using Microsoft.Data.SqlClient;
using Microsoft.EntityFrameworkCore;

namespace ScadaLink.ConfigurationDatabase.Tests.Migrations;

/// <summary>
/// Per-test-class MSSQL fixture for the Bundle C integration tests (#23 M1).
///
/// Creates a fresh, uniquely-named test database on the running infra/mssql
/// container, applies the EF migrations against it, and drops it on dispose.
/// When MSSQL is not reachable (CI without the container), <see cref="Available"/>
/// is set to false so each test can early-return cleanly — keeping the test
/// suite green wherever it runs.
/// </summary>
/// <remarks>
/// xUnit 2.9.x has no dynamic Skip; the early-return-after-output pattern is
/// the project convention. Tests calling <see cref="EnsureAvailableOrSkip"/>
/// receive a clear log line in the output explaining why they did not run.
/// </remarks>
public sealed class MsSqlMigrationFixture : IDisposable
{
    // Same credentials infra/mssql/setup.sql + docker-compose use. Not a committed
    // production secret — this is a local dev container connection string.
    private const string DefaultAdminConnectionString =
        "Server=localhost,1433;User Id=sa;Password=ScadaLink_Dev1#;TrustServerCertificate=true;Encrypt=false";

    private const string AdminEnvVar = "SCADALINK_MSSQL_TEST_CONN";

    public string DatabaseName { get; }

    public string ConnectionString { get; }

    /// <summary>
    /// True when the MSSQL container was reachable at fixture construction
    /// time AND the per-fixture test database was successfully created. When
    /// false, the integration tests using this fixture must early-return.
    /// </summary>
    public bool Available { get; }

    /// <summary>
    /// Populated when <see cref="Available"/> is false; describes why the
    /// fixture chose to skip (env var unset, connect failed, etc.).
    /// </summary>
    public string SkipReason { get; }

    private readonly string _adminConnectionString;

    public MsSqlMigrationFixture()
    {
        // Short, lowercase guid suffix keeps the database identifier under SQL Server's
        // 128-char limit and safe for raw concatenation (no quoting required).
        DatabaseName = $"ScadaLinkAuditMigTest_{Guid.NewGuid():N}".Substring(0, 38);

        // Env var lets CI / power users override the admin endpoint; absent
        // defaults to the local docker dev container's sa connection.
        var fromEnv = Environment.GetEnvironmentVariable(AdminEnvVar);
        _adminConnectionString = string.IsNullOrWhiteSpace(fromEnv)
            ? DefaultAdminConnectionString
            : fromEnv;

        try
        {
            using var connection = new SqlConnection(_adminConnectionString);
            // Short timeout so the suite skips quickly in a no-container environment
            // rather than hanging on SqlClient's default 30s connect timeout.
            connection.Open();

            using var createCmd = connection.CreateCommand();
            createCmd.CommandText = $"CREATE DATABASE [{DatabaseName}];";
            createCmd.ExecuteNonQuery();

            ConnectionString = BuildPerDbConnectionString(_adminConnectionString, DatabaseName);
            Available = true;
            SkipReason = string.Empty;
        }
        catch (Exception ex)
        {
            // Don't fail fixture construction — the surrounding test classes
            // must remain runnable on a CI box without MSSQL. Each [Fact] gates
            // on Available and skips with a clear reason via test output.
            ConnectionString = string.Empty;
            Available = false;
            SkipReason = $"MSSQL not reachable at '{RedactPassword(_adminConnectionString)}': {ex.GetType().Name}: {ex.Message}";
        }
    }

    /// <summary>
    /// Applies the EF migrations to the per-fixture test database via a freshly
    /// constructed <see cref="ScadaLinkDbContext"/> pointed at it. Uses the
    /// schema-only single-argument constructor — the AuditLog migration does
    /// not write secret-bearing columns at apply time.
    /// </summary>
    public async Task ApplyAuditMigrationAsync(CancellationToken cancellationToken = default)
    {
        ThrowIfUnavailable();

        var options = new DbContextOptionsBuilder<ScadaLinkDbContext>()
            .UseSqlServer(ConnectionString)
            .Options;

        await using var context = new ScadaLinkDbContext(options);
        await context.Database.MigrateAsync(cancellationToken);
    }

    /// <summary>
    /// Convenience for opening a fresh <see cref="SqlConnection"/> to the test
    /// database. Caller is responsible for disposal.
    /// </summary>
    public SqlConnection OpenConnection()
    {
        ThrowIfUnavailable();

        var connection = new SqlConnection(ConnectionString);
        connection.Open();
        return connection;
    }

    public void Dispose()
    {
        if (!Available)
        {
            return;
        }

        // Best-effort drop — never let a teardown failure pollute later runs.
        // SINGLE_USER WITH ROLLBACK IMMEDIATE detaches lingering pooled connections
        // so the DROP DATABASE doesn't fail with "database is in use".
        try
        {
            // Connection-pool cleanup is necessary because EF's MigrateAsync leaves
            // pooled connections behind; SqlConnection.ClearAllPools() forces them
            // closed so the SINGLE_USER + DROP sequence below can complete.
            SqlConnection.ClearAllPools();

            using var connection = new SqlConnection(_adminConnectionString);
            connection.Open();

            using var cmd = connection.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
        {
            // Swallow — the database name carries a random guid suffix so a
            // stranded test database does not collide with future runs.
        }
    }

    /// <summary>
    /// Throws an <see cref="InvalidOperationException"/> when invoked on an
    /// unavailable fixture; tests should branch on <see cref="Available"/>
    /// before reaching this code path.
    /// </summary>
    private void ThrowIfUnavailable()
    {
        if (!Available)
        {
            throw new InvalidOperationException(
                $"MsSqlMigrationFixture is not Available: {SkipReason}");
        }
    }

    private static string BuildPerDbConnectionString(string adminConnectionString, string databaseName)
    {
        var builder = new SqlConnectionStringBuilder(adminConnectionString)
        {
            InitialCatalog = databaseName,
        };
        return builder.ConnectionString;
    }

    private static string RedactPassword(string connectionString)
    {
        try
        {
            var builder = new SqlConnectionStringBuilder(connectionString)
            {
                Password = "***",
            };
            return builder.ConnectionString;
        }
        catch
        {
            return "<unparseable>";
        }
    }
}