using System.Data.Common;
using Microsoft.Data.SqlClient;
using Microsoft.EntityFrameworkCore;
using Xunit;
using ZB.MOM.WW.OtOpcUa.Configuration;

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

/// <summary>
///     A real SQL Server database for the handful of AdminUI tests whose subject is the SQL Server
///     provider's LINQ <b>translation</b> rather than the C# around it — EF InMemory evaluates those
///     queries in-process, so it can neither fail on an untranslatable shape nor reproduce SQL Server's
///     collation semantics. Creates a uniquely-named database, applies the EF migrations to it, and drops
///     it at collection teardown.
/// </summary>
/// <remarks>
///     <para>
///         Shaped after <c>ZB.MOM.WW.OtOpcUa.Configuration.Tests.SchemaComplianceFixture</c> (same env
///         vars, same unique-name + <c>Migrate()</c> + drop-via-master lifecycle) with <b>one deliberate
///         deviation</b>: that fixture lets the connection failure surface as a constructor throw, so
///         Configuration.Tests fails hard when SQL Server is unreachable. AdminUI.Tests is an ordinary
///         unit suite that must stay green offline, so this fixture probes reachability FIRST and records
///         a <see cref="SkipReason"/> instead of throwing. Tests carry <see cref="SqlServerFactAttribute"/>,
///         which skips them when the probe failed.
///     </para>
///     <para>
///         The skip is an attribute rather than the <c>Assert.Skip(fixture.SkipReason)</c> call the S7
///         integration suite uses, because AdminUI.Tests is one of the three projects pinned to
///         <b>xunit v2</b> by <c>Akka.TestKit.Xunit2</c> (see <c>Directory.Packages.props</c>) and
///         <c>Assert.Skip</c> is xunit v3 only. Overriding <c>FactAttribute.Skip</c> is the v2 equivalent
///         and reports a genuine "skipped", not a vacuous pass. Both the attribute and this fixture read
///         the same one-shot probe in <see cref="AdminUiSqlServer"/>, so a session probes once.
///     </para>
///     <para>
///         The probe being <b>one-shot</b> bounds what "stays green offline" guarantees: it covers SQL
///         being unreachable <i>before the run</i>. A connectivity blip <i>during</i> a run is never
///         re-probed, so the affected tests surface as <c>SqlException</c> <b>failures</b>, not skips.
///     </para>
///     <para>
///         Every test in the collection shares ONE database (migrating is the expensive part), so tests
///         must isolate themselves by seeding uniquely-named rows, or by clearing the table they measure.
///         xunit serialises a collection's tests, so a clear-then-seed is safe.
///     </para>
/// </remarks>
public sealed class AdminUiSqlServerFixture : IDisposable
{
    /// <summary>Gets the name of the per-run test database, or <see langword="null"/> when SQL is unreachable.</summary>
    public string? DatabaseName { get; }

    /// <summary>Gets the connection string for the test database, or <see langword="null"/> when SQL is unreachable.</summary>
    public string? ConnectionString { get; }

    /// <summary>
    ///     Gets the reason the SQL-backed tests cannot run (server unreachable, migration failed), or
    ///     <see langword="null"/> when the database is ready.
    /// </summary>
    public string? SkipReason { get; }

    /// <summary>
    ///     Gets a context factory pointed at the migrated test database — the seam the services under test
    ///     (<c>DeploymentDriftProbe</c>, <c>RawTreeService</c>) take. Throws when <see cref="SkipReason"/>
    ///     is set; guard with <see cref="SqlServerFactAttribute"/>.
    /// </summary>
    public IDbContextFactory<OtOpcUaConfigDbContext> Factory =>
        _factory ?? throw new InvalidOperationException(SkipReason ?? "SQL Server fixture is not available.");

    private readonly SqlServerContextFactory? _factory;

    /// <summary>Initializes a new instance of the <see cref="AdminUiSqlServerFixture"/> class.</summary>
    public AdminUiSqlServerFixture()
    {
        // Probe FIRST — see the remarks. A dead server must leave this constructor without throwing,
        // because xunit builds collection fixtures before it discovers that every test is skipped.
        SkipReason = AdminUiSqlServer.SkipReason;
        if (SkipReason is not null) return;

        DatabaseName = $"OtOpcUaAdminUi_Test_{DateTime.UtcNow:yyyyMMddHHmmss}_{Guid.NewGuid():N}";
        ConnectionString = AdminUiSqlServer.ConnectionStringFor(DatabaseName);

        try
        {
            var options = new DbContextOptionsBuilder<OtOpcUaConfigDbContext>()
                .UseSqlServer(ConnectionString)
                .Options;

            using var ctx = new OtOpcUaConfigDbContext(options);
            ctx.Database.Migrate();
        }
        catch (Exception ex)
        {
            // A half-created database would leak, so tear it down before standing the suite down.
            TryDropDatabase();
            SkipReason = $"Could not migrate the AdminUI SQL test database: {ex.Message}";
            DatabaseName = null;
            ConnectionString = null;
            return;
        }

