01Bottom spinner fade — a loading indicator computing its opacity from the remaining scroll distance

<main class="stage">
<div class="bsf is-demo" id="bsf">
  <div class="bsf__view" id="bsfView" tabindex="0">
    <ul class="bsf__track" id="bsfTrack" aria-live="polite">
      <li class="bsf__sentinel" id="bsfSentinel" aria-hidden="true">
        <span class="bsf__ring" id="bsfRing"></span>
      </li>
    </ul>
  </div>
  <p class="bsf__hint" id="bsfHint">Scroll to the bottom to load the next batch</p>
</div>
</main>

@use "../../../../site/static/demo-tokens" as *;

// 하단 스피너 페이드 — 스피너 불투명도는 표시 시간이 아니라 남은 스크롤 거리 값에서 매번
// 다시 계산된다(recomputeFade). 회전 각도도 CSS 키프레임이 아니라 rAF 로 매 틱 계산해 더한다.

$duration: $dur-base;
$easing: $ease-spring;
$color: $subject-blue;

@include stage($stage-ink);

.bsf {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: $sp-3;
  width: min(100%, 280px);
}

.bsf__view {
  position: relative;
  box-sizing: border-box;
  width: 100%;
  height: 188px;
  overflow-y: auto;
  overflow-x: hidden;
  border-radius: $r-card;
  background: rgba(255, 255, 255, .06);
  padding: $sp-3;
  scrollbar-width: thin;
}

.bsf__track {
  list-style: none;
  margin: 0;
  padding: 0 0 $sp-12;
  display: flex;
  flex-direction: column;
  gap: $sp-2;
}

.bsf__row {
  box-sizing: border-box;
  padding: $sp-3 $sp-4;
  border-radius: $r-sm;
  background: rgba(255, 255, 255, .08);
  color: $stage-paper;
  font-weight: 600;
  font-size: 12px;
}

.bsf__sentinel {
  display: flex;
  justify-content: center;
  align-items: center;
  height: 30px;
  pointer-events: none;
}

.bsf__ring {
  display: block;
  width: 22px;
  height: 22px;
  opacity: 0;
  border-radius: $r-pill;
  border: 3px solid rgba(255, 255, 255, .18);
  border-top-color: $color;
  box-sizing: border-box;
}

.bsf__hint {
  margin: 0;
  font-size: 11px;
  color: rgba(255, 255, 255, .55);
  text-align: center;
}

@media (max-width: 340px) {
  .bsf { gap: $sp-1; }
  .bsf__view { height: 90px; }
  .bsf__row { padding: $sp-2 $sp-3; font-size: 11px; }
}

@media (prefers-reduced-motion: reduce) {
  .bsf__ring { animation: none !important; }
}

html, body {
  margin: 0;
  overflow: hidden;
}

.stage {
  box-sizing: border-box;
  min-height: 100vh;
  display: grid;
  place-items: center;
  margin: 0;
  background: #17141a;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  padding: clamp(8px, 4vw, 24px);
}

.bsf {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 12px;
  width: min(100%, 280px);
}

.bsf__view {
  position: relative;
  box-sizing: border-box;
  width: 100%;
  height: 188px;
  overflow-y: auto;
  overflow-x: hidden;
  border-radius: 16px;
  background: rgba(255, 255, 255, 0.06);
  padding: 12px;
  scrollbar-width: thin;
}

.bsf__track {
  list-style: none;
  margin: 0;
  padding: 0 0 48px;
  display: flex;
  flex-direction: column;
  gap: 8px;
}

.bsf__row {
  box-sizing: border-box;
  padding: 12px 16px;
  border-radius: 8px;
  background: rgba(255, 255, 255, 0.08);
  color: #ffffff;
  font-weight: 600;
  font-size: 12px;
}

.bsf__sentinel {
  display: flex;
  justify-content: center;
  align-items: center;
  height: 30px;
  pointer-events: none;
}

.bsf__ring {
  display: block;
  width: 22px;
  height: 22px;
  opacity: 0;
  border-radius: 999px;
  border: 3px solid rgba(255, 255, 255, 0.18);
  border-top-color: #2f6df6;
  box-sizing: border-box;
}

.bsf__hint {
  margin: 0;
  font-size: 11px;
  color: rgba(255, 255, 255, 0.55);
  text-align: center;
}

@media (max-width: 340px) {
  .bsf {
    gap: 4px;
  }
  .bsf__view {
    height: 90px;
  }
  .bsf__row {
    padding: 8px 12px;
    font-size: 11px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .bsf__ring {
    animation: none !important;
  }
}

