08Chapter page turn

<main class="stage">
  <div class="pt is-demo">
    <div class="pt__scroller">
      <div class="pt__pad">
        <div class="pt__pin">
          <div class="pt__book">
            <div class="pt__half pt__half--left">
              <svg viewBox="0 0 256 256" width="28" height="28" aria-hidden="true"><g fill="currentColor"><path d="M232 56v144h-72a32 32 0 0 0-32 32a32 32 0 0 0-32-32H24V56h72a32 32 0 0 1 32 32a32 32 0 0 1 32-32Z" opacity=".2"/><path d="M232 48h-72a40 40 0 0 0-32 16a40 40 0 0 0-32-16H24a8 8 0 0 0-8 8v144a8 8 0 0 0 8 8h72a24 24 0 0 1 24 24a8 8 0 0 0 16 0a24 24 0 0 1 24-24h72a8 8 0 0 0 8-8V56a8 8 0 0 0-8-8M96 192H32V64h64a24 24 0 0 1 24 24v112a39.8 39.8 0 0 0-24-8m128 0h-64a39.8 39.8 0 0 0-24 8V88a24 24 0 0 1 24-24h64Z"/></g></svg>
              <span class="pt__small">Contents</span>
            </div>
            <div class="pt__half pt__half--right">
              <span class="pt__no">02</span>
              <span class="pt__title">Growth</span>
            </div>
            <div class="pt__page">
              <div class="pt__face pt__face--front">
                <span class="pt__no">01</span>
                <span class="pt__title">Beginning</span>
              </div>
              <div class="pt__face pt__face--back" aria-hidden="true"></div>
            </div>
          </div>
          <div class="pt__rail" aria-hidden="true"><span class="pt__fill"></span></div>
        </div>
      </div>
    </div>
  </div>
</main>

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

// ── 변수 3개 ──────────────────────────────────────────
$duration: 1s;          // alternate 라 한 바퀴(넘김 → 되넘김)는 2s
$easing: linear;        // 스크롤 스크럽은 등속이라야 스크롤 양과 회전각이 1:1 로 맞는다
$color: $subject-blue;

@include stage($stage-paper);

.pt {
  --h: clamp(148px, 58vh, 176px);
  width: min(340px, 92vw);
}

.pt__scroller {
  height: var(--h);
  overflow-y: auto;
  scrollbar-width: none;
  &::-webkit-scrollbar { display: none; }
}

// ⚠ 여기는 padding-bottom 이 아니라 height 다. sticky 가 붙어 있을 수 있는 범위는 부모의
// **콘텐츠 박스**라, padding 으로만 늘린 자리는 안 쳐준다 — 창이 곧바로 위로 흘러나간다 (실측)
.pt__pad { height: calc(var(--h) * 2.2); }

.pt__pin {
  position: sticky;
  top: 0;
  display: grid;
  justify-items: center;
  align-content: center;
  gap: $sp-3;
  height: var(--h);
}

.pt__book {
  position: relative;
  display: grid;
  grid-template-columns: 1fr 1fr;
  width: 240px;
  height: 112px;
  border-radius: $r-card;
  background: #f2eff5;
  perspective: 900px;
}

.pt__half {
  display: grid;
  place-content: center;
  justify-items: center;
  gap: $sp-1;
  color: rgba(23, 20, 26, .72);
}
.pt__half--left { border-right: 1px dashed rgba(23, 20, 26, .2); }

.pt__no {
  color: $subject-blue-deep;   // 크림 면 위 파란 글자 4.25:1 → deep 5.98:1
  font-size: 11px;
  line-height: 14px;
  font-weight: 700;
}
.pt__title {
  color: $subject-ink;
  font-size: 18px;
  line-height: 24px;
  font-weight: 800;
}
.pt__small {
  font-size: 11px;
  line-height: 14px;
  font-weight: 700;
}

// ── 실제 동작: 오른쪽 장이 왼쪽 모서리를 축으로 넘어간다.
//    스크롤 진행이 곧 회전각이고, 뒷면은 가려 둬서 앞면 글자가 비치지 않는다 ──
.pt__page {
  position: absolute;
  top: 0;
  right: 0;
  width: 120px;
  height: 112px;
  transform-origin: left center; // 규칙8: 책장 왼쪽 경첩 회전
  transform-style: preserve-3d;
  animation-name: pt-turn;
  animation-duration: 1s;
  animation-timing-function: $easing;
  animation-fill-mode: both;
  animation-timeline: scroll(nearest block);
}

@keyframes pt-turn {
  from { transform: rotateY(0deg); }
  to   { transform: rotateY(-180deg); }
}

