from datetime import datetime
from typing import Optional

from pydantic import BaseModel, Field


class TodoBase(BaseModel):
    """
    Base schema for Todo items with common attributes.
    """
    title: str = Field(
        ..., 
        min_length=1, 
        max_length=255, 
        description="The title of the todo item"
    )
    description: Optional[str] = Field(
        None, 
        description="An optional detailed description of the todo item"
    )
    completed: bool = Field(
        False, 
        description="Whether the todo item has been completed"
    )


class TodoCreate(TodoBase):
    """
    Schema for creating a new Todo item.
    """
    pass


class TodoUpdate(BaseModel):
    """
    Schema for updating an existing Todo item.
    All fields are optional to allow partial updates.
    """
    title: Optional[str] = Field(
        None, 
        min_length=1, 
        max_length=255, 
        description="The title of the todo item"
    )
    description: Optional[str] = Field(
        None, 
        description="An optional detailed description of the todo item"
    )
    completed: Optional[bool] = Field(
        None, 
        description="Whether the todo item has been completed"
    )


class TodoInDBBase(TodoBase):
    """
    Schema for Todo items as stored in the database.
    """
    id: int
    created_at: datetime
    updated_at: datetime

    class Config:
        from_attributes = True


class Todo(TodoInDBBase):
    """
    Schema for Todo items returned to the client.
    """
    pass


class TodoList(BaseModel):
    """
    Schema for a list of Todo items.
    """
    items: list[Todo]
    count: int