partner_project/src/service/ExamService.java

package service;

import auth.User;
import generator.Problem;
import generator.ProblemGenerator;
import generator.PrimaryGenerator;
import generator.MiddleGenerator;
import generator.HighGenerator;
import util.FileUtils;
import java.util.ArrayList;
import java.util.List;
import java.util.Set;

public class ExamService {

    public ProblemGenerator getGenerator(String type) {
        switch (type) {
            case "小学": return new PrimaryGenerator();
            case "初中": return new MiddleGenerator();
            case "高中": return new HighGenerator();
            default: return null;
        }
    }

    private Problem generateUniqueProblem(ProblemGenerator generator,
                                          Set<String> historyExpressions) {
        int attempts = 0;
        final int maxAttemptsPerProblem = 1000;

        while (attempts < maxAttemptsPerProblem) {
            Problem problem = generator.generateProblems(1).get(0);
            // 查重基于题干 (表达式字符串)
            if (!historyExpressions.contains(problem.getExpression())) {
                historyExpressions.add(problem.getExpression());
                return problem;
            }
            attempts++;
        }
        return null;
    }

    // R5: 生成一张唯一试卷，并将其保存到用户的历史记录中。
    public List<Problem> generateExam(User currentUser, int count) {
        if (count < 10 || count > 30) {
            throw new IllegalArgumentException("题目数量必须在 10 到 30 之间");
        }

        ProblemGenerator generator = getGenerator(currentUser.getType());
        if (generator == null) {
            System.err.println("错误: 无法获取题目生成器，用户类型: " + currentUser.getType());
            return new ArrayList<>();
        }
        
        Set<String> historyExpressions = FileUtils.loadHistory(currentUser.getUsername());
        List<Problem> problems = new ArrayList<>();

        for(int i = 0; i < count; i++) {
            Problem problem = generateUniqueProblem(generator, historyExpressions);
            if (problem != null) {
                problems.add(problem);
            } else {
                System.err.println("警告: 无法生成足够数量的唯一题目。已生成: " + problems.size() + " 题");
                break;
            }
        }

        if (!problems.isEmpty()) {
            FileUtils.saveProblems(currentUser.getUsername(), problems);
        } else {
            System.err.println("错误: 未能生成任何题目");
        }
        
        return problems;
    }

    // 将这个私有方法改为公共方法，以便在其他类中调用
    public boolean isAnswerCorrect(Problem problem, String userAnswer) {
        if (userAnswer == null || problem.getCorrectAnswerOption() == null) {
            return false;
        }
        
        boolean isCorrect = userAnswer.trim().equalsIgnoreCase(problem.getCorrectAnswerOption().trim());
        return isCorrect;
    }

    // R6: 根据答对的百分比计算分数。
    public int calculateScore(List<Problem> problems, List<String> answers) {
        if (problems == null || answers == null || 
            problems.size() != answers.size() || 
            problems.isEmpty()) {
            System.err.println("评分错误: 题目和答案数量不匹配");
            return 0;
        }

        int correctCount = 0;
        for (int i = 0; i < problems.size(); i++) {
            Problem problem = problems.get(i);
            String userAnswer = answers.get(i);
            
            if (isAnswerCorrect(problem, userAnswer)) {
                correctCount++;
            }
        }

        double score = ((double) correctCount / problems.size()) * 100;
        int finalScore = (int) Math.round(score);
        return finalScore;
    }
}