"""Cache-path helpers for workshop content.

The cache lives at `$LEFT4ME_ROOT/workshop_cache/{steam_id}.vpk`. Steam IDs
are validated digit-only here so callers don't need to guard separately.
"""
from __future__ import annotations

import re
from pathlib import Path

from l4d2host.paths import get_left4me_root


_NUMERIC_ID_RE = re.compile(r"^\d+$")


def workshop_cache_root() -> Path:
    return get_left4me_root() / "workshop_cache"


def cache_path(steam_id: str) -> Path:
    if not isinstance(steam_id, str) or not _NUMERIC_ID_RE.fullmatch(steam_id):
        raise ValueError(f"steam_id must be digits only: {steam_id!r}")
    return workshop_cache_root() / f"{steam_id}.vpk"
