08Keyboard arrow focus slide — as the arrow keys move the focus value, the focus outline's position value travels along the buttons' measured coordinates

<main class="stage">
<div class="kfs is-demo" id="kfs">
  <div class="kfs__group" id="kfsGroup" role="radiogroup" aria-label="View mode"></div>
  <span class="kfs__ring" id="kfsRing" aria-hidden="true"></span>
</div>
</main>

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

// 계산 겹: index.html 이 선택된 버튼의 실측 좌표(getBoundingClientRect, 그룹 기준 상대값)를 매번 재고
// FOCUS_EASE 로 진행률을 보간해 포커스 링을 translate·리사이즈한다 — % 나 고정폭이 아니라 실측이다.
@include stage($stage-ink);

.kfs {
  position: relative;
  display: inline-flex;
  max-width: 100%;
}

.kfs__group {
  position: relative;
  display: flex;
  flex-wrap: wrap;
  gap: $sp-2;
  max-width: 100%;
}

.kfs__btn {
  position: relative;
  z-index: 1;
  appearance: none;
  border: none;
  border-radius: $r-sm;
  background: transparent;
  color: $subject-cream;
  font-size: 12px;
  font-weight: 600;
  padding: $sp-2 $sp-3;
  cursor: pointer;
  white-space: nowrap;
  flex: 0 0 auto;

  &:focus-visible { outline: 2px solid $subject-blue; outline-offset: 2px; }
  &[aria-checked="true"] { color: $stage-ink; }
}

.kfs__ring {
  position: absolute;
  top: 0;
  left: 0;
  z-index: 0;
  border-radius: $r-sm;
  background: $subject-blue-light;
  will-change: transform, width, height;
}

@media (max-width: 340px) {
  .kfs__btn { font-size: 11px; padding: $sp-1 $sp-2; }
}

@media (prefers-reduced-motion: reduce) {
  .kfs__ring { 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);
}

.kfs {
  position: relative;
  display: inline-flex;
  max-width: 100%;
}

.kfs__group {
  position: relative;
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  max-width: 100%;
}

.kfs__btn {
  position: relative;
  z-index: 1;
  appearance: none;
  border: none;
  border-radius: 8px;
  background: transparent;
  color: #fff7e6;
  font-size: 12px;
  font-weight: 600;
  padding: 8px 12px;
  cursor: pointer;
  white-space: nowrap;
  flex: 0 0 auto;
}
.kfs__btn:focus-visible {
  outline: 2px solid #2f6df6;
  outline-offset: 2px;
}
.kfs__btn[aria-checked=true] {
  color: #17141a;
}

.kfs__ring {
  position: absolute;
  top: 0;
  left: 0;
  z-index: 0;
  border-radius: 8px;
  background: #5b8cf8;
  will-change: transform, width, height;
}

@media (max-width: 340px) {
  .kfs__btn {
    font-size: 11px;
    padding: 4px 8px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .kfs__ring {
    transition: none;
  }
}

(function () {
  var LABELS = ['Grid view', 'List view', 'Timeline view', 'Board view'];
  var CYCLE_MS = 500; // 데모 자동 순회 간격 — 측정 창(2s) 안에 전환이 여러 번 들어오게 짧게 잡음
  var FOCUS_EASE = 'easeInOut'; // 변형: easeInOut → linear (등속)
  var EASES = {
    linear: function (t) { return t; },
    easeInOut: function (t) { return t < 0.5 ? 2 * t * t : 1 - Math.pow(-2 * t + 2, 2) / 2; }
  };
  var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;

  var root = document.getElementById('kfs');
  var group = document.getElementById('kfsGroup');
  var ring = document.getElementById('kfsRing');
  var isDemo = true;
  var current = 0;

  var btns = LABELS.map(function (label, i) {
    var b = document.createElement('button');
    b.type = 'button';
    b.className = 'kfs__btn';
    b.textContent = label;
    b.setAttribute('role', 'radio');
    b.setAttribute('aria-checked', i === 0 ? 'true' : 'false');
    b.tabIndex = i === 0 ? 0 : -1;
    group.appendChild(b);
    return b;
  });

