using System.Net.Http.Headers;
using System.Net.Http.Json;
using Azaion.Missions.E2E.Fixtures;
using Azaion.Missions.E2E.Helpers;
using Npgsql;
using Xunit;

namespace Azaion.Missions.E2E.Tests.Resilience;

/// <summary>
/// NFT-RES-08 — TOCTOU race on <c>vehicles.is_default</c>.
/// </summary>
/// <remarks>
/// <para>
/// Spec AC-1.4 expects the race to be OBSERVABLE — i.e. at least one of 100
/// concurrent iterations leaves two rows with <c>is_default=true</c>. The
/// current migrator ships
/// <c>ux_vehicles_one_default ON vehicles (is_default) WHERE is_default = TRUE</c>,
/// which closes the race at the storage layer: the second writer always
/// fails with <c>23505</c>.
/// </para>
/// <para>
/// Following <c>CascadeF4Tests</c> precedent we pin the CURRENT behaviour
/// (max-one default after the race) and mark the divergence with the
/// <c>carry_forward</c> trait. If the index is ever removed without an
/// application-level guard replacing it, this test fails loudly — that
/// failure is the signal to revisit the AC-1.4 carry-forward in the
/// traceability matrix.
/// </para>
/// </remarks>
[Collection("MigratorRestart")]
[Trait("Category", "Res")]
[Trait("carry_forward", "AC-1.4/index-closes-race")]
[Trait("db_access", "seed-or-assert-only")]
public sealed class DefaultVehicleRaceTests : TestBase, IClassFixture<DbResetFixture>
{
    private const int Iterations = 100;

    [Fact]
    [Trait("Traces", "AC-1.4")]
    [Trait("max_ms", "30000")]
    public async Task NFT_RES_08_concurrent_default_writes_converge_on_one_default_today()
    {
        // Arrange — fresh DB and a valid token reused across iterations.
        DbResetFixture.ResetDatabase(TestEnvironment.DbSideChannel);
        var token = await Tokens.MintDefaultAsync();
        Missions.DefaultRequestHeaders.Authorization =
            new AuthenticationHeaderValue("Bearer", token.Jwt);

        var observations = new int[Iterations];

        // Act
        for (int i = 0; i < Iterations; i++)
        {
            ResetVehiclesAndSeedOneDefault();

            // Each writer carries a unique id so PK collisions never mask
            // the race that AC-1.4 is interested in.
            var postTask = TryPostVehicleAsync(Guid.NewGuid());
            var insertTask = TrySideChannelInsertAsync(Guid.NewGuid());

            await Task.WhenAll(postTask, insertTask);
            observations[i] = CountDefaultVehicles();
        }

        var maxObserved = observations.Max();

        // Assert — CURRENT behaviour: the partial unique index forces
        // every iteration to converge on a single default vehicle.
        // If this assertion ever fails (max >= 2), the index has been
        // removed/relaxed and AC-1.4 carry-forward should be revisited.
        Assert.True(maxObserved <= 1,
            $"observed >= 2 defaults in some iteration (max={maxObserved}). " +
            "Index ux_vehicles_one_default appears removed/relaxed — revisit " +
            "AC-1.4 carry-forward in traceability_matrix.csv.");
    }

    private async Task<HttpRequestState> TryPostVehicleAsync(Guid vehicleId)
    {
        try
        {
            var body = new
            {
                Id = vehicleId,
                Name = $"race-api-{vehicleId:N}",
                IsDefault = true,
            };
            using var resp = await Missions.PostAsJsonAsync("/vehicles", body);
            return new HttpRequestState((int)resp.StatusCode, null);
        }
        catch (Exception ex)
        {
            return new HttpRequestState(-1, ex);
        }
    }

    private static async Task<SideChannelState> TrySideChannelInsertAsync(Guid vehicleId)
    {
        try
        {
            await using var conn = new NpgsqlConnection(TestEnvironment.DbSideChannel);
            await conn.OpenAsync();
            await using var cmd = conn.CreateCommand();
            cmd.CommandText = """
                INSERT INTO vehicles (id, model, name, is_default)
                VALUES (@id, @model, @name, TRUE);
                """;
            cmd.Parameters.AddWithValue("id", vehicleId);
            cmd.Parameters.AddWithValue("model", "race-model");
            cmd.Parameters.AddWithValue("name", $"race-side-{vehicleId:N}");
            await cmd.ExecuteNonQueryAsync();
            return new SideChannelState(true, null);
        }
        catch (PostgresException ex)
        {
            return new SideChannelState(false, ex);
        }
    }

    private static void ResetVehiclesAndSeedOneDefault()
    {
        using var conn = new NpgsqlConnection(TestEnvironment.DbSideChannel);
        conn.Open();
        using var cmd = conn.CreateCommand();
        cmd.CommandText = """
            TRUNCATE vehicles RESTART IDENTITY CASCADE;
            INSERT INTO vehicles (id, model, name, is_default)
            VALUES (gen_random_uuid(), 'seed-model', 'seed-default', TRUE);
            """;
        cmd.ExecuteNonQuery();
    }

    private static int CountDefaultVehicles()
    {
        using var conn = new NpgsqlConnection(TestEnvironment.DbSideChannel);
        conn.Open();
        using var cmd = conn.CreateCommand();
        cmd.CommandText = "SELECT COUNT(*) FROM vehicles WHERE is_default = TRUE;";
        return Convert.ToInt32(cmd.ExecuteScalar());
    }

    private sealed record HttpRequestState(int StatusCode, Exception? Error);
    private sealed record SideChannelState(bool Inserted, Exception? Error);
}