09스냅 섹션 전환

<main class="stage">
  <section class="ss is-demo" id="ss" aria-label="스냅 섹션 전환 데모">
    <header class="ss__head">
      <p class="ss__title">스냅 섹션 전환</p>
      <p class="ss__attr"><code>scroll-snap-type: y mandatory</code></p>
    </header>
    <div class="ss__view" id="ss-view" tabindex="0" role="region" aria-label="특징 섹션 세 장 — 스크롤하면 한 장씩 화면에 붙습니다">
      <div class="ss__track" id="ss-track">
        <article class="ss__panel" aria-current="true">
          <b>01</b>
          <h3>한 화면에 하나</h3>
          <p>섹션이 스크롤 끝에 딱 붙어 멈춥니다</p>
        </article>
        <article class="ss__panel">
          <b>02</b>
          <h3>중앙 감지</h3>
          <p>관찰자가 화면 가운데 섹션을 고릅니다</p>
        </article>
        <article class="ss__panel">
          <b>03</b>
          <h3>상태 전달</h3>
          <p>고른 섹션에 aria-current 를 붙입니다</p>
        </article>
      </div>
    </div>
    <footer class="ss__foot">
      <nav class="ss__dots" aria-label="섹션 바로가기">
        <button class="ss__dot" type="button" aria-current="true" aria-label="첫 번째 섹션으로"></button>
        <button class="ss__dot" type="button" aria-label="두 번째 섹션으로"></button>
        <button class="ss__dot" type="button" aria-label="세 번째 섹션으로"></button>
      </nav>
      <span class="ss__state">중앙에 온 섹션이 <b>aria-current</b></span>
    </footer>
  </section>
</main>

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

// 스냅 섹션 전환 — CSS 가 붙이고(scroll-snap) JS 가 알린다(aria-current)
// 262-02 함정 대비: .is-demo 동안만 scroll-snap-type 을 none 으로 둔다 — 스냅이 트랙 transform 을 재붙잡아
// 움직임을 통째로 먹는 일을 막는다. 손을 대면 is-demo 가 떨어지며 스냅이 돌아온다
$duration: $dur-loop;
$easing: $ease-spring;
$color: $subject-blue;

@include stage($stage-paper);

.ss {
  --ss-travel: -160px;
  position: relative;
  box-sizing: border-box;
  width: min(320px, 92vw);
  border-radius: $r-card;
  background: $subject-cream;
  color: $subject-ink;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  overflow: hidden;
  box-shadow: $shadow-raised;
}

.ss__head {
  display: flex;
  align-items: baseline;
  justify-content: space-between;
  gap: $sp-2;
  padding: $sp-2 $sp-3;
}
.ss__title {
  margin: 0;
  font-size: 13px;
  font-weight: 800;
  line-height: 1.3;
}
.ss__attr {
  margin: 0;
  font-size: 10px;
  line-height: 1.3;
  color: rgba($subject-ink, .72);
  code { font-family: "Consolas", "Menlo", monospace; }
}

// 스크롤 상자(view)와 콘텐츠 트랙(track) 분리 — transform 은 트랙에만 건다 (051 함정)
.ss__view {
  position: relative;
  height: 168px;
  overflow-y: auto;
  scroll-snap-type: y mandatory;
  padding: 0 $sp-3;
  outline: none;
}
.ss__track {
  display: grid;
  gap: $sp-2;
  padding: $sp-2 0;
}
.ss__panel {
  scroll-snap-align: center;
  display: grid;
  align-content: center;
  justify-items: center;
  gap: $sp-1;
  box-sizing: border-box;
  height: 152px;
  padding: $sp-2;
  border-radius: $r-control;
  background: $stage-paper;
  color: $subject-ink;
  box-shadow: $shadow-press;
  transition: background $dur-quick $ease-out, color $dur-quick $ease-out;

  b {
    font-size: 13px;
    font-weight: 800;
    line-height: 1;
    letter-spacing: .08em;
    padding: $sp-1 $sp-2;
    border-radius: $r-pill;
    background: rgba($subject-cream, .18);
  }
  h3 { margin: 0; font-size: 15px; font-weight: 800; line-height: 1.3; }
  p { margin: 0; font-size: 11px; font-weight: 500; line-height: 1.4; text-align: center; }
}
// 중앙에 온 섹션 — 파란 면은 크림 글자를 얹는 규칙대로 진한 파랑이다
.ss__panel[aria-current="true"] {
  background: $subject-blue-deep;
  color: $subject-cream;
}

