/**
 * @fileoverview Accept empty, untyped API POSTs even when a reverse proxy frames them as chunked.
 *
 * Cloudflare Tunnel (cloudflared, Go's HTTP client) forwards a bodyless POST as an HTTP/1.1
 * chunked request with no Content-Type and a zero-length body. Fastify only skips its
 * content-type check for a `Content-Length: 0` request, so this framing was refused 415
 * (`FST_ERR_CTP_INVALID_MEDIA_TYPE`) before the route ran, breaking actions such as opening a
 * saved web tab. This parser lets such a request reach its route with `request.body === undefined`,
 * exactly as a `Content-Length: 0` request does.
 *
 * Scope is POST under `/api/` only: Go frames an empty body of unknown length as chunked for
 * POST, PUT and PATCH and drops it for DELETE, and every PUT/PATCH the frontend sends carries a
 * JSON body. Anything else (another method, a non-API route, a Content-Type, a non-zero
 * Content-Length, or a single body byte) is still the 415 Fastify would have answered.
 *
 * ⚠️ It owns the ROOT `'*'` content-type slot. The JSON, `text/plain` (kept RAW, see the CSRF
 * note in CLAUDE.md) and multipart parsers match first; the web-tab proxy registers its own
 * `'*'` in an encapsulated scope and is unaffected. Fastify refuses a second root `'*'` parser at
 * boot (`FST_ERR_CTP_ALREADY_PRESENT`), so extend this function instead of adding one.
 */
import { errorCodes, type FastifyInstance, type FastifyRequest } from 'fastify';
import type { Readable } from 'node:stream';

export function installEmptyApiPostParser(app: FastifyInstance): void {
  // Existing JSON, text and multipart parsers take precedence. The webview
  // proxy installs its own parser in an encapsulated scope.
  app.addContentTypeParser('*', async (req: FastifyRequest, payload: Readable) => {
    // Fastify normally skips an unsupported parser on its 404 path. Preserve
    // that behavior, including the unread stream used by referer fallbacks.
    if (req.is404) return undefined;

    if (
      req.method !== 'POST' ||
      !req.routeOptions.url?.startsWith('/api/') ||
      req.headers['content-type'] !== undefined ||
      (req.headers['content-length'] !== undefined && req.headers['content-length'] !== '0')
    ) {
      throw new errorCodes.FST_ERR_CTP_INVALID_MEDIA_TYPE();
    }

    // Wait for the terminating chunk to prove the body is empty. Reject on the
    // first byte instead of buffering an unsupported body. Leave the socket
    // alive so Fastify can send its 415 and close the connection on parser errors.
    try {
      for await (const chunk of payload.iterator({ destroyOnReturn: false })) {
        if (Buffer.byteLength(chunk) > 0) throw new errorCodes.FST_ERR_CTP_INVALID_MEDIA_TYPE();
      }
    } catch (error) {
      // Match Fastify's body reader: an interrupted request is a client error.
      const err = error as Error & { statusCode?: number };
      if (typeof err.statusCode !== 'number' || err.statusCode < 400) err.statusCode = 400;
      throw err;
    }

    // No synthetic JSON or header rewriting: required-body validation still
    // sees the same undefined value as a direct Content-Length: 0 request.
    return undefined;
  });
}