06Footer loader that fetches the next page at the end of the list

<main class="stage">
  <section class="inf is-demo" id="inf" aria-label="Infinite scroll list">
    <div class="inf__box" id="inf-box" tabindex="0" aria-label="Scrollable list">
      <ol class="inf__list" id="inf-list">
        <li class="inf__card"><span class="inf__no">1</span><span class="inf__t">Today's log</span></li>
        <li class="inf__card"><span class="inf__no">2</span><span class="inf__t">A short note</span></li>
        <li class="inf__card"><span class="inf__no">3</span><span class="inf__t">Weekend plan</span></li>
        <li class="inf__card"><span class="inf__no">4</span><span class="inf__t">The book I left</span></li>
        <li class="inf__card"><span class="inf__no">5</span><span class="inf__t">Saved links</span></li>
        <li class="inf__card"><span class="inf__no">6</span><span class="inf__t">Photo cleanup</span></li>
      </ol>
      <div class="inf__loader" id="inf-loader">
        <span class="inf__pulse" aria-hidden="true"></span>
        <span class="inf__loader-t">Fetching the next page</span>
      </div>
    </div>
    <p class="inf__live" id="inf-live" aria-live="polite">Showing 6 cards</p>
  </section>
</main>

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

// 무한 스크롤 바닥 로더 — 목록 상자 안에서만 스크롤이 일어난다.
// 무대(480×300)는 stage 믹스인이 overflow: hidden 으로 잡아 두므로 무대 자체가 넘치면 안 된다.
// IntersectionObserver 는 CSS 시계로 못 재니, 미리보기 루프는 로더가 맥박 치고
// 마지막 카드 셋이 animation-delay 시차로 translateY 올라오는 모습만 보여 준다.
// 카드가 사라지는 장면은 재현하지 않는다 — 복귀는 86% 안에서 한 프레임 컷이다.
$duration: $dur-base;
$easing: $ease-spring;
$color: $subject-ink;

@include stage($stage-yellow);

.inf {
  box-sizing: border-box;
  display: grid;
  gap: $sp-2;
  width: min(300px, 94vw);
  color: $color;
}
.inf * { box-sizing: border-box; }

// ── 목록 상자: 스크롤은 여기 안에서만 ──
.inf__box {
  height: 196px;
  overflow-y: auto;
  overscroll-behavior: contain;
  scrollbar-width: thin;
  display: grid;
  align-content: start;
  gap: $sp-2;
  padding: $sp-2;
  border-radius: $r-card;
  background: rgba(23, 20, 26, .08);
}
.inf__box:focus-visible { outline: 2px solid $color; outline-offset: 2px; }

.inf__list {
  display: grid;
  gap: $sp-2;
  margin: 0;
  padding: 0;
  list-style: none;
}
.inf__card {
  display: flex;
  align-items: center;
  gap: $sp-2;
  height: 32px;
  padding: 0 $sp-3;
  border-radius: $r-control;
  background: $subject-cream;
  font-size: 13px;
  font-weight: 700;
  line-height: 1;
}
.inf__no {
  display: inline-grid;
  place-items: center;
  width: 20px;
  height: 20px;
  border-radius: 50%;
  background: rgba(23, 20, 26, .12);
  font-size: 11px;
  font-weight: 700;
}

// ── 바닥 로더 카드 ──
.inf__loader {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: $sp-2;
  height: 34px;
  border: 2px dashed rgba(23, 20, 26, .38);
  border-radius: $r-control;
  font-size: 12px;
  font-weight: 700;
  line-height: 1;
}
.inf__pulse {
  width: 12px;
  height: 12px;
  border-radius: 50%;
  background: $color;
}

.inf__live {
  margin: 0;
  font-size: 12px;
  font-weight: 700;
  line-height: 1.3;
}

// ── 실제로 붙은 카드: 한 번만 올라온다 (사람이 스크롤한 경로) ──
@keyframes inf-in {
  from { transform: translateY(6px); opacity: 0; }
  to { transform: translateY(0); opacity: 1; }
}
.inf__card--in {
  animation-name: inf-in;
  animation-duration: $duration;
  animation-timing-function: $easing;
  animation-iteration-count: 1;
  animation-fill-mode: backwards;
}

