06Empty-state crossfade — a message that fades out the instant the item count value leaves zero

<main class="stage">
<div class="cesc is-demo" id="cesc">
  <div class="cesc__panel">
    <header class="cesc__head">Cart</header>
    <div class="cesc__body">
      <div class="cesc__empty" id="cescEmpty">
        <span class="cesc__icon" aria-hidden="true">
          <svg viewBox="0 0 256 256" width="34" height="34"><g fill="currentColor" opacity=".6"><path d="M216 48h-40v-8a24 24 0 0 0-24-24h-48a24 24 0 0 0-24 24v8H40a8 8 0 0 0 0 16h8v144a16 16 0 0 0 16 16h128a16 16 0 0 0 16-16V64h8a8 8 0 0 0 0-16ZM96 40a8 8 0 0 1 8-8h48a8 8 0 0 1 8 8v8H96Zm96 168H64V64h128Z"/></g></svg>
        </span>
        <p class="cesc__msg">Your cart is empty</p>
      </div>
      <ul class="cesc__list" id="cescList">
        <li class="cesc__row"><span>Leather Wallet</span><b>$36</b></li>
        <li class="cesc__row"><span>Sunglasses</span><b>$29</b></li>
      </ul>
    </div>
    <button class="cesc__toggle" id="cescToggle" type="button">Fill / Empty</button>
  </div>
</div>
</main>

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

// 계산 겹: 하나의 진행값(p)을 이징해 두 상태의 opacity·scale 을 상보적으로 계산한다
// (crossfadeApply(), index.html) — 빈 상태와 목록을 각각 애니메이션하지 않고 한 값에서 도출.

$duration: $dur-base;
$easing: $ease-out;
$color: $subject-ink;

@include stage($stage-yellow);

.stage { position: relative; }

.cesc__panel {
  width: min(240px, 70vw);
  display: flex;
  flex-direction: column;
  gap: $sp-3;
}

.cesc__head {
  color: $color;
  font-weight: 700;
  font-size: 14px;
}

.cesc__body {
  position: relative;
  height: 130px;
}

.cesc__empty,
.cesc__list {
  position: absolute;
  inset: 0;
  transform-origin: center;
}

.cesc__empty {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  gap: $sp-2;
  color: $color;
  text-align: center;
}

.cesc__msg {
  margin: 0;
  font-size: 12px;
  font-weight: 600;
  opacity: .72;
}

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

.cesc__row {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: $sp-3;
  border-radius: $r-control;
  background: $subject-cream;
  color: $color;
  font-weight: 600;
  font-size: 13px;
}

.cesc__toggle {
  border: 0;
  border-radius: $r-pill;
  padding: $sp-2 $sp-5;
  background: $color;
  color: $stage-yellow;
  font-family: inherit;
  font-weight: 700;
  font-size: 12px;
  cursor: pointer;
  align-self: flex-start;
}

@media (max-width: 340px) {
  .cesc__panel { width: min(190px, 66vw); gap: $sp-2; }
  .cesc__head { font-size: 12px; }
  .cesc__body { height: 84px; }
  .cesc__row { padding: $sp-2; font-size: 12px; }
  .cesc__toggle { padding: $sp-1 $sp-4; font-size: 11px; }
}

@media (prefers-reduced-motion: reduce) {
  .cesc__empty, .cesc__list { transition: none !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);
}

.stage {
  position: relative;
}

.cesc__panel {
  width: min(240px, 70vw);
  display: flex;
  flex-direction: column;
  gap: 12px;
}

.cesc__head {
  color: #17141a;
  font-weight: 700;
  font-size: 14px;
}

.cesc__body {
  position: relative;
  height: 130px;
}

.cesc__empty,
.cesc__list {
  position: absolute;
  inset: 0;
  transform-origin: center;
}

.cesc__empty {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  gap: 8px;
  color: #17141a;
  text-align: center;
}

.cesc__msg {
  margin: 0;
  font-size: 12px;
  font-weight: 600;
  opacity: 0.72;
}

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

.cesc__row {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 12px;
  border-radius: 12px;
  background: #fff7e6;
  color: #17141a;
  font-weight: 600;
  font-size: 13px;
}

.cesc__toggle {
  border: 0;
  border-radius: 999px;
  padding: 8px 20px;
  background: #17141a;
  color: #ffd23f;
  font-family: inherit;
  font-weight: 700;
  font-size: 12px;
  cursor: pointer;
  align-self: flex-start;
}

@media (max-width: 340px) {
  .cesc__panel {
    width: min(190px, 66vw);
    gap: 8px;
  }
  .cesc__head {
    font-size: 12px;
  }
  .cesc__body {
    height: 84px;
  }
  .cesc__row {
    padding: 8px;
    font-size: 12px;
  }
  .cesc__toggle {
    padding: 4px 16px;
    font-size: 11px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .cesc__empty, .cesc__list {
    transition: none !important;
  }
}

(function () {
  var root = document.getElementById('cesc');
  var emptyEl = document.getElementById('cescEmpty');
  var listEl = document.getElementById('cescList');
  var toggleBtn = document.getElementById('cescToggle');

