using System.Security.Cryptography;
using System.Text;
using Microsoft.Win32;
using System.Numerics;

namespace MxAsbClient;

internal static class AsbRegistry
{
    private const string Entropy = "wonderware";

    private static string RegistryPath => Environment.Is64BitProcess
        ? @"SOFTWARE\Wow6432Node\ArchestrA\ArchestrAServices"
        : @"SOFTWARE\ArchestrA\ArchestrAServices";

    public static string GetDefaultSolutionName()
    {
        return Registry.GetValue($@"HKEY_LOCAL_MACHINE\{RegistryPath}", "DefaultASBSolution", string.Empty)?.ToString() ?? string.Empty;
    }

    public static string GetSolutionPassphrase(string? solutionName, Action<string>? trace = null)
    {
        trace?.Invoke("asb.stage=registry-solution");
        string effectiveSolution = string.IsNullOrWhiteSpace(solutionName) ? GetDefaultSolutionName() : solutionName!;
        if (string.IsNullOrWhiteSpace(effectiveSolution))
        {
            throw new InvalidOperationException("ASB default solution name was not found in the registry.");
        }

        trace?.Invoke("asb.stage=registry-open-solution");
        using RegistryKey? key = Registry.LocalMachine.OpenSubKey($@"{RegistryPath}\{effectiveSolution}", writable: false);
        if (key?.GetValue("sharedsecret") is not byte[] protectedBytes)
        {
            throw new InvalidOperationException($"ASB sharedsecret was not found for solution '{effectiveSolution}'.");
        }

        trace?.Invoke("asb.stage=registry-unprotect");
        byte[] clear = ProtectedData.Unprotect(protectedBytes, Encoding.Unicode.GetBytes(Entropy), DataProtectionScope.LocalMachine);
        trace?.Invoke("asb.stage=registry-passphrase-ready");
        return Encoding.Unicode.GetString(clear);
    }

    public static AsbSolutionCryptoParameters GetCryptoParameters(string? solutionName)
    {
        string effectiveSolution = string.IsNullOrWhiteSpace(solutionName) ? GetDefaultSolutionName() : solutionName!;
        using RegistryKey? key = Registry.LocalMachine.OpenSubKey($@"{RegistryPath}\{effectiveSolution}", writable: false);
        if (key is null)
        {
            throw new InvalidOperationException($"ASB solution registry key was not found for '{effectiveSolution}'.");
        }

        string primeText = key.GetValue("Prime")?.ToString() ?? AsbSolutionCryptoParameters.DefaultPrimeText;
        string generatorText = key.GetValue("Generator")?.ToString() ?? "22";
        string hashAlgorithm = key.GetValue("HashAlgorthim")?.ToString() ?? "MD5";
        int keySize = int.TryParse(key.GetValue("keySize")?.ToString(), out int parsedKeySize) ? parsedKeySize : 256;
        return new AsbSolutionCryptoParameters(
            BigInteger.Parse(primeText),
            BigInteger.Parse(generatorText),
            hashAlgorithm,
            keySize);
    }
}

internal sealed record AsbSolutionCryptoParameters(BigInteger Prime, BigInteger Generator, string HashAlgorithm, int KeySize)
{
    public const string DefaultPrimeText = "179769313486231590770839156793787453197860296048756011706444423684197180216158519368947833795864925541502180565485980503646440548199239100050792877003355816639229553136239076508735759914822574862575007425302077447712589550957937778424442426617334727629299387668709205606050270810842907692932019128194";
}