        _factory = new SqlServerContextFactory(ConnectionString);
    }

    /// <summary>Disposes the fixture, dropping the test database.</summary>
    public void Dispose() => TryDropDatabase();

    private void TryDropDatabase()
    {
        if (ConnectionString is null || DatabaseName is null) return;

        try
        {
            var master = new SqlConnectionStringBuilder(ConnectionString) { InitialCatalog = "master" }.ConnectionString;

            using var conn = new SqlConnection(master);
            conn.Open();

            using var cmd = conn.CreateCommand();
            cmd.CommandText = $@"
IF DB_ID(N'{DatabaseName}') IS NOT NULL
BEGIN
    ALTER DATABASE [{DatabaseName}] SET SINGLE_USER WITH ROLLBACK IMMEDIATE;
    DROP DATABASE [{DatabaseName}];
END";
            cmd.ExecuteNonQuery();
        }
        catch (DbException)
        {
            // Teardown is best-effort: a dropped connection here must not fail an otherwise-green run.
            // The database name carries a timestamp, so a leaked one is identifiable.
        }
    }

    private sealed class SqlServerContextFactory(string connectionString)
        : IDbContextFactory<OtOpcUaConfigDbContext>
    {
        public OtOpcUaConfigDbContext CreateDbContext() =>
            new(new DbContextOptionsBuilder<OtOpcUaConfigDbContext>()
                .UseSqlServer(connectionString)
                .Options);

        public Task<OtOpcUaConfigDbContext> CreateDbContextAsync(CancellationToken cancellationToken = default) =>
            Task.FromResult(CreateDbContext());
    }
}

/// <summary>
///     One-shot reachability probe + connection-string builder shared by
///     <see cref="AdminUiSqlServerFixture"/> and <see cref="SqlServerFactAttribute"/>. The attribute is
///     constructed at discovery time and the fixture at collection start, so the probe must be cached or
///     a run pays the connect timeout twice.
/// </summary>
internal static class AdminUiSqlServer
{
    private const string DefaultServer = "10.100.0.35,14330";
    private const string DefaultSaPassword = "OtOpcUaDev_2026!";
    private const int ProbeTimeoutSeconds = 3;

    private static readonly Lazy<string?> Probe = new(RunProbe, LazyThreadSafetyMode.ExecutionAndPublication);

    /// <summary>Gets the reason SQL Server is unusable, or <see langword="null"/> when it answered.</summary>
    public static string? SkipReason => Probe.Value;

    /// <summary>Builds a connection string for the named database on the configured test server.</summary>
    /// <param name="database">The database to connect to.</param>
    /// <returns>The connection string.</returns>
    public static string ConnectionStringFor(string database)
    {
        var server = Environment.GetEnvironmentVariable("OTOPCUA_CONFIG_TEST_SERVER") ?? DefaultServer;
        var password = Environment.GetEnvironmentVariable("OTOPCUA_CONFIG_TEST_SA_PASSWORD") ?? DefaultSaPassword;

        return $"Server={server};Database={database};User Id=sa;Password={password};" +
               "TrustServerCertificate=True;Encrypt=False;";
    }

    private static string? RunProbe()
    {
        var server = Environment.GetEnvironmentVariable("OTOPCUA_CONFIG_TEST_SERVER") ?? DefaultServer;

        try
        {
            var probe = new SqlConnectionStringBuilder(ConnectionStringFor("master"))
            {
                ConnectTimeout = ProbeTimeoutSeconds,
            }.ConnectionString;

            using var conn = new SqlConnection(probe);
            conn.Open();
            return null;
        }
        catch (Exception ex)
        {
            return $"SQL Server at '{server}' is unreachable ({ex.GetType().Name}: {ex.Message}); " +
                   "set OTOPCUA_CONFIG_TEST_SERVER / OTOPCUA_CONFIG_TEST_SA_PASSWORD to point at a reachable instance.";
        }
    }
}

/// <summary>
///     A <see cref="FactAttribute"/> that skips itself when the shared test SQL Server is unreachable.
///     The xunit v2 equivalent of xunit v3's <c>Assert.Skip</c> — see
///     <see cref="AdminUiSqlServerFixture"/>'s remarks for why this project cannot use the latter.
/// </summary>
[AttributeUsage(AttributeTargets.Method)]
public sealed class SqlServerFactAttribute : FactAttribute
{
    /// <summary>Initializes a new instance of the <see cref="SqlServerFactAttribute"/> class.</summary>
    public SqlServerFactAttribute()
    {
        if (AdminUiSqlServer.SkipReason is { } reason) Skip = reason;
    }
}

/// <summary>Collection definition binding the SQL-backed AdminUI tests to one shared database.</summary>
[CollectionDefinition(nameof(AdminUiSqlServerCollection))]
public sealed class AdminUiSqlServerCollection : ICollectionFixture<AdminUiSqlServerFixture>
{
}