04끝까지 가면 처음으로 이어붙는 무한 루프 캐러셀

<main class="stage">
<section class="carousel is-demo" id="carousel" role="region" aria-roledescription="carousel" aria-label="카드 캐러셀">
  <div class="viewport" id="viewport" tabindex="0">
    <div class="track" id="track"></div>
  </div>
  <button type="button" class="navBtn navBtn--prev" id="prevBtn" aria-label="이전 카드">
    <svg viewBox="0 0 256 256" width="18" height="18" aria-hidden="true"><g fill="currentColor"><path d="M112 56v144l-72-72Z" opacity=".2"/><path d="M216 120h-96V56a8 8 0 0 0-13.66-5.66l-72 72a8 8 0 0 0 0 11.32l72 72A8 8 0 0 0 120 200v-64h96a8 8 0 0 0 0-16m-112 60.69L51.31 128L104 75.31Z"/></g></svg>
  </button>
  <button type="button" class="navBtn navBtn--next" id="nextBtn" aria-label="다음 카드">
    <svg viewBox="0 0 256 256" width="18" height="18" aria-hidden="true"><g fill="currentColor"><path d="m216 128l-72 72V56Z" opacity=".2"/><path d="m221.66 122.34l-72-72A8 8 0 0 0 136 56v64H40a8 8 0 0 0 0 16h96v64a8 8 0 0 0 13.66 5.66l72-72a8 8 0 0 0 0-11.32M152 180.69V75.31L204.69 128Z"/></g></svg>
  </button>
  <div class="readout" id="readout" aria-live="polite"></div>
</section>
</main>

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

// 변수 3개
$duration: $dur-base;
$easing: $ease-out;
$color: $subject-mint;

// 계산 겹: index.html 의 wrapIfNeeded() 가 전환이 끝난 순간에만 transition 을 끄고
// pos 를 TOTAL 만큼 순간 이동시켜, 화면에 보이는 카드는 그대로인 채 무한히 순환한다.
@include stage($stage-ink);

.carousel {
  position: relative;
  width: 300px;
}

.viewport {
  position: relative;
  width: 300px;
  height: 168px;
  border-radius: $r-card;
  overflow: hidden;
  box-shadow: $shadow-raised;
  background: $stage-ink;
  outline: none;
}

.track {
  display: flex;
  height: 100%;
  will-change: transform;
  touch-action: none;
  cursor: grab;

  &.isDragging { cursor: grabbing; }
}

// BD15: 무한 루프 트랙은 flex gap 을 쓰지 않는다 — margin-right 로만 간격을 준다.
.card {
  flex: 0 0 200px;
  height: 100%;
  margin-right: $sp-4;
  border-radius: $r-card;
  display: grid;
  place-items: center;

  .num {
    font-weight: 700;
    font-size: 56px;
    line-height: 1;
  }
}

.card--0 { background: linear-gradient(160deg, $subject-mint, #63b299); .num { color: $subject-ink; } }
.card--1 { background: linear-gradient(160deg, $subject-pink, #d97fa0); .num { color: $subject-ink; } }
.card--2 { background: linear-gradient(160deg, $subject-blue-deep, #475690); .num { color: $subject-cream; } }
.card--3 { background: linear-gradient(160deg, $subject-lilac, #bdb3da); .num { color: $subject-ink; } }
.card--4 { background: linear-gradient(160deg, $subject-sky, #9cb8ce); .num { color: $subject-ink; } }

.navBtn {
  position: absolute;
  top: 50%;
  margin-top: -18px;
  width: 36px;
  height: 36px;
  border-radius: $r-pill;
  border: none;
  display: grid;
  place-items: center;
  background: rgba($stage-ink, .6);
  color: $subject-cream;
  cursor: pointer;

  &:focus-visible { outline: 2px solid $color; outline-offset: 2px; }
}
.navBtn--prev { left: -($sp-3); }
.navBtn--next { right: -($sp-3); }

.readout {
  position: absolute;
  left: $sp-3;
  bottom: $sp-3;
  padding: $sp-1 $sp-2;
  border-radius: $r-pill;
  background: rgba($stage-ink, .6);
  color: rgba($subject-cream, .9);
  font-size: 11px;
  font-weight: 600;
  line-height: 1;
  font-variant-numeric: tabular-nums;
}

@media (max-width: 340px) {
  .carousel { width: 220px; }
  .viewport { width: 220px; height: 106px; }
  .card { flex-basis: 148px; margin-right: $sp-2; .num { font-size: 36px; } }
  .navBtn { width: 28px; height: 28px; margin-top: -14px; }
  .readout { font-size: 9px; }
}

