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

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

/// <summary>
///     Spins up a dedicated test database, applies the EF migrations against it, and exposes a
///     <see cref="SqlConnection"/> factory. Disposed at collection teardown (drops the DB).
///     Gated by the <c>OTOPCUA_CONFIG_TEST_SERVER</c> env var so CI runs can opt in explicitly;
///     local runs default to the shared Docker host's SQL Server on <c>10.100.0.35:14330</c>.
/// </summary>
public sealed class SchemaComplianceFixture : IDisposable
{
    /// <summary>The name prefix every Configuration test database carries; also the reaper's LIKE anchor.</summary>
    internal const string TestDatabasePrefix = "OtOpcUaConfig_Test_";

    private const string DefaultServer = "10.100.0.35,14330";
    private const string DefaultSaPassword = "OtOpcUaDev_2026!";

    /// <summary>How long a test database must have existed before the reaper considers it certainly orphaned.</summary>
    private static readonly TimeSpan OrphanAge = TimeSpan.FromHours(24);

    private static readonly Lazy<int> Reaper = new(RunReaper, LazyThreadSafetyMode.ExecutionAndPublication);

    /// <summary>Gets the name of the test database.</summary>
    public string DatabaseName { get; }
    /// <summary>Gets the connection string for the test database.</summary>
    public string ConnectionString { get; }

    /// <summary>Initializes a new instance of the SchemaComplianceFixture class.</summary>
    public SchemaComplianceFixture()
    {
        var server = Environment.GetEnvironmentVariable("OTOPCUA_CONFIG_TEST_SERVER") ?? DefaultServer;
        var saPassword = Environment.GetEnvironmentVariable("OTOPCUA_CONFIG_TEST_SA_PASSWORD") ?? DefaultSaPassword;

        // A killed test process never reaches Dispose, so its database outlives the run. Reap the ones old
        // enough to be certainly nobody's, once per process. This fixture has no reachability probe, so an
        // unreachable server must leave behaviour exactly as it was: the reaper silently does nothing and
        // Migrate() below throws as it always has.
        _ = Reaper.Value;

        DatabaseName = $"{TestDatabasePrefix}{DateTime.UtcNow:yyyyMMddHHmmss}_{Guid.NewGuid():N}";
        ConnectionString =
            $"Server={server};Database={DatabaseName};User Id=sa;Password={saPassword};TrustServerCertificate=True;Encrypt=False;";

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

        using var ctx = new OtOpcUaConfigDbContext(options);
        ctx.Database.Migrate();
    }

    /// <summary>Opens a new SQL connection to the test database.</summary>
    /// <returns>An open SQL connection.</returns>
    public SqlConnection OpenConnection()
    {
        var conn = new SqlConnection(ConnectionString);
        conn.Open();
        return conn;
    }

    private static int RunReaper()
    {
        var server = Environment.GetEnvironmentVariable("OTOPCUA_CONFIG_TEST_SERVER") ?? DefaultServer;
        var saPassword = Environment.GetEnvironmentVariable("OTOPCUA_CONFIG_TEST_SA_PASSWORD") ?? DefaultSaPassword;
        var master =
            $"Server={server};Database=master;User Id=sa;Password={saPassword};TrustServerCertificate=True;Encrypt=False;";

        return SqlTestDatabaseReaper.ReapOrphans(master, TestDatabasePrefix, DateTime.UtcNow - OrphanAge).Count;
    }

    /// <summary>Disposes the fixture and drops the test database.</summary>
    public void Dispose()
    {
        var masterConnection =
            new SqlConnectionStringBuilder(ConnectionString) { InitialCatalog = "master" }.ConnectionString;

        using var conn = new SqlConnection(masterConnection);
        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();
    }
}

/// <summary>
///     Drops test databases that a killed test process left behind on the <b>shared</b> SQL Server.
/// </summary>
/// <remarks>
///     <para>
///         <see cref="SchemaComplianceFixture"/> names its database
///         <c>{prefix}{yyyyMMddHHmmss-UTC}_{guid:N}</c> and drops it in <c>Dispose</c> — which a
///         <c>Ctrl-C</c>, a crashed runner or a killed container never reaches, so the database survives
///         forever on an instance nobody gardens.
///     </para>
///     <para>
///         This is <c>DROP DATABASE</c> against a server other people share, so the rules are deliberately
///         narrow and every one of them is load-bearing:
///     </para>
///     <list type="bullet">
///         <item>
///             the <c>LIKE</c> is an <b>exact prefix</b> with <c>_</c> escaped (an unescaped <c>_</c> is a
///             single-character wildcard in T-SQL) — never widen it;
///         </item>
///         <item>
///             a name whose embedded timestamp does not parse is <b>left alone</b>, because an unparseable
///             name is by definition not one this code created;
///         </item>
///         <item>
///             only names <b>strictly older than the cutoff</b> are dropped. At 24 hours that is far beyond
///             any run, so the reaper can never race a live sibling run on the same server; and
///         </item>
///         <item>
///             nothing here ever throws. Unlike this project's <c>Dispose</c>, which deliberately lets a
///             teardown failure surface, opportunistic housekeeping must never fail a green run.
///         </item>
///     </list>
///     <para>
///         Deliberately duplicated from the AdminUI.Tests copy rather than shared: the two suites have no
///         common test-support assembly, and a new one purely for ~100 lines of best-effort housekeeping
///         costs more than the duplication.
///     </para>
/// </remarks>
internal static class SqlTestDatabaseReaper
{
    private const string TimestampFormat = "yyyyMMddHHmmss";

