swarm/lib/src/nostr_signer_actor.dart

import 'package:actors/actors.dart';
import 'package:bip340/bip340.dart' as bip340;

import 'nip44.dart';
import 'nostr_event.dart';

sealed class SignerMessage {
  const SignerMessage();
}

final class SignEvent extends SignerMessage {
  final int kind;
  final List<List<String>> tags;
  final String content;
  final int? createdAt;
  const SignEvent({
    required this.kind,
    this.tags = const [],
    required this.content,
    this.createdAt,
  });
}

final class GetPublicKey extends SignerMessage {
  const GetPublicKey();
}

/// NIP-44 v2 encrypt-to-self: encrypts [plaintext] with this signer's own key
/// (conversation key derived from its private key and public key).
final class Nip44Encrypt extends SignerMessage {
  final String plaintext;
  const Nip44Encrypt(this.plaintext);
}

/// NIP-44 v2 decrypt-from-self: inverse of [Nip44Encrypt]. Throws on a version
/// mismatch or HMAC failure (e.g. a payload sealed with a different key).
final class Nip44Decrypt extends SignerMessage {
  final String payload;
  const Nip44Decrypt(this.payload);
}

sealed class SignerResult {
  const SignerResult();
}

final class EventSigned extends SignerResult {
  final String event;
  const EventSigned(this.event);
}

final class PublicKeyResult extends SignerResult {
  final String publicKey;
  const PublicKeyResult(this.publicKey);
}

/// Result of a [Nip44Encrypt] (base64 payload) or [Nip44Decrypt] (plaintext).
final class Nip44Text extends SignerResult {
  final String value;
  const Nip44Text(this.value);
}

class NostrSignerActor with Handler<SignerMessage, SignerResult> {
  final String _privateKey;
  final String _publicKey;

  NostrSignerActor(String privateKey)
      : _privateKey = privateKey,
        _publicKey = bip340.getPublicKey(privateKey);

  @override
  Future<SignerResult> handle(SignerMessage message) => switch (message) {
        SignEvent(:final kind, :final tags, :final content, :final createdAt) =>
          Future.value(_signEvent(kind, tags, content, createdAt)),
        GetPublicKey() => Future.value(PublicKeyResult(_publicKey)),
        Nip44Encrypt(:final plaintext) => Future.value(
            Nip44Text(nip44Encrypt(plaintext, _privateKey, _publicKey)),
          ),
        Nip44Decrypt(:final payload) => Future.value(
            Nip44Text(nip44Decrypt(payload, _privateKey, _publicKey)),
          ),
      };

  EventSigned _signEvent(
    int kind,
    List<List<String>> tags,
    String content,
    int? createdAt,
  ) =>
      EventSigned(signNostrEvent(
        privateKey: _privateKey,
        publicKey: _publicKey,
        kind: kind,
        tags: tags,
        content: content,
        createdAt: createdAt,
      ));
}