.ss__foot {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: $sp-2;
  padding: $sp-2 $sp-3;
  border-top: 1px solid rgba($subject-ink, .12);
  font-size: 10px;
  font-weight: 700;
  line-height: 1.3;
  b { color: $subject-orange-deep; font-weight: 800; }
}
.ss__dots {
  display: flex;
  align-items: center;
  gap: $sp-1;
}
.ss__dot {
  width: 8px;
  height: 8px;
  padding: 0;
  border: 0;
  border-radius: $r-pill;
  background: rgba($subject-ink, .25);
  cursor: pointer;
  transition: width $dur-quick $ease-out, background $dur-quick $ease-out;
}
.ss__dot[aria-current="true"] {
  width: 20px;
  background: $color;
}
.ss__dot:focus-visible {
  outline: 2px solid $color;
  outline-offset: 2px;
}
.ss__view:focus-visible {
  outline: 2px solid $color;
  outline-offset: -2px;
}

// 미리보기 — 트랙을 한 패널 폭만큼 밀었다 되돌린다. 상태 교체는 도착(36%) 뒤 44% 에, 복귀(82%) 뒤 90% 에
// 한 프레임 컷(steps) 으로 끊는다 — 반투명 중간 프레임이 poster 에 남지 않는다
.ss.is-demo {
  .ss__view { scroll-snap-type: none; }
  .ss__track {
    animation-name: ss-slide;
    animation-duration: $duration;
    animation-timing-function: $easing;
    animation-iteration-count: infinite;
  }
  .ss__panel:nth-child(1) {
    animation-name: ss-state-1;
    animation-duration: $duration;
    animation-timing-function: steps(1, end);
    animation-iteration-count: infinite;
  }
  .ss__panel:nth-child(2) {
    animation-name: ss-state-2;
    animation-duration: $duration;
    animation-timing-function: steps(1, end);
    animation-iteration-count: infinite;
  }
  .ss__dot:nth-child(1) {
    animation-name: ss-dot-1;
    animation-duration: $duration;
    animation-timing-function: steps(1, end);
    animation-iteration-count: infinite;
  }
  .ss__dot:nth-child(2) {
    animation-name: ss-dot-2;
    animation-duration: $duration;
    animation-timing-function: steps(1, end);
    animation-iteration-count: infinite;
  }
}

@keyframes ss-slide {
  0%, 8% { transform: translate3d(0, 0, 0); }
  36%, 56% { transform: translate3d(0, var(--ss-travel), 0); }
  82%, 100% { transform: translate3d(0, 0, 0); }
}
@keyframes ss-state-1 {
  0%, 40% { background: $subject-blue-deep; color: $subject-cream; }
  44%, 86% { background: $stage-paper; color: $subject-ink; }
  90%, 100% { background: $subject-blue-deep; color: $subject-cream; }
}
@keyframes ss-state-2 {
  0%, 40% { background: $stage-paper; color: $subject-ink; }
  44%, 86% { background: $subject-blue-deep; color: $subject-cream; }
  90%, 100% { background: $stage-paper; color: $subject-ink; }
}
@keyframes ss-dot-1 {
  0%, 40% { width: 20px; background: $color; }
  44%, 86% { width: 8px; background: rgba($subject-ink, .25); }
  90%, 100% { width: 20px; background: $color; }
}
@keyframes ss-dot-2 {
  0%, 40% { width: 8px; background: rgba($subject-ink, .25); }
  44%, 86% { width: 20px; background: $color; }
  90%, 100% { width: 8px; background: rgba($subject-ink, .25); }
}

@media (max-width: 340px) {
  .ss { width: 100%; --ss-travel: -104px; }
  .ss__head,
  .ss__foot { padding: $sp-1 $sp-2; }
  .ss__view { height: 112px; }
  .ss__panel { height: 96px; }
  .ss__panel h3 { font-size: 13px; }
  .ss__panel p { font-size: 10px; }
}

@media (prefers-reduced-motion: reduce) {
  .ss__panel { transition: none !important; }
  .ss__dot { transition: none !important; }
  .ss.is-demo .ss__track,
  .ss.is-demo .ss__panel,
  .ss.is-demo .ss__dot { animation: none !important; }
  // 정지 상태 — 첫 섹션이 중앙에 붙은 모습 그대로 보인다
}

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);
}

.ss {
  --ss-travel: -160px;
  position: relative;
  box-sizing: border-box;
  width: min(320px, 92vw);
  border-radius: 16px;
  background: #fff7e6;
  color: #17141a;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  overflow: hidden;
  box-shadow: 0 14px 24px rgba(23, 20, 26, 0.32);
}

