import os
import streamlit as st
from typing import Optional

def current_uid() -> Optional[str]:
    """Return the signed-in user's id/email from session, if any."""
    return st.session_state.get("uid")

def get_current_uid() -> str:
    """Get current user ID with validation. Raises error if not logged in."""
    uid = current_uid()
    if not uid:
        st.error("Please log in to continue.")
        st.stop()
    return uid