package com.studentmanagement.model;

import com.studentmanagement.exception.DuplicateStudentException;
import com.studentmanagement.exception.StudentNotFoundException;

import java.util.*;
import java.util.stream.Collectors;

/**
 * 学生数据访问对象
 * 负责学生数据的存储和访问操作，使用单例模式
 */
public class StudentDAO {
    private static StudentDAO instance;
    private Map<String, Student> students; // 存储学生对象的集合

    /**
     * 私有构造函数，防止外部实例化
     */
    private StudentDAO() {
        students = new HashMap<>();
        // 添加一些示例数据
        initSampleData();
    }

    /**
     * 获取单例实例
     * @return StudentDAO的唯一实例
     */
    public static synchronized StudentDAO getInstance() {
        if (instance == null) {
            instance = new StudentDAO();
        }
        return instance;
    }

    /**
     * 初始化示例数据
     */
    private void initSampleData() {
        Student s1 = new Student("001", "张三", 20, "男");
        s1.addCourseGrade("数学", 85.5);
        s1.addCourseGrade("英语", 92.0);
        s1.addCourseGrade("计算机", 88.5);

        Student s2 = new Student("002", "李四", 21, "女");
        s2.addCourseGrade("数学", 90.0);
        s2.addCourseGrade("英语", 88.0);
        s2.addCourseGrade("计算机", 95.0);

        Student s3 = new Student("003", "王五", 19, "男");
        s3.addCourseGrade("数学", 78.5);
        s3.addCourseGrade("英语", 82.0);
        s3.addCourseGrade("计算机", 80.0);

        try {
            addStudent(s1);
            addStudent(s2);
            addStudent(s3);
        } catch (DuplicateStudentException e) {
            // 示例数据初始化不应抛出重复异常
            System.err.println("示例数据初始化错误: " + e.getMessage());
        }
    }

    /**
     * 添加学生
     * @param student 学生对象
     * @throws DuplicateStudentException 如果学生ID已存在
     */
    public void addStudent(Student student) throws DuplicateStudentException {
        if (students.containsKey(student.getId())) {
            throw new DuplicateStudentException("学生ID已存在: " + student.getId(), student.getId());
        }
        students.put(student.getId(), student);
    }

    /**
     * 获取所有学生
     * @return 学生列表
     */
    public List<Student> getAllStudents() {
        return new ArrayList<>(students.values());
    }

    /**
     * 根据ID查找学生
     * @param id 学生ID
     * @return 学生对象
     * @throws StudentNotFoundException 如果学生不存在
     */
    public Student getStudentById(String id) throws StudentNotFoundException {
        Student student = students.get(id);
        if (student == null) {
            throw new StudentNotFoundException("未找到ID为" + id + "的学生", id);
        }
        return student;
    }

    /**
     * 更新学生信息
     * @param student 学生对象
     * @throws StudentNotFoundException 如果学生不存在
     */
    public void updateStudent(Student student) throws StudentNotFoundException {
        if (!students.containsKey(student.getId())) {
            throw new StudentNotFoundException("未找到ID为" + student.getId() + "的学生", student.getId());
        }
        students.put(student.getId(), student);
    }

    /**
     * 删除学生
     * @param id 学生ID
     * @throws StudentNotFoundException 如果学生不存在
     */
    public void deleteStudent(String id) throws StudentNotFoundException {
        if (!students.containsKey(id)) {
            throw new StudentNotFoundException("未找到ID为" + id + "的学生", id);
        }
        students.remove(id);
    }

    /**
     * 根据课程筛选学生
     * @param course 课程名称
     * @return 选修该课程的学生列表
     */
    public List<Student> getStudentsByCourse(String course) {
        List<Student> result = new ArrayList<>();
        for (Student student : students.values()) {
            if (student.getCourseGrades().containsKey(course)) {
                result.add(student);
            }
        }
        return result;
    }

    /**
     * 根据成绩范围筛选学生
     * @param minGrade 最低成绩
     * @param maxGrade 最高成绩
     * @return 平均成绩在范围内的学生列表
     */
    public List<Student> getStudentsByGradeRange(double minGrade, double maxGrade) {
        List<Student> result = new ArrayList<>();
        for (Student student : students.values()) {
            double avgGrade = student.calculateAverageGrade();
            if (avgGrade >= minGrade && avgGrade <= maxGrade) {
                result.add(student);
            }
        }
        return result;
    }
}