LehrerApp/LehrerApp.Core/Services/AppLockService.cs

using System.Security.Cryptography;
using System.Text.Json;

namespace LehrerApp.Core.Services;

internal class AppLockConfig
{
    public bool Enabled { get; set; }
    public string? Salt { get; set; }
    public string? PasswordHash { get; set; }
    public int TimeoutMinutes { get; set; } = 10;
}

/// <summary>
/// App-Sperre nach Inaktivität: eigenes Passwort (unabhängig von einer eventuellen
/// Datenbank-Verschlüsselung), als gesalzener Hash in <c>&lt;AppData&gt;/LehrerApp/applock.json</c>
/// abgelegt. Das Klartext-Passwort wird nie gespeichert.
/// </summary>
public class AppLockService
{
    private const int Pbkdf2Iterations = 100_000;
    private readonly string _configPath;
    private AppLockConfig _config;

    public bool IsEnabled => _config.Enabled;
    public int TimeoutMinutes => _config.TimeoutMinutes;
    public bool HasPassword => !string.IsNullOrEmpty(_config.PasswordHash);

    public AppLockService(string appDataPath)
    {
        _configPath = Path.Combine(appDataPath, "applock.json");
        _config = Load();
    }

    public void Configure(bool enabled, int timeoutMinutes)
    {
        _config.Enabled = enabled;
        _config.TimeoutMinutes = Math.Max(1, timeoutMinutes);
        Save();
    }

    public void SetPassword(string password)
    {
        var salt = RandomNumberGenerator.GetBytes(16);
        _config.Salt = Convert.ToBase64String(salt);
        _config.PasswordHash = Hash(password, salt);
        Save();
    }

    public bool VerifyPassword(string password)
    {
        if (string.IsNullOrEmpty(_config.PasswordHash) || string.IsNullOrEmpty(_config.Salt)) return false;
        var salt = Convert.FromBase64String(_config.Salt);
        return _config.PasswordHash == Hash(password, salt);
    }

    private static string Hash(string password, byte[] salt) =>
        Convert.ToBase64String(Rfc2898DeriveBytes.Pbkdf2(password, salt, Pbkdf2Iterations, HashAlgorithmName.SHA256, 32));

    private AppLockConfig Load()
    {
        try
        {
            if (File.Exists(_configPath))
                return JsonSerializer.Deserialize<AppLockConfig>(File.ReadAllText(_configPath)) ?? new AppLockConfig();
        }
        catch { /* beschädigte Konfiguration -> Standardwerte, Sperre bleibt deaktiviert */ }
        return new AppLockConfig();
    }

    private void Save() =>
        File.WriteAllText(_configPath, JsonSerializer.Serialize(_config));
}