"""Utility functions"""
from datetime import datetime, timezone, timedelta


def utc_to_ist(utc_datetime: datetime) -> datetime:
    """Convert UTC datetime to IST (Indian Standard Time)"""
    ist_offset = timezone(timedelta(hours=5, minutes=30))
    return utc_datetime.replace(tzinfo=timezone.utc).astimezone(ist_offset)


def format_ist_timestamp(utc_iso_string: str) -> str:
    """Convert UTC ISO string to IST ISO string"""
    try:
        utc_dt = datetime.fromisoformat(utc_iso_string.replace('Z', '+00:00'))
        ist_dt = utc_to_ist(utc_dt)
        return ist_dt.isoformat()
    except Exception as e:
        raise ValueError(f"Invalid datetime format: {str(e)}")