using Microsoft.Data.SqlClient;
using Microsoft.EntityFrameworkCore;
using Microsoft.EntityFrameworkCore.Diagnostics;
using Shouldly;
using Xunit;
using ZB.MOM.WW.OtOpcUa.Configuration.Entities;
using ZB.MOM.WW.OtOpcUa.Configuration.Enums;
using ZB.MOM.WW.OtOpcUa.Configuration.Validation;

namespace ZB.MOM.WW.OtOpcUa.Configuration.Tests;

/// <summary>
///     R03:3.2 on the real provider: the migrated config database allows SNAPSHOT isolation (migration
///     <c>EnableSnapshotIsolation</c>) and <see cref="DraftSnapshotFactory.FromConfigDbAsync"/> reads under
///     it. The InMemory tests cannot see either — the provider has no transactions — so this is the one
///     place the deploy path's "one consistent read" is proven against SQL Server.
/// </summary>
[Trait("Category", "SchemaCompliance")]
[Collection(nameof(SchemaComplianceCollection))]
public sealed class DraftSnapshotFactorySqlServerTests
{
    private readonly SchemaComplianceFixture _fixture;

    /// <summary>Initializes a new instance of the <see cref="DraftSnapshotFactorySqlServerTests"/> class.</summary>
    /// <param name="fixture">The migrated test database.</param>
    public DraftSnapshotFactorySqlServerTests(SchemaComplianceFixture fixture) => _fixture = fixture;

    /// <summary>The migration leaves the database with snapshot isolation allowed.</summary>
    [Fact]
    public void Migrated_database_allows_snapshot_isolation()
    {
        using var conn = _fixture.OpenConnection();
        using var cmd = new SqlCommand(
            "SELECT snapshot_isolation_state_desc FROM sys.databases WHERE name = DB_NAME();", conn);
        cmd.ExecuteScalar().ShouldBe("ON");
    }

    /// <summary>
    ///     A row committed by another connection while the snapshot read is in progress is NOT observed by
    ///     the tables read after it — every table reflects the instant the transaction started. Positive
    ///     control: a read started after the commit does see the row.
    /// </summary>
    [Fact]
    public async Task FromConfigDb_reads_every_table_as_of_one_instant()
    {
        var clusterId = $"SNAP-{Guid.NewGuid():N}"[..24];
        var scriptId = $"late-{Guid.NewGuid():N}";
        await using (var seed = NewContext())
        {
            seed.ServerClusters.Add(new ServerCluster
            {
                ClusterId = clusterId, Name = "snapshot-read", Enterprise = "zb", Site = "test",
                NodeCount = 1, RedundancyMode = RedundancyMode.None, CreatedBy = "test",
            });
            await seed.SaveChangesAsync();
        }

        try
        {
            var options = new DbContextOptionsBuilder<OtOpcUaConfigDbContext>()
                .UseSqlServer(_fixture.ConnectionString)
                .AddInterceptors(new LateEditInterceptor(_fixture.ConnectionString, clusterId, scriptId))
                .Options;

            await using (var db = new OtOpcUaConfigDbContext(options))
            {
                var snapshot = await DraftSnapshotFactory.FromConfigDbAsync(db);
                // The interceptor committed a Script while ServerClusters (the FIRST table read) was being
                // materialised. Scripts is read later in the same transaction and must not see it.
                snapshot.ServerClusters.ShouldContain(c => c.ClusterId == clusterId);
                snapshot.Scripts.ShouldNotContain(s => s.ScriptId == scriptId);
            }

            await using (var verify = NewContext())
            {
                // Positive control: the edit really landed, and a read started afterwards sees it.
                (await verify.Scripts.AnyAsync(s => s.ScriptId == scriptId)).ShouldBeTrue();
                var later = await DraftSnapshotFactory.FromConfigDbAsync(verify);
                later.Scripts.ShouldContain(s => s.ScriptId == scriptId);
            }
        }
        finally
        {
            await using var cleanup = NewContext();
            await cleanup.Scripts.Where(s => s.ScriptId == scriptId).ExecuteDeleteAsync();
            await cleanup.ServerClusters.Where(c => c.ClusterId == clusterId).ExecuteDeleteAsync();
        }
    }

    private OtOpcUaConfigDbContext NewContext() => new(
        new DbContextOptionsBuilder<OtOpcUaConfigDbContext>().UseSqlServer(_fixture.ConnectionString).Options);

    /// <summary>
    ///     Commits a Script on a SEPARATE connection the first time the snapshot read materialises the
    ///     seeded ServerCluster row — i.e. mid-read, after the first table and before Scripts.
    /// </summary>
    private sealed class LateEditInterceptor(string connectionString, string clusterId, string scriptId)
        : IMaterializationInterceptor
    {
        private int _fired;

        public object InitializedInstance(MaterializationInterceptionData materializationData, object entity)
        {
            if (entity is ServerCluster c && c.ClusterId == clusterId && Interlocked.Exchange(ref _fired, 1) == 0)
            {
                using var other = new OtOpcUaConfigDbContext(
                    new DbContextOptionsBuilder<OtOpcUaConfigDbContext>().UseSqlServer(connectionString).Options);
                other.Scripts.Add(new Script
                {
                    ScriptId = scriptId, Name = "late edit", SourceCode = "return 1;", SourceHash = "late-hash",
                });
                other.SaveChanges();
            }
            return entity;
        }
    }
}