@media (prefers-reduced-motion: reduce) {
  // 실사용 경로 적용 — 드래그·키보드·버튼은 index.html 이 그대로 모듈로 감기 계산을 돌린다.
  // scss 만: 포커스 아웃라인 전환만 꺼서 잔여 트랜지션을 없앤다.
  .navBtn { transition: none; }
}

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

.stage {
  box-sizing: border-box;
  min-height: 100vh;
  display: grid;
  place-items: center;
  margin: 0;
  background: #17141a;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  padding: clamp(8px, 4vw, 24px);
}

.carousel {
  position: relative;
  width: 300px;
}

.viewport {
  position: relative;
  width: 300px;
  height: 168px;
  border-radius: 16px;
  overflow: hidden;
  box-shadow: 0 14px 24px rgba(23, 20, 26, 0.32);
  background: #17141a;
  outline: none;
}

.track {
  display: flex;
  height: 100%;
  will-change: transform;
  touch-action: none;
  cursor: grab;
}
.track.isDragging {
  cursor: grabbing;
}

.card {
  flex: 0 0 200px;
  height: 100%;
  margin-right: 16px;
  border-radius: 16px;
  display: grid;
  place-items: center;
}
.card .num {
  font-weight: 700;
  font-size: 56px;
  line-height: 1;
}

.card--0 {
  background: linear-gradient(160deg, #4cd4a6, #63b299);
}
.card--0 .num {
  color: #17141a;
}

.card--1 {
  background: linear-gradient(160deg, #ff9ebb, #d97fa0);
}
.card--1 .num {
  color: #17141a;
}

.card--2 {
  background: linear-gradient(160deg, #0a4fe8, #475690);
}
.card--2 .num {
  color: #fff7e6;
}

.card--3 {
  background: linear-gradient(160deg, #b9a0ff, #bdb3da);
}
.card--3 .num {
  color: #17141a;
}

.card--4 {
  background: linear-gradient(160deg, #6ec8ff, #9cb8ce);
}
.card--4 .num {
  color: #17141a;
}

.navBtn {
  position: absolute;
  top: 50%;
  margin-top: -18px;
  width: 36px;
  height: 36px;
  border-radius: 999px;
  border: none;
  display: grid;
  place-items: center;
  background: rgba(23, 20, 26, 0.6);
  color: #fff7e6;
  cursor: pointer;
}
.navBtn:focus-visible {
  outline: 2px solid #4cd4a6;
  outline-offset: 2px;
}

.navBtn--prev {
  left: -12px;
}

.navBtn--next {
  right: -12px;
}

.readout {
  position: absolute;
  left: 12px;
  bottom: 12px;
  padding: 4px 8px;
  border-radius: 999px;
  background: rgba(23, 20, 26, 0.6);
  color: rgba(255, 247, 230, 0.9);
  font-size: 11px;
  font-weight: 600;
  line-height: 1;
  font-variant-numeric: tabular-nums;
}

@media (max-width: 340px) {
  .carousel {
    width: 220px;
  }
  .viewport {
    width: 220px;
    height: 106px;
  }
  .card {
    flex-basis: 148px;
    margin-right: 8px;
  }
  .card .num {
    font-size: 36px;
  }
  .navBtn {
    width: 28px;
    height: 28px;
    margin-top: -14px;
  }
  .readout {
    font-size: 9px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .navBtn {
    transition: none;
  }
}

(function () {
  var TOTAL = 5;
  var CLONE_COUNT = 1;      // 앞뒤로 각 1장씩 이웃 카드를 복제해 둔다 — 경계에서도 다음 칸이 항상 보인다
  var CARD_W = 200;
  var GAP = 16;             // BD15: flex gap 대신 margin-right 로 간격을 준다(무한 루프 트랙 금지 규칙) — style.scss $sp-4 와 동일값
  var STEP = CARD_W + GAP;
  var TRANSITION_MS = 360;

  var carousel = document.getElementById('carousel');
  var viewport = document.getElementById('viewport');
  var track = document.getElementById('track');
  var readout = document.getElementById('readout');
  var prevBtn = document.getElementById('prevBtn');
  var nextBtn = document.getElementById('nextBtn');
  var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;

  var LABEL_PREFIX = '카드 ';
  var LABEL_SEP = ' / ';
  var COLOR_CLASSES = ['card--0', 'card--1', 'card--2', 'card--3', 'card--4'];

