import 'dart:async';
import 'dart:collection';

import 'package:injectable/injectable.dart';
import 'package:isar/isar.dart';
import 'package:mnemo_cards_common_backend/mnemo_cards_common_backend.dart';

/// Service for tracking and managing user study sessions
///
/// Automatically creates, updates, and manages study sessions based on user activity.
/// Sessions are created when users start studying and are ended based on inactivity timeouts.
@lazySingleton
class SessionTracker {
  final Isar _isar;

  /// Active sessions cache: userId -> sessionId
  final Map<int, String> _activeSessions = {};

  /// Session timers for automatic timeout: sessionId -> timer
  final Map<String, Timer> _sessionTimers = {};

  /// Session timeout duration (30 minutes by default)
  static const Duration _sessionTimeout = Duration(minutes: 30);

  SessionTracker(this._isar);

  /// Get or create an active session for a user
  ///
  /// Returns the session ID of the active session.
  /// If no active session exists, creates a new one.
  Future<String> getOrCreateSession(int userId, {
    String? packId,
    String? testId,
  }) async {
    // Check if user already has an active session
    if (_activeSessions.containsKey(userId)) {
      final sessionId = _activeSessions[userId]!;

      // Reset timeout timer
      _resetSessionTimer(sessionId);

      // Update session activity
      await _updateSessionActivity(sessionId);

      return sessionId;
    }

    // Create new session
    final sessionId = _generateSessionId();
    final session = StudySessionModel(
      sessionId: sessionId,
      userId: userId,
      startTime: DateTime.now(),
      packId: packId,
      testId: testId,
    );

    // Save to database
    await _isar.writeTxn(() async {
      await _isar.studySessionModels.put(session);
    });

    // Track as active
    _activeSessions[userId] = sessionId;
    _resetSessionTimer(sessionId);

    return sessionId;
  }

  /// Update session with progress data
  ///
  /// Called when user completes a test or makes progress.
  Future<void> updateSessionProgress(
    String sessionId, {
    int wordsLearned = 0,
    int testsCompleted = 0,
    double? accuracy,
  }) async {
    final session = await _isar.studySessionModels
        .filter()
        .sessionIdEqualTo(sessionId)
        .findFirst();

    if (session == null || !session.isActive) return;

    // Update session with new progress
    final updatedSession = session.addProgress(
      wordsLearned: wordsLearned,
      testsCompleted: testsCompleted,
      accuracy: accuracy,
    );

    await _isar.writeTxn(() async {
      await _isar.studySessionModels.put(updatedSession);
    });

    // Reset timeout timer
    _resetSessionTimer(sessionId);
  }

  /// End a session manually with final statistics
  ///
  /// Called when user explicitly ends a session or when session times out.
  Future<void> endSession(
    String sessionId, {
    int wordsLearned = 0,
    int testsCompleted = 0,
    double accuracy = 0.0,
  }) async {
    final session = await _isar.studySessionModels
        .filter()
        .sessionIdEqualTo(sessionId)
        .findFirst();

    if (session == null || !session.isActive) return;

    // End session with final statistics
    final endedSession = session.end(
      wordsLearned: wordsLearned,
      testsCompleted: testsCompleted,
      accuracy: accuracy,
    );

    await _isar.writeTxn(() async {
      await _isar.studySessionModels.put(endedSession);
    });

    // Clean up tracking
    final userId = session.userId;
    _activeSessions.remove(userId);
    _cancelSessionTimer(sessionId);
  }

  /// End session for a specific user
  Future<void> endUserSession(int userId) async {
    final sessionId = _activeSessions[userId];
    if (sessionId != null) {
      await endSession(sessionId);
    }
  }

  /// Get active session for a user
  Future<StudySessionModel?> getActiveSession(int userId) async {
    final sessionId = _activeSessions[userId];
    if (sessionId == null) return null;

    return await _isar.studySessionModels
        .filter()
        .sessionIdEqualTo(sessionId)
        .findFirst();
  }