.pt__face {
  position: absolute;
  inset: 0;
  display: grid;
  place-content: center;
  justify-items: center;
  gap: $sp-1;
  border-radius: 0 $r-card $r-card 0;
  backface-visibility: hidden;
  box-shadow: $shadow-press;
}
.pt__face--front { background: $subject-cream; }
.pt__face--back {
  background: repeating-linear-gradient(135deg, #e3ddef 0 8px, #d6cee6 8px 16px);
  transform: rotateY(180deg);
}

.pt__rail {
  width: 240px;
  height: 4px;
  border-radius: $r-pill;
  background: rgba(23, 20, 26, .12);
}
.pt__fill {
  display: block;
  height: 4px;
  border-radius: $r-pill;
  background: $color;
  transform: scaleX(0);
  transform-origin: left center; // 규칙8: 읽기막대 left 채움
  animation-name: pt-read;
  animation-duration: 1s;
  animation-timing-function: linear;
  animation-fill-mode: both;
  animation-timeline: scroll(nearest block);
}

@keyframes pt-read {
  from { transform: scaleX(0); }
  to   { transform: scaleX(1); }
}

// ── 격자 미리보기 루프 ────────────────────────────────
// 넘김만 steps(1, end) 로 끊는다. 회전한 면의 폭은 |cos θ| 라 프레임당 변화율이 90° 에서
// 언제나 최대라, 부드럽게 두면 대표 이미지가 늘 모서리뷰로 뽑힌다(252 실측).
// 진행 막대는 그대로 이어져 프레임을 채운다 — transform 이라 반투명 유령이 안 생긴다.
.pt.is-demo .pt__page {
  animation-name: pt-cut;
  animation-duration: $duration;
  animation-timing-function: steps(1, end);
  animation-direction: alternate;
  animation-iteration-count: infinite;
  animation-timeline: auto;
}
.pt.is-demo .pt__fill {
  animation-duration: $duration;
  animation-direction: alternate;
  animation-iteration-count: infinite;
  animation-timeline: auto;
}

@keyframes pt-cut {
  0%, 49%   { transform: rotateY(0deg); }
  50%, 100% { transform: rotateY(-180deg); }
}

@media (prefers-reduced-motion: reduce) {
  .pt__page { animation: none !important; transform: rotateY(0deg); }
  .pt__fill { animation: none !important; transform: scaleX(.5); }
}

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

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

.pt {
  --h: clamp(148px, 58vh, 176px);
  width: min(340px, 92vw);
}

.pt__scroller {
  height: var(--h);
  overflow-y: auto;
  scrollbar-width: none;
}
.pt__scroller::-webkit-scrollbar {
  display: none;
}

.pt__pad {
  height: calc(var(--h) * 2.2);
}

.pt__pin {
  position: sticky;
  top: 0;
  display: grid;
  justify-items: center;
  align-content: center;
  gap: 12px;
  height: var(--h);
}

.pt__book {
  position: relative;
  display: grid;
  grid-template-columns: 1fr 1fr;
  width: 240px;
  height: 112px;
  border-radius: 16px;
  background: #f2eff5;
  perspective: 900px;
}

.pt__half {
  display: grid;
  place-content: center;
  justify-items: center;
  gap: 4px;
  color: rgba(23, 20, 26, 0.72);
}

.pt__half--left {
  border-right: 1px dashed rgba(23, 20, 26, 0.2);
}

.pt__no {
  color: #0a4fe8;
  font-size: 11px;
  line-height: 14px;
  font-weight: 700;
}

.pt__title {
  color: #17141a;
  font-size: 18px;
  line-height: 24px;
  font-weight: 800;
}

.pt__small {
  font-size: 11px;
  line-height: 14px;
  font-weight: 700;
}

.pt__page {
  position: absolute;
  top: 0;
  right: 0;
  width: 120px;
  height: 112px;
  transform-origin: left center;
  transform-style: preserve-3d;
  animation-name: pt-turn;
  animation-duration: 1s;
  animation-timing-function: linear;
  animation-fill-mode: both;
  animation-timeline: scroll(nearest block);
}

@keyframes pt-turn {
  from {
    transform: rotateY(0deg);
  }
  to {
    transform: rotateY(-180deg);
  }
}
.pt__face {
  position: absolute;
  inset: 0;
  display: grid;
  place-content: center;
  justify-items: center;
  gap: 4px;
  border-radius: 0 16px 16px 0;
  backface-visibility: hidden;
  box-shadow: 0 6px 12px rgba(23, 20, 26, 0.32);
}

.pt__face--front {
  background: #fff7e6;
}

.pt__face--back {
  background: repeating-linear-gradient(135deg, #e3ddef 0 8px, #d6cee6 8px 16px);
  transform: rotateY(180deg);
}

.pt__rail {
  width: 240px;
  height: 4px;
  border-radius: 999px;
  background: rgba(23, 20, 26, 0.12);
}