  // 실제 카드 앞뒤에 이웃 카드를 복제해 그린다. realIndex = -1 은 마지막 카드의 복제, TOTAL 은 첫 카드의 복제.
  var sequence = [];
  for (var s = -CLONE_COUNT; s < TOTAL + CLONE_COUNT; s++) sequence.push(((s % TOTAL) + TOTAL) % TOTAL);

  sequence.forEach(function (realIdx) {
    var el = document.createElement('div');
    el.className = 'card ' + COLOR_CLASSES[realIdx];
    var num = document.createElement('span');
    num.className = 'num';
    num.textContent = String(realIdx + 1);
    el.appendChild(num);
    track.appendChild(el);
  });

  var pos = CLONE_COUNT;      // 트랙 안에서의 칸 위치(복제 포함) — CLONE_COUNT 가 실제 인덱스 0
  var dragging = false;
  var dragOriginPos = 0;
  var startX = 0;
  var demoTimers = [];
  var transitioning = false;

  function realIndex() {
    return ((pos - CLONE_COUNT) % TOTAL + TOTAL) % TOTAL;
  }
  function paint(withTransition) {
    track.style.transition = withTransition ? 'transform ' + TRANSITION_MS + 'ms cubic-bezier(.22,.61,.36,1)' : 'none';
    track.style.transform = 'translate3d(' + (-pos * STEP).toFixed(1) + 'px,0,0)';
    readout.textContent = LABEL_PREFIX + (realIndex() + 1) + LABEL_SEP + TOTAL;
  }

  // 모듈로 감기 — 위치가 복제 구간(첫 칸 미만 또는 마지막 칸 초과)에 닿으면, 전환이 끝난 그 순간
  // transition 을 끄고 같은 그림의 실제 칸으로 pos 만 순간 이동시킨다(화면상 티가 나지 않는다).
  function wrapIfNeeded() {
    if (pos < CLONE_COUNT) {
      pos += TOTAL;
      paint(false);
      void track.offsetWidth; // 강제 리플로우로 transition:none 을 확정시킨다
    } else if (pos >= CLONE_COUNT + TOTAL) {
      pos -= TOTAL;
      paint(false);
      void track.offsetWidth;
    }
  }

  function onTransitionEnd() {
    transitioning = false;
    wrapIfNeeded();
  }
  track.addEventListener('transitionend', onTransitionEnd);

  function human() {
    if (carousel.classList.contains('is-demo')) {
      carousel.classList.remove('is-demo');
      demoTimers.forEach(function (t) { clearTimeout(t); });
      demoTimers = [];
    }
  }

  function go(dir) {
    pos += dir;
    transitioning = true;
    paint(true);
  }
  function step(dir) {
    human();
    go(dir);
  }

  function onPointerDown(e) {
    human();
    dragging = true;
    dragOriginPos = pos;
    startX = e.clientX;
    viewport.setPointerCapture(e.pointerId);
    track.classList.add('isDragging');
    track.style.transition = 'none';
  }
  function onPointerMove(e) {
    if (!dragging) return;
    var dx = e.clientX - startX;
    pos = dragOriginPos - dx / STEP;
    track.style.transform = 'translate3d(' + (-pos * STEP).toFixed(1) + 'px,0,0)';
  }
  function onPointerUp(e) {
    if (!dragging) return;
    dragging = false;
    track.classList.remove('isDragging');
    try { viewport.releasePointerCapture(e.pointerId); } catch (err) {}
    pos = Math.round(pos);
    transitioning = true;
    paint(true);
  }
  function onKeydown(e) {
    if (e.key === 'ArrowLeft') { step(-1); e.preventDefault(); }
    else if (e.key === 'ArrowRight') { step(1); e.preventDefault(); }
  }

  viewport.addEventListener('pointerdown', onPointerDown);
  viewport.addEventListener('pointermove', onPointerMove);
  viewport.addEventListener('pointerup', onPointerUp);
  viewport.addEventListener('pointercancel', onPointerUp);
  viewport.addEventListener('keydown', onKeydown);
  prevBtn.addEventListener('click', function () { step(-1); });
  nextBtn.addEventListener('click', function () { step(1); });

  // reduce: 실사용 경로 적용 — 드래그·키보드·버튼은 위 리스너가 그대로 모듈로 감기 계산을 돌린다.
  // 아래 demoCycle() 은 시연 게이트만이고 reduce 에서는 돌지 않는다.
  function demoCycle(i) {
    if (!carousel.classList.contains('is-demo')) return;
    go(1);
    demoTimers.push(setTimeout(function () { demoCycle(i + 1); }, TRANSITION_MS + 420));
  }

  function init() {
    paint(false);
    if (!reduce) demoCycle(0);
  }
  init();
})();

import { useEffect, useRef } from 'react';
import styles from './CarouselInfiniteLoopWrap.module.scss';