(function () {
  var view = document.getElementById('bsfView');
  var track = document.getElementById('bsfTrack');
  var sentinel = document.getElementById('bsfSentinel');
  var ring = document.getElementById('bsfRing');
  var hint = document.getElementById('bsfHint');
  var root = document.getElementById('bsf');

  var TOPICS = ['Alert', 'Note', 'Photo', 'Song', 'Event', 'Doc'];
  var THRESHOLD_PX = 96;   // 계산에 쓰는 임계 거리(스피너가 서서히 짙어지는 구간의 폭)
  var LOAD_DELAY_MS = 620;
  var BATCH_SIZE = 3;
  var MAX_ROWS = 21;
  var AUTOPLAY_STEP_PX = 6;

  var rowCount = 0;
  var loading = false;
  var spinAngle = 0;
  var spinRaf = null;
  var autoplayTimer = null;
  var dir = 1;

  function addRow() {
    var li = document.createElement('li');
    li.className = 'bsf__row';
    var topic = TOPICS[rowCount % TOPICS.length];
    li.textContent = topic + ' ' + String(rowCount + 1).padStart(2, '0');
    track.insertBefore(li, sentinel);
    rowCount += 1;
  }

  for (var i = 0; i < 6; i += 1) { addRow(); }

  function spinTick() {
    spinAngle = (spinAngle + 9) % 360;
    ring.style.transform = 'rotate(' + spinAngle + 'deg)';
    if (loading) { spinRaf = requestAnimationFrame(spinTick); }
  }

  // 계산 겹: 스피너(sentinel) 상단과 스크롤 뷰 하단 사이의 실측 거리 값을 임계 거리로 나눠
  // 0~1 진행값을 만들고, 그 값을 그대로 스피너 불투명도로 쓴다 — scrollTop 이 아니라
  // getBoundingClientRect 로 잰 실제 화면 위 거리이므로 패딩·보더가 바뀌어도 계산이 맞는다.
  function recomputeFade() {
    var viewBottom = view.getBoundingClientRect().bottom;
    var sentinelTop = sentinel.getBoundingClientRect().top;
    var remaining = sentinelTop - viewBottom;
    var progress = 1 - Math.min(Math.max(remaining / THRESHOLD_PX, 0), 1);
    ring.style.opacity = String(progress);
    if (remaining <= 0 && !loading && rowCount < MAX_ROWS) {
      startLoad();
    }
    hint.textContent = (remaining <= 0 && rowCount >= MAX_ROWS)
      ? 'Scroll further to return to the start'
      : 'Scroll to the bottom to load the next batch';
  }

  function startLoad() {
    loading = true;
    spinRaf = requestAnimationFrame(spinTick);
    setTimeout(function () {
      for (var n = 0; n < BATCH_SIZE && rowCount < MAX_ROWS; n += 1) { addRow(); }
      loading = false;
      cancelAnimationFrame(spinRaf);
      recomputeFade();
    }, LOAD_DELAY_MS);
  }

  view.addEventListener('scroll', recomputeFade);

  function userTakesOver() {
    if (!root.classList.contains('is-demo')) { return; }
    root.classList.remove('is-demo');
    stopAutoplay();
  }
  view.addEventListener('wheel', userTakesOver, { passive: true });
  view.addEventListener('touchstart', userTakesOver, { passive: true });

  function autoplayTick() {
    var max = view.scrollHeight - view.clientHeight;
    if (rowCount >= MAX_ROWS && view.scrollTop >= max - 1 && dir !== 0) {
      dir = 0;
      setTimeout(function () {
        while (track.firstChild !== sentinel) { track.removeChild(track.firstChild); }
        rowCount = 0;
        for (var i = 0; i < 6; i += 1) { addRow(); }
        view.scrollTop = 0;
        dir = 1;
        recomputeFade();
      }, 500);
      return;
    }
    if (dir === 0) { return; }
    view.scrollTop = Math.min(view.scrollTop + AUTOPLAY_STEP_PX * dir, max);
    recomputeFade();
  }

  function stopAutoplay() {
    if (autoplayTimer) { clearInterval(autoplayTimer); autoplayTimer = null; }
  }

  var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;
  if (!reduce) {
    autoplayTimer = setInterval(autoplayTick, 60);
  }
  recomputeFade();
})();

import { useEffect, useRef, useState, useCallback } from "react";
import type { ReactNode } from "react";
import styles from "./BottomSpinnerFade.module.scss";

// 하단 스피너 페이드 — 스피너 불투명도는 남은 스크롤 거리 값에서 매번 다시 계산된다.
// 계산 겹: getBoundingClientRect 로 잰 sentinel 상단-뷰 하단 거리를 임계 거리로 나눠 0~1 진행값.
const TOPICS = ["알림", "메모", "사진", "노래", "일정", "문서"];
const THRESHOLD_PX = 96;
const LOAD_DELAY_MS = 620;
const BATCH_SIZE = 3;
const MAX_ROWS = 21;
const AUTOPLAY_STEP_PX = 6;

type Spin = { angle: number };

export default function BottomSpinnerFade() {
  const rootRef = useRef<HTMLDivElement>(null);
  const viewRef = useRef<HTMLDivElement>(null);
  const trackRef = useRef<HTMLUListElement>(null);
  const sentinelRef = useRef<HTMLLIElement>(null);
  const ringRef = useRef<HTMLSpanElement>(null);
  const [rowCount, setRowCount] = useState(6);
  const [hint, setHint] = useState("끝까지 내리면 다음 묶음을 불러옵니다");
  const loadingRef = useRef(false);
  const spinRef = useRef<Spin>({ angle: 0 });
  const spinRafRef = useRef<number | null>(null);
  const rowCountRef = useRef(6);
  rowCountRef.current = rowCount;
  const dirRef = useRef(1);
  const autoplayRef = useRef<number | null>(null);

