namespace AcDream.App.Tests.Rendering;

/// <summary>
/// Fix #406: before this change, <c>GameWindow.CompleteShutdown</c> wrote
/// a hardcoded <c>exited{code:0,reason:"graceful"}</c> status event
/// whenever the resource-shutdown transaction converged — even when
/// <c>Dispose()</c> (and therefore <c>CompleteShutdown</c>) ran mid-unwind
/// of an exception that escaped <c>Run()</c>'s Silk.NET frame loop and was
/// about to crash the process via the CLR's unhandled-exception path.
/// <c>GameWindow</c> cannot be constructed without a live GPU/window (see
/// the established pattern in <c>GameWindowSlice8BoundaryTests</c>), so
/// this pins the fix as a source-shape test exactly like that file does
/// for the surrounding shutdown machinery.
/// </summary>
public sealed class GameWindowCrashStatusTests
{
    [Fact]
    public void Run_LatchesRunFailureBeforeRethrowingFromTheFrameLoopCatch()
    {
        string body = MethodBody(
            "public void Run()",
            "void IGameWindowPlatformPublication<GameWindowGraphics, IInputContext>.PublishGraphics(");
        string tryBlock = Slice(body, "try\n        {\n            _window.Run();", "}\n    }");

        AssertAppearsInOrder(
            tryBlock,
            "_window.Run();",
            "catch (Exception failure)",
            "_constructionCleanup.RetainFrom(failure);",
            // The latch MUST happen before the rethrow: Dispose() (and
            // therefore CompleteShutdown/ReportExited) can run mid-unwind
            // of this exact exception, via Program.cs's
            // `using var window = ...`.
            "_runFailure = failure;",
            "throw;");
    }

    [Fact]
    public void ReportExited_ChecksRunFailureBeforeEitherGracefulOrShutdownIncompletePaths()
    {
        string source = GameWindowSource();
        string reportExited = Slice(
            source,
            "private void ReportExited(GameWindowLifetimeReport report)",
            "\n    }\n");

        Assert.Contains(
            "string sessionId = _options.SessionId ?? \"app\";",
            reportExited,
            StringComparison.Ordinal);
        AssertAppearsInOrder(
            reportExited,
            "if (_runFailure is not null)",
            "_statusWriter.Exited(sessionId, 1, \"crashed\");",
            "return;",
            "if (report.Status == GameWindowLifetimeStatus.Complete)",
            "_statusWriter.Exited(sessionId, 0, \"graceful\");",
            "_statusWriter.Exited(sessionId, 1, \"shutdown-incomplete\");");

        // Every terminal-status write in CompleteShutdown funnels through
        // this ONE method — a second, uncoordinated call site would be
        // exactly how the pre-fix bug reappears.
        Assert.Equal(
            2,
            CountOccurrences(source, "ReportExited(report)"));
        Assert.DoesNotContain(
            "_statusWriter.Exited(_options.SessionId ?? \"app\", 0, \"graceful\")",
            source,
            StringComparison.Ordinal);
    }

    [Fact]
    public void RunFailureFieldExistsAndDefaultsToNull()
    {
        string source = GameWindowSource();

        Assert.Contains(
            "private Exception? _runFailure;",
            source,
            StringComparison.Ordinal);
    }

    private static string MethodBody(string start, string end) =>
        Slice(GameWindowSource(), start, end);

    private static string Slice(string source, string start, string end)
    {
        int first = source.IndexOf(start, StringComparison.Ordinal);
        int last = source.IndexOf(end, first + 1, StringComparison.Ordinal);
        Assert.True(first >= 0, $"Missing source boundary: {start}");
        Assert.True(last > first, $"Missing source boundary: {end}");
        return source[first..last];
    }

    private static int CountOccurrences(string source, string value)
    {
        int count = 0;
        int cursor = 0;
        while ((cursor = source.IndexOf(value, cursor, StringComparison.Ordinal)) >= 0)
        {
            count++;
            cursor += value.Length;
        }

        return count;
    }

    private static void AssertAppearsInOrder(string source, params string[] fragments)
    {
        int cursor = -1;
        foreach (string fragment in fragments)
        {
            int next = source.IndexOf(fragment, cursor + 1, StringComparison.Ordinal);
            Assert.True(next >= 0, $"Missing expected source fragment: {fragment}");
            Assert.True(next > cursor, $"Out-of-order source fragment: {fragment}");
            cursor = next;
        }
    }

    private static string GameWindowSource() => File.ReadAllText(Path.Combine(
        FindRepoRoot(),
        "src",
        "AcDream.App",
        "Rendering",
        "GameWindow.cs")).Replace("\r\n", "\n", StringComparison.Ordinal);

    private static string FindRepoRoot()
    {
        DirectoryInfo? directory = new(AppContext.BaseDirectory);
        while (directory is not null)
        {
            if (File.Exists(Path.Combine(directory.FullName, "AcDream.slnx")))
                return directory.FullName;
            directory = directory.Parent;
        }

        throw new DirectoryNotFoundException("Could not find AcDream.slnx.");
    }
}