import 'dart:convert';
import 'dart:math';

import 'package:crypto/crypto.dart';

/// Binds a guardian login request to the device that started it (PKCE-style):
/// the request carries only [challengeFor] of a secret that never leaves the
/// device, verification sends the secret itself. A mail link opened on another
/// device therefore cannot complete the login.
abstract final class DeviceBinding {
  static String generateSecret([Random? random]) {
    final rng = random ?? Random.secure();
    final bytes = List<int>.generate(32, (_) => rng.nextInt(256));
    return _base64UrlNoPad(bytes);
  }

  static String challengeFor(String secret) =>
      _base64UrlNoPad(sha256.convert(utf8.encode(secret)).bytes);

  static String _base64UrlNoPad(List<int> bytes) =>
      base64Url.encode(bytes).replaceAll('=', '');
}