feat(学生): 添加成绩分析功能及密码修改功能

- 新增成绩分析页面，包含GPA趋势图、成绩分布图和学分进度
- 实现学生密码修改功能，包括前端表单和后端验证逻辑
- 添加课程类别分析功能，展示不同类别课程的GPA表现
- 优化学生仪表板和课程页面导航链接
- 增加数据加载状态提示和错误处理

backend/services/studentService.js

@@ -1,6 +1,7 @@
 const Score = require('../models/Score');
 const Student = require('../models/Student');
 const Course = require('../models/Course');
+const db = require('../config/database');
 
 class StudentService {
     static async getStudentCourses(userId) {
@@ -65,6 +66,100 @@ class StudentService {
         }
         return grade;
     }
+
+    static async getGradeStatistics(userId) {
+        const student = await Student.findById(userId);
+        if (!student) {
+            throw new Error('学生信息不存在');
+        }
+
+        const sql = `
+            SELECT g.total_score as score, g.grade_point, g.grade_level, 
+                   c.course_name, CAST(c.credit AS CHAR) as credit, c.semester, c.academic_year, c.category
+            FROM grades g
+            JOIN courses c ON g.course_id = c.id
+            WHERE g.student_id = ?
+            ORDER BY c.semester ASC
+        `;
+        const grades = await db.query(sql, [userId]);
+
+        // 1. 学期 GPA 趋势
+        const semesterGPA = {};
+        // 5. 课程类别分析
+        const categoryStats = {};
+
+        grades.forEach(g => {
+            // console.log('Processing grade:', g);
+            // 学期统计
+            const semester = g.semester || '未知学期';
+            if (!semesterGPA[semester]) {
+                semesterGPA[semester] = { totalGP: 0, totalCredits: 0 };
+            }
+            const credit = parseFloat(g.credit || 0);
+            semesterGPA[semester].totalGP += parseFloat(g.grade_point || 0) * credit;
+            semesterGPA[semester].totalCredits += credit;
+
+            // 类别统计
+            const catName = g.category || '其他';
+            if (!categoryStats[catName]) {
+                categoryStats[catName] = { totalGP: 0, totalCredits: 0 };
+            }
+            categoryStats[catName].totalGP += parseFloat(g.grade_point || 0) * credit;
+            categoryStats[catName].totalCredits += credit;
+        });
+
+        const trend = Object.keys(semesterGPA).map(semester => ({
+            semester,
+            gpa: (semesterGPA[semester].totalGP / semesterGPA[semester].totalCredits).toFixed(2)
+        }));
+
+        const categories = Object.keys(categoryStats).map(cat => {
+            const stats = categoryStats[cat];
+            const gpa = stats.totalCredits > 0 ? (stats.totalGP / stats.totalCredits).toFixed(2) : '0.00';
+            return {
+                category: cat,
+                gpa: gpa,
+                totalCredits: Number(stats.totalCredits) || 0
+            };
+        });
+
+        // 2. 成绩等第分布
+        const distribution = {
+            'A': 0, 'B': 0, 'C': 0, 'D': 0, 'F': 0
+        };
+        grades.forEach(g => {
+            if (distribution[g.grade_level] !== undefined) {
+                distribution[g.grade_level]++;
+            }
+        });
+
+        // 3. 学分进度
+        let earnedCredits = 0;
+        grades.forEach(g => {
+            const score = parseFloat(g.score || 0);
+            const credit = parseFloat(g.credit || 0);
+            if (score >= 60) {
+                earnedCredits += credit;
+            }
+        });
+
+        // 4. 每学期学分详情
+        const semesterCredits = Object.keys(semesterGPA).map(semester => ({
+            semester,
+            credits: semesterGPA[semester].totalCredits
+        }));
+
+        return {
+            trend,
+            distribution,
+            categories,
+            credits: {
+                earned: earnedCredits,
+                target: 160 // 假设目标学分为 160
+            },
+            semesterCredits
+        };
+    }
 }
 
 module.exports = StudentService;