import 'dart:math';
import '../models/deck.dart';
import '../models/question.dart';
import '../models/attempt.dart';
import '../models/attempt_result.dart';
import '../algorithms/weighted_selector.dart';
import 'deck_service.dart';

/// Service for managing attempt/quiz operations.
class AttemptService {
  final WeightedSelector _selector;

  /// Creates an attempt service with an optional random seed.
  AttemptService({int? seed}) : _selector = WeightedSelector(seed: seed);

  /// Creates a new attempt by selecting questions from the deck.
  ///
  /// Selects [attemptSize] questions (defaults to deck config default).
  /// Uses weighted random selection with no duplicates.
  /// Excludes known questions unless [DeckConfig.includeKnownInAttempts] is true.
  /// [includeKnown] can override the config setting for this attempt.
  Attempt createAttempt({
    required Deck deck,
    int? attemptSize,
    bool? includeKnown,
  }) {
    final size = attemptSize ?? deck.config.defaultAttemptSize;
    
    // Filter candidates based on includeKnownInAttempts setting
    // Use override parameter if provided, otherwise use config
    final shouldIncludeKnown = includeKnown ?? deck.config.includeKnownInAttempts;
    final candidates = shouldIncludeKnown
        ? deck.questions
        : deck.questions.where((q) => !q.isKnown).toList();
    
    final selected = _selector.selectQuestions(
      candidates: candidates,
      count: size,
      currentAttemptIndex: deck.currentAttemptIndex,
    );

    return Attempt(
      id: _generateAttemptId(),
      questions: selected,
      startTime: DateTime.now().millisecondsSinceEpoch,
    );
  }

  /// Processes an attempt result and updates the deck.
  ///
  /// [answers] is a map of questionId -> userAnswerIndex (for single answer) or questionId -> List<int> (for multiple answers).
  /// [manualOverrides] is an optional map of questionId -> bool (true if marked as needs practice).
  /// Returns the updated deck and attempt result.
  ({
    Deck updatedDeck,
    AttemptResult result,
  }) processAttempt({
    required Deck deck,
    required Attempt attempt,
    required Map<String, dynamic> answers,
    Map<String, bool>? manualOverrides,
    int? endTime,
  }) {
    final overrides = manualOverrides ?? {};
    final finishTime = endTime ?? DateTime.now().millisecondsSinceEpoch;
    final timeSpent = finishTime - attempt.startTime;

    final answerResults = <AnswerResult>[];
    final updatedQuestions = <Question>[];

    // Process each question in the attempt.
    // Use the deck's current question state (not the attempt snapshot) so that
    // manual "mark as known" during the attempt is preserved when applying results.
    for (final questionInAttempt in attempt.questions) {
      final currentQuestion = deck.questions
          .where((q) => q.id == questionInAttempt.id)
          .firstOrNull ?? questionInAttempt;

      final userAnswer = answers[currentQuestion.id];
      if (userAnswer == null) {
        // Question not answered, treat as incorrect
        continue;
      }

      // Handle both single answer (int) and multiple answers (List<int>)
      final List<int> userAnswerIndices;
      if (userAnswer is int) {
        userAnswerIndices = [userAnswer];
      } else if (userAnswer is List<int>) {
        userAnswerIndices = userAnswer;
      } else {
        // Invalid format, treat as incorrect
        continue;
      }

      // Check if answer is correct
      // For multiple correct answers: user must select all correct answers and no incorrect ones
      final correctIndices = currentQuestion.correctIndices;
      final userSet = userAnswerIndices.toSet();
      final correctSet = correctIndices.toSet();
      final isCorrect = userSet.length == correctSet.length &&
                       userSet.every((idx) => correctSet.contains(idx));
      final userMarkedNeedsPractice = overrides[currentQuestion.id] ?? false;

      // Determine status change (from current deck state)
      final oldIsKnown = currentQuestion.isKnown;
      final oldStreak = currentQuestion.consecutiveCorrect;

      // Update question from current deck state so manual marks are preserved
      final updated = userMarkedNeedsPractice
          ? DeckService.updateQuestionWithManualOverride(
              question: currentQuestion,
              isCorrect: isCorrect,
              userMarkedNeedsPractice: true,
              config: deck.config,
              currentAttemptIndex: deck.currentAttemptIndex,
            )
          : DeckService.updateQuestionAfterAnswer(
              question: currentQuestion,
              isCorrect: isCorrect,
              config: deck.config,
              currentAttemptIndex: deck.currentAttemptIndex,
            );

      // Determine status change
      QuestionStatusChange statusChange;
      if (userMarkedNeedsPractice) {
        statusChange = QuestionStatusChange.unchanged;
      } else if (isCorrect) {
        if (!oldIsKnown && updated.isKnown) {
          statusChange = QuestionStatusChange.improved;
        } else if (updated.consecutiveCorrect > oldStreak) {
          statusChange = QuestionStatusChange.improved;
        } else {
          statusChange = QuestionStatusChange.unchanged;
        }
      } else {
        if (oldIsKnown && !updated.isKnown) {
          statusChange = QuestionStatusChange.regressed;
        } else if (oldStreak > 0 && updated.consecutiveCorrect == 0) {
          statusChange = QuestionStatusChange.regressed;
        } else {
          statusChange = QuestionStatusChange.unchanged;
        }
      }

      answerResults.add(AnswerResult(
        question: updated,
        userAnswerIndices: userAnswerIndices,
        isCorrect: isCorrect,
        statusChange: statusChange,
      ));

      updatedQuestions.add(updated);
    }

    // Update deck with new question states
    final questionMap = Map.fromEntries(
      deck.questions.map((q) => MapEntry(q.id, q)),
    );

    for (final updated in updatedQuestions) {
      questionMap[updated.id] = updated;
    }

    final allUpdatedQuestions = deck.questions.map((q) {
      return questionMap[q.id] ?? q;
    }).toList();

    final updatedDeck = deck.copyWith(
      questions: allUpdatedQuestions,
      currentAttemptIndex: deck.currentAttemptIndex + 1,
    );

    final result = AttemptResult.fromAnswers(
      results: answerResults,
      timeSpent: timeSpent,
    );

    return (
      updatedDeck: updatedDeck,
      result: result,
    );
  }

  /// Generates a unique attempt ID.
  String _generateAttemptId() {
    return 'attempt_${DateTime.now().millisecondsSinceEpoch}_${Random().nextInt(10000)}';
  }
}