/** Svelte action: calls `onIntersect` when the element scrolls into view.
 *  The callback should guard against re-entry (e.g. check `!isFetchingNextPage`). */
export function infiniteScroll(node: HTMLElement, onIntersect: () => void) {
  const observer = new IntersectionObserver(
    (entries) => {
      if (entries[0]?.isIntersecting) {
        onIntersect();
      }
    },
    { rootMargin: "200px" },
  );
  observer.observe(node);
  return {
    update(newFn: () => void) {
      onIntersect = newFn;
    },
    destroy() {
      observer.disconnect();
    },
  };
}