basedFood-app/lib/data/nostr/nostr_service.dart

import 'dart:async';
import 'dart:convert';
import 'package:web_socket_channel/web_socket_channel.dart';
import 'models/nostr_keypair.dart';
import 'models/nostr_event.dart';
import 'models/nostr_relay.dart';

/// Exception thrown when Nostr operations fail.
class NostrException implements Exception {
  /// Error message.
  final String message;

  /// Creates a [NostrException] with the provided message.
  NostrException(this.message);

  @override
  String toString() => 'NostrException: $message';
}

/// Service for interacting with Nostr protocol.
/// 
/// This service provides:
/// - Keypair generation
/// - Event publishing to relays
/// - Metadata synchronization with multiple relays
/// 
/// The service is modular and UI-independent, designed for testing without real relays.
class NostrService {
  /// List of configured relays.
  final List<NostrRelay> _relays = [];

  /// Active WebSocket connections to relays.
  final Map<String, WebSocketChannel?> _connections = {};

  /// Stream controllers for relay messages.
  final Map<String, StreamController<Map<String, dynamic>>> _messageControllers = {};

  /// Creates a [NostrService] instance.
  NostrService();

  /// Generates a new Nostr keypair.
  /// 
  /// Returns a [NostrKeyPair] with random private and public keys.
  NostrKeyPair generateKeyPair() {
    return NostrKeyPair.generate();
  }

  /// Adds a relay to the service.
  /// 
  /// [relayUrl] - The WebSocket URL of the relay (e.g., 'wss://relay.example.com').
  void addRelay(String relayUrl) {
    final relay = NostrRelay.fromUrl(relayUrl);
    if (!_relays.contains(relay)) {
      _relays.add(relay);
    }
  }

  /// Removes a relay from the service.
  /// 
  /// [relayUrl] - The URL of the relay to remove.
  void removeRelay(String relayUrl) {
    _relays.removeWhere((r) => r.url == relayUrl);
    disconnectRelay(relayUrl);
  }

  /// Gets the list of configured relays.
  List<NostrRelay> getRelays() {
    return List.unmodifiable(_relays);
  }

  /// Connects to a relay.
  /// 
  /// [relayUrl] - The URL of the relay to connect to.
  /// 
  /// Returns a [Stream] of messages from the relay.
  /// 
  /// Throws [NostrException] if connection fails.
  Future<Stream<Map<String, dynamic>>> connectRelay(String relayUrl) async {
    try {
      if (_connections.containsKey(relayUrl) && _connections[relayUrl] != null) {
        // Already connected
        return _messageControllers[relayUrl]!.stream;
      }

      // WebSocketChannel.connect can throw synchronously (e.g., host lookup failure)
      // Wrap in try-catch to ensure it's caught
      WebSocketChannel channel;
      try {
        channel = WebSocketChannel.connect(Uri.parse(relayUrl));
      } catch (e) {
        throw NostrException('Failed to connect to relay: $e');
      }
      _connections[relayUrl] = channel;

      final controller = StreamController<Map<String, dynamic>>();
      _messageControllers[relayUrl] = controller;

      // Update relay status
      final relay = _relays.firstWhere((r) => r.url == relayUrl, orElse: () => NostrRelay.fromUrl(relayUrl));
      relay.isConnected = true;

      // Listen for messages
      channel.stream.listen(
        (message) {
          try {
            final data = jsonDecode(message as String);
            if (data is List) {
              controller.add({
                'type': data[0] as String,
                'data': data.length > 1 ? data[1] : null,
              });
            }
          } catch (e) {
            // Ignore invalid messages
          }
        },
        onError: (error) {
          relay.isConnected = false;
          controller.addError(NostrException('Relay error: $error'));
        },
        onDone: () {
          relay.isConnected = false;
          controller.close();
        },
      );

      return controller.stream;
    } catch (e) {
      throw NostrException('Failed to connect to relay: $e');
    }
  }

  /// Disconnects from a relay.
  /// 
  /// [relayUrl] - The URL of the relay to disconnect from.
  void disconnectRelay(String relayUrl) {
    final channel = _connections[relayUrl];
    if (channel != null) {
      channel.sink.close();
      _connections.remove(relayUrl);
    }

    final controller = _messageControllers[relayUrl];
    if (controller != null) {
      controller.close();
      _messageControllers.remove(relayUrl);
    }

    final relay = _relays.firstWhere((r) => r.url == relayUrl, orElse: () => NostrRelay.fromUrl(relayUrl));
    relay.isConnected = false;
  }

  /// Publishes an event to a relay.
  /// 
  /// [event] - The Nostr event to publish.
  /// [relayUrl] - The URL of the relay to publish to.
  /// 
  /// Returns a [Future] that completes when the event is published.
  /// 
  /// Throws [NostrException] if publishing fails.
  Future<void> publishEvent(NostrEvent event, String relayUrl) async {
    try {
      final channel = _connections[relayUrl];
      if (channel == null) {
        throw NostrException('Not connected to relay: $relayUrl');
      }

      // Send event in Nostr format: ["EVENT", <event_json>]
      final message = jsonEncode(['EVENT', event.toJson()]);
      channel.sink.add(message);
    } catch (e) {
      throw NostrException('Failed to publish event: $e');
    }
  }

  /// Publishes an event to all connected relays.
  /// 
  /// [event] - The Nostr event to publish.
  /// 
  /// Returns a map of relay URLs to success/failure status.
  Future<Map<String, bool>> publishEventToAllRelays(NostrEvent event) async {
    final results = <String, bool>{};

    for (final relay in _relays) {
      if (relay.isConnected) {
        try {
          await publishEvent(event, relay.url);
          results[relay.url] = true;
        } catch (e) {
          results[relay.url] = false;
        }
      } else {
        results[relay.url] = false;
      }
    }

    return results;
  }

  /// Syncs metadata by publishing an event with metadata content.
  /// 
  /// [metadata] - The metadata to sync (as a Map).
  /// [privateKey] - Private key for signing the event.
  /// [kind] - Event kind (default: 0 for metadata).
  /// 
  /// Returns the created and published event.
  /// 
  /// Throws [NostrException] if sync fails.
  Future<NostrEvent> syncMetadata({
    required Map<String, dynamic> metadata,
    required String privateKey,
    int kind = 0,
  }) async {
    try {
      // Create event with metadata as content
      final content = jsonEncode(metadata);
      final event = NostrEvent.create(
        content: content,
        kind: kind,
        privateKey: privateKey,
      );

      // Publish to all connected relays
      await publishEventToAllRelays(event);

      return event;
    } catch (e) {
      throw NostrException('Failed to sync metadata: $e');
    }
  }

  /// Closes all connections and cleans up resources.
  void dispose() {
    for (final relayUrl in _connections.keys.toList()) {
      disconnectRelay(relayUrl);
    }
    _relays.clear();
  }
}