using System.IO.MemoryMappedFiles;
using ZB.MOM.WW.CBDD.Bson;
using ZB.MOM.WW.CBDD.Core.Indexing;
using ZB.MOM.WW.CBDD.Core.Storage;
using ZB.MOM.WW.CBDD.Shared;

namespace ZB.MOM.WW.CBDD.Tests;

public class CompactionOfflineTests
{
    /// <summary>
    /// Tests offline compact should preserve logical data equivalence.
    /// </summary>
    [Fact]
    public void OfflineCompact_ShouldPreserveLogicalDataEquivalence()
    {
        var dbPath = NewDbPath();

        try
        {
            using var db = new TestDbContext(dbPath);

            var ids = new List<ObjectId>();
            for (var i = 0; i < 160; i++)
            {
                ids.Add(db.Users.Insert(new User { Name = $"user-{i:D4}", Age = i % 31 }));
            }

            for (var i = 0; i < ids.Count; i += 9)
            {
                if (db.Users.FindById(ids[i]) != null)
                {
                    db.Users.Delete(ids[i]).ShouldBeTrue();
                }
            }

            var updateTargets = db.Users.FindAll(u => u.Age % 4 == 0)
                .Select(u => u.Id)
                .ToList();
            foreach (var id in updateTargets)
            {
                var user = db.Users.FindById(id);
                if (user == null)
                {
                    continue;
                }

                user.Name += "-updated";
                db.Users.Update(user).ShouldBeTrue();
            }

            db.SaveChanges();
            db.ForceCheckpoint();

            var expected = db.Users.FindAll()
                .ToDictionary(u => u.Id, u => (u.Name, u.Age));
            db.SaveChanges();

            var stats = db.Compact();
            stats.OnlineMode.ShouldBeFalse();

            var actual = db.Users.FindAll()
                .ToDictionary(u => u.Id, u => (u.Name, u.Age));

            actual.Count.ShouldBe(expected.Count);
            foreach (var kvp in expected)
            {
                actual.ShouldContainKey(kvp.Key);
                actual[kvp.Key].ShouldBe(kvp.Value);
            }
        }
        finally
        {
            CleanupFiles(dbPath);
        }
    }

    /// <summary>
    /// Tests offline compact should keep index results consistent.
    /// </summary>
    [Fact]
    public void OfflineCompact_ShouldKeepIndexResultsConsistent()
    {
        var dbPath = NewDbPath();

        try
        {
            using var db = new TestDbContext(dbPath);

            for (var i = 0; i < 300; i++)
            {
                db.People.Insert(new Person
                {
                    Name = $"person-{i:D4}",
                    Age = i % 12
                });
            }

            db.SaveChanges();
            db.ForceCheckpoint();

            var expectedByAge = db.People.FindAll()
                .GroupBy(p => p.Age)
                .ToDictionary(g => g.Key, g => g.Select(x => x.Name).OrderBy(x => x).ToArray());
            db.SaveChanges();

            var indexNamesBefore = db.People.GetIndexes().Select(x => x.Name).OrderBy(x => x).ToArray();

            var stats = db.Compact(new CompactionOptions
            {
                DefragmentSlottedPages = true,
                NormalizeFreeList = true,
                EnableTailTruncation = true
            });
            stats.PrePageCount.ShouldBeGreaterThanOrEqualTo(stats.PostPageCount);

            var indexNamesAfter = db.People.GetIndexes().Select(x => x.Name).OrderBy(x => x).ToArray();
            indexNamesAfter.ShouldBe(indexNamesBefore);

            foreach (var age in expectedByAge.Keys.OrderBy(x => x))
            {
                var actual = db.People.FindAll(p => p.Age == age)
                    .Select(x => x.Name)
                    .OrderBy(x => x)
                    .ToArray();

                actual.ShouldBe(expectedByAge[age]);
            }
        }
        finally
        {
            CleanupFiles(dbPath);
        }
    }

    /// <summary>
    /// Tests offline compact should rebuild hash index metadata and preserve results.
    /// </summary>
    [Fact]
    public void OfflineCompact_ShouldRebuildHashIndexMetadataAndPreserveResults()
    {
        var dbPath = NewDbPath();

        try
        {
            using var db = new TestDbContext(dbPath);

            for (var i = 0; i < 300; i++)
            {
                db.People.Insert(new Person
                {
                    Name = $"hash-person-{i:D4}",
                    Age = i % 12
                });
            }

            db.SaveChanges();
            db.ForceCheckpoint();

            var expectedByAge = db.People.FindAll()
                .GroupBy(p => p.Age)
                .ToDictionary(g => g.Key, g => g.Select(x => x.Name).OrderBy(x => x).ToArray());

            var metadata = db.Storage.GetCollectionMetadata("people_collection");
            metadata.ShouldNotBeNull();

            var targetIndex = metadata!.Indexes
                .FirstOrDefault(index => index.PropertyPaths.Any(path => path.Equals("Age", StringComparison.OrdinalIgnoreCase)));
            targetIndex.ShouldNotBeNull();

            targetIndex!.Type = IndexType.Hash;
            db.Storage.SaveCollectionMetadata(metadata);
            db.SaveChanges();

