from typing import Optional, Dict, List
from pydantic import BaseModel, validator
from datetime import datetime

class Product(BaseModel):
    name: str
    description: Optional[str] = None
    price: float
    category: str
    created_at: datetime = datetime.now()
    updated_at: datetime = datetime.now()

    @validator('name')
    def validate_name(cls, value):
        if len(value) < 3:
            raise ValueError('Name must be at least 3 characters long')
        return value

    @validator('price')
    def validate_price(cls, value):
        if value < 0:
            raise ValueError('Price cannot be negative')
        return value

def validate_product_data(data: Dict) -> Product:
    """
    Validate the product data dictionary and return a Product instance.

    Args:
        data (Dict): The product data dictionary.

    Returns:
        Product: A validated Product instance.

    Raises:
        ValueError: If the product data is invalid.
    """
    try:
        product = Product(**data)
    except ValueError as e:
        raise ValueError(str(e))
    return product

def create_product(db, product_data: Dict) -> Product:
    """
    Create a new product in the database.

    Args:
        db: The database session.
        product_data (Dict): The product data dictionary.

    Returns:
        Product: The created product instance.

    Raises:
        ValueError: If the product data is invalid.
    """
    validated_product = validate_product_data(product_data)
    db_product = db.query(Product).filter(Product.name == validated_product.name).first()
    if db_product:
        raise ValueError(f'Product with name "{validated_product.name}" already exists')
    db.add(validated_product)
    db.commit()
    db.refresh(validated_product)
    return validated_product

def get_products_by_category(db, category: str) -> List[Product]:
    """
    Get a list of products by category.

    Args:
        db: The database session.
        category (str): The category to filter by.

    Returns:
        List[Product]: A list of products in the specified category.
    """
    return db.query(Product).filter(Product.category == category).all()

def update_product(db, product_id: int, data: Dict) -> Product:
    """
    Update an existing product in the database.

    Args:
        db: The database session.
        product_id (int): The ID of the product to update.
        data (Dict): The updated product data dictionary.

    Returns:
        Product: The updated product instance.

    Raises:
        ValueError: If the product data is invalid or the product is not found.
    """
    validated_product = validate_product_data(data)
    db_product = db.query(Product).filter(Product.id == product_id).first()
    if not db_product:
        raise ValueError(f'Product with ID {product_id} not found')
    for field, value in validated_product.dict(exclude_unset=True).items():
        setattr(db_product, field, value)
    db_product.updated_at = datetime.now()
    db.commit()
    db.refresh(db_product)
    return db_product