08Flowing wait — a button whose surface brightness value sweeps in one direction while content isn't ready

<main class="stage">
<div class="ctaskm is-demo" id="ctaskm">
  <div class="ctaskm__panel">
    <button class="ctaskm__btn ctaskm__btn--loading" id="ctaskmBtn" type="button">
      <span class="ctaskm__sweep" id="ctaskmSweep"></span>
      <span class="ctaskm__label" id="ctaskmLabel">Submit the form</span>
    </button>
    <span class="ctaskm__hint">Click and it switches to a submission-pending state</span>
  </div>
</div>
</main>

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

// 계산 겹(sweep 위치의 sin 가감속)은 JS 에 있다 — 여기는 정적 배치만.
@include stage($stage-yellow);

.stage { position: relative; }

.ctaskm__panel {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: $sp-4;
  padding: $sp-5;
  border-radius: $r-card;
  background: $stage-paper;
}

.ctaskm__btn {
  position: relative;
  overflow: hidden;
  border: 0;
  border-radius: $r-control;
  background: $subject-sky;
  color: $subject-ink;
  font-family: inherit;
  font-weight: 700;
  font-size: 15px;
  padding: $sp-4 $sp-5;
  min-width: 168px;
  cursor: pointer;
}

.ctaskm__btn--loading {
  background: rgba($subject-sky, .45);
}

.ctaskm__sweep {
  position: absolute;
  top: 0;
  bottom: 0;
  left: 0;
  width: 34%;
  background: linear-gradient(90deg, rgba(255, 255, 255, 0) 0%, rgba(255, 255, 255, .75) 50%, rgba(255, 255, 255, 0) 100%);
  pointer-events: none;
}

.ctaskm__label {
  position: relative;
  transition: opacity $dur-quick $ease-out;
}

.ctaskm__hint {
  color: rgba($subject-ink, .72);
  font-size: 12px;
  text-align: center;
}

@media (max-width: 340px) {
  .ctaskm__panel { padding: $sp-4; gap: $sp-3; }
  .ctaskm__btn { padding: $sp-3 $sp-4; font-size: 14px; min-width: 148px; }
}

@media (prefers-reduced-motion: reduce) {
  .ctaskm__label { 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;
}

.ctaskm__panel {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 16px;
  padding: 20px;
  border-radius: 16px;
  background: #ffffff;
}

.ctaskm__btn {
  position: relative;
  overflow: hidden;
  border: 0;
  border-radius: 12px;
  background: #6ec8ff;
  color: #17141a;
  font-family: inherit;
  font-weight: 700;
  font-size: 15px;
  padding: 16px 20px;
  min-width: 168px;
  cursor: pointer;
}

.ctaskm__btn--loading {
  background: rgba(110, 200, 255, 0.45);
}

.ctaskm__sweep {
  position: absolute;
  top: 0;
  bottom: 0;
  left: 0;
  width: 34%;
  background: linear-gradient(90deg, rgba(255, 255, 255, 0) 0%, rgba(255, 255, 255, 0.75) 50%, rgba(255, 255, 255, 0) 100%);
  pointer-events: none;
}

.ctaskm__label {
  position: relative;
  transition: opacity 220ms ease-out;
}

.ctaskm__hint {
  color: rgba(23, 20, 26, 0.72);
  font-size: 12px;
  text-align: center;
}

@media (max-width: 340px) {
  .ctaskm__panel {
    padding: 16px;
    gap: 12px;
  }
  .ctaskm__btn {
    padding: 12px 16px;
    font-size: 14px;
    min-width: 148px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .ctaskm__label {
    transition: none !important;
  }
}

(function () {
  var root = document.getElementById('ctaskm');
  var btn = document.getElementById('ctaskmBtn');
  var sweep = document.getElementById('ctaskmSweep');
  var label = document.getElementById('ctaskmLabel');