    /// <summary>
    ///     Drops every database matching <paramref name="prefix"/> whose embedded creation timestamp is
    ///     strictly older than <paramref name="cutoffUtc"/>.
    /// </summary>
    /// <param name="masterConnectionString">A connection string pointed at <c>master</c>.</param>
    /// <param name="prefix">The exact test-database name prefix, e.g. <c>OtOpcUaConfig_Test_</c>.</param>
    /// <param name="cutoffUtc">Databases created strictly before this UTC instant are dropped.</param>
    /// <returns>The names actually dropped; empty when there was nothing to reap or anything went wrong.</returns>
    internal static IReadOnlyList<string> ReapOrphans(string masterConnectionString, string prefix, DateTime cutoffUtc)
    {
        var reaped = new List<string>();

        try
        {
            foreach (var name in ListCandidates(masterConnectionString, prefix))
            {
                if (!TryParseCreatedUtc(name, prefix, out var createdUtc)) continue;
                if (createdUtc >= cutoffUtc) continue;

                try
                {
                    if (TryDropDatabase(masterConnectionString, name)) reaped.Add(name);
                }
                catch (Exception)
                {
                    // One stubborn database must not stop the sweep, nor fail the run that triggered it.
                }
            }
        }
        catch (Exception)
        {
            // Enumeration failed (server down, no permission). Reaping is opportunistic housekeeping.
        }

        if (reaped.Count > 0)
        {
            Console.WriteLine(
                $"[sql-test-reaper] dropped {reaped.Count} orphaned test database(s) older than " +
                $"{cutoffUtc:yyyy-MM-dd HH:mm:ss}Z: {string.Join(", ", reaped)}");
        }

        return reaped;
    }

    /// <summary>Drops the named database, swallowing database errors — reaping is best-effort.</summary>
    /// <param name="masterConnectionString">A connection string pointed at <c>master</c>.</param>
    /// <param name="databaseName">The database to drop.</param>
    /// <returns><see langword="true"/> when the statement ran without error.</returns>
    internal static bool TryDropDatabase(string masterConnectionString, string databaseName)
    {
        try
        {
            using var conn = new SqlConnection(masterConnectionString);
            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();
            return true;
        }
        catch (DbException)
        {
            return false;
        }
    }

    private static List<string> ListCandidates(string masterConnectionString, string prefix)
    {
        var names = new List<string>();

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

        using var cmd = conn.CreateCommand();
        cmd.CommandText = @"SELECT name FROM sys.databases WHERE name LIKE @pattern ESCAPE '\'";
        cmd.Parameters.Add(new SqlParameter("@pattern", prefix.Replace("_", @"\_", StringComparison.Ordinal) + "%"));

        using var reader = cmd.ExecuteReader();
        while (reader.Read()) names.Add(reader.GetString(0));

        return names;
    }

    private static bool TryParseCreatedUtc(string databaseName, string prefix, out DateTime createdUtc)
    {
        createdUtc = default;

        if (!databaseName.StartsWith(prefix, StringComparison.Ordinal)) return false;

        var rest = databaseName.AsSpan(prefix.Length);

        // Expect exactly "<14-digit timestamp>_<guid>" — anything else is not a name this code minted.
        if (rest.Length < TimestampFormat.Length + 1 || rest[TimestampFormat.Length] != '_') return false;

        return DateTime.TryParseExact(
            rest[..TimestampFormat.Length],
            TimestampFormat,
            CultureInfo.InvariantCulture,
            DateTimeStyles.AssumeUniversal | DateTimeStyles.AdjustToUniversal,
            out createdUtc);
    }
}

[CollectionDefinition(nameof(SchemaComplianceCollection))]
public sealed class SchemaComplianceCollection : ICollectionFixture<SchemaComplianceFixture>
{
}