Performance Engineering and Cost Optimization Questions

// Node.js batching utility
function createBatcher({ sendBatch, maxSize = 10, maxWait = 50 }) {
  let queue = []; // { payload, resolve, reject }
  let timer = null;

  function flush() {
    if (timer) { clearTimeout(timer); timer = null; }
    const batch = queue;
    if (!batch.length) return;
    queue = [];

    const batchPayload = batch.map((item, idx) => ({ id: idx, data: item.payload }));
    // call external API
    sendBatch(batchPayload)
      .then(batchResp => {
        // Expect batchResp as array of { id, ok, result, error }
        const byId = new Map(batchResp.map(r => [r.id, r]));
        batch.forEach((item, idx) => {
          const r = byId.get(idx);
          if (r === undefined) item.reject(new Error('Missing response'));
          else if (r.ok) item.resolve(r.result);
          else item.reject(new Error(r.error || 'Item failed'));
        });
      })
      .catch(err => {
        // whole-batch failure
        batch.forEach(item => item.reject(err));
      });
  }

  return {
    submit(payload) {
      return new Promise((resolve, reject) => {
        queue.push({ payload, resolve, reject });
        if (queue.length >= maxSize) flush();
        else if (!timer) timer = setTimeout(flush, maxWait);
      });
    }
  };
}
module.exports = { createBatcher };