import 'dart:convert';
import 'dart:async';
import 'package:flutter/services.dart';
import 'package:shared_preferences/shared_preferences.dart';
import '../game/models/level.dart';

class LevelService {
  static const String _progressKey = 'level_progress';
  static LevelService? _instance;
  static LevelService get instance => _instance ??= LevelService._();

  LevelService._();

  List<Level>? _levels;
  Map<int, LevelProgress>? _progress;

  /// Load all levels from JSON configuration
  Future<List<Level>> loadLevels() async {
    if (_levels != null) return _levels!;

    try {
      final String jsonString =
          await rootBundle.loadString('assets/levels/levels.json');
      final Map<String, dynamic> jsonData = json.decode(jsonString);

      _levels = (jsonData['levels'] as List)
          .map((levelJson) => Level.fromJson(levelJson))
          .toList();

      return _levels!;
    } catch (e) {
      throw Exception('Failed to load levels: $e');
    }
  }

  /// Get a specific level by ID
  Future<Level?> getLevel(int levelId) async {
    final levels = await loadLevels();
    try {
      return levels.firstWhere((level) => level.id == levelId);
    } catch (e) {
      return null;
    }
  }

  /// Load level progress from persistent storage
  Future<Map<int, LevelProgress>> loadProgress() async {
    if (_progress != null) return _progress!;

    try {
      final prefs = await SharedPreferences.getInstance();
      final String? progressJson = prefs.getString(_progressKey);

      if (progressJson != null) {
        final Map<String, dynamic> progressData = json.decode(progressJson);
        _progress = progressData.map(
          (key, value) => MapEntry(
            int.parse(key),
            LevelProgress.fromJson(value),
          ),
        );
      } else {
        // Initialize default progress - level 1 is unlocked
        _progress = {1: const LevelProgress(levelId: 1, unlocked: true)};
        await saveProgress();
      }

      return _progress!;
    } catch (e) {
      // Fallback to default progress
      _progress = {1: const LevelProgress(levelId: 1, unlocked: true)};
      return _progress!;
    }
  }

  /// Save level progress to persistent storage
  Future<void> saveProgress() async {
    if (_progress == null) return;

    try {
      final prefs = await SharedPreferences.getInstance();
      final Map<String, dynamic> progressData = _progress!.map(
        (key, value) => MapEntry(key.toString(), value.toJson()),
      );

      await prefs.setString(_progressKey, json.encode(progressData));
    } catch (e) {
      throw Exception('Failed to save progress: $e');
    }
  }

  /// Get progress for a specific level
  Future<LevelProgress> getLevelProgress(int levelId) async {
    final progress = await loadProgress();
    return progress[levelId] ?? LevelProgress(levelId: levelId);
  }

  /// Update progress for a specific level
  Future<void> updateLevelProgress(LevelProgress newProgress) async {
    final progress = await loadProgress();
    _progress![newProgress.levelId] = newProgress;

    // Auto-unlock next level if current level is completed
    if (newProgress.completed) {
      final nextLevelId = newProgress.levelId + 1;
      final levels = await loadLevels();

      // Check if next level exists
      if (levels.any((level) => level.id == nextLevelId)) {
        final nextProgress =
            progress[nextLevelId] ?? LevelProgress(levelId: nextLevelId);
        if (!nextProgress.unlocked) {
          _progress![nextLevelId] = nextProgress.copyWith(unlocked: true);
        }
      }
    }

    await saveProgress();
  }

  /// Get all levels with their current progress
  Future<List<LevelWithProgress>> getLevelsWithProgress() async {
    final levels = await loadLevels();
    final progress = await loadProgress();

    return levels.map((level) {
      final levelProgress =
          progress[level.id] ?? LevelProgress(levelId: level.id);
      return LevelWithProgress(level: level, progress: levelProgress);
    }).toList();
  }