  const addRows = useCallback((count: number) => {
    setRowCount((prev) => Math.min(prev + count, MAX_ROWS));
  }, []);

  const spinTick = useCallback(() => {
    const spin = spinRef.current ?? { angle: 0 };
    spin.angle = (spin.angle + 9) % 360;
    if (ringRef.current) {
      ringRef.current.style.transform = `rotate(${spin.angle}deg)`;
    }
    if (loadingRef.current) {
      spinRafRef.current = window.requestAnimationFrame(spinTick);
    }
  }, []);

  // 계산 겹: 남은 스크롤 거리 값을 임계 거리로 나눠 0~1 진행값을 만들고 그 값을
  // 스피너 불투명도로 그대로 쓴다 — 표시 시간이 아니라 거리 값 하나로 짙기가 정해진다.
  const recomputeFade = useCallback(() => {
    const view = viewRef.current;
    const sentinel = sentinelRef.current;
    const ring = ringRef.current;
    if (!view || !sentinel || !ring) { return; }
    const viewBottom = view.getBoundingClientRect().bottom;
    const sentinelTop = sentinel.getBoundingClientRect().top;
    const remaining = sentinelTop - viewBottom;
    const progress = 1 - Math.min(Math.max(remaining / THRESHOLD_PX, 0), 1);
    ring.style.opacity = String(progress);
    const count = rowCountRef.current ?? 0;
    setHint(remaining <= 0 && count >= MAX_ROWS
      ? "더 내리면 처음으로 되돌아갑니다"
      : "끝까지 내리면 다음 묶음을 불러옵니다");
    if (remaining <= 0 && !loadingRef.current && count < MAX_ROWS) {
      loadingRef.current = true;
      spinRafRef.current = window.requestAnimationFrame(spinTick);
      window.setTimeout(() => {
        addRows(BATCH_SIZE);
        loadingRef.current = false;
        if (spinRafRef.current !== null) { window.cancelAnimationFrame(spinRafRef.current); }
      }, LOAD_DELAY_MS);
    }
  }, [addRows, spinTick]);

  useEffect(() => {
    const view = viewRef.current;
    if (!view) { return; }
    const onScroll = () => recomputeFade();
    view.addEventListener("scroll", onScroll);
    const takeover = () => {
      rootRef.current?.classList.remove(styles["is-demo"]);
      if (autoplayRef.current !== null) { window.clearInterval(autoplayRef.current); }
    };
    view.addEventListener("wheel", takeover, { passive: true });
    view.addEventListener("touchstart", takeover, { passive: true });

    const reduce = window.matchMedia("(prefers-reduced-motion: reduce)").matches;
    if (!reduce) {
      autoplayRef.current = window.setInterval(() => {
        const v = viewRef.current;
        if (!v) { return; }
        const max = v.scrollHeight - v.clientHeight;
        const count = rowCountRef.current ?? 0;
        if (count >= MAX_ROWS && v.scrollTop >= max - 1 && dirRef.current !== 0) {
          dirRef.current = 0;
          window.setTimeout(() => {
            setRowCount(6);
            v.scrollTop = 0;
            dirRef.current = 1;
            recomputeFade();
          }, 500);
          return;
        }
        if (dirRef.current === 0) { return; }
        v.scrollTop = Math.min(v.scrollTop + AUTOPLAY_STEP_PX, max);
        recomputeFade();
      }, 60);
    }
    recomputeFade();
    return () => {
      view.removeEventListener("scroll", onScroll);
      view.removeEventListener("wheel", takeover);
      view.removeEventListener("touchstart", takeover);
      if (autoplayRef.current !== null) { window.clearInterval(autoplayRef.current); }
      if (spinRafRef.current !== null) { window.cancelAnimationFrame(spinRafRef.current); }
    };
  }, [recomputeFade]);

  const rows: ReactNode[] = [];
  for (let i = 0; i < rowCount; i += 1) {
    rows.push(
      <li key={i} className={styles["bsf__row"]}>
        {TOPICS[i % TOPICS.length]} {String(i + 1).padStart(2, "0")}
      </li>
    );
  }

  return (
    <main className={styles.stage}>
      <div ref={rootRef} className={`${styles.bsf} ${styles["is-demo"]}`} id="bsf">
        <div ref={viewRef} className={styles["bsf__view"]} tabIndex={0}>
          <ul ref={trackRef} className={styles["bsf__track"]} aria-live="polite">
            {rows}
            <li ref={sentinelRef} className={styles["bsf__sentinel"]} aria-hidden="true">
              <span ref={ringRef} className={styles["bsf__ring"]} />
            </li>
          </ul>
        </div>
        <p className={styles["bsf__hint"]}>{hint}</p>
      </div>
    </main>
  );
}