02インデックス差の値が方向を決めるスライドパネル

<main class="stage">
<div class="sp is-demo" id="sp">
  <div class="sp__tabs" role="tablist" aria-label="ステップタブ">
    <button type="button" class="sp__tab is-active" role="tab" id="sp-tab-0" aria-selected="true" aria-controls="sp-panel-0" data-idx="0">ステップ1</button>
    <button type="button" class="sp__tab" role="tab" id="sp-tab-1" aria-selected="false" aria-controls="sp-panel-1" data-idx="1" tabindex="-1">ステップ2</button>
    <button type="button" class="sp__tab" role="tab" id="sp-tab-2" aria-selected="false" aria-controls="sp-panel-2" data-idx="2" tabindex="-1">ステップ3</button>
    <button type="button" class="sp__tab" role="tab" id="sp-tab-3" aria-selected="false" aria-controls="sp-panel-3" data-idx="3" tabindex="-1">ステップ4</button>
  </div>
  <div class="sp__viewport" id="spViewport">
    <div class="sp__track" id="spTrack">
      <div class="sp__panel" id="sp-panel-0" role="tabpanel" aria-labelledby="sp-tab-0" tabindex="0"><span class="sp__num">1</span></div>
      <div class="sp__panel" id="sp-panel-1" role="tabpanel" aria-labelledby="sp-tab-1" tabindex="0" aria-hidden="true"><span class="sp__num">2</span></div>
      <div class="sp__panel" id="sp-panel-2" role="tabpanel" aria-labelledby="sp-tab-2" tabindex="0" aria-hidden="true"><span class="sp__num">3</span></div>
      <div class="sp__panel" id="sp-panel-3" role="tabpanel" aria-labelledby="sp-tab-3" tabindex="0" aria-hidden="true"><span class="sp__num">4</span></div>
    </div>
  </div>
  <p class="sp__meta" id="spMeta">移動 <b id="spDist">0</b>マス・方向 <b id="spDir">-</b></p>
</div>
</main>

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

// 계산 겹: index.html select() 가 (새 인덱스 - 이전 인덱스) 의 부호로 방향을, 절댓값으로 건너뛴 칸
// 수를 구해 전환 시간(BASE_MS + (거리-1)*STEP_MS)을 늘린다 — 두 칸을 건너뛰면 한 칸보다 오래 미끄러진다.
@include stage($stage-yellow);

.sp { width: min(100%, 300px); min-width: 0; display: flex; flex-direction: column; gap: $sp-3; }
.sp__tabs { display: flex; gap: $sp-1; background: rgba($subject-ink, .08); padding: $sp-1; border-radius: $r-pill; }
.sp__tab {
  flex: 1 1 0; border: none; background: transparent; border-radius: $r-pill; cursor: pointer;
  padding: $sp-2 $sp-2; font-size: 11px; font-weight: 700; color: rgba($subject-ink, .72);
}
.sp__tab.is-active { background: $subject-ink; color: $stage-yellow; }
.sp__tab:focus-visible { outline: 2px solid $subject-ink; outline-offset: 2px; }

.sp__viewport { overflow: hidden; min-width: 0; border-radius: $r-card; background: rgba($subject-ink, .06); }
.sp__track {
  display: flex; will-change: transform;
  transition: transform var(--sp-dur, #{$dur-base}) $ease-spring;
}
.sp__panel {
  flex: 0 0 auto; box-sizing: border-box; height: 120px; display: grid; place-items: center;
}
.sp__num { font-size: 40px; font-weight: 800; color: $subject-ink; opacity: .82; }
.sp__meta { margin: 0; font-size: 11px; color: rgba($subject-ink, .78); text-align: center; }
.sp__meta b { color: $subject-ink; font-weight: 700; }

@media (max-width: 340px) {
  .sp { width: 100%; }
  .sp__panel { height: 96px; }
  .sp__num { font-size: 32px; }
}

@media (prefers-reduced-motion: reduce) {
  .sp__track { transition: none; }
}

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);
}

.sp {
  width: min(100%, 300px);
  min-width: 0;
  display: flex;
  flex-direction: column;
  gap: 12px;
}

.sp__tabs {
  display: flex;
  gap: 4px;
  background: rgba(23, 20, 26, 0.08);
  padding: 4px;
  border-radius: 999px;
}

