"""Definition of check_env function."""
from __future__ import annotations

import os


def check_env() -> None:
    """Check necessary environment variables are set."""
    necesasary_var_list = {
        'MONGO_HOST',
        'MONGO_DB',
        'MONGO_COLLECTION',
        'MONGO_USER',
        'MONGO_PASSWORD',
        'DASH_AUTH_USERNAME',
        'DASH_AUTH_PASSWORD',
    }
    for env_var in necesasary_var_list:
        # ensure env var set
        assert (
            env_var in os.environ
        ), (
            f"environment variable not set: {env_var}"
        )