basic nostr actors

lib/src/nostr_signer_actor.dart

@@ -0,0 +1,85 @@
+import 'dart:convert';
+import 'dart:math';
+
+import 'package:actors/actors.dart';
+import 'package:bip340/bip340.dart' as bip340;
+import 'package:crypto/crypto.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();
+}
+
+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);
+}
+
+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)),
+      };
+
+  EventSigned _signEvent(
+    int kind,
+    List<List<String>> tags,
+    String content,
+    int? createdAt,
+  ) {
+    final ts = createdAt ?? DateTime.now().millisecondsSinceEpoch ~/ 1000;
+    final ser = jsonEncode([0, _publicKey, ts, kind, tags, content]);
+    final idBytes = sha256.convert(utf8.encode(ser)).bytes;
+    final id = idBytes.map((b) => b.toRadixString(16).padLeft(2, '0')).join();
+
+    final rng = Random.secure();
+    final auxBytes = List.generate(32, (_) => rng.nextInt(256));
+    final aux = auxBytes.map((b) => b.toRadixString(16).padLeft(2, '0')).join();
+
+    final sig = bip340.sign(_privateKey, id, aux);
+
+    return EventSigned(jsonEncode({
+      'id': id,
+      'pubkey': _publicKey,
+      'created_at': ts,
+      'kind': kind,
+      'tags': tags,
+      'content': content,
+      'sig': sig,
+    }));
+  }
+}