  // 계산 겹: 하나의 진행값(p, 0~1)을 이징해 두 상태의 opacity 를 서로 반대 방향으로 동시에
  // 계산한다(crossfadeApply()) — 두 애니메이션을 따로 걸지 않고 한 값에서 상보적으로 도출한다.
  function easeInOutCubic(p) {
    return p < 0.5 ? 4 * p * p * p : 1 - Math.pow(-2 * p + 2, 3) / 2;
  }
  var DUR_MS = 420;
  var hasItems = false;
  var raf = null;

  function crossfadeApply(p, toItems) {
    var eased = easeInOutCubic(p);
    var itemsOpacity = toItems ? eased : 1 - eased;
    var emptyOpacity = 1 - itemsOpacity;
    listEl.style.opacity = itemsOpacity.toFixed(3);
    listEl.style.transform = 'scale(' + (0.96 + itemsOpacity * 0.04).toFixed(3) + ')';
    emptyEl.style.opacity = emptyOpacity.toFixed(3);
    emptyEl.style.transform = 'scale(' + (0.96 + emptyOpacity * 0.04).toFixed(3) + ')';
  }

  function run(toItems) {
    if (raf) { cancelAnimationFrame(raf); }
    var start = performance.now();
    function frame(now) {
      var p = Math.min(1, (now - start) / DUR_MS);
      crossfadeApply(p, toItems);
      if (p < 1) {
        raf = requestAnimationFrame(frame);
      } else {
        raf = null;
        hasItems = toItems;
      }
    }
    raf = requestAnimationFrame(frame);
  }

  toggleBtn.addEventListener('click', function () {
    root.classList.remove('is-demo');
    stopAutoplay();
    run(!hasItems);
  });

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

  crossfadeApply(0, false);
  var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;
  if (!reduce) {
    autoplayTimer = setInterval(function () { run(!hasItems); }, 1300);
  }
})();

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

export type CartDrawerEmptyStateCrossfadeProps = {
  duration?: number;
  color?: string;
};

// 계산 겹: 하나의 진행값(p, 0~1)을 이징해 두 상태의 opacity 를 서로 반대 방향으로 동시에
// 계산한다(crossfadeApply()) — 두 애니메이션을 따로 걸지 않고 한 값에서 상보적으로 도출한다.
function easeInOutCubic(p: number): number {
  return p < 0.5 ? 4 * p * p * p : 1 - Math.pow(-2 * p + 2, 3) / 2;
}

const DUR_MS = 420;

export default function CartDrawerEmptyStateCrossfade({
  color = "#17141a",
}: CartDrawerEmptyStateCrossfadeProps) {
  const rootRef = useRef<HTMLDivElement | null>(null);
  const emptyRef = useRef<HTMLDivElement | null>(null);
  const listRef = useRef<HTMLUListElement | null>(null);
  const hasItemsRef = useRef(false);
  const rafRef = useRef<number | null>(null);
  const timerRef = useRef<ReturnType<typeof setInterval> | null>(null);

  useEffect(() => {
    function crossfadeApply(p: number, toItems: boolean) {
      const list = listRef.current;
      const empty = emptyRef.current;
      if (!list || !empty) return;
      const eased = easeInOutCubic(p);
      const itemsOpacity = toItems ? eased : 1 - eased;
      const emptyOpacity = 1 - itemsOpacity;
      list.style.opacity = itemsOpacity.toFixed(3);
      list.style.transform = `scale(${(0.96 + itemsOpacity * 0.04).toFixed(3)})`;
      empty.style.opacity = emptyOpacity.toFixed(3);
      empty.style.transform = `scale(${(0.96 + emptyOpacity * 0.04).toFixed(3)})`;
    }

    function run(toItems: boolean) {
      if (rafRef.current) cancelAnimationFrame(rafRef.current);
      const start = performance.now();
      function frame(now: number) {
        const p = Math.min(1, (now - start) / DUR_MS);
        crossfadeApply(p, toItems);
        if (p < 1) {
          rafRef.current = requestAnimationFrame(frame);
        } else {
          rafRef.current = null;
          hasItemsRef.current = toItems;
        }
      }
      rafRef.current = requestAnimationFrame(frame);
    }

    function stopAutoplay() {
      if (timerRef.current) {
        clearInterval(timerRef.current);
        timerRef.current = null;
      }
    }

    const onToggle = () => {
      rootRef.current?.classList.remove(styles.isDemo);
      stopAutoplay();
      run(!hasItemsRef.current);
    };
    const toggleEl = rootRef.current?.querySelector<HTMLButtonElement>(`.${styles.toggle}`);
    toggleEl?.addEventListener("click", onToggle);

    crossfadeApply(0, false);
    const reduce = window.matchMedia("(prefers-reduced-motion: reduce)").matches;
    if (!reduce) {
      timerRef.current = setInterval(() => run(!hasItemsRef.current), 1300);
    }

    return () => {
      stopAutoplay();
      if (rafRef.current) cancelAnimationFrame(rafRef.current);
      toggleEl?.removeEventListener("click", onToggle);
    };
  }, []);

  return (
    <div ref={rootRef} className={`${styles.stage} ${styles.isDemo}`} style={{ "--color": color } as CSSProperties}>
      <div className={styles.panel}>
        <header className={styles.head}>장바구니</header>
        <div className={styles.body}>
          <div ref={emptyRef} className={styles.empty}>
            <span className={styles.icon} aria-hidden="true">
              <svg viewBox="0 0 256 256" width="34" height="34"><g fill="currentColor" opacity=".6"><path d="M216 48h-40v-8a24 24 0 0 0-24-24h-48a24 24 0 0 0-24 24v8H40a8 8 0 0 0 0 16h8v144a16 16 0 0 0 16 16h128a16 16 0 0 0 16-16V64h8a8 8 0 0 0 0-16ZM96 40a8 8 0 0 1 8-8h48a8 8 0 0 1 8 8v8H96Zm96 168H64V64h128Z"/></g></svg>
            </span>
            <p className={styles.msg}>장바구니가 비어 있어요</p>
          </div>
          <ul ref={listRef} className={styles.list}>
            <li className={styles.row}><span>가죽 지갑</span><b>$36</b></li>
            <li className={styles.row}><span>선글라스</span><b>$29</b></li>
          </ul>
        </div>
        <button className={styles.toggle} type="button">담기 / 비우기</button>
      </div>
    </div>
  );
}