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

class ProductBase(BaseModel):
    name: str
    description: Optional[str] = None
    price: float
    category: str

class ProductCreate(ProductBase):
    pass

class ProductUpdate(ProductBase):
    pass

class Product(ProductBase):
    id: int
    created_at: datetime
    updated_at: Optional[datetime] = None

    @validator('price')
    def price_must_be_positive(cls, value):
        if value <= 0:
            raise ValueError('Price must be a positive value')
        return value

def validate_product_data(product_data: ProductCreate) -> Dict[str, str]:
    errors = {}
    
    if not product_data.name.strip():
        errors['name'] = 'Product name cannot be empty'
    
    if not product_data.category.strip():
        errors['category'] = 'Product category cannot be empty'
    
    return errors

def create_product(db, product_data: ProductCreate):
    errors = validate_product_data(product_data)
    if errors:
        return errors
    
    product = Product(
        name=product_data.name,
        description=product_data.description,
        price=product_data.price,
        category=product_data.category,
        created_at=datetime.utcnow()
    )
    
    db.add(product)
    db.commit()
    db.refresh(product)
    
    return product

def update_product(db, product_id: int, product_data: ProductUpdate):
    product = db.query(Product).filter(Product.id == product_id).first()
    if not product:
        return {'error': 'Product not found'}
    
    for field, value in product_data.dict(exclude_unset=True).items():
        setattr(product, field, value)
    
    product.updated_at = datetime.utcnow()
    db.commit()
    db.refresh(product)
    
    return product

def get_product_by_id(db, product_id: int):
    return db.query(Product).filter(Product.id == product_id).first()

def get_products_by_category(db, category: str):
    return db.query(Product).filter(Product.category == category).all()