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

class UserCreate(BaseModel):
    username: str
    email: EmailStr
    password: str

    @validator('username')
    def validate_username(cls, username):
        if len(username) < 3:
            raise ValueError('Username must be at least 3 characters long')
        return username

    @validator('password')
    def validate_password(cls, password):
        if len(password) < 8:
            raise ValueError('Password must be at least 8 characters long')
        return password

def validate_email(email: str) -> bool:
    """
    Validate an email address format.
    
    Args:
        email: The email address to validate
        
    Returns:
        bool: True if email format is valid, False otherwise
    """
    pattern = r'^[a-zA-Z0-9_.+-]+@[a-zA-Z0-9-]+\.[a-zA-Z0-9-.]+$'
    return bool(re.match(pattern, email))

def get_user_by_email(db: Session, email: str) -> Optional[User]:
    """
    Get a user by their email address.
    
    Args:
        db: Database session
        email: Email to search for
        
    Returns:
        User object if found, None otherwise
    """
    return db.query(User).filter(User.email == email).first()

def create_user(db: Session, user_data: UserCreate) -> User:
    """
    Create a new user with validation and error handling.
    
    Args:
        db: Database session
        user_data: User data for creation
        
    Returns:
        User object if created successfully, raises ValueError otherwise
    """
    # Check if email is valid
    if not validate_email(user_data.email):
        raise ValueError("Invalid email format")
    
    # Check if user already exists
    existing_user = get_user_by_email(db, user_data.email)
    if existing_user:
        raise ValueError("Email already registered")
    
    # Create the user
    db_user = User(
        username=user_data.username,
        email=user_data.email,
        password=user_data.password  # In a real app, hash this password
    )
    
    db.add(db_user)
    db.commit()
    db.refresh(db_user)
    
    return db_user