// ── 격자 미리보기 전용 2초 루프 ──
// 카드는 한순간도 사라지지 않는다. 올라온 뒤 86% 에 제자리로 한 프레임 컷.
// 내려간 폭(6px)은 카드 사이 간격(8px)보다 작다 — 되돌아간 순간에도 카드끼리 붙어 보이지 않는다.
@keyframes inf-rise {
  0%, 8% { transform: translateY(6px); }
  34%, 86% { transform: translateY(0); }
  86.01%, 100% { transform: translateY(6px); }
}
@keyframes inf-pulse {
  0% { transform: scale(1); }
  22% { transform: scale(1.5); }
  44% { transform: scale(1); }
  66% { transform: scale(1.5); }
  88%, 100% { transform: scale(1); }
}

.inf.is-demo {
  // 지연이 걸린 애니메이션은 backwards 가 없으면 첫 프레임에 기본 상태로 번쩍인다
  .inf__card:nth-last-child(-n + 3) {
    animation-name: inf-rise;
    animation-duration: $dur-loop;
    animation-timing-function: $easing;
    animation-iteration-count: infinite;
    animation-fill-mode: backwards;
  }
  .inf__card:nth-last-child(2) { animation-delay: 180ms; }
  .inf__card:nth-last-child(1) { animation-delay: 360ms; }
  .inf__pulse {
    animation-name: inf-pulse;
    animation-duration: $dur-loop;
    animation-timing-function: $easing;
    animation-iteration-count: infinite;
  }
}

@media (max-width: 340px) {
  .inf { width: min(252px, 96vw); }
  .inf__box { height: 144px; padding: $sp-1; }
  .inf__card { height: 28px; padding: 0 $sp-2; font-size: 11px; }
  .inf__no { width: 16px; height: 16px; font-size: 10px; }
  .inf__loader { height: 30px; font-size: 10px; }
  .inf__pulse { width: 10px; height: 10px; }
  .inf__live { font-size: 11px; }
}

@media (prefers-reduced-motion: reduce) {
  .inf.is-demo .inf__card,
  .inf.is-demo .inf__pulse,
  .inf__card--in { animation: none !important; }
  // 움직임만 끄고 "이미 도착한 카드" 라는 결과 상태는 남긴다
  .inf.is-demo .inf__card,
  .inf__card--in { transform: translateY(0) !important; opacity: 1 !important; }
  .inf.is-demo .inf__pulse { transform: scale(1) !important; }
}

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

.stage {
  box-sizing: border-box;
  min-height: 100vh;
  display: grid;
  place-items: center;
  margin: 0;
  background: #ffd23f;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  padding: clamp(8px, 4vw, 24px);
}

.inf {
  box-sizing: border-box;
  display: grid;
  gap: 8px;
  width: min(300px, 94vw);
  color: #17141a;
}

.inf * {
  box-sizing: border-box;
}

.inf__box {
  height: 196px;
  overflow-y: auto;
  overscroll-behavior: contain;
  scrollbar-width: thin;
  display: grid;
  align-content: start;
  gap: 8px;
  padding: 8px;
  border-radius: 16px;
  background: rgba(23, 20, 26, 0.08);
}

.inf__box:focus-visible {
  outline: 2px solid #17141a;
  outline-offset: 2px;
}

.inf__list {
  display: grid;
  gap: 8px;
  margin: 0;
  padding: 0;
  list-style: none;
}

.inf__card {
  display: flex;
  align-items: center;
  gap: 8px;
  height: 32px;
  padding: 0 12px;
  border-radius: 12px;
  background: #fff7e6;
  font-size: 13px;
  font-weight: 700;
  line-height: 1;
}

.inf__no {
  display: inline-grid;
  place-items: center;
  width: 20px;
  height: 20px;
  border-radius: 50%;
  background: rgba(23, 20, 26, 0.12);
  font-size: 11px;
  font-weight: 700;
}

.inf__loader {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 8px;
  height: 34px;
  border: 2px dashed rgba(23, 20, 26, 0.38);
  border-radius: 12px;
  font-size: 12px;
  font-weight: 700;
  line-height: 1;
}

.inf__pulse {
  width: 12px;
  height: 12px;
  border-radius: 50%;
  background: #17141a;
}

.inf__live {
  margin: 0;
  font-size: 12px;
  font-weight: 700;
  line-height: 1.3;
}

@keyframes inf-in {
  from {
    transform: translateY(6px);
    opacity: 0;
  }
  to {
    transform: translateY(0);
    opacity: 1;
  }
}
.inf__card--in {
  animation-name: inf-in;
  animation-duration: 300ms;
  animation-timing-function: cubic-bezier(0.2, 0.8, 0.2, 1);
  animation-iteration-count: 1;
  animation-fill-mode: backwards;
}

