Rebuild useScroll, less states

src/app.css

@@ -1092,6 +1092,13 @@ a[href^='http'][rel*='nofollow']:visited:not(:has(div)) {
   transform: translate(-50%, 0);
   font-size: 90%;
   pointer-events: auto;
+  transition: all 0.3s ease-in-out;
+
+  header[hidden] & {
+    opacity: 0;
+    transform: translate(-50%, -100%) scale(0.9);
+    pointer-events: none;
+  }
 }
 .updates-button .icon {
   vertical-align: top;

src/components/timeline.jsx

@@ -12,6 +12,7 @@ import { groupBoosts, groupContext } from '../utils/timeline-utils';
 import useInterval from '../utils/useInterval';
 import usePageVisibility from '../utils/usePageVisibility';
 import useScroll from '../utils/useScroll';
+import useScrollFn from '../utils/useScrollFn';
 
 import Icon from './icon';
 import Link from './link';
@@ -203,17 +204,47 @@ function Timeline({
     }
   });
 
-  const {
+  // const {
+  //   scrollDirection,
+  //   nearReachStart,
+  //   nearReachEnd,
+  //   reachStart,
+  //   reachEnd,
+  // } = useScroll({
+  //   scrollableRef,
+  //   distanceFromEnd: 2,
+  //   scrollThresholdStart: 44,
+  // });
+  const headerRef = useRef();
+  // const [hiddenUI, setHiddenUI] = useState(false);
+  const [nearReachStart, setNearReachStart] = useState(false);
+  useScrollFn(
+    {
+      scrollableRef,
+      distanceFromEnd: 2,
+      scrollThresholdStart: 44,
+    },
+    ({
       scrollDirection,
       nearReachStart,
       nearReachEnd,
       reachStart,
       reachEnd,
-  } = useScroll({
-    scrollableRef,
-    distanceFromEnd: 2,
-    scrollThresholdStart: 44,
-  });
+    }) => {
+      // setHiddenUI(scrollDirection === 'end' && !nearReachEnd);
+      if (headerRef.current) {
+        const hiddenUI = scrollDirection === 'end' && !nearReachStart;
+        headerRef.current.hidden = hiddenUI;
+      }
+      setNearReachStart(nearReachStart);
+      if (reachStart) {
+        loadItems(true);
+      } else if (nearReachEnd || (reachEnd && showMore)) {
+        loadItems();
+      }
+    },
+    [],
+  );
 
   useEffect(() => {
     scrollableRef.current?.scrollTo({ top: 0 });
@@ -223,17 +254,17 @@ function Timeline({
     loadItems(true);
   }, [refresh]);
 
-  useEffect(() => {
-    if (reachStart) {
-      loadItems(true);
-    }
-  }, [reachStart]);
+  // useEffect(() => {
+  //   if (reachStart) {
+  //     loadItems(true);
+  //   }
+  // }, [reachStart]);
 
-  useEffect(() => {
-    if (nearReachEnd || (reachEnd && showMore)) {
-      loadItems();
-    }
-  }, [nearReachEnd, showMore]);
+  // useEffect(() => {
+  //   if (nearReachEnd || (reachEnd && showMore)) {
+  //     loadItems();
+  //   }
+  // }, [nearReachEnd, showMore]);
 
   const prevView = useRef(view);
   useEffect(() => {
@@ -304,7 +335,7 @@ function Timeline({
       : null,
   );
 
-  const hiddenUI = scrollDirection === 'end' && !nearReachStart;
+  // const hiddenUI = scrollDirection === 'end' && !nearReachStart;
 
   return (
     <FilterContext.Provider value={filterContext}>
@@ -321,7 +352,8 @@ function Timeline({
       >
         <div class="timeline-deck deck">
           <header
-            hidden={hiddenUI}
+            ref={headerRef}
+            // hidden={hiddenUI}
             onClick={(e) => {
               if (!e.target.closest('a, button')) {
                 scrollableRef.current?.scrollTo({
@@ -356,7 +388,7 @@ function Timeline({
             </div>
             {items.length > 0 &&
               uiState !== 'loading' &&
-              !hiddenUI &&
+              // !hiddenUI &&
               showNew && (
                 <button
                   class="updates-button shiny-pill"
@@ -657,13 +689,27 @@ function TimelineItem({
 
 function StatusCarousel({ title, class: className, children }) {
   const carouselRef = useRef();
-  const { reachStart, reachEnd, init } = useScroll({
+  // const { reachStart, reachEnd, init } = useScroll({
+  //   scrollableRef: carouselRef,
+  //   direction: 'horizontal',
+  // });
+  const startButtonRef = useRef();
+  const endButtonRef = useRef();
+  useScrollFn(
+    {
       scrollableRef: carouselRef,
       direction: 'horizontal',
-  });
-  useEffect(() => {
-    init?.();
-  }, []);
+      init: true,
+    },
+    ({ reachStart, reachEnd }) => {
+      if (startButtonRef.current) startButtonRef.current.disabled = reachStart;
+      if (endButtonRef.current) endButtonRef.current.disabled = reachEnd;
+    },
+    [],
+  );
+  // useEffect(() => {
+  //   init?.();
+  // }, []);
 
   return (
     <div class={`status-carousel ${className}`}>
@@ -671,9 +717,10 @@ function StatusCarousel({ title, class: className, children }) {
         <h3>{title}</h3>
         <span>
           <button
+            ref={startButtonRef}
             type="button"
             class="small plain2"
-            disabled={reachStart}
+            // disabled={reachStart}
             onClick={() => {
               carouselRef.current?.scrollBy({
                 left: -Math.min(320, carouselRef.current?.offsetWidth),
@@ -684,9 +731,10 @@ function StatusCarousel({ title, class: className, children }) {
             <Icon icon="chevron-left" />
           </button>{' '}
           <button
+            ref={endButtonRef}
             type="button"
             class="small plain2"
-            disabled={reachEnd}
+            // disabled={reachEnd}
             onClick={() => {
               carouselRef.current?.scrollBy({
                 left: Math.min(320, carouselRef.current?.offsetWidth),

src/utils/useScrollFn.js

@@ -0,0 +1,126 @@
+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'));
+  //     }
+  //   },
+  // };
+}