import 'dart:io';
import 'package:flutter/foundation.dart';
import 'package:path/path.dart' as path;
import 'package:path_provider/path_provider.dart';
import '../local/local_storage_service.dart';
import '../sync/sync_engine.dart';
import '../firebase/firebase_service.dart';
import '../nostr/nostr_service.dart';
import '../nostr/models/nostr_keypair.dart';
import '../nostr/models/nostr_profile.dart';
import 'models/user.dart';

/// Exception thrown when session operations fail.
class SessionException implements Exception {
  /// Error message.
  final String message;

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

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

/// Service for managing user sessions, login, logout, and session isolation.
/// 
/// This service provides:
/// - User login and logout
/// - Session switching between multiple users
/// - Data isolation per user session
/// - Cache clearing on logout
/// - Integration with local storage and sync engine
/// 
/// The service is modular and UI-independent, designed for offline-first behavior.
class SessionService {
  /// Current active user session (null if no user is logged in).
  User? _currentUser;

  /// Local storage service for data persistence.
  final LocalStorageService _localStorage;

  /// Sync engine for coordinating sync operations (optional).
  final SyncEngine? _syncEngine;

  /// Firebase service for optional cloud sync (optional).
  final FirebaseService? _firebaseService;

  /// Nostr service for Nostr authentication (optional).
  final NostrService? _nostrService;

  /// Map of user IDs to their session storage paths.
  final Map<String, String> _userDbPaths = {};

  /// Map of user IDs to their cache directories.
  final Map<String, Directory> _userCacheDirs = {};

  /// Optional test database path for testing.
  final String? _testDbPath;

  /// Optional test cache directory for testing.
  final Directory? _testCacheDir;

  /// Creates a [SessionService] instance.
  /// 
  /// [localStorage] - Local storage service for data persistence.
  /// [syncEngine] - Optional sync engine for coordinating sync operations.
  /// [firebaseService] - Optional Firebase service for cloud sync.
  /// [nostrService] - Optional Nostr service for Nostr authentication.
  /// [testDbPath] - Optional database path for testing.
  /// [testCacheDir] - Optional cache directory for testing.
  SessionService({
    required LocalStorageService localStorage,
    SyncEngine? syncEngine,
    FirebaseService? firebaseService,
    NostrService? nostrService,
    String? testDbPath,
    Directory? testCacheDir,
  })  : _localStorage = localStorage,
        _syncEngine = syncEngine,
        _firebaseService = firebaseService,
        _nostrService = nostrService,
        _testDbPath = testDbPath,
        _testCacheDir = testCacheDir;

  /// Gets the current active user session.
  /// 
  /// Returns the current [User] if logged in, null otherwise.
  User? get currentUser => _currentUser;

  /// Checks if a user is currently logged in.
  bool get isLoggedIn => _currentUser != null;

  /// Logs in a user and creates an isolated session.
  /// 
  /// [id] - Unique identifier for the user.
  /// [username] - Display name or username.
  /// [token] - Optional authentication token.
  /// 
  /// Returns the logged-in [User].
  /// 
  /// Throws [SessionException] if login fails or if user is already logged in.
  Future<User> login({
    required String id,
    required String username,
    String? token,
  }) async {
    if (_currentUser != null) {
      throw SessionException('User already logged in. Logout first.');
    }

    try {
      final user = User(
        id: id,
        username: username,
        token: token,
      );

      // Create user-specific storage paths
      await _setupUserStorage(user);

      // Sync with Firebase if enabled
      if (_firebaseService != null && _firebaseService!.isEnabled) {
        try {
          await _firebaseService!.syncItemsFromFirestore(user.id);
        } catch (e) {
          // Log error but don't fail login - offline-first behavior
          debugPrint('Warning: Failed to sync from Firebase on login: $e');
        }
      }

      // Set as current user
      _currentUser = user;

      return user;
    } catch (e) {
      throw SessionException('Failed to login: $e');
    }
  }

  /// Logs in a user using Nostr key (nsec or npub).
  /// 
  /// [nsecOrNpub] - Nostr key in nsec (private) or npub (public) format.
  /// 
  /// Returns the logged-in [User] with fetched profile data.
  /// 
  /// Throws [SessionException] if login fails or if user is already logged in.
  Future<User> loginWithNostr(String nsecOrNpub) async {
    if (_currentUser != null) {
      throw SessionException('User already logged in. Logout first.');
    }

    if (_nostrService == null) {
      throw SessionException('Nostr service not available');
    }

    try {
      // Parse the key
      NostrKeyPair keyPair;
      String? storedPrivateKey;
      if (nsecOrNpub.startsWith('nsec')) {
        keyPair = NostrKeyPair.fromNsec(nsecOrNpub);
        // Store the nsec for event publishing
        storedPrivateKey = nsecOrNpub;
      } else if (nsecOrNpub.startsWith('npub')) {
        keyPair = NostrKeyPair.fromNpub(nsecOrNpub);
        // No private key available when using npub
        storedPrivateKey = null;
      } else {
        throw SessionException('Invalid Nostr key format. Expected nsec or npub.');
      }

