# 示例：一个简单的"待办事项"命令行应用 (todo_app.py)
# 这是一个MVP（最小可行产品）示例，你可以在此基础上扩展。

import json
import os
from datetime import datetime

DATA_FILE = "todo_list.json"

def load_tasks():
    """从JSON文件加载任务列表。如果文件不存在，则返回空列表。"""
    if os.path.exists(DATA_FILE):
        with open(DATA_FILE, 'r', encoding='utf-8') as f:
            try:
                return json.load(f)
            except json.JSONDecodeError:
                return []
    return []

def save_tasks(tasks):
    """将任务列表保存到JSON文件。"""
    with open(DATA_FILE, 'w', encoding='utf-8') as f:
        json.dump(tasks, f, ensure_ascii=False, indent=2)

def add_task(tasks, description):
    """添加一个新任务。"""
    new_task = {
        "id": len(tasks) + 1,
        "description": description,
        "created_at": datetime.now().strftime("%Y-%m-%d %H:%M:%S"),
        "completed": False
    }
    tasks.append(new_task)
    print(f"✅ 任务已添加: {description}")

def list_tasks(tasks):
    """列出所有任务。"""
    if not tasks:
        print("📭 当前没有待办事项。")
        return
    print("\n--- 待办事项列表 ---")
    for task in tasks:
        status = "✔️" if task["completed"] else "❌"
        print(f"{task['id']}. [{status}] {task['description']} (创建于: {task['created_at']})")
    print()

def complete_task(tasks, task_id):
    """完成指定任务。"""
    for task in tasks:
        if task["id"] == task_id:
            task["completed"] = True
            print(f"🎉 任务已完成: {task['description']}")
            return
    print("⚠️ 未找到该ID的任务。")

def main():
    """主函数：提供命令行交互界面。"""
    tasks = load_tasks()
    print("欢迎使用简易待办事项应用！")
    print("命令: add <描述>, list, done <ID>, quit")

    while True:
        try:
            user_input = input("> ").strip().split()
            if not user_input:
                continue
            
            command = user_input[0].lower()
            
            if command == "add" and len(user_input) > 1:
                description = " ".join(user_input[1:])
                add_task(tasks, description)
            elif command == "list":
                list_tasks(tasks)
            elif command == "done" and len(user_input) == 2:
                try:
                    task_id = int(user_input[1])
                    complete_task(tasks, task_id)
                except ValueError:
                    print("⚠️ ID必须是数字。")
            elif command == "quit":
                save_tasks(tasks)
                print("👋 任务已保存，再见！")
                break
            else:
                print("⚠️ 未知命令。请使用 add, list, done, quit。")
        except KeyboardInterrupt:
            save_tasks(tasks)
            print("\n👋 任务已保存，再见！")
            break

if __name__ == "__main__":
    main()