"""Parse boolean values from environment variables."""

from __future__ import annotations

import os

_TRUTHY = frozenset({"1", "true", "yes", "on"})
_FALSY = frozenset({"0", "false", "no", "off"})


def env_bool(name: str, default: bool) -> bool:
    """Parse an environment variable as a boolean value."""
    raw = os.getenv(name)
    if raw is None:
        return default
    normalized = raw.strip().lower()
    if normalized in _TRUTHY:
        return True
    if normalized in _FALSY:
        return False
    raise ValueError(f"Invalid boolean value for {name}: {raw!r}")