.sp__tab {
  flex: 1 1 0;
  border: none;
  background: transparent;
  border-radius: 999px;
  cursor: pointer;
  padding: 8px 8px;
  font-size: 11px;
  font-weight: 700;
  color: rgba(23, 20, 26, 0.72);
}

.sp__tab.is-active {
  background: #17141a;
  color: #ffd23f;
}

.sp__tab:focus-visible {
  outline: 2px solid #17141a;
  outline-offset: 2px;
}

.sp__viewport {
  overflow: hidden;
  min-width: 0;
  border-radius: 16px;
  background: rgba(23, 20, 26, 0.06);
}

.sp__track {
  display: flex;
  will-change: transform;
  transition: transform var(--sp-dur, 300ms) cubic-bezier(0.2, 0.8, 0.2, 1);
}

.sp__panel {
  flex: 0 0 auto;
  box-sizing: border-box;
  height: 120px;
  display: grid;
  place-items: center;
}

.sp__num {
  font-size: 40px;
  font-weight: 800;
  color: #17141a;
  opacity: 0.82;
}

.sp__meta {
  margin: 0;
  font-size: 11px;
  color: rgba(23, 20, 26, 0.78);
  text-align: center;
}

.sp__meta b {
  color: #17141a;
  font-weight: 700;
}

@media (max-width: 340px) {
  .sp {
    width: 100%;
  }
  .sp__panel {
    height: 96px;
  }
  .sp__num {
    font-size: 32px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .sp__track {
    transition: none;
  }
}

(function () {
  var BASE_MS = 220; // 계산 겹 상수: 한 칸 이동의 기본 시간
  var STEP_MS = 90; // 계산 겹 상수: 건너뛴 칸 하나마다 늘어나는 시간
  var MAX_MS = 640;
  var HOLD_MS = 700;
  var COUNT = 4;
  var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;

  var root = document.getElementById('sp');
  var viewport = document.getElementById('spViewport');
  var track = document.getElementById('spTrack');
  var distEl = document.getElementById('spDist');
  var dirEl = document.getElementById('spDir');
  var tabs = [0, 1, 2, 3].map(function (i) { return document.getElementById('sp-tab-' + i); });
  var panels = [0, 1, 2, 3].map(function (i) { return document.getElementById('sp-panel-' + i); });

  var isDemo = true;
  var active = 0;

  function human() {
    if (isDemo) { root.classList.remove('is-demo'); isDemo = false; }
  }

  function select(idx) {
    if (idx === active) return;
    var delta = idx - active; // 계산 겹: 새 인덱스 - 이전 인덱스
    var dir = delta > 0 ? 1 : -1; // 계산 겹: 부호가 슬라이드 방향을 정한다
    var dist = Math.abs(delta); // 계산 겹: 건너뛴 칸 수
    var dur = Math.min(MAX_MS, BASE_MS + (dist - 1) * STEP_MS); // 계산 겹: 건너뛴 칸이 많을수록 오래 이동한다
    var w = viewport.clientWidth;

    track.style.setProperty('--sp-dur', dur.toFixed(0) + 'ms');
    track.style.transform = 'translateX(' + (-idx * w).toFixed(2) + 'px)';

    tabs[active].classList.remove('is-active');
    tabs[active].setAttribute('aria-selected', 'false');
    tabs[active].setAttribute('tabindex', '-1');
    panels[active].setAttribute('aria-hidden', 'true');

    tabs[idx].classList.add('is-active');
    tabs[idx].setAttribute('aria-selected', 'true');
    tabs[idx].setAttribute('tabindex', '0');
    panels[idx].setAttribute('aria-hidden', 'false');

    distEl.textContent = String(dist);
    dirEl.textContent = dir > 0 ? '→' : '←';
    active = idx;
  }

  function place(initial) {
    var w = viewport.clientWidth; // 계산 겹: 패널 폭은 실측 뷰포트 폭 — 짐작 px 를 쓰지 않는다
    panels.forEach(function (p) { p.style.width = w + 'px'; });
    if (initial) track.style.transition = 'none'; // 최초 배치는 transition 없이 — 'none'→translateX(0) 전이가 애니메이션으로 잡혀 측정을 망가뜨린다
    track.style.transform = 'translateX(' + (-active * w).toFixed(2) + 'px)';
    if (initial) { track.getBoundingClientRect(); track.style.transition = ''; }
  }