@keyframes inf-rise {
  0%, 8% {
    transform: translateY(6px);
  }
  34%, 86% {
    transform: translateY(0);
  }
  86.01%, 100% {
    transform: translateY(6px);
  }
}
@keyframes inf-pulse {
  0% {
    transform: scale(1);
  }
  22% {
    transform: scale(1.5);
  }
  44% {
    transform: scale(1);
  }
  66% {
    transform: scale(1.5);
  }
  88%, 100% {
    transform: scale(1);
  }
}
.inf.is-demo .inf__card:nth-last-child(-n+3) {
  animation-name: inf-rise;
  animation-duration: 2s;
  animation-timing-function: cubic-bezier(0.2, 0.8, 0.2, 1);
  animation-iteration-count: infinite;
  animation-fill-mode: backwards;
}
.inf.is-demo .inf__card:nth-last-child(2) {
  animation-delay: 180ms;
}
.inf.is-demo .inf__card:nth-last-child(1) {
  animation-delay: 360ms;
}
.inf.is-demo .inf__pulse {
  animation-name: inf-pulse;
  animation-duration: 2s;
  animation-timing-function: cubic-bezier(0.2, 0.8, 0.2, 1);
  animation-iteration-count: infinite;
}

@media (max-width: 340px) {
  .inf {
    width: min(252px, 96vw);
  }
  .inf__box {
    height: 144px;
    padding: 4px;
  }
  .inf__card {
    height: 28px;
    padding: 0 8px;
    font-size: 11px;
  }
  .inf__no {
    width: 16px;
    height: 16px;
    font-size: 10px;
  }
  .inf__loader {
    height: 30px;
    font-size: 10px;
  }
  .inf__pulse {
    width: 10px;
    height: 10px;
  }
  .inf__live {
    font-size: 11px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .inf.is-demo .inf__card,
  .inf.is-demo .inf__pulse,
  .inf__card--in {
    animation: none !important;
  }
  .inf.is-demo .inf__card,
  .inf__card--in {
    transform: translateY(0) !important;
    opacity: 1 !important;
  }
  .inf.is-demo .inf__pulse {
    transform: scale(1) !important;
  }
}

// 바닥 로더가 스크롤로 화면에 닿으면 IntersectionObserver 가 잡아 카드 3장을 붙인다.
// 미리보기(.is-demo)에서는 시계가 CSS 라 관찰을 걸지 않는다 — 사람이 손을 대는 순간 시작한다.
var inf = document.getElementById('inf');
var infBox = document.getElementById('inf-box');
var infList = document.getElementById('inf-list');
var infLoader = document.getElementById('inf-loader');
var infLive = document.getElementById('inf-live');
var infN = infList.children.length;
var infIo = null;
function infAdd() {
  for (var k = 0; k < 3; k++) {
    infN++;
    var li = document.createElement('li');
    li.className = 'inf__card inf__card--in';
    li.style.animationDelay = (k * 90) + 'ms';
    li.innerHTML = '<span class="inf__no">' + infN + '</span><span class="inf__t">Just arrived</span>';
    infList.appendChild(li);
  }
  infLive.textContent = '3 more cards arrived';
}
function infWake() {
  if (infIo) return;
  inf.classList.remove('is-demo');
  infIo = new IntersectionObserver(function (es) {
    if (es[0] && es[0].isIntersecting) infAdd();
  }, { root: infBox, threshold: 0.9 });
  infIo.observe(infLoader);
}
['wheel', 'pointerdown', 'keydown', 'touchstart'].forEach(function (ev) {
  infBox.addEventListener(ev, infWake);
});
// 미리보기에서는 바닥(로더가 있는 쪽)부터 보여 준다
if (inf.classList.contains('is-demo') && infBox.scrollHeight > infBox.clientHeight) {
  infBox.scrollTop = infBox.scrollHeight;
}

import { useEffect, useRef, useState } from "react";
import type { CSSProperties } from "react";
import styles from "./InfiniteFooterLoader.module.scss";