  /// Get recent sessions for a user
  Future<List<StudySessionModel>> getRecentSessions(
    int userId, {
    int limit = 10,
  }) async {
    return await _isar.studySessionModels
        .filter()
        .userIdEqualTo(userId)
        .sortByStartTimeDesc()
        .limit(limit)
        .findAll();
  }

  /// Clean up expired sessions
  ///
  /// Should be called periodically (e.g., via cron job)
  Future<void> cleanupExpiredSessions() async {
    final cutoffTime = DateTime.now().subtract(_sessionTimeout);

    // Find sessions that should have expired but are still marked as active
    final expiredSessions = await _isar.studySessionModels
        .filter()
        .endTimeIsNull()
        .startTimeLessThan(cutoffTime)
        .findAll();

    for (final session in expiredSessions) {
      await endSession(session.sessionId!);
    }
  }

  /// Get session statistics for a user over a time period
  Future<Map<String, dynamic>> getSessionStatistics(
    int userId, {
    DateTime? from,
    DateTime? to,
  }) async {
    final query = _isar.studySessionModels.filter().userIdEqualTo(userId);

    if (from != null) {
      query.startTimeGreaterThan(from);
    }
    if (to != null) {
      query.startTimeLessThan(to);
    }

    final sessions = await query.findAll();

    if (sessions.isEmpty) {
      return {
        'totalSessions': 0,
        'totalDurationMinutes': 0,
        'totalWordsLearned': 0,
        'totalTestsCompleted': 0,
        'averageAccuracy': 0.0,
        'averageSessionLength': 0.0,
      };
    }

    final completedSessions = sessions.where((s) => !s.isActive).toList();
    final totalDuration = completedSessions.fold<int>(
      0,
      (sum, session) => sum + session.durationMinutes,
    );
    final totalWordsLearned = completedSessions.fold<int>(
      0,
      (sum, session) => sum + session.wordsLearned,
    );
    final totalTestsCompleted = completedSessions.fold<int>(
      0,
      (sum, session) => sum + session.testsCompleted,
    );
    final averageAccuracy = completedSessions.isEmpty
        ? 0.0
        : completedSessions.fold<double>(
              0,
              (sum, session) => sum + session.accuracy,
            ) /
            completedSessions.length;

    return {
      'totalSessions': sessions.length,
      'completedSessions': completedSessions.length,
      'totalDurationMinutes': totalDuration,
      'totalWordsLearned': totalWordsLearned,
      'totalTestsCompleted': totalTestsCompleted,
      'averageAccuracy': averageAccuracy,
      'averageSessionLength': completedSessions.isEmpty
          ? 0.0
          : totalDuration / completedSessions.length,
    };
  }

  /// Generate a unique session ID
  String _generateSessionId() {
    final timestamp = DateTime.now().millisecondsSinceEpoch;
    final random = DateTime.now().microsecondsSinceEpoch % 10000;
    return 'session_${timestamp}_$random';
  }

  /// Reset the timeout timer for a session
  void _resetSessionTimer(String sessionId) {
    _cancelSessionTimer(sessionId);

    _sessionTimers[sessionId] = Timer(_sessionTimeout, () {
      // Session timed out - end it
      endSession(sessionId);
    });
  }

  /// Cancel the timeout timer for a session
  void _cancelSessionTimer(String sessionId) {
    final timer = _sessionTimers.remove(sessionId);
    timer?.cancel();
  }

  /// Update session last activity time
  Future<void> _updateSessionActivity(String sessionId) async {
    // For now, we just reset the timer
    // In the future, we could track last activity timestamps
  }

  /// Dispose of all timers (for cleanup)
  void dispose() {
    for (final timer in _sessionTimers.values) {
      timer.cancel();
    }
    _sessionTimers.clear();
    _activeSessions.clear();
  }
}