using System.Globalization;
using System.Runtime.CompilerServices;

namespace AcDream.Tests;

/// <summary>
/// Lets a test run pin the ambient culture, so a locale-dependent failure can
/// be reproduced on any machine instead of only on one with the right Windows
/// locale.
///
/// <para><b>Why this exists.</b> On 2026-08-19 the Windows CI runner went red on
/// 37 tests across four assemblies with failures like
/// <c>Expected: "You have 1 500p" / Actual: "You have 1,500p"</c>. The
/// production code was right — it formats retail text with
/// <see cref="CultureInfo.InvariantCulture"/>, so every player sees retail's
/// comma. The TESTS were wrong: they built their expected strings with
/// <c>$"{value:N0}"</c>, which uses the machine's current culture, so they only
/// passed on a machine that happens to format like the invariant culture. The
/// runner is Swedish (space as the group separator), and the tests had been
/// passing there only because its registry locale had been pinned by hand —
/// a machine-state fix that silently came undone.</para>
///
/// <para>The expectations are fixed to be invariant. This knob is the
/// apparatus that makes such a break reproducible next time:
/// <c>ACDREAM_TEST_CULTURE=sv-SE dotnet test ...</c> runs the suite as the
/// Swedish runner sees it. Unset (the default, and what CI runs) changes
/// nothing at all.</para>
/// </summary>
internal static class TestCultureInitializer
{
    internal const string CultureVariable = "ACDREAM_TEST_CULTURE";

    [ModuleInitializer]
    internal static void Initialize()
    {
        string? requested = Environment.GetEnvironmentVariable(CultureVariable);
        if (string.IsNullOrWhiteSpace(requested))
        {
            return;
        }

        try
        {
            var culture = CultureInfo.GetCultureInfo(requested);
            CultureInfo.DefaultThreadCurrentCulture = culture;
            CultureInfo.DefaultThreadCurrentUICulture = culture;
        }
        catch (CultureNotFoundException)
        {
            // A typo in an opt-in diagnostic must not fail an unrelated suite;
            // the run simply keeps the machine's own culture.
        }
    }
}