// Bounds how many async tasks run at once. Used both for fanning out
// concurrent DB upserts and concurrent HTTP requests.
export function createLimiter(concurrency: number) {
  let active = 0;
  const queue: Array<() => void> = [];

  function release() {
    active--;
    queue.shift()?.();
  }

  return async function limit<T>(fn: () => Promise<T>): Promise<T> {
    if (active >= concurrency) {
      await new Promise<void>((resolve) => queue.push(resolve));
    }
    active++;
    try {
      return await fn();
    } finally {
      release();
    }
  };
}