  // 계산 겹: sweep 의 가로 위치 값을 ease-in-out(사인 곡선)으로 매 프레임 계산해
  // 한쪽 끝(-BAND)에서 반대쪽 끝(100+BAND)까지 흐르게 한다 — 등속 CSS keyframe 이 아니라
  // 위치 자체를 sin() 로 가감속시킨다.
  var BAND = 34, CYCLE = 1100;
  var raf = null, startT = 0, loading = false;

  function easeInOutSine(t) { return -(Math.cos(Math.PI * t) - 1) / 2; }

  function frame(now) {
    var t = ((now - startT) % CYCLE) / CYCLE;
    var e = easeInOutSine(t);
    var pos = -BAND + e * (100 + BAND * 2);
    sweep.style.transform = 'translateX(' + pos.toFixed(1) + '%)';
    if (loading) { raf = requestAnimationFrame(frame); } else { raf = null; }
  }
  function startLoading() {
    if (loading) { return; }
    loading = true;
    btn.classList.add('ctaskm__btn--loading');
    label.style.opacity = '0';
    startT = performance.now();
    raf = requestAnimationFrame(frame);
    setTimeout(function () {
      loading = false;
      btn.classList.remove('ctaskm__btn--loading');
      label.style.opacity = '1';
      label.textContent = 'Submission complete';
      setTimeout(function () { label.textContent = 'Submit the form'; }, 500);
    }, 1400);
  }

  function wireReal() {
    btn.addEventListener('click', function () { root.classList.remove('is-demo'); stopAutoplay(); startLoading(); });
  }
  wireReal();

  var autoplayTimer = null;
  function stopAutoplay() { if (autoplayTimer) { clearInterval(autoplayTimer); autoplayTimer = null; } }
  var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;
  if (!reduce) { startLoading(); autoplayTimer = setInterval(startLoading, 2000); }
})();

import { useEffect, useRef } from "react";
import styles from "./CtaBtnSkeletonShimmer.module.scss";

export type CtaBtnSkeletonShimmerProps = {
  color?: string;
};

export default function CtaBtnSkeletonShimmer({
  color = "#8fd3ff",
}: CtaBtnSkeletonShimmerProps) {
  const rootRef = useRef<HTMLDivElement | null>(null);

  useEffect(() => {
    const root = rootRef.current;
    if (!root) return;
    const btn = root.querySelector<HTMLButtonElement>(`.${styles.btn}`);
    const sweep = root.querySelector<HTMLSpanElement>(`.${styles.sweep}`);
    const label = root.querySelector<HTMLSpanElement>(`.${styles.label}`);
    if (!btn || !sweep || !label) return;

    // 계산 겹: sweep 의 가로 위치 값을 ease-in-out(사인 곡선)으로 매 프레임 계산해
    // 한쪽 끝(-BAND)에서 반대쪽 끝(100+BAND)까지 흐르게 한다 — 등속 CSS keyframe 이 아니라
    // 위치 자체를 sin() 로 가감속시킨다.
    const BAND = 34, CYCLE = 1100;
    let raf: number | null = null, startT = 0, loading = false;

    function easeInOutSine(t: number) { return -(Math.cos(Math.PI * t) - 1) / 2; }

    function frame(now: number) {
      const t = ((now - startT) % CYCLE) / CYCLE;
      const e = easeInOutSine(t);
      const pos = -BAND + e * (100 + BAND * 2);
      sweep!.style.transform = "translateX(" + pos.toFixed(1) + "%)";
      raf = loading ? requestAnimationFrame(frame) : null;
    }
    function startLoading() {
      if (loading) return;
      loading = true;
      btn!.classList.add(styles.isLoading);
      label!.style.opacity = "0";
      startT = performance.now();
      raf = requestAnimationFrame(frame);
      window.setTimeout(() => {
        loading = false;
        btn!.classList.remove(styles.isLoading);
        label!.style.opacity = "1";
        label!.textContent = "제출 완료";
        window.setTimeout(() => { label!.textContent = "양식 제출하기"; }, 500);
      }, 1400);
    }

    function onClick() { stopAutoplay(); startLoading(); }
    btn.addEventListener("click", onClick);

    let autoplayTimer: number | null = null;
    function stopAutoplay() { if (autoplayTimer !== null) { window.clearInterval(autoplayTimer); autoplayTimer = null; } }
    const reduce = window.matchMedia("(prefers-reduced-motion: reduce)").matches;
    if (!reduce) { startLoading(); autoplayTimer = window.setInterval(startLoading, 2000); }

    return () => {
      stopAutoplay();
      if (raf !== null) cancelAnimationFrame(raf);
      btn.removeEventListener("click", onClick);
    };
  }, []);

  return (
    <div ref={rootRef} className={styles.stage}>
      <div className={styles.panel}>
        <button className={`${styles.btn} ${styles.isLoading}`} type="button" style={{ background: color }}>
          <span className={styles.sweep} />
          <span className={styles.label}>양식 제출하기</span>
        </button>
        <span className={styles.hint}>클릭하면 제출 대기 상태로 바뀝니다</span>
      </div>
    </div>
  );
}