/**
 * Network guard for the translation worker.
 *
 * The worker is allowed to fetch exactly two kinds of URLs:
 *   1. the self-hosted model files (GET/HEAD only), and
 *   2. same-origin ONNX runtime assets (.wasm/.mjs/.js).
 *
 * Everything else throws before the request leaves the worker. Message text is
 * never put into a URL or a request body; it only travels through
 * `postMessage` between the UI and the worker.
 */
export interface TranslationGuardOptions {
  modelOrigin: string;
  modelPathPrefix: string;
  appOrigin: string;
  /** Only the self-hosted ONNX runtime (e.g. `/ort/`) may be fetched app-side. */
  appAssetPathPrefix: string;
}

const APP_ASSET = /\.(?:wasm|mjs|js)$/i;

export function createGuardedFetch(
  realFetch: typeof fetch,
  options: TranslationGuardOptions,
): typeof fetch {
  return (async (input: RequestInfo | URL, init?: RequestInit) => {
    const request = input instanceof Request ? input : null;
    const raw = typeof input === 'string'
      ? input
      : input instanceof URL
        ? input.href
        : input.url;
    const url = new URL(raw, request?.url ?? options.appOrigin);
    const method = (init?.method ?? request?.method ?? 'GET').toUpperCase();
    const read = method === 'GET' || method === 'HEAD';
    const isModel = url.origin === options.modelOrigin
      && url.pathname.startsWith(options.modelPathPrefix)
      && !url.search
      && read;
    const isAppAsset = url.origin === options.appOrigin
      && url.pathname.startsWith(options.appAssetPathPrefix)
      && APP_ASSET.test(url.pathname)
      && read;

    if (!isModel && !isAppAsset) {
      throw new Error('blocked network request');
    }
    return realFetch(input as RequestInfo, init);
  }) as typeof fetch;
}