using System.Runtime.InteropServices;
using System.Runtime.Versioning;
using Microsoft.Win32;

namespace ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Proxy.Tests.LiveStack;

/// <summary>
///     Resolves the pipe name + shared secret the live <see cref="GalaxyProxyDriver"/> needs
///     to connect to a running <c>OtOpcUaGalaxyHost</c> Windows service. Two sources are
///     consulted, first match wins:
///     <list type="number">
///         <item>Explicit env vars (<c>OTOPCUA_GALAXY_PIPE</c>, <c>OTOPCUA_GALAXY_SECRET</c>) — lets CI / benchwork override.</item>
///         <item>The service's per-process <c>Environment</c> registry values under
///               <c>HKLM\SYSTEM\CurrentControlSet\Services\OtOpcUaGalaxyHost</c> — what
///               <c>Install-Services.ps1</c> writes at install time. Requires the test to run as a
///               principal with read access to that registry key (typically Administrators).</item>
///     </list>
/// </summary>
/// <remarks>
///     Explicitly NOT baked-in-to-source: the shared secret is rotated per install (the
///     installer generates 32 random bytes and stores the base64 string). A hard-coded secret
///     in tests would diverge from production the moment someone re-installed the service.
/// </remarks>
public sealed record LiveStackConfig(string PipeName, string SharedSecret, string? Source)
{
    public const string EnvPipeName = "OTOPCUA_GALAXY_PIPE";
    public const string EnvSharedSecret = "OTOPCUA_GALAXY_SECRET";
    public const string ServiceRegistryKey =
        @"SYSTEM\CurrentControlSet\Services\OtOpcUaGalaxyHost";
    public const string DefaultPipeName = "OtOpcUaGalaxy";

    public static LiveStackConfig? Resolve()
    {
        var envPipe = Environment.GetEnvironmentVariable(EnvPipeName);
        var envSecret = Environment.GetEnvironmentVariable(EnvSharedSecret);
        if (!string.IsNullOrWhiteSpace(envPipe) && !string.IsNullOrWhiteSpace(envSecret))
            return new LiveStackConfig(envPipe, envSecret, "env vars");

        if (!RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
            return null;

        return FromServiceRegistry();
    }

    [SupportedOSPlatform("windows")]
    private static LiveStackConfig? FromServiceRegistry()
    {
        try
        {
            using var key = Registry.LocalMachine.OpenSubKey(ServiceRegistryKey);
            if (key is null) return null;
            var env = key.GetValue("Environment") as string[];
            if (env is null || env.Length == 0) return null;

            string? pipe = null, secret = null;
            foreach (var line in env)
            {
                var eq = line.IndexOf('=');
                if (eq <= 0) continue;
                var name = line[..eq];
                var value = line[(eq + 1)..];
                if (name.Equals(EnvPipeName, StringComparison.OrdinalIgnoreCase)) pipe = value;
                else if (name.Equals(EnvSharedSecret, StringComparison.OrdinalIgnoreCase)) secret = value;
            }

            if (string.IsNullOrWhiteSpace(secret)) return null;
            return new LiveStackConfig(pipe ?? DefaultPipeName, secret, "service registry");
        }
        catch
        {
            // Access denied / key missing / malformed — caller gets null and surfaces a Skip.
            return null;
        }
    }
}