// 상수 — vanilla demo 04 (run/384/demo/04-carousel-slide-infinite-loop-wrap/index.html) 과 동일
const TOTAL = 5;
const CLONE_COUNT = 1;      // 앞뒤로 각 1장씩 이웃 카드를 복제해 둔다 — 경계에서도 다음 칸이 항상 보인다
const CARD_W = 200;
const GAP = 16;             // BD15: flex gap 대신 margin-right 로 간격을 준다(무한 루프 트랙 금지 규칙) — module.scss $sp-4 와 동일값
const STEP = CARD_W + GAP;
const TRANSITION_MS = 360;
const LABEL_PREFIX = '카드 ';
const LABEL_SEP = ' / ';
const COLOR_CLASSES = ['card--0', 'card--1', 'card--2', 'card--3', 'card--4'] as const;

export default function CarouselInfiniteLoopWrap() {
  const carouselRef = useRef<HTMLElement>(null);

  useEffect(() => {
    const carousel = carouselRef.current;
    if (!carousel) return undefined;
    const viewport = carousel.querySelector<HTMLDivElement>('.' + styles.viewport);
    const track = carousel.querySelector<HTMLDivElement>('.' + styles.track);
    const readout = carousel.querySelector<HTMLDivElement>('.' + styles.readout);
    const prevBtn = carousel.querySelector<HTMLButtonElement>('.' + styles['navBtn--prev']);
    const nextBtn = carousel.querySelector<HTMLButtonElement>('.' + styles['navBtn--next']);
    if (!viewport || !track || !readout || !prevBtn || !nextBtn) return undefined;

    // 실제 카드 앞뒤에 이웃 카드를 복제해 그린다. realIndex = -1 은 마지막 카드의 복제, TOTAL 은 첫 카드의 복제.
    const sequence: number[] = [];
    for (let s = -CLONE_COUNT; s < TOTAL + CLONE_COUNT; s++) sequence.push(((s % TOTAL) + TOTAL) % TOTAL);

    track.innerHTML = '';
    sequence.forEach((realIdx) => {
      const el = document.createElement('div');
      el.className = styles.card + ' ' + styles[COLOR_CLASSES[realIdx]];
      const num = document.createElement('span');
      num.className = styles.num;
      num.textContent = String(realIdx + 1);
      el.appendChild(num);
      track.appendChild(el);
    });

    let pos = CLONE_COUNT;   // 트랙 안에서의 칸 위치(복제 포함) — CLONE_COUNT 가 실제 인덱스 0
    let dragging = false;
    let dragOriginPos = 0;
    let startX = 0;
    let demoTimers: number[] = [];

    function realIndex() {
      return ((pos - CLONE_COUNT) % TOTAL + TOTAL) % TOTAL;
    }
    function paint(withTransition: boolean) {
      track!.style.transition = withTransition ? 'transform ' + TRANSITION_MS + 'ms cubic-bezier(.22,.61,.36,1)' : 'none';
      track!.style.transform = 'translate3d(' + (-pos * STEP).toFixed(1) + 'px,0,0)';
      readout!.textContent = LABEL_PREFIX + (realIndex() + 1) + LABEL_SEP + TOTAL;
    }

    // 모듈로 감기 — 위치가 복제 구간(첫 칸 미만 또는 마지막 칸 초과)에 닿으면, 전환이 끝난 그 순간
    // transition 을 끄고 같은 그림의 실제 칸으로 pos 만 순간 이동시킨다(화면상 티가 나지 않는다).
    function wrapIfNeeded() {
      if (pos < CLONE_COUNT) {
        pos += TOTAL;
        paint(false);
        void track!.offsetWidth; // 강제 리플로우로 transition:none 을 확정시킨다
      } else if (pos >= CLONE_COUNT + TOTAL) {
        pos -= TOTAL;
        paint(false);
        void track!.offsetWidth;
      }
    }

    function onTransitionEnd() {
      wrapIfNeeded();
    }
    track.addEventListener('transitionend', onTransitionEnd);

    function human() {
      if (carousel!.classList.contains(styles['is-demo'])) {
        carousel!.classList.remove(styles['is-demo']);
        demoTimers.forEach((t) => window.clearTimeout(t));
        demoTimers = [];
      }
    }

