"""Small helpers."""
from __future__ import annotations

import os
from pathlib import Path
from typing import Optional


def find_latest_ckpt(run_dir: str | Path) -> Optional[str]:
    """Locate the latest `*.ckpt` under run_dir, for auto-resume after server restart."""
    rd = Path(run_dir)
    if not rd.exists():
        return None
    ckpts = sorted(rd.rglob("*.ckpt"), key=lambda p: p.stat().st_mtime, reverse=True)
    return str(ckpts[0]) if ckpts else None


def env_or(default: str, key: str) -> str:
    return os.environ.get(key, default)