"""HTTP helpers for file downloads (latin-1 safe Content-Disposition)."""
from __future__ import annotations

import unicodedata
from urllib.parse import quote


def attachment_content_disposition(filename: str) -> str:
    """RFC 5987 filename* plus ASCII fallback for Starlette/HTTP latin-1 headers."""
    clean = (
        (filename or "download")
        .replace('"', "")
        .replace("\n", "")
        .replace("\r", "")
        .replace("/", "-")
        .replace("\\", "-")
    )
    ascii_fallback = (
        unicodedata.normalize("NFKD", clean)
        .encode("ascii", "ignore")
        .decode("ascii")
        .strip()
        or "download"
    )
    return (
        f'attachment; filename="{ascii_fallback}"; '
        f"filename*=UTF-8''{quote(clean, safe='')}"
    )