.pt__fill {
  display: block;
  height: 4px;
  border-radius: 999px;
  background: #2f6df6;
  transform: scaleX(0);
  transform-origin: left center;
  animation-name: pt-read;
  animation-duration: 1s;
  animation-timing-function: linear;
  animation-fill-mode: both;
  animation-timeline: scroll(nearest block);
}

@keyframes pt-read {
  from {
    transform: scaleX(0);
  }
  to {
    transform: scaleX(1);
  }
}
.pt.is-demo .pt__page {
  animation-name: pt-cut;
  animation-duration: 1s;
  animation-timing-function: steps(1, end);
  animation-direction: alternate;
  animation-iteration-count: infinite;
  animation-timeline: auto;
}

.pt.is-demo .pt__fill {
  animation-duration: 1s;
  animation-direction: alternate;
  animation-iteration-count: infinite;
  animation-timeline: auto;
}

@keyframes pt-cut {
  0%, 49% {
    transform: rotateY(0deg);
  }
  50%, 100% {
    transform: rotateY(-180deg);
  }
}
@media (prefers-reduced-motion: reduce) {
  .pt__page {
    animation: none !important;
    transform: rotateY(0deg);
  }
  .pt__fill {
    animation: none !important;
    transform: scaleX(0.5);
  }
}

// 실제 동작: 스크롤이 rotateY 를 0 → -180deg 로 끌고 간다(animation-timeline: scroll()).
// 격자 미리보기 루프만 steps(1, end) 로 끊는다 — 3D 플립은 90° 부근이 항상 최대 변화라
// 그대로 두면 대표 이미지가 늘 모서리뷰(선 한 줄)가 된다.
var r = document.querySelector('.pt');
var s = r.querySelector('.pt__scroller');
function stopDemo(){ r.classList.remove('is-demo'); }
r.addEventListener('pointerdown', stopDemo);
s.addEventListener('scroll', stopDemo, { passive: true });

import type { CSSProperties, ReactNode } from "react";
import styles from "./PageTurnChapters.module.scss";

export type PageTurnChaptersProps = {
  tocLabel?: string;
  frontTitle?: string;
  backTitle?: string;
  preview?: boolean;
  duration?: number;
  easing?: string;
  color?: string;
};

type Vars = CSSProperties & { "--duration"?: string; "--easing"?: string; "--color"?: string };

const IconBook = (): ReactNode => (
  <svg viewBox="0 0 256 256" width="28" height="28" aria-hidden="true"><g fill="currentColor"><path d="M232 56v144h-72a32 32 0 0 0-32 32a32 32 0 0 0-32-32H24V56h72a32 32 0 0 1 32 32a32 32 0 0 1 32-32Z" opacity=".2"/><path d="M232 48h-72a40 40 0 0 0-32 16a40 40 0 0 0-32-16H24a8 8 0 0 0-8 8v144a8 8 0 0 0 8 8h72a24 24 0 0 1 24 24a8 8 0 0 0 16 0a24 24 0 0 1 24-24h72a8 8 0 0 0 8-8V56a8 8 0 0 0-8-8M96 192H32V64h64a24 24 0 0 1 24 24v112a39.8 39.8 0 0 0-24-8m128 0h-64a39.8 39.8 0 0 0-24 8V88a24 24 0 0 1 24-24h64Z"/></g></svg>
);

export default function PageTurnChapters({
  tocLabel = "Contents",
  frontTitle = "Beginning",
  backTitle = "Growth",
  preview = true,
  duration = 1000,
  easing = "linear",
  color = "#2f6df6",
}: PageTurnChaptersProps): ReactNode {
  const vars: Vars = { "--duration": `${duration}ms`, "--easing": easing, "--color": color };
  const cls = preview ? `${styles.pt} ${styles.isDemo}` : styles.pt;

  return (
    <div className={cls} style={vars}>
      <div className={styles.scroller}>
        <div className={styles.pad}>
          <div className={styles.pin}>
            <div className={styles.book}>
              <div className={`${styles.half} ${styles.halfLeft}`}>
                <IconBook />
                <span className={styles.small}>{tocLabel}</span>
              </div>
              <div className={`${styles.half} ${styles.halfRight}`}>
                <span className={styles.no}>02</span>
                <span className={styles.title}>{backTitle}</span>
              </div>
              <div className={styles.page}>
                <div className={`${styles.face} ${styles.faceFront}`}>
                  <span className={styles.no}>01</span>
                  <span className={styles.title}>{frontTitle}</span>
                </div>
                <div className={`${styles.face} ${styles.faceBack}`} aria-hidden="true" />
              </div>
            </div>
            <div className={styles.rail} aria-hidden="true"><span className={styles.fill} /></div>
          </div>
        </div>
      </div>
    </div>
  );
}