    function go(dir: number) {
      pos += dir;
      paint(true);
    }
    function step(dir: number) {
      human();
      go(dir);
    }

    function onPointerDown(e: PointerEvent) {
      human();
      dragging = true;
      dragOriginPos = pos;
      startX = e.clientX;
      viewport!.setPointerCapture(e.pointerId);
      track!.classList.add(styles.isDragging);
      track!.style.transition = 'none';
    }
    function onPointerMove(e: PointerEvent) {
      if (!dragging) return;
      const dx = e.clientX - startX;
      pos = dragOriginPos - dx / STEP;
      track!.style.transform = 'translate3d(' + (-pos * STEP).toFixed(1) + 'px,0,0)';
    }
    function onPointerUp(e: PointerEvent) {
      if (!dragging) return;
      dragging = false;
      track!.classList.remove(styles.isDragging);
      try { viewport!.releasePointerCapture(e.pointerId); } catch { /* 캡처가 이미 풀린 경우 */ }
      pos = Math.round(pos);
      paint(true);
    }
    function onKeydown(e: KeyboardEvent) {
      if (e.key === 'ArrowLeft') { step(-1); e.preventDefault(); }
      else if (e.key === 'ArrowRight') { step(1); e.preventDefault(); }
    }
    function onPrev() { step(-1); }
    function onNext() { step(1); }

    viewport.addEventListener('pointerdown', onPointerDown);
    viewport.addEventListener('pointermove', onPointerMove);
    viewport.addEventListener('pointerup', onPointerUp);
    viewport.addEventListener('pointercancel', onPointerUp);
    viewport.addEventListener('keydown', onKeydown);
    prevBtn.addEventListener('click', onPrev);
    nextBtn.addEventListener('click', onNext);

    const reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;

    // reduce: 실사용 경로 적용 — 드래그·키보드·버튼은 위 리스너가 그대로 모듈로 감기 계산을 돌린다.
    // 아래 demoCycle() 은 시연 게이트만이고 reduce 에서는 돌지 않는다.
    function demoCycle(i: number) {
      if (!carousel!.classList.contains(styles['is-demo'])) return;
      go(1);
      demoTimers.push(window.setTimeout(() => demoCycle(i + 1), TRANSITION_MS + 420));
    }

    paint(false);
    if (!reduce) demoCycle(0);

    return () => {
      track.removeEventListener('transitionend', onTransitionEnd);
      viewport.removeEventListener('pointerdown', onPointerDown);
      viewport.removeEventListener('pointermove', onPointerMove);
      viewport.removeEventListener('pointerup', onPointerUp);
      viewport.removeEventListener('pointercancel', onPointerUp);
      viewport.removeEventListener('keydown', onKeydown);
      prevBtn.removeEventListener('click', onPrev);
      nextBtn.removeEventListener('click', onNext);
      demoTimers.forEach((t) => window.clearTimeout(t));
    };
  }, []);

  return (
    <main className={styles.stage}>
      <section
        className={styles.carousel + ' ' + styles['is-demo']}
        ref={carouselRef}
        role="region"
        aria-roledescription="carousel"
        aria-label="카드 캐러셀"
      >
        <div className={styles.viewport} tabIndex={0}>
          <div className={styles.track}></div>
        </div>
        <button type="button" className={styles.navBtn + ' ' + styles['navBtn--prev']} aria-label="이전 카드">
          <svg viewBox="0 0 256 256" width={18} height={18} aria-hidden="true"><g fill="currentColor"><path d="M112 56v144l-72-72Z" opacity=".2" /><path d="M216 120h-96V56a8 8 0 0 0-13.66-5.66l-72 72a8 8 0 0 0 0 11.32l72 72A8 8 0 0 0 120 200v-64h96a8 8 0 0 0 0-16m-112 60.69L51.31 128L104 75.31Z" /></g></svg>
        </button>
        <button type="button" className={styles.navBtn + ' ' + styles['navBtn--next']} aria-label="다음 카드">
          <svg viewBox="0 0 256 256" width={18} height={18} aria-hidden="true"><g fill="currentColor"><path d="m216 128l-72 72V56Z" opacity=".2" /><path d="m221.66 122.34l-72-72A8 8 0 0 0 136 56v64H40a8 8 0 0 0 0 16h96v64a8 8 0 0 0 13.66 5.66l72-72a8 8 0 0 0 0-11.32M152 180.69V75.31L204.69 128Z" /></g></svg>
        </button>
        <div className={styles.readout} aria-live="polite"></div>
      </section>
    </main>
  );
}