using System;
using System.IO;
using System.Security.Cryptography;
using Microsoft.Extensions.Configuration;

namespace SNote.Server.Security;

public class RsaKeyManager
{
    private readonly string _publicKeyPath;
    private readonly string _privateKeyPath;
    private RSA? _privateKeyRsa;
    private RSA? _publicKeyRsa;
    private string _publicKeyPem = string.Empty;
    private string _privateKeyPem = string.Empty;

    public RsaKeyManager(IConfiguration configuration)
    {
        _publicKeyPath = Path.Combine(AppContext.BaseDirectory, "snote-public.pem");
        _privateKeyPath = Path.Combine(AppContext.BaseDirectory, "snote-private.pem");

        var configPublicKey = configuration["Sync:PublicKey"];
        var configPrivateKey = configuration["Sync:PrivateKey"];

        if (!string.IsNullOrEmpty(configPublicKey) && !string.IsNullOrEmpty(configPrivateKey))
        {
            _publicKeyPem = configPublicKey;
            _privateKeyPem = configPrivateKey;
            InitializeKeys();
        }
        else
        {
            LoadOrGenerateKeys();
        }
    }

    private void InitializeKeys()
    {
        try
        {
            _publicKeyRsa = RSA.Create();
            _publicKeyRsa.ImportFromPem(_publicKeyPem);

            _privateKeyRsa = RSA.Create();
            _privateKeyRsa.ImportFromPem(_privateKeyPem);
        }
        catch (Exception ex)
        {
            Console.WriteLine($"[RsaKeyManager] Error initializing configured keys: {ex.Message}");
            throw;
        }
    }

    private void LoadOrGenerateKeys()
    {
        if (File.Exists(_privateKeyPath) && File.Exists(_publicKeyPath))
        {
            try
            {
                _publicKeyPem = File.ReadAllText(_publicKeyPath);
                _privateKeyPem = File.ReadAllText(_privateKeyPath);
                InitializeKeys();
                Console.WriteLine("[RsaKeyManager] Loaded existing RSA keys from disk.");
                return;
            }
            catch (Exception ex)
            {
                Console.WriteLine($"[RsaKeyManager] Error loading RSA keys from disk: {ex.Message}. Re-generating.");
            }
        }

        // Generate new keypair
        Console.WriteLine("[RsaKeyManager] Generating new secure 2048-bit RSA keypair...");
        using var rsa = RSA.Create(2048);

        _publicKeyPem = rsa.ExportSubjectPublicKeyInfoPem();
        _privateKeyPem = rsa.ExportPkcs8PrivateKeyPem();

        File.WriteAllText(_publicKeyPath, _publicKeyPem);
        File.WriteAllText(_privateKeyPath, _privateKeyPem);

        InitializeKeys();
        Console.WriteLine("[RsaKeyManager] Secure RSA keypair generated and saved to disk.");
    }

    public RSA GetPrivateKey()
    {
        if (_privateKeyRsa == null) throw new InvalidOperationException("Private key is not loaded.");
        return _privateKeyRsa;
    }

    public RSA GetPublicKey()
    {
        if (_publicKeyRsa == null) throw new InvalidOperationException("Public key is not loaded.");
        return _publicKeyRsa;
    }

    public string GetPublicKeyPem()
    {
        return _publicKeyPem;
    }

    public string GetPrivateKeyPem()
    {
        return _privateKeyPem;
    }
}