Error codes and how to handle them

export class MiraiError extends Error {
  constructor(status, code, message) {
    super(`${status} ${code}: ${message}`);
    this.status = status;
    this.code = code;
  }
}

const RETRYABLE = new Set([429, 500, 502, 503, 504]);
const sleep = (ms) => new Promise((r) => setTimeout(r, ms));

export async function request(path, init = {}, attempt = 0) {
  const res = await fetch(`https://sandbox.voice.miraiminds.co${path}`, {
    ...init,
    headers: {
      Authorization: `Bearer ${process.env.MIRAI_API_KEY}`,
      "Content-Type": "application/json",
      ...init.headers,
    },
  });

  if (res.ok) return res.status === 204 ? null : res.json();

  const body = await res.json().catch(() => ({}));
  const { code = "unknown", message = res.statusText } = body.error ?? {};

  if (RETRYABLE.has(res.status) && attempt < 4) {
    const retryAfter = Number(res.headers.get("Retry-After"));
    const wait = (Number.isFinite(retryAfter) ? retryAfter : 2 ** attempt) * 1000;
    await sleep(wait + Math.random() * 1000);
    return request(path, init, attempt + 1);
  }

  throw new MiraiError(res.status, code, message);
}

try {
  const call = await request("/v2/calls", {
    method: "POST",
    headers: { "Idempotency-Key": key },
    body: JSON.stringify(payload),
  });
} catch (e) {
  if (e.code === "insufficient_balance") {
    await pauseCampaign();
    await alertOps(e.message);
  } else if (e.code !== "duplicate_call") {
    throw e; // duplicate_call means the same key is still in flight
  }
}