const Course = require('../models/Course');
const Score = require('../models/Score');
const Student = require('../models/Student');

class TeacherService {
    static async getCourses(teacherId) {
        return await Course.findByTeacherId(teacherId);
    }

    static async addScore(teacherId, scoreData) {
        const { studentId, courseId, score } = scoreData;

        // 验证学生
        const student = await Student.findById(studentId);
        if (!student) {
            throw new Error('学生不存在');
        }

        // 验证课程（可选：验证是否是该教师的课程）
        // const course = await Course.findById(courseId);
        
        // 检查重复
        const existingScore = await Score.findByStudentAndCourse(studentId, courseId);
        if (existingScore) {
            throw new Error('该学生此课程成绩已存在');
        }

        // 计算绩点和等级
        const numericScore = parseFloat(score);
        let gradePoint = 0;
        let gradeLevel = 'F';

        if (numericScore >= 90) { gradePoint = 4.0; gradeLevel = 'A'; }
        else if (numericScore >= 80) { gradePoint = 3.0; gradeLevel = 'B'; }
        else if (numericScore >= 70) { gradePoint = 2.0; gradeLevel = 'C'; }
        else if (numericScore >= 60) { gradePoint = 1.0; gradeLevel = 'D'; }

        const fullScoreData = {
            ...scoreData,
            teacherId,
            gradePoint,
            gradeLevel
        };

        const gradeId = await Score.create(fullScoreData);
        return gradeId;
    }
}

module.exports = TeacherService;