math-learing/src/main/java/com/personalproject/service/ExamService.java

package com.personalproject.service;

import com.personalproject.generator.QuestionGenerator;
import com.personalproject.model.DifficultyLevel;
import com.personalproject.model.ExamSession;
import com.personalproject.model.QuizQuestion;
import com.personalproject.storage.QuestionStorageService;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Collections;
import java.util.EnumMap;
import java.util.LinkedHashSet;
import java.util.List;
import java.util.Map;
import java.util.Random;
import java.util.Set;

/**
 * 用于管理考试会话和生成测验题目的服务类.
 */
public final class ExamService {

  private static final int OPTIONS_COUNT = 4;
  private final Map<DifficultyLevel, QuestionGenerator> generators;
  private final Random random = new Random();
  private final QuestionGenerationService questionGenerationService;
  private final QuestionStorageService questionStorageService;

  /**
   * 创建新的考试服务.
   *
   * @param generatorMap              难度级别到题目生成器的映射
   * @param questionGenerationService 题目生成服务
   * @param questionStorageService    题目存储服务
   */
  public ExamService(
      Map<DifficultyLevel, QuestionGenerator> generatorMap,
      QuestionGenerationService questionGenerationService,
      QuestionStorageService questionStorageService) {
    this.generators = new EnumMap<>(DifficultyLevel.class);
    this.generators.putAll(generatorMap);
    this.questionGenerationService = questionGenerationService;
    this.questionStorageService = questionStorageService;
  }

  /**
   * 使用指定参数创建新的考试会话.
   *
   * @param username        考生用户名
   * @param difficultyLevel 考试难度级别
   * @param questionCount   考试中包含的题目数量
   * @return 新的考试会话
   */
  public ExamSession createExamSession(
      String username, DifficultyLevel difficultyLevel, int questionCount) {
    if (questionCount < 10 || questionCount > 30) {
      throw new IllegalArgumentException("题目数量必须在10到30之间");
    }

    // 根据难度级别生成题目
    if (!generators.containsKey(difficultyLevel)) {
      throw new IllegalArgumentException("找不到难度级别的生成器: " + difficultyLevel);
    }

    try {
      Set<String> existingQuestions = questionStorageService.loadExistingQuestions(username);
      List<String> uniqueQuestions = questionGenerationService.generateUniqueQuestions(
          difficultyLevel, questionCount, existingQuestions);

      List<QuizQuestion> quizQuestions = new ArrayList<>();
      for (String questionText : uniqueQuestions) {
        quizQuestions.add(buildQuizQuestion(questionText));
      }

      questionStorageService.saveQuestions(username, uniqueQuestions);
      return new ExamSession(username, difficultyLevel, quizQuestions);
    } catch (IOException exception) {
      throw new IllegalStateException("生成考试题目失败", exception);
    }
  }

  /**
   * 使用预定义题目创建考试会话（用于测试）.
   *
   * @param username        考生用户名
   * @param difficultyLevel 考试难度级别
   * @param questions       预定义题目列表
   * @return 新的考试会话
   */
  public ExamSession createExamSession(
      String username, DifficultyLevel difficultyLevel, List<QuizQuestion> questions) {
    if (questions.size() < 10 || questions.size() > 30) {
      throw new IllegalArgumentException("题目数量必须在10到30之间");
    }
    return new ExamSession(username, difficultyLevel, questions);
  }

  private QuizQuestion buildQuizQuestion(String questionText) {
    try {
      double correctAnswer = MathExpressionEvaluator.evaluate(questionText);
      String formattedCorrectAnswer = formatAnswer(correctAnswer);
      List<String> options = buildOptions(correctAnswer, formattedCorrectAnswer);
      int correctAnswerIndex = options.indexOf(formattedCorrectAnswer);
      if (correctAnswerIndex < 0) {
        options.set(0, formattedCorrectAnswer);
        correctAnswerIndex = 0;
      }
      return new QuizQuestion(questionText, options, correctAnswerIndex);
    } catch (RuntimeException exception) {
      List<String> fallbackOptions = new ArrayList<>();
      for (int i = 1; i <= OPTIONS_COUNT; i++) {
        fallbackOptions.add("选项" + i);
      }
      return new QuizQuestion(questionText, fallbackOptions, 0);
    }
  }

  private List<String> buildOptions(double correctAnswer, String formattedCorrectAnswer) {
    Set<String> optionSet = new LinkedHashSet<>();
    optionSet.add(formattedCorrectAnswer);

    int attempts = 0;
    while (optionSet.size() < OPTIONS_COUNT && attempts < 100) {
      double offset = generateOffset(correctAnswer);
      double candidateValue = correctAnswer + offset;
      if (Double.isNaN(candidateValue) || Double.isInfinite(candidateValue)) {
        attempts++;
        continue;
      }
      String candidate = formatAnswer(candidateValue);
      if (!candidate.equals(formattedCorrectAnswer)) {
        optionSet.add(candidate);
      }
      attempts++;
    }

    while (optionSet.size() < OPTIONS_COUNT) {
      optionSet.add(formatAnswer(correctAnswer + optionSet.size() * 1.5));
    }

    List<String> options = new ArrayList<>(optionSet);
    Collections.shuffle(options, random);
    return options;
  }

  private double generateOffset(double base) {
    double scale = Math.max(1.0, Math.abs(base) / 2.0);
    double offset = random.nextGaussian() * scale;
    if (Math.abs(offset) < 0.5) {
      offset += offset >= 0 ? 1.5 : -1.5;
    }
    return offset;
  }

  private String formatAnswer(double value) {
    return String.format("%.2f", value);
  }
}