Idempotency

// Send one logical create. `idempotencyKey` is generated by the caller ONCE per
// record and stored with that record BEFORE the first send, for example
// `order-${order.number}` or a UUID saved on the outgoing row. After a crash or a
// lost response, calling this again with the stored key replays the first result
// instead of creating a second record.
export async function postIdempotent(path, body, idempotencyKey, attempts = 6) {
  let lastError;
  for (let attempt = 1; attempt <= attempts; attempt++) {
    let response;
    try {
      response = await fetch(`${process.env.BASE}${path}`, {
        method: "POST",
        headers: {
          Authorization: `Bearer ${process.env.KEY}`,
          "Content-Type": "application/json",
          "Idempotency-Key": idempotencyKey,
        },
        body: JSON.stringify(body),
        signal: AbortSignal.timeout(30_000),
      });
    } catch (error) {
      // Network failure or timeout: Mikono may or may not have the request.
      // Retrying with the same key is safe either way.
      lastError = error;
    }
    if (response) {
      if (!(await isRetryable(response))) return response;
      lastError = new Error(`HTTP ${response.status} (${response.headers.get("x-request-id")})`);
    }
    if (attempt < attempts) await sleep(retryDelayMs(response, attempt));
  }
  throw new Error(`Not confirmed after ${attempts} attempts. Retry later with Idempotency-Key ${idempotencyKey}.`, {
    cause: lastError,
  });
}

async function isRetryable(response) {
  if (response.status === 409) {
    const problem = await response.clone().json().catch(() => null);
    return problem?.code === "idempotency_in_progress";
  }
  return response.status === 429 || response.status >= 500;
}

function retryDelayMs(response, attempt) {
  const retryAfter = Number(response?.headers.get("retry-after"));
  if (Number.isFinite(retryAfter) && retryAfter > 0) return retryAfter * 1000;
  return Math.min(2 ** attempt, 60) * 1000; // 2, 4, 8 … seconds, at most one minute
}

const sleep = (ms) => new Promise((resolve) => setTimeout(resolve, ms));

// Usage: the key is saved with the order first, then sent.
// const key = await saveIdempotencyKey(order.id, `order-${order.number}`);
// const response = await postIdempotent("/{resource}", payload, key);