using ZB.MOM.WW.CBDD.Bson;
using ZB.MOM.WW.CBDD.Bson.IO;
using ZB.MOM.WW.CBDD.Shared;

namespace ZB.MOM.WW.CBDD.Tests;

public class ScanTests : IDisposable
{
    private readonly TestDbContext _db;
    private readonly string _testFile;

    /// <summary>
    ///     Initializes a new instance of the <see cref="ScanTests" /> class.
    /// </summary>
    public ScanTests()
    {
        _testFile = Path.Combine(Path.GetTempPath(), $"scan_tests_{Guid.NewGuid()}.db");
        if (File.Exists(_testFile)) File.Delete(_testFile);
        string wal = Path.ChangeExtension(_testFile, ".wal");
        if (File.Exists(wal)) File.Delete(wal);

        _db = new TestDbContext(_testFile);
    }

    /// <summary>
    ///     Executes Dispose.
    /// </summary>
    public void Dispose()
    {
        _db.Dispose();
        if (File.Exists(_testFile)) File.Delete(_testFile);
        string wal = Path.ChangeExtension(_testFile, ".wal");
        if (File.Exists(wal)) File.Delete(wal);
    }

    /// <summary>
    ///     Executes Scan_FindsMatchingDocuments.
    /// </summary>
    [Fact]
    public void Scan_FindsMatchingDocuments()
    {
        // Arrange
        _db.Users.Insert(new User { Name = "Alice", Age = 30 });
        _db.Users.Insert(new User { Name = "Bob", Age = 25 });
        _db.Users.Insert(new User { Name = "Charlie", Age = 35 });
        _db.SaveChanges();

        // Act: Find users older than 28
        var results = _db.Users.Scan(reader => ParseAge(reader) > 28).ToList();

        // Assert
        results.Count.ShouldBe(2);
        results.ShouldContain(d => d.Name == "Alice");
        results.ShouldContain(d => d.Name == "Charlie");
    }

    /// <summary>
    ///     Executes Repro_Insert_Loop_Hang.
    /// </summary>
    [Fact]
    public void Repro_Insert_Loop_Hang()
    {
        // Reproduce hang reported by user at 501 documents
        var count = 600;
        for (var i = 0; i < count; i++) _db.Users.Insert(new User { Name = $"User_{i}", Age = i });
        _db.SaveChanges();
    }

    /// <summary>
    ///     Executes ParallelScan_FindsMatchingDocuments.
    /// </summary>
    [Fact]
    public void ParallelScan_FindsMatchingDocuments()
    {
        // Arrange
        var count = 1000;
        for (var i = 0; i < count; i++) _db.Users.Insert(new User { Name = $"User_{i}", Age = i });
        _db.SaveChanges();

        // Act: Find users with Age >= 500
        // Parallelism 2 to force partitioning
        var results = _db.Users.ParallelScan(reader => ParseAge(reader) >= 500, 2).ToList();

        // Assert
        results.Count.ShouldBe(500);
    }

    private int ParseAge(BsonSpanReader reader)
    {
        try
        {
            reader.ReadDocumentSize();
            while (reader.Remaining > 0)
            {
                var type = reader.ReadBsonType();
                if (type == 0) break; // End of doc

                string name = reader.ReadElementHeader();

                if (name == "age") return reader.ReadInt32();

                reader.SkipValue(type);
            }
        }
        catch
        {
            return -1;
        }

        return -1;
    }
}