from typing import Optional
from pydantic import BaseModel, validator
from sqlalchemy.orm import Session
from models import Pen

class PenCreate(BaseModel):
    name: str
    color: str
    brand: str
    price: int

    @validator('name', 'color', 'brand')
    def validate_string_not_empty(cls, value):
        if not value or not value.strip():
            raise ValueError('Field cannot be empty or contain only whitespace characters')
        return value

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

def create_pen(db: Session, pen_data: PenCreate) -> Pen:
    """
    Create a new pen in the database.

    Args:
        db: Database session
        pen_data: Pen data for creation

    Returns:
        Pen object
    """
    pen = Pen(**pen_data.dict())
    db.add(pen)
    db.commit()
    db.refresh(pen)
    return pen

def get_pen_by_name(db: Session, name: str) -> Optional[Pen]:
    """
    Get a pen by its name.

    Args:
        db: Database session
        name: Name of the pen

    Returns:
        Pen object if found, None otherwise
    """
    return db.query(Pen).filter(Pen.name == name).first()

def update_pen(db: Session, pen_id: int, pen_data: PenCreate) -> Optional[Pen]:
    """
    Update an existing pen in the database.

    Args:
        db: Database session
        pen_id: ID of the pen to update
        pen_data: Updated pen data

    Returns:
        Updated Pen object if successful, None otherwise
    """
    pen = db.query(Pen).filter(Pen.id == pen_id).first()
    if pen:
        for key, value in pen_data.dict(exclude_unset=True).items():
            setattr(pen, key, value)
        db.commit()
        db.refresh(pen)
        return pen
    return None

def delete_pen(db: Session, pen_id: int) -> bool:
    """
    Delete a pen from the database.

    Args:
        db: Database session
        pen_id: ID of the pen to delete

    Returns:
        True if successful, False otherwise
    """
    pen = db.query(Pen).filter(Pen.id == pen_id).first()
    if pen:
        db.delete(pen)
        db.commit()
        return True
    return False