import type { UpstreamConfig } from './upstream';
import { callUpstream } from './upstream';

// The Officer-owned route surface. This is an allow-list, not a passthrough.
//
// Immich's API is already REST and already shaped the way a photo UI wants it, so the value this sidecar
// adds is (a) holding the API key, (b) streaming the binary routes through without buffering them, and
// (c) refusing to expose the administrative half of the API at all.
//
// The gate is the FIRST path segment plus the method. Anything whose first segment is not listed here is a
// 404 before a request is made, so the deny side is closed by construction rather than by enumeration.
//
// DELIBERATELY NOT EXPOSED: admin/* (user creation, deletion, quotas), auth/* and oauth/* (session and
// password machinery — the key is the credential here, and nothing should be minting sessions through a
// dashboard), api-keys/* (a proxy that can mint its own credentials is not a proxy), sessions/*, jobs/*
//
// `auth/*` is STILL refused here, and locked.ts does not change that. Immich's private folder needs four auth
// routes (`auth/status`, `auth/pin-code`, `auth/session/unlock`, `auth/session/lock`), and they are reached
// through named endpoints on a separate `/_locked` surface that each do one thing — not by making `auth` a
// resource anything may address. The distinction is the point: the decision that was taken was "the sidecar
// may unlock the private folder", not "the sidecar may reach session and password machinery".
// (queue control), system-config/* and system-metadata/* (rewrites the deployment), libraries/* (external
// library paths and scans) and sync/*. Those either mutate the deployment or can lock the owner out of it.
// Adding one should be a decision, not an accident.

const RESOURCES: Record<string, readonly string[]> = {
  // The library itself.
  assets: ['GET', 'POST', 'PUT', 'DELETE'],
  albums: ['GET', 'POST', 'PUT', 'PATCH', 'DELETE'],
  timeline: ['GET'],
  memories: ['GET', 'POST', 'PUT', 'DELETE'],
  people: ['GET', 'POST', 'PUT'],
  faces: ['GET', 'PUT'],
  tags: ['GET', 'POST', 'PUT', 'DELETE'],
  stacks: ['GET', 'POST', 'PUT', 'DELETE'],
  // Finding things. `search/metadata`, `search/smart` and `search/random` are POSTs with a JSON body.
  search: ['GET', 'POST'],
  duplicates: ['GET'],
  map: ['GET'],
  view: ['GET'],
  // Getting things out. `download/info` then `download/archive` — both POST, the archive streams a zip.
  download: ['POST'],
  // Recoverable deletes. `trash/empty` is the one irreversible route in this list; it is here because it is
  // the counterpart of a delete the UI can already perform, not because it is safe.
  trash: ['GET', 'POST'],
  // Sharing and social. Read-mostly, but a shared link is the point of them.
  'shared-links': ['GET', 'POST', 'PATCH', 'DELETE'],
  activities: ['GET', 'POST', 'DELETE'],
  partners: ['GET'],
  notifications: ['GET', 'PUT', 'DELETE'],
  // Read-only context: who the key acts as, and what the server is.
  users: ['GET'],
  server: ['GET'],
};

// Response headers worth carrying back. Content-Type and Content-Length for every response; the rest so a
// thumbnail can be cached and revalidated and a video can be seeked without the proxy understanding either.
const PASSTHROUGH_HEADERS = [
  'content-type',
  'content-length',
  'content-disposition',
  'content-range',
  'accept-ranges',
  'etag',
  'last-modified',
  'cache-control',
] as const;

/**
 * Hand one Immich response back to the caller, keeping only the headers above.
 *
 * Shared with the locked-folder surface so both forwarders stream rather than buffer and agree on what a
 * thumbnail is allowed to carry back. 204 and 304 must not have a body attached — Bun throws if one is.
 */
export function relayResponse(res: Response): Response {
  const headers = new Headers();
  for (const name of PASSTHROUGH_HEADERS) {
    const value = res.headers.get(name);
    if (value) headers.set(name, value);
  }

  const body = res.status === 204 || res.status === 304 ? null : res.body;
  return new Response(body, { status: res.status, headers });
}

/**
 * The largest request body held in memory. Above this the body is STREAMED instead — never refused.
 *
 * The cap exists to bound heap, not to bound uploads: a 4 GB video must still go through. What is given
 * up above the cap is only the guarantee that a REJECTION carries its message, and an upload that big
 * which Immich rejects was going to fail either way — see `readBodyCapped`.
 */
const MAX_BUFFERED_BODY = 512 * 1024 * 1024;

