import json
import os


DATA_FILE = "students.json"


def init_data():
    if not os.path.exists(DATA_FILE):
        with open(DATA_FILE, "w", encoding="utf-8") as f:
            json.dump([], f)


def load_students():
    with open(DATA_FILE, "r", encoding="utf-8") as f:
        return json.load(f)


def save_students(students):
    with open(DATA_FILE, "w", encoding="utf-8") as f:
        json.dump(students, f, ensure_ascii=False, indent=2)


def add_student():
    students = load_students()
    student_id = input("请输入学号（唯一）：")
   
    for s in students:
        if s["id"] == student_id:
            print("❌ 该学号已存在！")
            return
   
    student = {
        "id": student_id,
        "name": input("请输入姓名："),
        "class": input("请输入班级："),
        "score": input("请输入成绩：")
    }
    students.append(student)
    save_students(students)
    print("✅ 学生信息添加成功！")


def query_student():
    students = load_students()
    student_id = input("请输入要查询的学号：")
    for s in students:
        if s["id"] == student_id:
            print("\n📋 查询结果：")
            print(f"学号：{s['id']}")
            print(f"姓名：{s['name']}")
            print(f"班级：{s['class']}")
            print(f"成绩：{s['score']}")
            return
    print("❌ 未找到该学生！")


def modify_student():
    students = load_students()
    student_id = input("请输入要修改的学号：")
    for s in students:
        if s["id"] == student_id:
            print("请输入新信息（不修改按回车保留原内容）：")
            s["name"] = input(f"姓名（原：{s['name']}）：") or s["name"]
            s["class"] = input(f"班级（原：{s['class']}）：") or s["class"]
            s["score"] = input(f"成绩（原：{s['score']}）：") or s["score"]
            save_students(students)
            print("✅ 学生信息修改成功！")
            return
    print("❌ 未找到该学生！")


def delete_student():
    students = load_students()
    student_id = input("请输入要删除的学号：")
    for i, s in enumerate(students):
        if s["id"] == student_id:
            del students[i]
            save_students(students)
            print("✅ 学生信息删除成功！")
            return
    print("❌ 未找到该学生！")


def main():
    init_data()
    while True:
        print("\n" + "="*30)
        print("      学生信息管理系统（Python）")
        print("="*30)
        print("1. 添加学生  2. 查询学生")
        print("3. 修改学生  4. 删除学生")
        print("5. 退出系统")
        print("="*30)
        choice = input("请输入操作编号（1-5）：")
        if choice == "1":
            add_student()
        elif choice == "2":
            query_student()
        elif choice == "3":
            modify_student()
        elif choice == "4":
            delete_student()
        elif choice == "5":
            print("👋 退出系统，再见！")
            break
        else:
            print("❌ 输入错误，请重新选择！")

if __name__ == "__main__":
    main()