import json
import os
from datetime import datetime

def save_session(user_id: str, session_file: str = "session.json"):
    """
    Save the current user session to a file.
    
    Args:
        user_id: The ID of the authenticated user.
        session_file: The path to the session file.
    """
    try:
        session_data = {
            "user_id": user_id,
            "last_login": datetime.now().isoformat()
        }
        with open(session_file, 'w') as f:
            json.dump(session_data, f, indent=2)
    except Exception as e:
        print(f"Error saving session: {e}")