// File names built from server-supplied metadata.
//
// A file's title and a collection's name are decrypted from data the server
// hands us, and quak does not trust the server. Any name taken from them and
// used on disk goes through here, so it can only ever name one file inside the
// directory the caller chose: never a path, never `..`, never hidden, never a
// Windows device name.
//
// A path the user typed (`--out`, `outPath`) is not passed through here: the
// caller is trusted, the server is not.

import { extname } from "node:path";

// Path separators, characters Windows forbids in file names, and control
// characters (NUL included).
// eslint-disable-next-line no-control-regex
const UNSAFE_CHARACTERS = /[/\\:*?"<>|\x00-\x1f\x7f]/g;

// Names Windows reserves for devices, with or without an extension.
const RESERVED_DEVICE_NAME = /^(con|prn|aux|nul|com[1-9]|lpt[1-9])(\.|$)/i;

// `name` made safe to use as a single file name. Each unsafe character becomes
// `_`, a leading run of dots becomes one `_`, and a device name gets a leading
// `_`. A name with none of these comes back unchanged. An empty name becomes
// `fallback`, which the caller derives from the record's ID.
export const sanitizeFileName = (name: string, fallback: string): string => {
    if (name === "") return fallback;
    const cleaned = name.replace(UNSAFE_CHARACTERS, "_").replace(/^\.+/, "_");
    return RESERVED_DEVICE_NAME.test(cleaned) ? `_${cleaned}` : cleaned;
};

// The extension of `title` (".jpg"), or ".bin" when it has none or it holds
// anything but letters and digits.
export const safeExtension = (title: string): string => {
    const ext = extname(title);
    return /^\.[A-Za-z0-9]+$/.test(ext) ? ext : ".bin";
};