phanpy/src/utils/useScrollFn.js

import { useEffect, useLayoutEffect, useState } from 'preact/hooks';

export default function useScrollFn(
  {
    scrollableRef,
    distanceFromStart = 1, // ratio of clientHeight/clientWidth
    distanceFromEnd = 1, // ratio of clientHeight/clientWidth
    scrollThresholdStart = 10,
    scrollThresholdEnd = 10,
    direction = 'vertical',
    distanceFromStartPx: _distanceFromStartPx,
    distanceFromEndPx: _distanceFromEndPx,
    init,
  } = {},
  callback,
  deps,
) {
  if (!callback) return;
  const [scrollDirection, setScrollDirection] = useState(null);
  const [reachStart, setReachStart] = useState(false);
  const [reachEnd, setReachEnd] = useState(false);
  const [nearReachStart, setNearReachStart] = useState(false);
  const [nearReachEnd, setNearReachEnd] = useState(false);
  const isVertical = direction === 'vertical';

  useLayoutEffect(() => {
    const scrollableElement = scrollableRef.current;
    if (!scrollableElement) return {};
    let previousScrollStart = isVertical
      ? scrollableElement.scrollTop
      : scrollableElement.scrollLeft;

    function onScroll() {
      const {
        scrollTop,
        scrollLeft,
        scrollHeight,
        scrollWidth,
        clientHeight,
        clientWidth,
      } = scrollableElement;
      const scrollStart = isVertical ? scrollTop : scrollLeft;
      const scrollDimension = isVertical ? scrollHeight : scrollWidth;
      const clientDimension = isVertical ? clientHeight : clientWidth;
      const scrollDistance = Math.abs(scrollStart - previousScrollStart);
      const distanceFromStartPx =
        _distanceFromStartPx ||
        Math.min(
          clientDimension * distanceFromStart,
          scrollDimension,
          scrollStart,
        );
      const distanceFromEndPx =
        _distanceFromEndPx ||
        Math.min(
          clientDimension * distanceFromEnd,
          scrollDimension,
          scrollDimension - scrollStart - clientDimension,
        );

      if (
        scrollDistance >=
        (previousScrollStart < scrollStart
          ? scrollThresholdEnd
          : scrollThresholdStart)
      ) {
        setScrollDirection(previousScrollStart < scrollStart ? 'end' : 'start');
        previousScrollStart = scrollStart;
      }

      setReachStart(scrollStart <= 0);
      setReachEnd(scrollStart + clientDimension >= scrollDimension);
      setNearReachStart(scrollStart <= distanceFromStartPx);
      setNearReachEnd(
        scrollStart + clientDimension >= scrollDimension - distanceFromEndPx,
      );
    }

    scrollableElement.addEventListener('scroll', onScroll, { passive: true });

    return () => scrollableElement.removeEventListener('scroll', onScroll);
  }, [
    distanceFromStart,
    distanceFromEnd,
    scrollThresholdStart,
    scrollThresholdEnd,
  ]);

  useEffect(() => {
    callback({
      scrollDirection,
      reachStart,
      reachEnd,
      nearReachStart,
      nearReachEnd,
    });
  }, [
    scrollDirection,
    reachStart,
    reachEnd,
    nearReachStart,
    nearReachEnd,
    ...deps,
  ]);

  useEffect(() => {
    if (init && scrollableRef.current) {
      queueMicrotask(() => {
        scrollableRef.current.dispatchEvent(new Event('scroll'));
      });
    }
  }, [init]);

  // return {
  //   scrollDirection,
  //   reachStart,
  //   reachEnd,
  //   nearReachStart,
  //   nearReachEnd,
  //   init: () => {
  //     if (scrollableRef.current) {
  //       scrollableRef.current.dispatchEvent(new Event('scroll'));
  //     }
  //   },
  // };
}