.ss__head {
  display: flex;
  align-items: baseline;
  justify-content: space-between;
  gap: 8px;
  padding: 8px 12px;
}

.ss__title {
  margin: 0;
  font-size: 13px;
  font-weight: 800;
  line-height: 1.3;
}

.ss__attr {
  margin: 0;
  font-size: 10px;
  line-height: 1.3;
  color: rgba(23, 20, 26, 0.72);
}
.ss__attr code {
  font-family: "Consolas", "Menlo", monospace;
}

.ss__view {
  position: relative;
  height: 168px;
  overflow-y: auto;
  scroll-snap-type: y mandatory;
  padding: 0 12px;
  outline: none;
}

.ss__track {
  display: grid;
  gap: 8px;
  padding: 8px 0;
}

.ss__panel {
  scroll-snap-align: center;
  display: grid;
  align-content: center;
  justify-items: center;
  gap: 4px;
  box-sizing: border-box;
  height: 152px;
  padding: 8px;
  border-radius: 12px;
  background: #ffffff;
  color: #17141a;
  box-shadow: 0 6px 12px rgba(23, 20, 26, 0.32);
  transition: background 220ms ease-out, color 220ms ease-out;
}
.ss__panel b {
  font-size: 13px;
  font-weight: 800;
  line-height: 1;
  letter-spacing: 0.08em;
  padding: 4px 8px;
  border-radius: 999px;
  background: rgba(255, 247, 230, 0.18);
}
.ss__panel h3 {
  margin: 0;
  font-size: 15px;
  font-weight: 800;
  line-height: 1.3;
}
.ss__panel p {
  margin: 0;
  font-size: 11px;
  font-weight: 500;
  line-height: 1.4;
  text-align: center;
}

.ss__panel[aria-current=true] {
  background: #0a4fe8;
  color: #fff7e6;
}

.ss__foot {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 8px;
  padding: 8px 12px;
  border-top: 1px solid rgba(23, 20, 26, 0.12);
  font-size: 10px;
  font-weight: 700;
  line-height: 1.3;
}
.ss__foot b {
  color: #c93000;
  font-weight: 800;
}

.ss__dots {
  display: flex;
  align-items: center;
  gap: 4px;
}

.ss__dot {
  width: 8px;
  height: 8px;
  padding: 0;
  border: 0;
  border-radius: 999px;
  background: rgba(23, 20, 26, 0.25);
  cursor: pointer;
  transition: width 220ms ease-out, background 220ms ease-out;
}

.ss__dot[aria-current=true] {
  width: 20px;
  background: #2f6df6;
}

.ss__dot:focus-visible {
  outline: 2px solid #2f6df6;
  outline-offset: 2px;
}

.ss__view:focus-visible {
  outline: 2px solid #2f6df6;
  outline-offset: -2px;
}

.ss.is-demo .ss__view {
  scroll-snap-type: none;
}
.ss.is-demo .ss__track {
  animation-name: ss-slide;
  animation-duration: 2s;
  animation-timing-function: cubic-bezier(0.2, 0.8, 0.2, 1);
  animation-iteration-count: infinite;
}
.ss.is-demo .ss__panel:nth-child(1) {
  animation-name: ss-state-1;
  animation-duration: 2s;
  animation-timing-function: steps(1, end);
  animation-iteration-count: infinite;
}
.ss.is-demo .ss__panel:nth-child(2) {
  animation-name: ss-state-2;
  animation-duration: 2s;
  animation-timing-function: steps(1, end);
  animation-iteration-count: infinite;
}
.ss.is-demo .ss__dot:nth-child(1) {
  animation-name: ss-dot-1;
  animation-duration: 2s;
  animation-timing-function: steps(1, end);
  animation-iteration-count: infinite;
}
.ss.is-demo .ss__dot:nth-child(2) {
  animation-name: ss-dot-2;
  animation-duration: 2s;
  animation-timing-function: steps(1, end);
  animation-iteration-count: infinite;
}

