"""Definition of check_env function."""

import logging
import os


def check_env(
    var_list: str | set[str] | list[str] | tuple[str, ...],
    missing_ok: bool = False,
) -> None:
    """Check if environment variables are set.

    Args:
        var_list (str | list[str]): A single environment variable name or a list of names to check.
        missing_ok (bool): If True, do not raise an error if the variable is not set. Defaults to False.

    Raises:
        OSError: If any environment variable is not set.
    """
    if not var_list:
        raise ValueError("List of environment variable names is empty.")
    # Handle single string input
    if isinstance(var_list, str):
        var_list = [var_list]
    # Avoid double-checking
    var_set = set(var_list)
    # Perform checks
    for var in var_set:
        if not os.getenv(var):
            msg = f"Environment variable {var} is not set."
            logging.error(msg)
            if not missing_ok:
                raise OSError(msg)