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

  // 계산 겹: 포커스 링을 목표 버튼의 실측 좌표(getBoundingClientRect, 그룹 기준 상대값)로 진행률 t 를
  // FOCUS_EASE 로 보간해 translate·scale 한다 — % 나 고정폭이 아니라 매번 실측한다.
  var raf = 0, from = null;
  function measure(i) {
    var r = btns[i].getBoundingClientRect();
    var gr = group.getBoundingClientRect();
    return { x: r.left - gr.left, y: r.top - gr.top, w: r.width, h: r.height };
  }

  function render(box) {
    ring.style.transform = 'translate(' + box.x + 'px,' + box.y + 'px)';
    ring.style.width = box.w + 'px';
    ring.style.height = box.h + 'px';
  }

  function moveRing(toIdx) {
    var to = measure(toIdx);
    if (reduce || !from) { render(to); from = to; return; }
    var start = from, dur = 260, t0 = 0;
    var ease = EASES[FOCUS_EASE] || EASES.linear;
    if (raf) cancelAnimationFrame(raf);
    function step(ts) {
      if (!t0) t0 = ts;
      var t = Math.min(1, (ts - t0) / dur);
      var e = ease(t);
      render({
        x: start.x + (to.x - start.x) * e,
        y: start.y + (to.y - start.y) * e,
        w: start.w + (to.w - start.w) * e,
        h: start.h + (to.h - start.h) * e
      });
      if (t < 1) raf = requestAnimationFrame(step);
      else { raf = 0; from = to; }
    }
    raf = requestAnimationFrame(step);
  }

  function select(i, focus) {
    btns.forEach(function (b, j) {
      b.setAttribute('aria-checked', String(j === i));
      b.tabIndex = j === i ? 0 : -1;
    });
    current = i;
    moveRing(i);
    if (focus) btns[i].focus({ preventScroll: true });
  }

  btns.forEach(function (b, i) {
    b.addEventListener('click', function () { human(); select(i, false); });
    b.addEventListener('keydown', function (e) {
      if (e.key !== 'ArrowRight' && e.key !== 'ArrowLeft') return;
      human();
      e.preventDefault();
      var dir = e.key === 'ArrowRight' ? 1 : -1;
      select((current + dir + btns.length) % btns.length, true);
    });
  });

  from = measure(0);
  render(from);

  var start0 = 0;
  function loop(ts) {
    if (!start0) start0 = ts;
    if (isDemo && !reduce) {
      var idx = Math.floor((ts - start0) / CYCLE_MS) % btns.length;
      if (idx !== current) select(idx, false);
    }
    requestAnimationFrame(loop);
  }
  requestAnimationFrame(loop);
})();

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

type Box<T> = { current: T };
type Rect = { x: number; y: number; w: number; h: number };

const LABELS = ['그리드 보기', '리스트 보기', '타임라인 보기', '보드 보기'];
const CYCLE_MS = 500; // 데모 자동 순회 간격 — 측정 창(2s) 안에 전환이 여러 번 들어오게 짧게 잡음
const FOCUS_EASE = 'easeInOut'; // 변형: easeInOut → linear (등속)
const EASES: Record<string, (t: number) => number> = {
  linear: (t) => t,
  easeInOut: (t) => (t < 0.5 ? 2 * t * t : 1 - Math.pow(-2 * t + 2, 2) / 2)
};

export default function KeyboardArrowFocusSlide() {
  const rootRef = useRef(null) as unknown as Box<HTMLDivElement>;
  const groupRef = useRef(null) as unknown as Box<HTMLDivElement>;
  const ringRef = useRef(null) as unknown as Box<HTMLSpanElement>;
  const btnRefs = useRef([]) as unknown as Box<HTMLButtonElement[]>;

  useEffect(() => {
    const root = rootRef.current;
    const group = groupRef.current;
    const ring = ringRef.current;
    const btns = btnRefs.current;
    const reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;

    let isDemo = true;
    let current = 0;
    let raf = 0;
    let from: Rect | null = null;

    function human() {
      if (isDemo) { root.classList.remove(styles.isDemo); isDemo = false; }
    }

