull();
        sm!.Seq.ShouldBe(4UL);

        (removed, _) = fs.RemoveMsg(4);
        removed.ShouldBeTrue();

        sm = fs.LoadLastMsg("foo", null);
        sm.ShouldNotBeNull();
        sm!.Seq.ShouldBe(2UL);

        fs.Stop();
    }

    // -----------------------------------------------------------------------
    // TestStoreDiscardNew (T:2954) — MemStore permutation only
    // -----------------------------------------------------------------------

    [Fact] // T:2954
    public void StoreDiscardNew_ShouldSucceed()
    {
        // Reference: golang/nats-server/server/store_test.go:TestStoreDiscardNew line 788
        // Helper that runs the discard-new test for a given config modifier
        void Test(Action<StreamConfig> updateConfig, Exception? expectedErr)
        {
            var cfg = new StreamConfig
            {
                Name = "zzz",
                Subjects = new[] { "foo" },
                Discard = DiscardPolicy.DiscardNew,
            };
            updateConfig(cfg);
            cfg.Storage = StorageType.MemoryStorage;
            var fs = new JetStreamMemStore(cfg);

            var ts = DateTimeOffset.UtcNow.ToUnixTimeMilliseconds() * 1_000_000L;
            var expectedSeq = 1UL;

            void RequireState()
            {
                var state = fs.State();
                state.Msgs.ShouldBe(1UL);
                state.FirstSeq.ShouldBe(expectedSeq);
                state.LastSeq.ShouldBe(expectedSeq);
            }

            fs.StoreMsg("foo", null, null, 0);

            // StoreRawMsg with discardNewCheck=true
            if (expectedErr == null)
            {
                fs.StoreRawMsg("foo", null, null, 0, ts, 0, true);
                expectedSeq++;
            }
            else
            {
                Should.Throw<Exception>(() => fs.StoreRawMsg("foo", null, null, 0, ts, 0, true));
            }
            RequireState();

            // StoreRawMsg with discardNewCheck=false (followers must always accept)
            fs.StoreRawMsg("foo", null, null, 0, ts, 0, false);
            expectedSeq++;

            // For MaxMsgsPer we stay at 1 msg; otherwise 2 msgs
            if (cfg.MaxMsgsPer > 0)
            {
                RequireState();
            }
            else
            {
                var state = fs.State();
                state.Msgs.ShouldBe(2UL);
                state.FirstSeq.ShouldBe(expectedSeq - 1);
                state.LastSeq.ShouldBe(expectedSeq);
            }

            fs.Stop();
        }

        Test(cfg => cfg.MaxMsgs = 1, StoreErrors.ErrMaxMsgs);
        Test(cfg => cfg.MaxBytes = 33, StoreErrors.ErrMaxBytes);
        Test(cfg => cfg.MaxMsgsPer = 1, null);
        Test(cfg => { cfg.DiscardNewPer = true; cfg.MaxMsgsPer = 1; }, StoreErrors.ErrMaxMsgsPerSubject);
        Test(cfg => { cfg.MaxMsgs = 1; cfg.MaxMsgsPer = 1; }, null);
        Test(cfg => { cfg.MaxBytes = 33; cfg.MaxMsgsPer = 1; }, null);
        Test(cfg => { cfg.DiscardNewPer = true; cfg.MaxMsgs = 1; cfg.MaxMsgsPer = 1; }, StoreErrors.ErrMaxMsgsPerSubject);
        Test(cfg => { cfg.DiscardNewPer = true; cfg.MaxBytes = 33; cfg.MaxMsgsPer = 1; }, StoreErrors.ErrMaxMsgsPerSubject);
    }
}