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

import 'dart:async';
import 'dart:convert';
import 'package:flutter/foundation.dart';
import 'package:web_socket_channel/web_socket_channel.dart';
import 'package:nostr_tools/nostr_tools.dart';
import 'package:http/http.dart' as http;
import 'models/nostr_keypair.dart';
import 'models/nostr_event.dart';
import 'models/nostr_relay.dart';
import 'models/nostr_profile.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);
  }

  /// Enables or disables a relay.
  /// 
  /// [relayUrl] - The URL of the relay to enable/disable.
  /// [enabled] - Whether the relay should be enabled.
  void setRelayEnabled(String relayUrl, bool enabled) {
    final relay = _relays.firstWhere(
      (r) => r.url == relayUrl,
      orElse: () => throw NostrException('Relay not found: $relayUrl'),
    );
    relay.isEnabled = enabled;
    
    // If disabling, also disconnect
    if (!enabled && relay.isConnected) {
      disconnectRelay(relayUrl);
    }
  }

  /// Toggles all relays enabled/disabled.
  /// 
  /// [enabled] - Whether all relays should be enabled.
  void setAllRelaysEnabled(bool enabled) {
    for (final relay in _relays) {
      relay.isEnabled = enabled;
      if (!enabled && relay.isConnected) {
        disconnectRelay(relay.url);
      }
    }
  }

  /// 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 {
      // Check if relay is enabled
      final relay = _relays.firstWhere(
        (r) => r.url == relayUrl,
        orElse: () => NostrRelay.fromUrl(relayUrl),
      );
      if (!relay.isEnabled) {
        throw NostrException('Relay is disabled: $relayUrl');
      }

      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>>.broadcast();
      _messageControllers[relayUrl] = controller;

      // Update relay status (relay already found above)
      relay.isConnected = true;

      // Listen for messages
      channel.stream.listen(
        (message) {
          try {
            final data = jsonDecode(message as String);
            if (data is List && data.isNotEmpty) {
              final messageType = data[0] as String;
              if (messageType == 'EVENT' && data.length >= 3) {
                // EVENT format: ["EVENT", <subscription_id>, <event_json>]
                // event_json can be either a JSON object or array format
                final eventData = data[2];
                controller.add({
                  'type': 'EVENT',
                  'subscription_id': data[1],
                  'data': eventData,
                });
              } else if (messageType == 'EOSE' && data.length >= 2) {
                // EOSE format: ["EOSE", <subscription_id>]
                controller.add({
                  'type': 'EOSE',
                  'subscription_id': data[1],
                  'data': null,
                });
              } else {
                // Other message types
                controller.add({
                  'type': messageType,
                  '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');
      }

      // Convert to nostr_tools Event and then to JSON
      final nostrToolsEvent = event.toNostrToolsEvent();
      final eventJson = nostrToolsEvent.toJson();
      
      // Send event in Nostr format: ["EVENT", <event_json>]
      final message = jsonEncode(['EVENT', eventJson]);
      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');
    }
  }

  /// Fetches user profile (kind 0 metadata event) from relays.
  /// 
  /// [publicKey] - The public key (hex format) of the user.
  /// [timeout] - Timeout for the request (default: 10 seconds).
  /// 
  /// Returns [NostrProfile] if found, null otherwise.
  /// 
  /// Throws [NostrException] if fetch fails.
  Future<NostrProfile?> fetchProfile(String publicKey, {Duration timeout = const Duration(seconds: 10)}) async {
    if (_relays.isEmpty) {
      throw NostrException('No relays configured');
    }

    // Try to fetch from connected relays first
    for (final relay in _relays) {
      if (relay.isConnected) {
        try {
          final profile = await _fetchProfileFromRelay(publicKey, relay.url, timeout);
          if (profile != null) {
            return profile;
          }
        } catch (e) {
          // Continue to next relay
          continue;
        }
      }
    }