  tabs.forEach(function (t, i) {
    t.addEventListener('click', function () { human(); select(i); });
  });

  root.addEventListener('keydown', function (e) {
    var idx = tabs.indexOf(document.activeElement);
    if (idx === -1) return;
    var next = null;
    if (e.key === 'ArrowRight') next = (idx + 1) % COUNT;
    else if (e.key === 'ArrowLeft') next = (idx - 1 + COUNT) % COUNT;
    else if (e.key === 'Home') next = 0;
    else if (e.key === 'End') next = COUNT - 1;
    if (next === null) return;
    e.preventDefault();
    human();
    tabs[next].focus({ preventScroll: true });
    select(next);
  });

  window.addEventListener('resize', place);

  var seq = [1, 3, 0, 2]; // 계산 겹 실연용 순서 — 1→4(건너뛰기 3) 처럼 다양한 거리를 자동 순환에서 보여준다
  var seqPos = 0;

  function loop() {
    if (!isDemo) return;
    seqPos = (seqPos + 1) % seq.length;
    select(seq[seqPos]);
    window.setTimeout(loop, HOLD_MS);
  }

  place(true);
  if (!reduce) {
    window.setTimeout(loop, HOLD_MS);
  } else {
    root.classList.remove('is-demo');
  }
})();

// TabSlideDirectionIndex — vanilla 판(run/394/demo/02-tab-panel-slide-direction-index/index.html) 의 React 포트.
// select() 가 (새 인덱스 - 이전 인덱스) 의 부호로 방향을, 절댓값으로 건너뛴 칸 수를 구해
// 전환 시간(BASE_MS + (거리-1)*STEP_MS)을 늘린다.
import { useEffect, useRef } from "react";
import styles from "./TabSlideDirectionIndex.module.scss";

type Box<T> = { current: T };

const BASE_MS = 220; // 계산 겹 상수: 한 칸 이동의 기본 시간
const STEP_MS = 90; // 계산 겹 상수: 건너뛴 칸 하나마다 늘어나는 시간
const MAX_MS = 640;
const HOLD_MS = 700;
const COUNT = 4;
const SEQ = [1, 3, 0, 2];

export default function TabSlideDirectionIndex() {
  const rootRef = useRef(null) as unknown as Box<HTMLDivElement>;
  const viewportRef = useRef(null) as unknown as Box<HTMLDivElement>;
  const trackRef = useRef(null) as unknown as Box<HTMLDivElement>;
  const distRef = useRef(null) as unknown as Box<HTMLElement>;
  const dirRef = useRef(null) as unknown as Box<HTMLElement>;
  const tabRefs = useRef([null, null, null, null]) as unknown as Box<(HTMLButtonElement | null)[]>;
  const panelRefs = useRef([null, null, null, null]) as unknown as Box<(HTMLDivElement | null)[]>;
  const timerRef = useRef(0) as unknown as Box<number>;

  useEffect(() => {
    const reduce = window.matchMedia("(prefers-reduced-motion: reduce)").matches;
    let isDemo = true;
    let active = 0;
    let seqPos = 0;

    function human() {
      if (isDemo) { rootRef.current?.classList.remove(styles.isDemo); isDemo = false; }
    }

    function select(idx: number) {
      if (idx === active) return;
      const track = trackRef.current, viewport = viewportRef.current;
      if (!track || !viewport) return;
      const delta = idx - active; // 계산 겹: 새 인덱스 - 이전 인덱스
      const dir = delta > 0 ? 1 : -1; // 계산 겹: 부호가 슬라이드 방향을 정한다
      const dist = Math.abs(delta); // 계산 겹: 건너뛴 칸 수
      const dur = Math.min(MAX_MS, BASE_MS + (dist - 1) * STEP_MS); // 계산 겹: 건너뛴 칸이 많을수록 오래 이동한다
      const w = viewport.clientWidth;

      track.style.setProperty("--sp-dur", dur.toFixed(0) + "ms");
      track.style.transform = "translateX(" + (-idx * w).toFixed(2) + "px)";

