"""Internal module for loading proxy-related env variables"""
import logging
import os
from typing import Optional

_default_logger = logging.getLogger(__name__)


def load_http_proxy_from_env(logger: logging.Logger = _default_logger) -> Optional[str]:
    proxy_url = (
        os.environ.get("HTTPS_PROXY")
        or os.environ.get("https_proxy")
        or os.environ.get("HTTP_PROXY")
        or os.environ.get("http_proxy")
    )
    if proxy_url is None:
        return None
    if len(proxy_url.strip()) == 0:
        # If the value is an empty string, the intention should be unsetting it
        logger.debug("The Slack SDK ignored the proxy env variable as an empty value is set.")
        return None

    logger.debug(f"HTTP proxy URL has been loaded from an env variable: {proxy_url}")
    return proxy_url