    // If no connected relays or all failed, try connecting to first relay
    if (_relays.isNotEmpty) {
      try {
        final firstRelay = _relays.first;
        if (!firstRelay.isConnected) {
          await connectRelay(firstRelay.url).timeout(timeout);
        }
        return await _fetchProfileFromRelay(publicKey, firstRelay.url, timeout);
      } catch (e) {
        throw NostrException('Failed to fetch profile: $e');
      }
    }

    return null;
  }

  /// Fetches profile from a specific relay.
  Future<NostrProfile?> _fetchProfileFromRelay(String publicKey, String relayUrl, Duration timeout) async {
    final channel = _connections[relayUrl];
    final messageController = _messageControllers[relayUrl];
    if (channel == null || messageController == null) {
      return null;
    }

    // Send REQ message to request kind 0 events for this public key
    // Nostr REQ format: ["REQ", <subscription_id>, <filters>]
    final reqId = 'profile_${DateTime.now().millisecondsSinceEpoch}';
    
    final completer = Completer<NostrProfile?>();
    final subscription = messageController.stream.listen(
      (message) {
        // Message format from connectRelay: 
        // {'type': 'EVENT', 'subscription_id': <id>, 'data': <event_json>}
        // or {'type': 'EOSE', 'subscription_id': <id>, 'data': null}
        if (message['type'] == 'EVENT' && 
            message['subscription_id'] == reqId &&
            message['data'] != null) {
          try {
            final eventData = message['data'];
            Event nostrToolsEvent;
            
            // Handle both JSON object and array formats
            if (eventData is Map<String, dynamic>) {
              // JSON object format
              nostrToolsEvent = Event(
                id: eventData['id'] as String? ?? '',
                pubkey: eventData['pubkey'] as String? ?? '',
                created_at: eventData['created_at'] as int? ?? 0,
                kind: eventData['kind'] as int? ?? 0,
                tags: (eventData['tags'] as List<dynamic>?)
                    ?.map((tag) => (tag as List<dynamic>).map((e) => e.toString()).toList())
                    .toList() ?? [],
                content: eventData['content'] as String? ?? '',
                sig: eventData['sig'] as String? ?? '',
                verify: false, // Skip verification for profile fetching
              );
            } else if (eventData is List && eventData.length >= 7) {
              // Array format: [id, pubkey, created_at, kind, tags, content, sig]
              nostrToolsEvent = Event(
                id: eventData[0] as String? ?? '',
                pubkey: eventData[1] as String? ?? '',
                created_at: eventData[2] as int? ?? 0,
                kind: eventData[3] as int? ?? 0,
                tags: (eventData[4] as List<dynamic>?)
                    ?.map((tag) => (tag as List<dynamic>).map((e) => e.toString()).toList())
                    .toList() ?? [],
                content: eventData[5] as String? ?? '',
                sig: eventData[6] as String? ?? '',
                verify: false, // Skip verification for profile fetching
              );
            } else {
              return; // Invalid format
            }
            
            // Convert to our NostrEvent model
            final event = NostrEvent.fromNostrToolsEvent(nostrToolsEvent);
            
            // Check if it's a kind 0 (metadata) event for this public key
            if (event.kind == 0 && event.pubkey.toLowerCase() == publicKey.toLowerCase()) {
              final profile = NostrProfile.fromEventContent(
                publicKey: publicKey,
                content: event.content,
                updatedAt: DateTime.fromMillisecondsSinceEpoch(event.createdAt * 1000),
              );
              if (!completer.isCompleted) {
                completer.complete(profile);
              }
            }
          } catch (e) {
            // Ignore parsing errors
            debugPrint('Error parsing profile event: $e');
          }
        } else if (message['type'] == 'EOSE' && 
                   message['subscription_id'] == reqId) {
          // End of stored events - no profile found
          if (!completer.isCompleted) {
            completer.complete(null);
          }
        }
      },
      onError: (error) {
        if (!completer.isCompleted) {
          completer.completeError(error);
        }
      },
    );

