/** Read gateway failures without exposing an HTML error page as a JSON parse error. */
export async function generationResponse(response: Response): Promise<any> {
  const text = await response.text();
  let value: any;
  try {
    value = JSON.parse(text);
  } catch {
    throw Error(
      [502, 503, 504].includes(response.status)
        ? `The deployment gateway could not complete this request (HTTP ${response.status}). Try again shortly.`
        : `The generation server returned an unreadable response (HTTP ${response.status}). Reload after deploying the latest server.`,
    );
  }
  if (!response.ok)
    throw Error(
      typeof value?.error === "string"
        ? value.error
        : `Generation request failed (HTTP ${response.status}).`,
    );
  return value;
}

export async function requestGeneration(
  url: URL,
  input: unknown,
  signal: AbortSignal,
  transport: typeof fetch = fetch,
) {
  let jobUrl: URL | undefined;
  const deadline = AbortSignal.any([signal, AbortSignal.timeout(75_000)]);
  try {
    let result = await generationResponse(
      await transport(url, {
        method: "POST",
        headers: { "content-type": "application/json", prefer: "respond-async" },
        body: JSON.stringify(input),
        signal: deadline,
      }),
    );
    if (!result.job) return result; // Compatible with local engines and older synchronous servers.
    if (typeof result.job.id !== "string" || !/^[a-f0-9-]{36}$/.test(result.job.id))
      throw Error("Invalid generation job response.");
    jobUrl = new URL(url.href.replace(/\/$/, "") + "/jobs/" + result.job.id);
    while (true) {
      await new Promise<void>((resolve, reject) => {
        const aborted = () => {
          clearTimeout(timer);
          reject(deadline.reason);
        };
        const timer = setTimeout(() => {
          deadline.removeEventListener("abort", aborted);
          resolve();
        }, 1000);
        if (deadline.aborted) aborted();
        else deadline.addEventListener("abort", aborted, { once: true });
      });
      result = await generationResponse(
        await transport(jobUrl, { signal: deadline, cache: "no-store" }),
      );
      if (result.status === "complete") return result.result;
      if (result.status === "failed" || result.status === "cancelled")
        throw Error(result.error ?? "Generation did not complete.");
      if (result.status !== "pending") throw Error("Invalid generation job status.");
    }
  } finally {
    if (jobUrl && deadline.aborted) {
      void transport(jobUrl, { method: "DELETE", signal: AbortSignal.timeout(3000) }).catch(
        () => {},
      );
    }
  }
}