package com.personalproject.service;

import com.personalproject.generator.QuestionGenerator;
import com.personalproject.model.DifficultyLevel;
import java.security.SecureRandom;
import java.util.ArrayList;
import java.util.EnumMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Random;
import java.util.Set;

/**
 * 负责批量生成题目并避免与历史题库重复.
 */
public final class QuestionGenerationService {

  private static final int MAX_ATTEMPTS = 10_000;
  private final Map<DifficultyLevel, QuestionGenerator> generators;
  private final Random random = new SecureRandom();

  /**
   * 构造函数：复制难度与生成器的映射，保留内部安全副本.
   *
   * @param generatorMap 难度到题目生成器的外部映射.
   */
  public QuestionGenerationService(Map<DifficultyLevel, QuestionGenerator> generatorMap) {
    generators = new EnumMap<>(DifficultyLevel.class);
    generators.putAll(generatorMap);
  }

  /**
   * 根据指定难度批量生成不与历史题目重复的新题目.
   *
   * @param level             目标题目难度.
   * @param count             需要生成的题目数量.
   * @param existingQuestions 已存在的题目集合，用于查重.
   * @return 生成的题目列表.
   * @throws IllegalArgumentException 当难度未配置时抛出.
   * @throws IllegalStateException    当达到最大尝试次数仍无法生成足够题目时抛出.
   */
  public List<String> generateUniqueQuestions(
      DifficultyLevel level, int count, Set<String> existingQuestions) {
    QuestionGenerator generator = generators.get(level);
    if (generator == null) {
      throw new IllegalArgumentException("Unsupported difficulty level: " + level);
    }
    Set<String> produced = new HashSet<>();
    List<String> results = new ArrayList<>();
    int attempts = 0;
    while (results.size() < count) {
      if (attempts >= MAX_ATTEMPTS) {
        throw new IllegalStateException("Unable to generate enough unique questions.");
      }
      attempts++;
      String question = generator.generateQuestion(random).trim();
      if (question.isEmpty()) {
        continue;
      }
      if (existingQuestions.contains(question)) {
        continue;
      }
      if (!produced.add(question)) {
        continue;
      }
      results.add(question);
    }
    return results;
  }
}