053D flip face — a button whose rotation value turns to 180 degrees on click, revealing its opposite face

<main class="stage">
<div class="ctaflp is-demo" id="ctaflp">
  <div class="ctaflp__panel">
    <div class="ctaflp__scene">
      <button class="ctaflp__btn" id="ctaflpBtn" type="button">
        <span class="ctaflp__face ctaflp__face--front">This item</span>
        <span class="ctaflp__face ctaflp__face--back">That item</span>
      </button>
    </div>
    <span class="ctaflp__hint">Each click flips to the opposite face</span>
  </div>
</div>
</main>

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

// 계산 겹(오버슈트 감쇠 진동)은 JS 에 있다 — 여기는 정적 배치·원근만.
@include stage($stage-orange);

.stage { position: relative; }

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

.ctaflp__scene {
  perspective: 480px;
}

.ctaflp__btn {
  position: relative;
  width: 140px;
  height: 52px;
  border: 0;
  border-radius: $r-control;
  background: none;
  padding: 0;
  cursor: pointer;
  transform-style: preserve-3d;
}

.ctaflp__face {
  position: absolute;
  inset: 0;
  display: grid;
  place-items: center;
  border-radius: $r-control;
  font-family: inherit;
  font-weight: 700;
  font-size: 15px;
  backface-visibility: hidden;
}

.ctaflp__face--front {
  background: $subject-blue-deep;
  color: $subject-cream;
}

.ctaflp__face--back {
  background: $subject-lilac;
  color: $subject-ink;
  transform: rotateY(180deg);
}

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

@media (max-width: 340px) {
  .ctaflp__panel { padding: $sp-4; gap: $sp-3; }
  .ctaflp__btn { width: 120px; height: 46px; }
  .ctaflp__face { font-size: 14px; }
}

@media (prefers-reduced-motion: reduce) {
  .ctaflp__btn { 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: #ff4d1f;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  padding: clamp(8px, 4vw, 24px);
}

.stage {
  position: relative;
}

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

.ctaflp__scene {
  perspective: 480px;
}

.ctaflp__btn {
  position: relative;
  width: 140px;
  height: 52px;
  border: 0;
  border-radius: 12px;
  background: none;
  padding: 0;
  cursor: pointer;
  transform-style: preserve-3d;
}

.ctaflp__face {
  position: absolute;
  inset: 0;
  display: grid;
  place-items: center;
  border-radius: 12px;
  font-family: inherit;
  font-weight: 700;
  font-size: 15px;
  backface-visibility: hidden;
}

.ctaflp__face--front {
  background: #0a4fe8;
  color: #fff7e6;
}

.ctaflp__face--back {
  background: #b9a0ff;
  color: #17141a;
  transform: rotateY(180deg);
}

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

@media (max-width: 340px) {
  .ctaflp__panel {
    padding: 16px;
    gap: 12px;
  }
  .ctaflp__btn {
    width: 120px;
    height: 46px;
  }
  .ctaflp__face {
    font-size: 14px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .ctaflp__btn {
    transition: none !important;
  }
}

(function () {
  var root = document.getElementById('ctaflp');
  var btn = document.getElementById('ctaflpBtn');

  // 계산 겹: 회전 값이 목표(180도 배수)를 향해 감쇠 진동식으로 접근한다 —
  // 매 프레임 목표를 살짝 넘었다가(오버슈트) 스프링 곡선으로 제자리에 앉는다.
  var current = 0, base = 0, raf = null, startT = 0;
  var OVERSHOOT_DEG = 18, FREQ = 14, DECAY = 9, DUR = 500;

  function ease(tSec) {
    if (tSec <= 0) { return 0; }
    var settle = 1 - Math.exp(-DECAY * tSec);
    var wobble = Math.sin(tSec * FREQ) * Math.exp(-DECAY * tSec) * (OVERSHOOT_DEG / 180);
    return settle + wobble;
  }
  function frame(now) {
    var t = (now - startT) / 1000;
    var p = Math.min(1, ease(t));
    current = base + p * 180;
    btn.style.transform = 'rotateY(' + current.toFixed(2) + 'deg)';
    if (t < DUR / 1000) {
      raf = requestAnimationFrame(frame);
    } else {
      base = base + 180;
      current = base;
      btn.style.transform = 'rotateY(' + current.toFixed(2) + 'deg)';
      raf = null;
    }
  }
  function flip() {
    if (raf) { return; }
    startT = performance.now();
    raf = requestAnimationFrame(frame);
  }

  function wireReal() {
    btn.addEventListener('click', function () { root.classList.remove('is-demo'); stopAutoplay(); flip(); });
    btn.addEventListener('keydown', function (e) {
      if (e.key === 'Enter' || e.key === ' ') { root.classList.remove('is-demo'); stopAutoplay(); flip(); }
    });
  }
  wireReal();

  var autoplayTimer = null;
  function stopAutoplay() { if (autoplayTimer) { clearInterval(autoplayTimer); autoplayTimer = null; } }
  var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;
  if (!reduce) { autoplayTimer = setInterval(flip, 700); }
})();

import { useEffect, useRef } from "react";
import styles from "./CtaBtnFlip3dFace.module.scss";

export type CtaBtnFlip3dFaceProps = {
  color?: string;
};

export default function CtaBtnFlip3dFace({
  color = "#0a4fe8",
}: CtaBtnFlip3dFaceProps) {
  const rootRef = useRef<HTMLDivElement | null>(null);

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

    // 계산 겹: 회전 값이 목표(180도 배수)를 향해 감쇠 진동식으로 접근한다 —
    // 매 프레임 목표를 살짝 넘었다가(오버슈트) 스프링 곡선으로 제자리에 앉는다.
    let base = 0;
    let raf: number | null = null;
    let startT = 0;
    const OVERSHOOT_DEG = 18, FREQ = 14, DECAY = 9, DUR = 500;

    function ease(tSec: number) {
      if (tSec <= 0) return 0;
      const settle = 1 - Math.exp(-DECAY * tSec);
      const wobble = Math.sin(tSec * FREQ) * Math.exp(-DECAY * tSec) * (OVERSHOOT_DEG / 180);
      return settle + wobble;
    }
    function frame(now: number) {
      const t = (now - startT) / 1000;
      const p = Math.min(1, ease(t));
      const current = base + p * 180;
      btn!.style.transform = "rotateY(" + current.toFixed(2) + "deg)";
      if (t < DUR / 1000) {
        raf = requestAnimationFrame(frame);
      } else {
        base = base + 180;
        btn!.style.transform = "rotateY(" + base.toFixed(2) + "deg)";
        raf = null;
      }
    }
    function flip() {
      if (raf !== null) return;
      startT = performance.now();
      raf = requestAnimationFrame(frame);
    }

    function onClick() { stopAutoplay(); flip(); }
    function onKeydown(e: KeyboardEvent) { if (e.key === "Enter" || e.key === " ") { stopAutoplay(); flip(); } }
    btn.addEventListener("click", onClick);
    btn.addEventListener("keydown", onKeydown);

    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) { autoplayTimer = window.setInterval(flip, 700); }

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

  return (
    <div ref={rootRef} className={styles.stage}>
      <div className={styles.panel}>
        <div className={styles.scene}>
          <button className={styles.btn} type="button">
            <span className={styles.faceFront} style={{ background: color }}>이 상품</span>
            <span className={styles.faceBack}>저 상품</span>
          </button>
        </div>
        <span className={styles.hint}>클릭할 때마다 반대 면으로 뒤집힙니다</span>
      </div>
    </div>
  );
}