  /// Calculate stars earned based on level performance
  int calculateStars(Level level, int score, int movesUsed, int timeUsed,
      Map<int, int> gemsCleared) {
    final criteria = level.starRating.criteria;
    final thresholds = level.starRating.thresholds;

    int value;
    switch (criteria) {
      case StarCriteria.SCORE:
        value = score;
        break;
      case StarCriteria.MOVES_REMAINING:
        value = (level.constraints.maxMoves ?? 0) - movesUsed;
        break;
      case StarCriteria.TIME_REMAINING:
        value = (level.constraints.timeLimit ?? 0) - timeUsed;
        break;
      case StarCriteria.EFFICIENCY:
        // For efficiency, we use score but consider objectives completion
        value = score;
        // Bonus for completing objectives
        if (_areObjectivesCompleted(level.objectives, gemsCleared)) {
          value += 500; // Bonus points for completing objectives
        }
        break;
      case StarCriteria.COMBINED:
        // Combined scoring considers multiple factors
        value = score;
        if (level.constraints.hasMoveLimit) {
          final movesRemaining = (level.constraints.maxMoves ?? 0) - movesUsed;
          value += movesRemaining * 50; // Bonus for efficient moves
        }
        if (_areObjectivesCompleted(level.objectives, gemsCleared)) {
          value += 500; // Bonus for completing objectives
        }
        break;
    }

    if (value >= thresholds.threeStar) return 3;
    if (value >= thresholds.twoStar) return 2;
    if (value >= thresholds.oneStar) return 1;
    return 0;
  }

  /// Check if level objectives are completed
  bool _areObjectivesCompleted(
      LevelObjectives objectives, Map<int, int> gemsCleared) {
    // If there are no objectives, they are considered completed
    if (!objectives.hasGemTypeObjectives) {
      return true;
    }
    
    for (final entry in objectives.clearGemTypes.entries) {
      final requiredCount = entry.value;
      final clearedCount = gemsCleared[entry.key] ?? 0;
      if (clearedCount < requiredCount) {
        return false;
      }
    }
    return true;
  }

  /// Check if level is completed (all constraints and objectives met)
  bool isLevelCompleted(Level level, int score, int moves, int timeUsed,
      Map<int, int> gemsCleared) {
    // Check score constraint
    if (level.constraints.hasScoreTarget &&
        score < level.constraints.targetScore!) {
      return false;
    }

    // Check move constraint
    if (level.constraints.hasMoveLimit && moves > level.constraints.maxMoves!) {
      return false;
    }

    // Check time constraint
    if (level.constraints.hasTimeLimit &&
        timeUsed > level.constraints.timeLimit!) {
      return false;
    }

    // Check objectives
    if (!_areObjectivesCompleted(level.objectives, gemsCleared)) {
      return false;
    }

    return true;
  }

  /// Check if level is failed (constraints violated but not completed)
  bool isLevelFailed(Level level, int score, int moves, int timeUsed,
      Map<int, int> gemsCleared) {
    // Failed if move limit exceeded and not completed
    if (level.constraints.hasMoveLimit &&
        moves >= level.constraints.maxMoves!) {
      return !isLevelCompleted(level, score, moves, timeUsed, gemsCleared);
    }

    // Failed if time limit exceeded and not completed
    if (level.constraints.hasTimeLimit &&
        timeUsed >= level.constraints.timeLimit!) {
      return !isLevelCompleted(level, score, moves, timeUsed, gemsCleared);
    }

    return false;
  }

  /// Reset all progress (for testing or new game)
  Future<void> resetProgress() async {
    _progress = {1: const LevelProgress(levelId: 1, unlocked: true)};
    await saveProgress();
  }
}

/// Helper class to combine level and progress data
class LevelWithProgress {
  final Level level;
  final LevelProgress progress;

  const LevelWithProgress({
    required this.level,
    required this.progress,
  });

  bool get isUnlocked => progress.unlocked || level.unlocked;
  bool get isCompleted => progress.completed;
  int get stars => progress.stars;
  int get bestScore => progress.bestScore;
}