    // Send REQ message to request kind 0 events for this public key
    final reqMessage = jsonEncode([
      'REQ',
      reqId,
      {
        'authors': [publicKey],
        'kinds': [0],
        'limit': 1,
      }
    ]);
    
    channel.sink.add(reqMessage);

    try {
      final profile = await completer.future.timeout(timeout);
      subscription?.cancel();
      return profile;
    } catch (e) {
      subscription?.cancel();
      return null;
    }
  }

  /// Fetches preferred relays from a NIP-05 identifier.
  /// 
  /// NIP-05 verification endpoint format: https://<domain>/.well-known/nostr.json?name=<local-part>
  /// The response can include relay hints in the format:
  /// {
  ///   "names": { "<local-part>": "<hex-pubkey>" },
  ///   "relays": { "<hex-pubkey>": ["wss://relay1.com", "wss://relay2.com"] }
  /// }
  /// 
  /// [nip05] - The NIP-05 identifier (e.g., 'user@domain.com').
  /// [publicKey] - The public key (hex format) to match against relay hints.
  /// 
  /// Returns a list of preferred relay URLs, or empty list if none found.
  /// 
  /// Throws [NostrException] if fetch fails.
  Future<List<String>> fetchPreferredRelaysFromNip05(
    String nip05,
    String publicKey,
  ) async {
    try {
      // Parse NIP-05 identifier (format: local-part@domain)
      final parts = nip05.split('@');
      if (parts.length != 2) {
        throw NostrException('Invalid NIP-05 format: $nip05');
      }

      final localPart = parts[0];
      final domain = parts[1];

      // Construct the verification URL
      final url = Uri.https(domain, '/.well-known/nostr.json', {'name': localPart});

      // Fetch the NIP-05 verification data
      final response = await http.get(url).timeout(
        const Duration(seconds: 10),
        onTimeout: () {
          throw NostrException('Timeout fetching NIP-05 data');
        },
      );

      if (response.statusCode != 200) {
        throw NostrException('Failed to fetch NIP-05 data: ${response.statusCode}');
      }

      // Parse the JSON response
      final data = jsonDecode(response.body) as Map<String, dynamic>;

      // Extract relay hints for the public key
      final relays = data['relays'] as Map<String, dynamic>?;
      if (relays == null) {
        return [];
      }

      // Find relays for the matching public key (case-insensitive)
      final publicKeyLower = publicKey.toLowerCase();
      for (final entry in relays.entries) {
        final keyLower = entry.key.toLowerCase();
        if (keyLower == publicKeyLower) {
          final relayList = entry.value;
          if (relayList is List) {
            return relayList
                .map((r) => r.toString())
                .where((r) => r.isNotEmpty)
                .toList();
          }
        }
      }

      return [];
    } catch (e) {
      if (e is NostrException) {
        rethrow;
      }
      throw NostrException('Failed to fetch preferred relays from NIP-05: $e');
    }
  }

  /// Loads preferred relays from NIP-05 if available and adds them to the relay list.
  /// 
  /// [nip05] - The NIP-05 identifier (e.g., 'user@domain.com').
  /// [publicKey] - The public key (hex format) to match against relay hints.
  /// 
  /// Returns the number of relays added.
  /// 
  /// Throws [NostrException] if fetch fails.
  Future<int> loadPreferredRelaysFromNip05(
    String nip05,
    String publicKey,
  ) async {
    try {
      final preferredRelays = await fetchPreferredRelaysFromNip05(nip05, publicKey);
      
      int addedCount = 0;
      for (final relayUrl in preferredRelays) {
        try {
          addRelay(relayUrl);
          addedCount++;
        } catch (e) {
          // Skip invalid relay URLs
          debugPrint('Warning: Invalid relay URL from NIP-05: $relayUrl');
        }
      }

      return addedCount;
    } catch (e) {
      if (e is NostrException) {
        rethrow;
      }
      throw NostrException('Failed to load preferred relays from NIP-05: $e');
    }
  }

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