const Exam = require('../models/Exam');

// 获取所有考试
exports.getExams = async (req, res, next) => {
    try {
        const exams = await Exam.find({ isActive: true })
            .select('-questions.answer') // 不返回答案
            .populate('createdBy', 'username');

        res.json(exams);
    } catch (err) {
        next(err);
    }
};

// 获取单个考试详情
exports.getExam = async (req, res, next) => {
    try {
        const exam = await Exam.findById(req.params.id)
            .select('-questions.answer') // 不返回答案
            .populate('createdBy', 'username');

        if (!exam) {
            return res.status(404).json({ message: 'Exam not found' });
        }

        res.json(exam);
    } catch (err) {
        next(err);
    }
};

// 创建新考试 (教师/管理员)
exports.createExam = async (req, res, next) => {
    try {
        const { title, description, duration, questions } = req.body;

        const exam = new Exam({
            title,
            description,
            duration,
            questions,
            createdBy: req.user.id
        });

        await exam.save();

        res.status(201).json(exam);
    } catch (err) {
        next(err);
    }
};

// 验证考试答案
exports.validateAnswers = async (req, res, next) => {
    try {
        const { answers } = req.body;

        // 获取考试(包含正确答案)
        const exam = await Exam.findById(req.params.id);
        if (!exam) {
            return res.status(404).json({ message: 'Exam not found' });
        }

        // 计算分数
        let totalScore = 0;
        const results = exam.questions.map(question => {
            const userAnswer = answers[question._id];
            let isCorrect = false;
            let score = 0;

            if (question.type === 'text') {
                // 简答题默认给一半分
                if (userAnswer && userAnswer.trim().length > 0) {
                    isCorrect = true;
                    score = question.score / 2;
                }
            } else if (Array.isArray(question.answer)) {
                // 多选题
                const correctAnswers = [...question.answer].sort().toString();
                const userAns = [...userAnswer].sort().toString();
                isCorrect = correctAnswers === userAns;
                score = isCorrect ? question.score : 0;
            } else {
                // 单选题
                isCorrect = userAnswer === question.answer;
                score = isCorrect ? question.score : 0;
            }

            totalScore += score;

            return {
                questionId: question._id,
                question: question.question,
                userAnswer,
                correctAnswer: question.answer,
                isCorrect,
                score
            };
        });

        res.json({
            examId: exam._id,
            totalScore,
            maxScore: exam.questions.reduce((sum, q) => sum + q.score, 0),
            results
        });
    } catch (err) {
        next(err);
    }
};