using System.Reflection;

namespace ZB.MOM.WW.ScadaBridge.Host.Tests;

/// <summary>
/// Tests for CoordinatedShutdown configuration.
/// Verifies no Environment.Exit calls exist in source and HOCON config is correct.
/// </summary>
public class CoordinatedShutdownTests
{
    /// <summary>Verifies that host source does not contain environment exit.</summary>
    [Fact]
    public void HostSource_DoesNotContainEnvironmentExit()
    {
        var hostProjectDir = FindHostProjectDirectory();
        Assert.NotNull(hostProjectDir);

        var sourceFiles = Directory.GetFiles(hostProjectDir, "*.cs", SearchOption.AllDirectories);
        Assert.NotEmpty(sourceFiles);

        foreach (var file in sourceFiles)
        {
            var content = File.ReadAllText(file);

            // Sole permitted call site: Program.cs's AppDomain.UnhandledException handler
            // (ScadaBridge#34). That is the crash path — the alternative there was never a
            // CoordinatedShutdown but the runtime's abort(), which cannot terminate PID 1
            // and wedged the container; Environment.Exit still fires the CLR shutdown hook
            // Akka binds via run-by-clr-shutdown-hook = on, so it skips nothing abort kept.
            // Everywhere else the original rule stands: no code path may bypass
            // CoordinatedShutdown by exiting directly.
            if (Path.GetFileName(file) == "Program.cs")
            {
                var occurrences = CountOccurrences(content, "Environment.Exit(");
                Assert.Equal(1, occurrences);

                var handlerAt = content.IndexOf(
                    "AppDomain.CurrentDomain.UnhandledException +=", StringComparison.Ordinal);
                Assert.True(handlerAt >= 0, "Program.cs must register the UnhandledException handler");
                var handlerEnd = content.IndexOf("};", handlerAt, StringComparison.Ordinal);
                var exitAt = content.IndexOf("Environment.Exit(", StringComparison.Ordinal);
                Assert.True(exitAt > handlerAt && exitAt < handlerEnd,
                    "Environment.Exit in Program.cs is only permitted inside the UnhandledException handler");
                continue;
            }

            Assert.DoesNotContain("Environment.Exit", content,
                StringComparison.Ordinal);
        }
    }

    /// <summary>Verifies that akka hosted service hocon config includes coordinated shutdown settings.</summary>
    [Fact]
    public void AkkaHostedService_HoconConfig_IncludesCoordinatedShutdownSettings()
    {
        // Read the AkkaHostedService source to verify HOCON configuration
        var hostProjectDir = FindHostProjectDirectory();
        Assert.NotNull(hostProjectDir);

        var akkaServiceFile = Path.Combine(hostProjectDir, "Actors", "AkkaHostedService.cs");
        Assert.True(File.Exists(akkaServiceFile), $"AkkaHostedService.cs not found at {akkaServiceFile}");

        var content = File.ReadAllText(akkaServiceFile);

        // Verify critical HOCON settings are present
        Assert.Contains("run-by-clr-shutdown-hook = on", content);
        Assert.Contains("run-coordinated-shutdown-when-down = on", content);
    }

    /// <summary>Verifies that all central singletons register through registrar with drain.</summary>
    [Fact]
    public void AllCentralSingletons_RegisterThroughRegistrarWithDrain()
    {
        var hostProjectDir = FindHostProjectDirectory();
        Assert.NotNull(hostProjectDir);
        var content = File.ReadAllText(Path.Combine(hostProjectDir!, "Actors", "AkkaHostedService.cs"));

        // Review 01 [Medium]: notification-outbox and audit-log-ingest were the
        // only central singletons WITHOUT a cluster-leave drain task. All seven
        // now go through SingletonRegistrar.Start, which always adds the
        // PhaseClusterLeave GracefulStop drain.
        Assert.Contains("SingletonRegistrar.Start(", content);
        foreach (var name in new[] { "notification-outbox", "audit-log-ingest", "site-call-audit",
                                     "audit-log-purge", "site-audit-reconciliation",
                                     "kpi-history-recorder", "pending-deployment-purge" })
        {
            Assert.Contains($"\"{name}\"", content);
        }

        // No hand-rolled ClusterSingletonManager registrations remain anywhere:
        // the two role-scoped SITE singletons now also go through the registrar
        // (SingletonRegistrar.Start(..., role: siteRole)), so every singleton in
        // the file is created through the registrar with a drain task.
        Assert.Equal(0, CountOccurrences(content, "ClusterSingletonManager.Props("));
    }

    /// <summary>Verifies that site singletons register through registrar with drain.</summary>
    [Fact]
    public void SiteSingletons_RegisterThroughRegistrarWithDrain()
    {
        var hostProjectDir = FindHostProjectDirectory();
        Assert.NotNull(hostProjectDir);
        var content = File.ReadAllText(Path.Combine(hostProjectDir!, "Actors", "AkkaHostedService.cs"));

        // The two role-scoped SITE singletons previously stayed
        // hand-rolled (bare PoisonPill, no PhaseClusterLeave drain). They now
        // go through SingletonRegistrar.Start(..., role: siteRole), which
        // always adds the GracefulStop drain — in-flight SQLite writes
        // (static overrides, native_alarm_state) complete before handover.
        Assert.Contains("\"deployment-manager\"", content);
        Assert.Contains("\"event-log-handler\"", content);
        Assert.Contains("role: siteRole", content);
        Assert.Equal(0, CountOccurrences(content, "ClusterSingletonManager.Props("));
    }

    private static int CountOccurrences(string haystack, string needle)
    {
        int count = 0, i = 0;
        while ((i = haystack.IndexOf(needle, i, StringComparison.Ordinal)) >= 0)
        {
            count++;
            i += needle.Length;
        }
        return count;
    }

    private static string? FindHostProjectDirectory()
    {
        var assemblyDir = Path.GetDirectoryName(Assembly.GetExecutingAssembly().Location)!;
        var dir = new DirectoryInfo(assemblyDir);

        while (dir != null)
        {
            var hostPath = Path.Combine(dir.FullName, "src", "ZB.MOM.WW.ScadaBridge.Host");
            if (Directory.Exists(hostPath))
                return hostPath;
            dir = dir.Parent;
        }

        return null;
    }
}