      const prevTab = tabRefs.current[active], nextTab = tabRefs.current[idx];
      const prevPanel = panelRefs.current[active], nextPanel = panelRefs.current[idx];
      prevTab?.classList.remove(styles.isActive);
      prevTab?.setAttribute("aria-selected", "false");
      prevTab?.setAttribute("tabindex", "-1");
      prevPanel?.setAttribute("aria-hidden", "true");
      nextTab?.classList.add(styles.isActive);
      nextTab?.setAttribute("aria-selected", "true");
      nextTab?.setAttribute("tabindex", "0");
      nextPanel?.setAttribute("aria-hidden", "false");

      if (distRef.current) distRef.current.textContent = String(dist);
      if (dirRef.current) dirRef.current.textContent = dir > 0 ? "→" : "←";
      active = idx;
    }

    function place(initial?: boolean) {
      const viewport = viewportRef.current, track = trackRef.current;
      if (!viewport || !track) return;
      const w = viewport.clientWidth; // 계산 겹: 패널 폭은 실측 뷰포트 폭
      panelRefs.current.forEach((p) => { if (p) p.style.width = w + "px"; });
      if (initial) track.style.transition = "none"; // 최초 배치는 transition 없이 — 측정 훼손 방지
      track.style.transform = "translateX(" + (-active * w).toFixed(2) + "px)";
      if (initial) { track.getBoundingClientRect(); track.style.transition = ""; }
    }

    function onKeydown(e: KeyboardEvent) {
      const idx = tabRefs.current.indexOf(document.activeElement as HTMLButtonElement);
      if (idx === -1) return;
      let next: number | null = null;
      if (e.key === "ArrowRight") next = (idx + 1) % COUNT;
      else if (e.key === "ArrowLeft") next = (idx - 1 + COUNT) % COUNT;
      else if (e.key === "Home") next = 0;
      else if (e.key === "End") next = COUNT - 1;
      if (next === null) return;
      e.preventDefault();
      human();
      tabRefs.current[next]?.focus({ preventScroll: true });
      select(next);
    }

    function onTabClick(i: number) { return () => { human(); select(i); }; }
    const clickHandlers = [0, 1, 2, 3].map(onTabClick);
    tabRefs.current.forEach((t, i) => t?.addEventListener("click", clickHandlers[i]));
    rootRef.current?.addEventListener("keydown", onKeydown);
    function onResize() { place(); }
    window.addEventListener("resize", onResize);

    function loop() {
      if (!isDemo) return;
      seqPos = (seqPos + 1) % SEQ.length;
      select(SEQ[seqPos]);
      timerRef.current = window.setTimeout(loop, HOLD_MS);
    }

    place(true);
    if (!reduce) {
      timerRef.current = window.setTimeout(loop, HOLD_MS);
    } else {
      rootRef.current?.classList.remove(styles.isDemo);
    }

    return () => {
      window.clearTimeout(timerRef.current);
      window.removeEventListener("resize", onResize);
      tabRefs.current.forEach((t, i) => t?.removeEventListener("click", clickHandlers[i]));
      rootRef.current?.removeEventListener("keydown", onKeydown);
    };
  }, []);

  const labels = ["1단계", "2단계", "3단계", "4단계"];

  return (
    <main className={styles.stage}>
      <div className={styles.sp + " " + styles.isDemo} ref={rootRef}>
        <div className={styles.tabs} role="tablist" aria-label="단계 탭">
          {labels.map((label, i) => (
            <button
              key={label}
              type="button"
              className={styles.tab + (i === 0 ? " " + styles.isActive : "")}
              role="tab"
              aria-selected={i === 0 ? "true" : "false"}
              tabIndex={i === 0 ? 0 : -1}
              ref={(el: HTMLButtonElement | null) => { tabRefs.current[i] = el; }}
            >{label}</button>
          ))}
        </div>
        <div className={styles.viewport} ref={viewportRef}>
          <div className={styles.track} ref={trackRef}>
            {[1, 2, 3, 4].map((n, i) => (
              <div
                key={n}
                className={styles.panel}
                role="tabpanel"
                tabIndex={0}
                aria-hidden={i === 0 ? "false" : "true"}
                ref={(el: HTMLDivElement | null) => { panelRefs.current[i] = el; }}
              >
                <span className={styles.num}>{n}</span>
              </div>
            ))}
          </div>
        </div>
        <p className={styles.meta}>
          이동 <b ref={distRef}>0</b>칸 · 방향 <b ref={dirRef}>-</b>
        </p>
      </div>
    </main>
  );
}