            var stats = db.Compact(new CompactionOptions
            {
                DefragmentSlottedPages = true,
                NormalizeFreeList = true,
                EnableTailTruncation = true
            });
            stats.PrePageCount.ShouldBeGreaterThanOrEqualTo(stats.PostPageCount);

            var reloadedMetadata = db.Storage.GetCollectionMetadata("people_collection");
            reloadedMetadata.ShouldNotBeNull();
            var rebuiltIndex = reloadedMetadata!.Indexes.FirstOrDefault(index => index.Name == targetIndex.Name);
            rebuiltIndex.ShouldNotBeNull();
            rebuiltIndex!.Type.ShouldBe(IndexType.Hash);
            rebuiltIndex.RootPageId.ShouldBeGreaterThan(0u);

            var runtimeIndex = db.People.GetIndexes().FirstOrDefault(index => index.Name == targetIndex.Name);
            runtimeIndex.ShouldNotBeNull();
            runtimeIndex!.Type.ShouldBe(IndexType.Hash);

            foreach (var age in expectedByAge.Keys.OrderBy(x => x))
            {
                var actual = db.People.FindAll(p => p.Age == age)
                    .Select(x => x.Name)
                    .OrderBy(x => x)
                    .ToArray();

                actual.ShouldBe(expectedByAge[age]);
            }
        }
        finally
        {
            CleanupFiles(dbPath);
        }
    }

    /// <summary>
    /// Tests offline compact when tail is reclaimable should reduce file size.
    /// </summary>
    [Fact]
    public void OfflineCompact_WhenTailIsReclaimable_ShouldReduceFileSize()
    {
        var dbPath = NewDbPath();
        var ids = new List<ObjectId>();

        try
        {
            using var db = new TestDbContext(dbPath, SmallPageConfig());

            for (var i = 0; i < 240; i++)
            {
                var id = db.Users.Insert(new User
                {
                    Name = BuildPayload(i, 18_000),
                    Age = i
                });
                ids.Add(id);
            }

            db.SaveChanges();
            db.ForceCheckpoint();

            for (var i = ids.Count - 1; i >= 60; i--)
            {
                if (db.Users.FindById(ids[i]) != null)
                {
                    db.Users.Delete(ids[i]).ShouldBeTrue();
                }
            }

            db.SaveChanges();
            db.ForceCheckpoint();

            var preCompactSize = new FileInfo(dbPath).Length;
            var stats = db.Compact(new CompactionOptions
            {
                EnableTailTruncation = true,
                MinimumRetainedPages = 2
            });
            var postCompactSize = new FileInfo(dbPath).Length;

            postCompactSize.ShouldBeLessThanOrEqualTo(preCompactSize);
            stats.ReclaimedFileBytes.ShouldBeGreaterThanOrEqualTo(0);
        }
        finally
        {
            CleanupFiles(dbPath);
        }
    }

    /// <summary>
    /// Tests offline compact with invalid primary root metadata should fail validation.
    /// </summary>
    [Fact]
    public void OfflineCompact_WithInvalidPrimaryRootMetadata_ShouldFailValidation()
    {
        var dbPath = NewDbPath();

        try
        {
            using var db = new TestDbContext(dbPath);
            for (var i = 0; i < 32; i++)
            {
                db.Users.Insert(new User { Name = $"invalid-primary-{i:D3}", Age = i });
            }

            db.SaveChanges();
            db.ForceCheckpoint();

            var metadata = db.Storage.GetCollectionMetadata("users");
            metadata.ShouldNotBeNull();
            metadata!.PrimaryRootPageId = 1; // Metadata page, not an index page.
            db.Storage.SaveCollectionMetadata(metadata);

            Should.Throw<InvalidDataException>(() => db.Compact())
                .Message.ShouldContain("primary index root page id");
        }
        finally
        {
            CleanupFiles(dbPath);
        }
    }

    /// <summary>
    /// Tests offline compact with invalid secondary root metadata should fail validation.
    /// </summary>
    [Fact]
    public void OfflineCompact_WithInvalidSecondaryRootMetadata_ShouldFailValidation()
    {
        var dbPath = NewDbPath();

        try
        {
            using var db = new TestDbContext(dbPath);
            for (var i = 0; i < 48; i++)
            {
                db.People.Insert(new Person { Name = $"invalid-secondary-{i:D3}", Age = i % 10 });
            }

            db.SaveChanges();
            db.ForceCheckpoint();

            var metadata = db.Storage.GetCollectionMetadata("people_collection");
            metadata.ShouldNotBeNull();
            metadata!.Indexes.Count.ShouldBeGreaterThan(0);
            metadata.Indexes[0].RootPageId = uint.MaxValue; // Out-of-range page id.
            db.Storage.SaveCollectionMetadata(metadata);

            Should.Throw<InvalidDataException>(() => db.Compact())
                .Message.ShouldContain("out of range");
        }
        finally
        {
            CleanupFiles(dbPath);
        }
    }

