tane/apps/app_seeds/lib/services/social_service.dart

import 'dart:typed_data';

import 'package:commons_core/commons_core.dart';

/// The app-side entry point to the (Block 2) social layer.
///
/// Holds the user's Nostr identity — deterministically derived from the same
/// root seed the recovery QR backs up (so it needs no extra backup) — and opens
/// social sessions on demand. Local-first: constructing this is cheap and
/// offline; nothing connects to a relay until [openSession] is called, so the
/// app runs fully without network and the social layer only enriches.
class SocialService {
  SocialService({
    required this.identity,
    this.account = 0,
    this.rootSeedHex = '',
    List<String> relays = const [],
  }) : relays = List.unmodifiable(relays);

  /// The derived Nostr identity (secp256k1). Same key across reinstalls that
  /// restore the same seed (for a given [account]).
  final NostrIdentity identity;

  /// Which pseudonymous identity of the root seed this is (0 = the original).
  /// Switching account changes the social identity while the backup stays the
  /// single root seed. See [NostrKeyDerivation.deriveFromSeed].
  final int account;

  /// The root-seed hex, kept so the switcher can preview OTHER accounts'
  /// identities without re-reading the keystore. Empty when unknown (tests).
  final String rootSeedHex;

  /// Community relay URLs (may be empty — discovery/publishing degrade to
  /// nothing when offline or unconfigured).
  final List<String> relays;

  /// Shareable public identity (`npub…`) and its hex form.
  String get npub => identity.npub;
  String get publicKeyHex => identity.publicKeyHex;

  /// Derives the identity from the stored root-seed hex (32-byte, 64 chars) for
  /// the given [account] (0 = the original identity).
  static Future<SocialService> fromRootSeedHex(
    String rootSeedHex, {
    int account = 0,
    List<String> relays = const [],
  }) async {
    final identity = await NostrKeyDerivation.deriveFromSeed(
      _hexToBytes(rootSeedHex),
      account: account,
    );
    return SocialService(
      identity: identity,
      account: account,
      rootSeedHex: rootSeedHex,
      relays: relays,
    );
  }

  /// The `npub` for another [account] of the same root seed, so the switcher can
  /// show identities before committing to one. Returns null if the seed is
  /// unknown (e.g. in tests constructed without it).
  Future<String?> npubForAccount(int account) async {
    if (rootSeedHex.isEmpty) return null;
    final id = await NostrKeyDerivation.deriveFromSeed(
      _hexToBytes(rootSeedHex),
      account: account,
    );
    return id.npub;
  }

  /// Opens a session against [relayUrls]: one fault-tolerant pool carrying all
  /// three transports (offers, messaging, trust). Relays that are down are
  /// skipped; throws only when none are reachable. Caller closes it.
  Future<SocialSession> openSession(List<String> relayUrls) async {
    final pool = await RelayPool.connect(relayUrls, identity: identity);
    return SocialSession(pool);
  }
}

/// One relay channel with the three transports on top — the
/// "one channel, three interfaces" shape, at the app layer.
class SocialSession {
  SocialSession(this._channel)
      : offers = NostrOfferTransport(_channel),
        messages = NostrMessageTransport(_channel),
        trust = NostrTrustTransport(_channel),
        profile = NostrProfileTransport(_channel);

  final NostrChannel _channel;

  final OfferTransport offers;
  final MessageTransport messages;
  final TrustTransport trust;
  final ProfileTransport profile;

  Future<void> close() => _channel.close();
}

Uint8List _hexToBytes(String hex) {
  if (hex.length.isOdd) {
    throw ArgumentError('hex string must have an even length');
  }
  final out = Uint8List(hex.length ~/ 2);
  for (var i = 0; i < out.length; i++) {
    out[i] = int.parse(hex.substring(i * 2, i * 2 + 2), radix: 16);
  }
  return out;
}