      // Fetch profile from relays
      NostrProfile? profile;
      try {
        profile = await _nostrService!.fetchProfile(keyPair.publicKey);
      } catch (e) {
        debugPrint('Warning: Failed to fetch Nostr profile: $e');
        // Continue without profile - offline-first behavior
      }

      // Create user with Nostr profile and private key (if available)
      final user = User(
        id: keyPair.publicKey,
        username: profile?.displayName ?? keyPair.publicKey.substring(0, 16),
        nostrProfile: profile,
        nostrPrivateKey: storedPrivateKey,
      );

      // Create user-specific storage paths
      await _setupUserStorage(user);

      // Sync with Firebase if enabled
      if (_firebaseService != null && _firebaseService!.isEnabled) {
        try {
          await _firebaseService!.syncItemsFromFirestore(user.id);
        } catch (e) {
          // Log error but don't fail login - offline-first behavior
          debugPrint('Warning: Failed to sync from Firebase on login: $e');
        }
      }

      // Set as current user
      _currentUser = user;

      // Load preferred relays from NIP-05 if available
      await _loadPreferredRelaysIfAvailable();

      return user;
    } catch (e) {
      throw SessionException('Failed to login with Nostr: $e');
    }
  }

  /// Logs out the current user and clears session data.
  /// 
  /// [clearCache] - Whether to clear cached data (default: true).
  /// 
  /// Throws [SessionException] if logout fails or if no user is logged in.
  Future<void> logout({bool clearCache = true}) async {
    if (_currentUser == null) {
      throw SessionException('No user logged in.');
    }

    try {
      final userId = _currentUser!.id;

      // Sync to Firebase before logout if enabled
      if (_firebaseService != null && _firebaseService!.isEnabled) {
        try {
          await _firebaseService!.syncItemsToFirestore(userId);
        } catch (e) {
          // Log error but don't fail logout - offline-first behavior
          debugPrint('Warning: Failed to sync to Firebase on logout: $e');
        }
      }

      // Clear user-specific data if requested
      if (clearCache) {
        await _clearUserData(userId);
      }

      // Clear current user
      _currentUser = null;

      // Clean up user storage references
      _userDbPaths.remove(userId);
      _userCacheDirs.remove(userId);
    } catch (e) {
      throw SessionException('Failed to logout: $e');
    }
  }

  /// Switches to a different user session.
  /// 
  /// This method logs out the current user and logs in the new user.
  /// 
  /// [id] - Unique identifier for the new user.
  /// [username] - Display name or username for the new user.
  /// [token] - Optional authentication token for the new user.
  /// [clearCache] - Whether to clear cached data for the previous user (default: true).
  /// 
  /// Returns the new logged-in [User].
  /// 
  /// Throws [SessionException] if switch fails.
  Future<User> switchSession({
    required String id,
    required String username,
    String? token,
    bool clearCache = true,
  }) async {
    if (_currentUser != null) {
      await logout(clearCache: clearCache);
    }

    return await login(
      id: id,
      username: username,
      token: token,
    );
  }

  /// Sets up user-specific storage paths and reinitializes local storage.
  /// 
  /// [user] - The user to set up storage for.
  Future<void> _setupUserStorage(User user) async {
    try {
      // Get user-specific database path
      // In test mode, create per-user paths under the test directory
      // In production, create per-user paths under app documents
      String dbPath;
      if (_testDbPath != null) {
        // Create user-specific path under test directory
        final testDir = path.dirname(_testDbPath!);
        dbPath = path.join(testDir, 'user_${user.id}_storage.db');
      } else {
        final appDir = await getApplicationDocumentsDirectory();
        dbPath = path.join(appDir.path, 'users', user.id, 'storage.db');
      }
      _userDbPaths[user.id] = dbPath;

      // Get user-specific cache directory
      Directory cacheDir;
      if (_testCacheDir != null) {
        // Create user-specific cache under test directory
        final testCacheParent = _testCacheDir!.path;
        cacheDir = Directory(path.join(testCacheParent, 'user_${user.id}'));
      } else {
        final appDir = await getApplicationDocumentsDirectory();
        cacheDir = Directory(path.join(appDir.path, 'users', user.id, 'cache'));
      }
      
      if (!await cacheDir.exists()) {
        await cacheDir.create(recursive: true);
      }
      _userCacheDirs[user.id] = cacheDir;