@keyframes ss-slide {
  0%, 8% {
    transform: translate3d(0, 0, 0);
  }
  36%, 56% {
    transform: translate3d(0, var(--ss-travel), 0);
  }
  82%, 100% {
    transform: translate3d(0, 0, 0);
  }
}
@keyframes ss-state-1 {
  0%, 40% {
    background: #0a4fe8;
    color: #fff7e6;
  }
  44%, 86% {
    background: #ffffff;
    color: #17141a;
  }
  90%, 100% {
    background: #0a4fe8;
    color: #fff7e6;
  }
}
@keyframes ss-state-2 {
  0%, 40% {
    background: #ffffff;
    color: #17141a;
  }
  44%, 86% {
    background: #0a4fe8;
    color: #fff7e6;
  }
  90%, 100% {
    background: #ffffff;
    color: #17141a;
  }
}
@keyframes ss-dot-1 {
  0%, 40% {
    width: 20px;
    background: #2f6df6;
  }
  44%, 86% {
    width: 8px;
    background: rgba(23, 20, 26, 0.25);
  }
  90%, 100% {
    width: 20px;
    background: #2f6df6;
  }
}
@keyframes ss-dot-2 {
  0%, 40% {
    width: 8px;
    background: rgba(23, 20, 26, 0.25);
  }
  44%, 86% {
    width: 20px;
    background: #2f6df6;
  }
  90%, 100% {
    width: 8px;
    background: rgba(23, 20, 26, 0.25);
  }
}
@media (max-width: 340px) {
  .ss {
    width: 100%;
    --ss-travel: -104px;
  }
  .ss__head,
  .ss__foot {
    padding: 4px 8px;
  }
  .ss__view {
    height: 112px;
  }
  .ss__panel {
    height: 96px;
  }
  .ss__panel h3 {
    font-size: 13px;
  }
  .ss__panel p {
    font-size: 10px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .ss__panel {
    transition: none !important;
  }
  .ss__dot {
    transition: none !important;
  }
  .ss.is-demo .ss__track,
  .ss.is-demo .ss__panel,
  .ss.is-demo .ss__dot {
    animation: none !important;
  }
}

// 스냅 섹션 전환 — CSS 의 scroll-snap-type 이 붙이고, 관찰자가 중앙에 온 섹션을 골라 aria-current 로 알린다
var root = document.getElementById('ss');
var view = document.getElementById('ss-view');
var panels = Array.prototype.slice.call(document.querySelectorAll('.ss__panel'));
var dots = Array.prototype.slice.call(document.querySelectorAll('.ss__dot'));
var started = false;

function pick(entries) {
  entries.forEach(function (entry) {
    if (!entry.isIntersecting) return;
    var i = panels.indexOf(entry.target);
    if (i < 0) return;
    panels.forEach(function (panel, j) {
      if (j === i) { panel.setAttribute('aria-current', 'true'); }
      else { panel.removeAttribute('aria-current'); }
    });
    dots.forEach(function (dot, j) {
      if (j === i) { dot.setAttribute('aria-current', 'true'); }
      else { dot.removeAttribute('aria-current'); }
    });
  });
}

function goTo(i) {
  var target = panels[i];
  if (!target) return;
  // scroll-snap-align: center 기준 붙는 위치 = 패널 중심을 상자 중심에 맞춘 값
  var top = target.offsetTop - (view.clientHeight - target.offsetHeight) / 2;
  view.scrollTo({ top: top, behavior: 'smooth' });
}

function start() {
  root.classList.remove('is-demo');
  if (started) return;
  started = true;
  // 화면 가운데 10퍼센트 띠에 걸친 패널이 중앙 패널이다
  var io = new IntersectionObserver(pick, { root: view, rootMargin: '-45% 0px -45% 0px', threshold: 0 });
  panels.forEach(function (panel) { io.observe(panel); });
}
view.addEventListener('scroll', start, { passive: true });
view.addEventListener('pointerdown', start);
view.addEventListener('keydown', function (e) {
  if (e.key === 'ArrowDown' || e.key === 'ArrowUp' || e.key === 'PageDown' || e.key === 'PageUp' || e.key === ' ') start();
});
dots.forEach(function (dot, i) {
  dot.addEventListener('click', function () { start(); goTo(i); });
});

