import "dart:convert";
import "dart:typed_data";

import "package:pointycastle/export.dart";

// A keypair + a signer, shared by the tests. Lifted from garage_iap's verify
// test — generating a real 2048 bit RSA key beats a fixture, since the whole
// point is that we verify the same way the backend signs.

String b64uBig(BigInt n) {
  final bytes = <int>[];
  var v = n;
  while (v > BigInt.zero) {
    bytes.insert(0, (v & BigInt.from(0xff)).toInt());
    v = v >> 8;
  }
  return base64Url.encode(Uint8List.fromList(bytes)).replaceAll("=", "");
}

String b64uStr(String s) => base64Url.encode(utf8.encode(s)).replaceAll("=", "");

String b64uBytes(List<int> b) => base64Url.encode(b).replaceAll("=", "");

AsymmetricKeyPair<PublicKey, PrivateKey> genKey(int seed) {
  final rng = SecureRandom("Fortuna")
    ..seed(
      KeyParameter(Uint8List.fromList(List.generate(32, (i) => (i + seed) & 0xff))),
    );
  final gen = RSAKeyGenerator()
    ..init(
      ParametersWithRandom(
        RSAKeyGeneratorParameters(BigInt.parse("65537"), 2048, 64),
        rng,
      ),
    );
  return gen.generateKeyPair();
}

// build a compact RS256 JWT the same way the backend does — header.payload
// signed PKCS1v15 SHA-256.
String signJwt(
  RSAPrivateKey priv,
  Map<String, dynamic> header,
  Map<String, dynamic> payload,
) {
  final h = b64uStr(jsonEncode(header));
  final p = b64uStr(jsonEncode(payload));
  final input = utf8.encode("$h.$p");
  final signer = Signer("SHA-256/RSA") as RSASigner;
  signer.init(true, PrivateKeyParameter<RSAPrivateKey>(priv));
  final sig = signer.generateSignature(Uint8List.fromList(input));
  return "$h.$p.${b64uBytes(sig.bytes)}";
}

Map<String, dynamic> jwksOf(RSAPublicKey pub, {String kid = "k1"}) => {
  "keys": [
    {
      "kty": "RSA",
      "use": "sig",
      "alg": "RS256",
      "kid": kid,
      "n": b64uBig(pub.modulus!),
      "e": b64uBig(pub.exponent!),
    },
  ],
};

/// A key the way the store mints them. Everything is overridable so a test can
/// break exactly one claim.
String keyToken(
  RSAPrivateKey priv, {
  String kid = "k1",
  String sub = "user-123",
  String iss = "https://pay.imbenji.net",
  String project = "field-notes",
  String sku = "pro",
  String kind = "one_off",
  String mode = "live",
  String? entitlementExpiresAt,
  Duration life = const Duration(hours: 1),
  String? audOverride,
}) {
  final now = DateTime.now().toUtc();
  return signJwt(priv, {"alg": "RS256", "kid": kid, "typ": "JWT"}, {
    "sub": sub,
    "iss": iss,
    "aud": audOverride ?? "$project/$sku",
    "project": project,
    "sku": sku,
    "kind": kind,
    "mode": mode,
    if (entitlementExpiresAt != null) "expires_at": entitlementExpiresAt,
    "iat": now.millisecondsSinceEpoch ~/ 1000,
    "exp": now.add(life).millisecondsSinceEpoch ~/ 1000,
  });
}