export type InfiniteFooterLoaderProps = {
  /** 처음부터 들어 있는 카드 이름들 */
  items?: string[];
  /** 새로 붙는 카드 이름 */
  nextLabel?: string;
  loaderLabel?: string;
  boxLabel?: string;
  groupLabel?: string;
  /** aria-live 로 읽히는 첫 안내 */
  startMessage?: string;
  /** 새 카드가 붙었을 때의 안내 */
  moreMessage?: string;
  /** 한 번에 붙는 장수 */
  step?: number;
  /** 격자 미리보기용 2초 자동 루프. 사람이 손대면 꺼진다 */
  demo?: boolean;
  duration?: number;
  easing?: string;
  color?: string;
};

type Vars = CSSProperties & { "--duration"?: string; "--easing"?: string; "--color"?: string };
// ambient 가 얇아 DOM 이벤트 제네릭을 못 쓴다 — 필요한 꼴만 로컬 타입으로 선언
type Box<T> = { current: T };
type ScrollBox = { scrollTop: number; scrollHeight: number; clientHeight: number };
type IoEntry = { isIntersecting: boolean };
type IoLike = { observe(el: unknown): void; disconnect(): void };
type IoCtor = new (cb: (e: IoEntry[]) => void, opt: { root: unknown; threshold: number }) => IoLike;

const DEFAULT_ITEMS = ["Today's log", "A short note", "Weekend plan", "The book I left", "Saved links", "Photo cleanup"];

export default function InfiniteFooterLoader({
  items = DEFAULT_ITEMS,
  nextLabel = "Just arrived",
  loaderLabel = "Fetching the next page",
  boxLabel = "Scrollable list",
  groupLabel = "Infinite scroll list",
  startMessage = "Showing 6 cards",
  moreMessage = "3 more cards arrived",
  step = 3,
  demo = true,
  duration = 300,
  easing = "cubic-bezier(.2,.8,.2,1)",
  color = "#17141a",
}: InfiniteFooterLoaderProps) {
  const base = items.length;
  const [extra, setExtra] = useState(0);
  const [live, setLive] = useState(demo);
  const [msg, setMsg] = useState(startMessage);
  const boxRef = useRef<any>(null) as Box<any>;
  const loaderRef = useRef<any>(null) as Box<any>;

  const vars: Vars = { "--duration": `${duration}ms`, "--easing": easing, "--color": color };

  // 미리보기에서는 바닥(로더가 있는 쪽)부터 보여 준다
  useEffect(() => {
    const b: ScrollBox | null = boxRef.current;
    if (!live || !b) return;
    if (b.scrollHeight > b.clientHeight) b.scrollTop = b.scrollHeight;
  }, [live]);

  // 로더가 상자 안에 들어오면 다음 묶음을 붙인다. 미리보기 동안에는 관찰하지 않는다
  useEffect(() => {
    if (live) return;
    const box = boxRef.current;
    const target = loaderRef.current;
    if (!box || !target) return;
    const Ctor = IntersectionObserver as unknown as IoCtor;
    const io = new Ctor(
      (es: IoEntry[]) => {
        if (!es[0] || !es[0].isIntersecting) return;
        setExtra((n: number) => n + step);
        setMsg(moreMessage);
      },
      { root: box, threshold: 0.9 },
    );
    io.observe(target);
    return () => io.disconnect();
  }, [live]);

  function wake() {
    if (live) setLive(false);
  }

  const names: string[] = items.slice();
  for (let i = 0; i < extra; i++) names.push(nextLabel);

  const cls = [styles.inf, live ? styles.isDemo : ""].filter(Boolean).join(" ");

  return (
    <section className={cls} style={vars} aria-label={groupLabel}>
      <div
        className={styles.box}
        ref={boxRef}
        tabIndex={0}
        aria-label={boxLabel}
        onWheel={wake}
        onPointerDown={wake}
        onKeyDown={wake}
        onTouchStart={wake}
      >
        <ol className={styles.list}>
          {names.map((name, i) => (
            <li
              className={i < base ? styles.card : styles.card + " " + styles.isIn}
              key={String(i)}
              style={i < base ? undefined : { animationDelay: `${((i - base) % step) * 90}ms` }}
            >
              <span className={styles.no}>{i + 1}</span>
              <span className={styles.t}>{name}</span>
            </li>
          ))}
        </ol>
        <div className={styles.loader} ref={loaderRef}>
          <span className={styles.pulse} aria-hidden="true" />
          <span className={styles.loaderT}>{loaderLabel}</span>
        </div>
      </div>
      <p className={styles.live} aria-live="polite">{msg}</p>
    </section>
  );
}