import os
from pathlib import Path

_SUPPORTED = {".stl", ".3mf", ".gcode"}


def get_stl_dir() -> Path:
    d = Path(os.environ.get("STL_UPLOAD_DIR", "/data/stl"))
    d.mkdir(parents=True, exist_ok=True)
    return d


def list_stl_files() -> list[str]:
    try:
        return sorted(
            f.name for f in get_stl_dir().iterdir()
            if f.suffix.lower() in _SUPPORTED
        )
    except FileNotFoundError:
        return []