    // 계산 겹: 포커스 링을 목표 버튼의 실측 좌표(getBoundingClientRect, 그룹 기준 상대값)로 진행률 t 를
    // FOCUS_EASE 로 보간해 translate·리사이즈한다 — % 나 고정폭이 아니라 매번 실측한다.
    function measure(i: number): Rect {
      const r = btns[i].getBoundingClientRect();
      const gr = group.getBoundingClientRect();
      return { x: r.left - gr.left, y: r.top - gr.top, w: r.width, h: r.height };
    }

    function render(box: Rect) {
      ring.style.transform = `translate(${box.x}px,${box.y}px)`;
      ring.style.width = box.w + 'px';
      ring.style.height = box.h + 'px';
    }

    function moveRing(toIdx: number) {
      const to = measure(toIdx);
      if (reduce || !from) { render(to); from = to; return; }
      const start = from;
      const dur = 260;
      let t0 = 0;
      const ease = EASES[FOCUS_EASE] || EASES.linear;
      if (raf) cancelAnimationFrame(raf);
      function step(ts: number) {
        if (!t0) t0 = ts;
        const t = Math.min(1, (ts - t0) / dur);
        const e = ease(t);
        render({
          x: start.x + (to.x - start.x) * e,
          y: start.y + (to.y - start.y) * e,
          w: start.w + (to.w - start.w) * e,
          h: start.h + (to.h - start.h) * e
        });
        if (t < 1) raf = requestAnimationFrame(step);
        else { raf = 0; from = to; }
      }
      raf = requestAnimationFrame(step);
    }

    function select(i: number, focus: boolean) {
      btns.forEach((b, j) => {
        b.setAttribute('aria-checked', String(j === i));
        b.tabIndex = j === i ? 0 : -1;
      });
      current = i;
      moveRing(i);
      if (focus) btns[i].focus({ preventScroll: true });
    }

    const cleanups: Array<() => void> = [];
    btns.forEach((b, i) => {
      const onClick = () => { human(); select(i, false); };
      const onKeydown = (e: KeyboardEvent) => {
        if (e.key !== 'ArrowRight' && e.key !== 'ArrowLeft') return;
        human();
        e.preventDefault();
        const dir = e.key === 'ArrowRight' ? 1 : -1;
        select((current + dir + btns.length) % btns.length, true);
      };
      b.addEventListener('click', onClick);
      b.addEventListener('keydown', onKeydown);
      cleanups.push(() => {
        b.removeEventListener('click', onClick);
        b.removeEventListener('keydown', onKeydown);
      });
    });

    from = measure(0);
    render(from);

    let start0 = 0;
    let loopRaf = 0;
    function loop(ts: number) {
      if (!start0) start0 = ts;
      if (isDemo && !reduce) {
        const idx = Math.floor((ts - start0) / CYCLE_MS) % btns.length;
        if (idx !== current) select(idx, false);
      }
      loopRaf = requestAnimationFrame(loop);
    }
    loopRaf = requestAnimationFrame(loop);

    return () => {
      cancelAnimationFrame(loopRaf);
      if (raf) cancelAnimationFrame(raf);
      cleanups.forEach((fn) => fn());
    };
  }, []);

  return (
    <div className={`${styles.kfs} ${styles.isDemo}`} ref={(el: HTMLDivElement | null) => { if (el) rootRef.current = el; }}>
      <div
        className={styles.group}
        role="radiogroup"
        aria-label="보기 모드"
        ref={(el: HTMLDivElement | null) => { if (el) groupRef.current = el; }}
      >
        {LABELS.map((label, i) => (
          <button
            key={label}
            type="button"
            className={styles.btn}
            role="radio"
            aria-checked={i === 0}
            tabIndex={i === 0 ? 0 : -1}
            ref={(el: HTMLButtonElement | null) => { if (el) btnRefs.current[i] = el; }}
          >
            {label}
          </button>
        ))}
      </div>
      <span className={styles.ring} aria-hidden="true" ref={(el: HTMLSpanElement | null) => { if (el) ringRef.current = el; }} />
    </div>
  );
}