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

export type SnapSectionActiveProps = {
  title?: string;
  attr?: string;
  state?: string;
  stateBold?: string;
  groupLabel?: string;
  listLabel?: string;
  navLabel?: string;
  panels?: { title: string; sub: string }[];
  dotLabels?: string[];
  /** 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;
  "--ss-travel"?: string;
};
// ambient 가 얇아 DOM 요소 타입을 못 쓴다 — 필요한 꼴만 로컬 타입으로 선언
type Box<T> = { current: T };
type KeyEvt = { key: string };

const DEFAULT_PANELS: { title: string; sub: string }[] = [
  { title: "한 화면에 하나", sub: "섹션이 스크롤 끝에 딱 붙어 멈춥니다" },
  { title: "중앙 감지", sub: "관찰자가 화면 가운데 섹션을 고릅니다" },
  { title: "상태 전달", sub: "고른 섹션에 aria-current 를 붙입니다" },
];
const DEFAULT_DOTS = ["첫 번째 섹션으로", "두 번째 섹션으로", "세 번째 섹션으로"];

export default function SnapSectionActive({
  title = "스냅 섹션 전환",
  attr = "scroll-snap-type: y mandatory",
  state = "중앙에 온 섹션이",
  stateBold = "aria-current",
  groupLabel = "스냅 섹션 전환 데모",
  listLabel = "특징 섹션 세 장 — 스크롤하면 한 장씩 화면에 붙습니다",
  navLabel = "섹션 바로가기",
  panels = DEFAULT_PANELS,
  dotLabels = DEFAULT_DOTS,
  demo = true,
  duration = 2000,
  easing = "cubic-bezier(.2, .8, .2, 1)",
  color = "#2f6df6",
}: SnapSectionActiveProps) {
  const [live, setLive] = useState(demo);
  const [active, setActive] = useState(0);
  const viewRef = useRef<HTMLDivElement>(null) as unknown as Box<HTMLDivElement | null>;
  const panelRefs = useRef<(HTMLElement | null)[]>([]) as unknown as Box<(HTMLElement | null)[]>;

  useEffect(() => {
    if (live) return;
    const root = viewRef.current;
    if (!root) return;
    const items = panelRefs.current.filter((el): el is HTMLElement => el != null);
    // 화면 가운데 10퍼센트 띠에 걸친 패널이 중앙 패널이다
    const io = new IntersectionObserver(
      (entries) => {
        entries.forEach((entry) => {
          if (!entry.isIntersecting) return;
          const i = items.indexOf(entry.target as HTMLElement);
          if (i !== -1) setActive(i);
        });
      },
      { root, rootMargin: "-45% 0px -45% 0px", threshold: 0 }
    );
    items.forEach((el) => io.observe(el));
    return () => io.disconnect();
  }, [live]);

  const goTo = (i: number) => {
    setLive(false);
    const view = viewRef.current;
    const target = panelRefs.current[i];
    if (!view || !target) return;
    // scroll-snap-align: center 기준 붙는 위치 = 패널 중심을 상자 중심에 맞춘 값
    const top = target.offsetTop - (view.clientHeight - target.offsetHeight) / 2;
    view.scrollTo({ top, behavior: "smooth" });
  };

  const vars: Vars = {
    "--duration": `${duration}ms`,
    "--easing": easing,
    "--color": color,
    "--ss-travel": "-160px",
  };

  return (
    <section
      className={`${styles.ss} ${live ? styles.isDemo : ""}`}
      style={vars}
      aria-label={groupLabel}
    >
      <header className={styles.head}>
        <p className={styles.title}>{title}</p>
        <p className={styles.attr}><code>{attr}</code></p>
      </header>
      <div
        className={styles.view}
        ref={viewRef as unknown as Box<HTMLDivElement>}
        onScroll={() => setLive(false)}
        onPointerDown={() => setLive(false)}
        onKeyDown={(e: KeyEvt) => {
          if (e.key === "ArrowDown" || e.key === "ArrowUp" || e.key === "PageDown" || e.key === "PageUp" || e.key === " ") setLive(false);
        }}
        tabIndex={0}
        role="region"
        aria-label={listLabel}
      >
        <div className={styles.track}>
          {panels.map((panel, i) => (
            <article
              key={panel.title}
              ref={(el: HTMLElement | null) => {
                panelRefs.current[i] = el;
              }}
              className={styles.panel}
              aria-current={active === i ? "true" : undefined}
            >
              <b>{String(i + 1).padStart(2, "0")}</b>
              <h3>{panel.title}</h3>
              <p>{panel.sub}</p>
            </article>
          ))}
        </div>
      </div>
      <footer className={styles.foot}>
        <nav className={styles.dots} aria-label={navLabel}>
          {panels.map((panel, i) => (
            <button
              key={panel.title}
              type="button"
              className={styles.dot}
              aria-current={active === i ? "true" : undefined}
              aria-label={dotLabels[i]}
              onClick={() => goTo(i)}
            />
          ))}
        </nav>
        <span className={styles.state}>
          {state} <b>{stateBold}</b>
        </span>
      </footer>
    </section>
  );
}