/**
 * Read the whole request body into memory, refusing above `MAX_BUFFERED_BODY`.
 *
 * ── Why this is buffered rather than streamed ──
 *
 * It used to stream, which is the obvious thing for an upload and was wrong for one specific reason:
 * when the body is still being written and Immich answers early, the response is lost. Immich rejects
 * an asset as soon as it has enough of the file to judge it, then closes; our writer is still going;
 * Node's HTTP server calls the leftover bytes a protocol violation and replaces the app's answer with a
 * bodyless `400 Bad Request` + `Connection: close`. The app's real message never reaches the wire and
 * Immich logs nothing, so the client sees an unexplained 400 and the server has no record of it.
 *
 * Measured on this machine (COMMS/UPLOAD_EMPTY_400*.md): streamed lost the response in 2 of 4 attempts
 * at 8 MB, 32 MB and 64 MB alike; buffered lost it in 0 of 4 at every size. It is a race, not a size
 * limit — its probability just approaches certainty as the body grows, which is why a phone's video
 * failed every time while a small photo usually got through.
 *
 * A size threshold was considered and rejected: buffering only the small bodies would leave exactly the
 * large uploads that always fail on the broken path. Cancelling the write once the response arrives was
 * tried and does not help — by the time `fetch` resolves, the teardown has already happened.
 *
 * The cost is real and was accepted deliberately: a 300 MB video is 300 MB of this process's heap for
 * the duration of the upload. That is the price of the upload working at all.
 *
 * ── And why there is a ceiling on it ──
 *
 * Buffering everything would mean a 4 GB video sitting in this heap (and another copy in officer's), so
 * above MAX_BUFFERED_BODY the body is streamed as it always was. That is not a refusal and not a
 * degradation of uploads: a file Immich ACCEPTS never triggers the race, because it is read to the end
 * before anything is answered. The only thing lost above the cap is the error message on a file Immich
 * rejects — and an upload that size which Immich rejects fails either way. Refusing it outright would
 * break the legitimate case to improve the diagnosis of the doomed one.
 */
async function readBodyCapped(
  req: Request,
): Promise<{ ok: true; bytes: Uint8Array<ArrayBuffer> } | { ok: false; seen: number }> {
  // Decided from `content-length` alone. Officer sends one whenever IT buffered, so the two hops agree
  // without coordinating: a body small enough for officer to hold is small enough to hold here. When the
  // header is absent officer streamed, which means it was over the cap there too.
  const declared = Number(req.headers.get('content-length') ?? '');
  if (!Number.isFinite(declared) || declared <= 0 || declared > MAX_BUFFERED_BODY) return { ok: false, seen: declared };

  const reader = req.body!.getReader();
  const chunks: Uint8Array[] = [];
  let total = 0;
  for (;;) {
    const { done, value } = await reader.read();
    if (done) break;
    total += value.length;
    if (total > MAX_BUFFERED_BODY) {
      await reader.cancel().catch(() => {});
      return { ok: false, seen: total };
    }
    chunks.push(value);
  }

  const bytes = new Uint8Array(new ArrayBuffer(total));
  let at = 0;
  for (const chunk of chunks) {
    bytes.set(chunk, at);
    at += chunk.length;
  }
  return { ok: true, bytes };
}

/**
 * Forward one request to Immich and stream the answer back.
 *
 * The RESPONSE is still a stream, never an ArrayBuffer: a full-resolution original or a
 * `download/archive` zip is hundreds of megabytes and buffering it would hold all of it in the
 * sidecar's heap for no reason. Only the request body is held, and only for the reason above.
 */
export async function handleOfficerRoute(cfg: UpstreamConfig, req: Request, url: URL): Promise<Response | null> {
  const rest = url.pathname.slice('/_officer/'.length);
  if (!rest) return null;

  const [resource] = rest.split('/');
  const allowedMethods = resource ? RESOURCES[resource] : undefined;
  if (!allowedMethods) return null;
  if (!allowedMethods.includes(req.method)) {
    return Response.json({ error: `${req.method} not allowed on ${resource}` }, { status: 405 });
  }

  const hasBody = req.method !== 'GET' && req.method !== 'HEAD';

  // An <img>/<video> cannot send an Authorization header, so the browser puts Officer's JWT in `?token=`
  // (userMiddleware accepts it there). That token is Officer's, not Immich's: forwarding it would write the
  // owner's session credential into Immich's access log for every thumbnail. Drop it at the boundary.
  const query = new URLSearchParams(url.search);
  query.delete('token');
  const search = query.toString();

  // Buffered, not streamed — see readBodyCapped. A body that is still being written when Immich answers
  // loses the answer, which is what made every large upload fail with an unexplained empty 400.
  let body: BodyInit | null = null;
  if (hasBody && req.body) {
    const read = await readBodyCapped(req);
    // Over the cap (or no declared length): stream it, exactly as this always did. Not an error.
    body = read.ok ? read.bytes : req.body;
  }

  const res = await callUpstream(cfg, {
    path: `/api/${rest}`,
    method: req.method,
    query: search ? `?${search}` : '',
    body,
    contentType: req.headers.get('content-type'),
    range: req.headers.get('range'),
    ifNoneMatch: req.headers.get('if-none-match'),
  });

  return relayResponse(res);
}