from dataclasses import dataclass
from typing import Optional
from datetime import datetime

@dataclass
class User:
    """User model representing a user in the system."""
    id: str
    email: str
    created_at: datetime
    email_confirmed_at: Optional[datetime] = None

    @classmethod
    def from_dict(cls, data: dict):
        """Create a User instance from a dictionary."""
        return cls(
            id=data['id'],
            email=data['email'],
            created_at=data['created_at'] if data.get('created_at') else None,
            email_confirmed_at=data['email_confirmed_at'] if data.get('email_confirmed_at') else None
        )

    def to_dict(self):
        """Convert User instance to dictionary."""
        return {
            'id': self.id,
            'email': self.email,
            'created_at': self.created_at if self.created_at else None,
            'email_confirmed_at': self.email_confirmed_at if self.email_confirmed_at else None
        }