"""
核心Todo类，负责待办事项的业务逻辑
"""

from datetime import datetime
from typing import List, Optional, Dict


class TodoItem:
    """待办事项数据模型"""
    
    def __init__(self, id: int, title: str, completed: bool = False, 
                 created_at: Optional[str] = None):
        self.id = id
        self.title = title
        self.completed = completed
        self.created_at = created_at or datetime.now().strftime("%Y-%m-%d %H:%M:%S")
    
    def to_dict(self) -> Dict:
        """转换为字典格式"""
        return {
            "id": self.id,
            "title": self.title,
            "completed": self.completed,
            "created_at": self.created_at
        }
    
    @classmethod
    def from_dict(cls, data: Dict) -> 'TodoItem':
        """从字典创建TodoItem对象"""
        return cls(
            id=data["id"],
            title=data["title"],
            completed=data.get("completed", False),
            created_at=data.get("created_at")
        )
    
    def __repr__(self) -> str:
        status = "✓" if self.completed else " "
        return f"[{status}] {self.id}. {self.title}"


class Todo:
    """待办事项管理类"""
    
    def __init__(self):
        self.items: List[TodoItem] = []
        self.next_id: int = 1
    
    def add(self, title: str) -> TodoItem:
        """添加待办事项"""
        if not title or not title.strip():
            raise ValueError("待办事项标题不能为空")
        
        item = TodoItem(id=self.next_id, title=title.strip())
        self.items.append(item)
        self.next_id += 1
        return item
    
    def delete(self, item_id: int) -> bool:
        """删除待办事项"""
        for i, item in enumerate(self.items):
            if item.id == item_id:
                self.items.pop(i)
                return True
        return False
    
    def complete(self, item_id: int) -> bool:
        """标记待办事项为完成"""
        item = self.get_by_id(item_id)
        if item:
            item.completed = True
            return True
        return False
    
    def uncomplete(self, item_id: int) -> bool:
        """标记待办事项为未完成"""
        item = self.get_by_id(item_id)
        if item:
            item.completed = False
            return True
        return False
    
    def get_by_id(self, item_id: int) -> Optional[TodoItem]:
        """根据ID获取待办事项"""
        for item in self.items:
            if item.id == item_id:
                return item
        return None
    
    def get_all(self) -> List[TodoItem]:
        """获取所有待办事项"""
        return self.items.copy()
    
    def get_pending(self) -> List[TodoItem]:
        """获取未完成的待办事项"""
        return [item for item in self.items if not item.completed]
    
    def get_completed(self) -> List[TodoItem]:
        """获取已完成的待办事项"""
        return [item for item in self.items if item.completed]
    
    def clear_completed(self) -> int:
        """清除所有已完成的待办事项，返回清除的数量"""
        completed_count = len(self.get_completed())
        self.items = [item for item in self.items if not item.completed]
        return completed_count
    
    def to_dict(self) -> Dict:
        """转换为字典格式用于存储"""
        return {
            "todos": [item.to_dict() for item in self.items],
            "next_id": self.next_id
        }
    
    def from_dict(self, data: Dict):
        """从字典加载数据"""
        self.items = [TodoItem.from_dict(item_data) for item_data in data.get("todos", [])]
        self.next_id = data.get("next_id", 1)