      // Reinitialize local storage with user-specific paths
      await _localStorage.reinitializeForSession(
        newDbPath: dbPath,
        newCacheDir: cacheDir,
      );
    } catch (e) {
      throw SessionException('Failed to setup user storage: $e');
    }
  }

  /// Clears all data for a specific user.
  /// 
  /// [userId] - The ID of the user whose data should be cleared.
  Future<void> _clearUserData(String userId) async {
    try {
      // Clear all data from local storage if it's the current user's storage
      if (_currentUser?.id == userId) {
        await _localStorage.clearAllData();
      }

      // Clear cache directory
      final cacheDir = _userCacheDirs[userId];
      if (cacheDir != null && await cacheDir.exists()) {
        await cacheDir.delete(recursive: true);
      }

      // Clear database path reference
      _userDbPaths.remove(userId);
      _userCacheDirs.remove(userId);

      // Notify sync engine if available
      if (_syncEngine != null) {
        // Sync engine will handle session cleanup internally
        // This is a placeholder for future sync engine integration
      }
    } catch (e) {
      throw SessionException('Failed to clear user data: $e');
    }
  }

  /// Gets the database path for the current user.
  /// 
  /// Returns the database path if user is logged in, null otherwise.
  String? getCurrentUserDbPath() {
    if (_currentUser == null) return null;
    return _userDbPaths[_currentUser!.id];
  }

  /// Gets the cache directory for the current user.
  /// 
  /// Returns the cache directory if user is logged in, null otherwise.
  Directory? getCurrentUserCacheDir() {
    if (_currentUser == null) return null;
    return _userCacheDirs[_currentUser!.id];
  }

  /// Loads preferred relays from NIP-05 if the current user has an active nip05.
  /// 
  /// This method checks if the logged-in user has a nip05 identifier and,
  /// if so, fetches preferred relays from the NIP-05 verification endpoint
  /// and adds them to the Nostr service relay list.
  /// 
  /// This is called automatically after Nostr login, but can also be called
  /// manually to refresh preferred relays.
  Future<void> loadPreferredRelaysIfAvailable() async {
    await _loadPreferredRelaysIfAvailable();
  }

  /// Refreshes the current user's Nostr profile and preferred relays.
  /// 
  /// Re-fetches the profile from relays and reloads preferred relays from NIP-05.
  /// 
  /// Throws [SessionException] if refresh fails or if no user is logged in.
  Future<void> refreshNostrProfile() async {
    if (_currentUser == null) {
      throw SessionException('No user logged in.');
    }

    if (_nostrService == null) {
      throw SessionException('Nostr service not available');
    }

    // Only refresh if user has Nostr profile (logged in with Nostr)
    if (_currentUser!.nostrProfile == null && _currentUser!.nostrPrivateKey == null) {
      throw SessionException('User is not logged in with Nostr');
    }

    try {
      // Re-fetch profile from relays
      NostrProfile? profile;
      try {
        profile = await _nostrService!.fetchProfile(_currentUser!.id);
      } catch (e) {
        debugPrint('Warning: Failed to refresh Nostr profile: $e');
        // Continue without profile update - offline-first behavior
      }

      // Update user with refreshed profile
      if (profile != null) {
        _currentUser = _currentUser!.copyWith(nostrProfile: profile);
      }

      // Reload preferred relays from NIP-05 if available
      await _loadPreferredRelaysIfAvailable();
    } catch (e) {
      if (e is SessionException) {
        rethrow;
      }
      throw SessionException('Failed to refresh Nostr profile: $e');
    }
  }

  /// Internal method to load preferred relays from NIP-05 if available.
  Future<void> _loadPreferredRelaysIfAvailable() async {
    if (_currentUser == null || _nostrService == null) {
      return;
    }

    final profile = _currentUser!.nostrProfile;
    if (profile == null || profile.nip05 == null || profile.nip05!.isEmpty) {
      return;
    }

    try {
      final nip05 = profile.nip05!;
      final publicKey = _currentUser!.id; // User ID is the public key for Nostr users

      final addedCount = await _nostrService!.loadPreferredRelaysFromNip05(
        nip05,
        publicKey,
      );

      if (addedCount > 0) {
        debugPrint('Loaded $addedCount preferred relay(s) from NIP-05: $nip05');
      }
    } catch (e) {
      // Log error but don't fail - offline-first behavior
      debugPrint('Warning: Failed to load preferred relays from NIP-05: $e');
    }
  }
}