    /// <summary>
    /// Tests offline compact should report live bytes relocation and throughput telemetry.
    /// </summary>
    [Fact]
    public void OfflineCompact_ShouldReportLiveBytesRelocationAndThroughputTelemetry()
    {
        var dbPath = NewDbPath();

        try
        {
            using var db = new TestDbContext(dbPath, SmallPageConfig());

            var ids = new List<ObjectId>();
            for (var i = 0; i < 160; i++)
            {
                ids.Add(db.Users.Insert(new User
                {
                    Name = BuildPayload(i, 9_000),
                    Age = i
                }));
            }

            for (var i = 0; i < ids.Count; i += 7)
            {
                if (db.Users.FindById(ids[i]) != null)
                {
                    db.Users.Delete(ids[i]).ShouldBeTrue();
                }
            }

            db.SaveChanges();
            db.ForceCheckpoint();

            var stats = db.Compact(new CompactionOptions
            {
                DefragmentSlottedPages = true,
                NormalizeFreeList = true,
                EnableTailTruncation = true
            });

            stats.PreLiveBytes.ShouldBe(Math.Max(0, stats.PreFileSizeBytes - stats.PreFreeBytes));
            stats.PostLiveBytes.ShouldBe(Math.Max(0, stats.PostFileSizeBytes - stats.PostFreeBytes));
            stats.DocumentsRelocated.ShouldBeGreaterThanOrEqualTo(0);
            stats.PagesRelocated.ShouldBeGreaterThanOrEqualTo(0);
            stats.ThroughputBytesPerSecond.ShouldBeGreaterThan(0);
            stats.ThroughputPagesPerSecond.ShouldBeGreaterThanOrEqualTo(0);
            stats.ThroughputDocumentsPerSecond.ShouldBeGreaterThanOrEqualTo(0);
        }
        finally
        {
            CleanupFiles(dbPath);
        }
    }

    /// <summary>
    /// Tests offline compact when primary index points to deleted slot should fail validation.
    /// </summary>
    [Fact]
    public void OfflineCompact_WhenPrimaryIndexPointsToDeletedSlot_ShouldFailValidation()
    {
        var dbPath = NewDbPath();

        try
        {
            using var db = new TestDbContext(dbPath, SmallPageConfig());
            var id = db.Users.Insert(new User { Name = BuildPayload(1, 7_500), Age = 9 });
            db.SaveChanges();
            db.ForceCheckpoint();

            var metadata = db.Storage.GetCollectionMetadata("users");
            metadata.ShouldNotBeNull();
            metadata!.PrimaryRootPageId.ShouldBeGreaterThan(0u);

            var primaryIndex = new BTreeIndex(db.Storage, IndexOptions.CreateUnique("_id"), metadata.PrimaryRootPageId);
            primaryIndex.TryFind(new IndexKey(id), out var location).ShouldBeTrue();

            var page = new byte[db.Storage.PageSize];
            db.Storage.ReadPage(location.PageId, null, page);

            var header = SlottedPageHeader.ReadFrom(page);
            var slotOffset = SlottedPageHeader.Size + (location.SlotIndex * SlotEntry.Size);
            var slot = SlotEntry.ReadFrom(page.AsSpan(slotOffset, SlotEntry.Size));
            slot.Flags |= SlotFlags.Deleted;
            slot.WriteTo(page.AsSpan(slotOffset, SlotEntry.Size));
            header.WriteTo(page);
            db.Storage.WritePageImmediate(location.PageId, page);

            var ex = Should.Throw<InvalidDataException>(() => db.Compact(new CompactionOptions
            {
                DefragmentSlottedPages = true,
                NormalizeFreeList = true,
                EnableTailTruncation = true
            }));
            ex.Message.ShouldContain("Compaction validation failed");
        }
        finally
        {
            CleanupFiles(dbPath);
        }
    }

    private static PageFileConfig SmallPageConfig()
    {
        return new PageFileConfig
        {
            PageSize = 4096,
            InitialFileSize = 1024 * 1024,
            Access = MemoryMappedFileAccess.ReadWrite
        };
    }

    private static string BuildPayload(int seed, int approxLength)
    {
        var builder = new System.Text.StringBuilder(approxLength + 256);
        var i = 0;
        while (builder.Length < approxLength)
        {
            builder.Append("compact-tail-");
            builder.Append(seed.ToString("D4"));
            builder.Append('-');
            builder.Append(i.ToString("D6"));
            builder.Append('|');
            i++;
        }

        return builder.ToString();
    }

    private static string NewDbPath()
        => Path.Combine(Path.GetTempPath(), $"compaction_offline_{Guid.NewGuid():N}.db");

    private static void CleanupFiles(string dbPath)
    {
        var walPath = Path.ChangeExtension(dbPath, ".wal");
        var markerPath = $"{dbPath}.compact.state";
        var tempPath = $"{dbPath}.compact.tmp";
        var backupPath = $"{dbPath}.compact.bak";
        if (File.Exists(dbPath)) File.Delete(dbPath);
        if (File.Exists(walPath)) File.Delete(walPath);
        if (File.Exists(markerPath)) File.Delete(markerPath);
        if (File.Exists(tempPath)) File.Delete(tempPath);
        if (File.Exists(backupPath)) File.Delete(backupPath);
    }
}