import { mkdir, readFile, writeFile } from 'node:fs/promises';
import path from 'node:path';

let cacheDir = process.env.ICON_CACHE || '/var/lib/void/icons';
let fetcher = defaultFetcher;
export function _setCacheDir(d) { cacheDir = d; }
export function _setFetcher(fn) { fetcher = fn || defaultFetcher; }

const VALID = /^[a-z0-9-]+$/;
export function validSlug(slug) { return VALID.test(slug); }

async function defaultFetcher(slug) {
  const url = `https://cdn.jsdelivr.net/gh/walkxcode/dashboard-icons/png/${slug}.png`;
  const res = await fetch(url, { signal: AbortSignal.timeout(8000) });
  if (!res.ok) return null;
  return Buffer.from(await res.arrayBuffer());
}

function isPng(buf) { return buf && buf.length > 8 && buf[0] === 0x89 && buf[1] === 0x50 && buf[2] === 0x4e && buf[3] === 0x47; }

// Returns a Buffer (cached or freshly fetched) or null if upstream has no icon.
export async function getIcon(slug) {
  if (!validSlug(slug)) throw new Error('invalid slug');
  const file = path.join(cacheDir, `${slug}.png`);
  try { return await readFile(file); } catch { /* miss → fetch */ }
  const buf = await fetcher(slug);
  if (!isPng(buf)) return null;
  await mkdir(cacheDir, { recursive: true });
  await writeFile(file, buf);
  return buf;
}