07Lightbox With a Focus Ring That Glides Inside a Trap

<main class="stage">
<div class="scene is-demo" id="scene">
  <ul class="grid" id="grid">
    <li><button class="thumb" id="thumb0" type="button" aria-haspopup="dialog"><span class="thumbImg"></span></button></li>
  </ul>
  <div class="backdrop" id="backdrop"></div>
  <div class="lightbox" id="lightbox" role="dialog" aria-modal="true" aria-hidden="true" aria-label="Lightbox moved by keyboard only">
    <span class="fullImg" id="fullImg"></span>
    <div class="toolbar" id="toolbar">
      <button class="ctrlBtn" id="prevBtn" type="button">Previous</button>
      <button class="ctrlBtn" id="infoBtn" type="button">Info</button>
      <button class="ctrlBtn ctrlBtn--primary" id="nextBtn" type="button">Next</button>
    </div>
    <button class="closeBtn" id="closeBtn" type="button">Close</button>
    <span class="focusRing" id="focusRing" aria-hidden="true"></span>
  </div>
</div>
</main>

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

// 변수 3개
$duration: $dur-quick;
$easing: $ease-out;
$color: $subject-sky;

// 계산 겹: index.html 의 glideRingTo() 가 링의 실제 이전 위치와 다음 포커스 요소의 실제 위치를
// (getBoundingClientRect, FLIP) 측정해 그 차이만큼 이동·스케일 보간한다 — 좌표를 하드코딩하지 않는다.
@include stage($stage-orange);

.scene {
  position: relative;
  width: 320px;
  height: 180px;
  border-radius: $r-card;
  overflow: hidden;
  box-shadow: $shadow-raised;
  background: linear-gradient(160deg, #ffe3b0, $stage-orange 85%);
}

.grid {
  position: absolute;
  inset: 0;
  margin: 0;
  padding: 0;
  list-style: none;
  display: flex;
  align-items: center;
  justify-content: center;
}

.thumb {
  appearance: none;
  border: none;
  background: none;
  padding: 0;
  cursor: pointer;

  &:focus-visible .thumbImg { outline: 2px solid $color; outline-offset: 2px; }
}

.thumbImg {
  display: block;
  width: 72px;
  height: 72px;
  border-radius: $r-sm;
  box-shadow: $shadow-press;
  background: linear-gradient(135deg, $subject-blue, $subject-sky);
}

.backdrop {
  position: absolute;
  inset: 0;
  background: $subject-ink;
  opacity: 0;
  visibility: hidden;
  pointer-events: none;
}

.lightbox {
  position: absolute;
  inset: 0;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  gap: $sp-3;
  visibility: hidden;
}

.fullImg {
  display: block;
  width: 190px;
  height: 108px;
  border-radius: $r-card;
  background: linear-gradient(135deg, $subject-blue, $subject-sky 60%, $subject-mint);
}

.toolbar {
  display: flex;
  gap: $sp-2;
}

.ctrlBtn {
  appearance: none;
  border: none;
  border-radius: $r-pill;
  padding: $sp-1 $sp-3;
  font-size: 11px;
  font-weight: 600;
  color: $subject-ink;
  background: rgba($subject-cream, .92);
  cursor: pointer;
  position: relative;

  &--primary { background: $subject-sky; color: $subject-ink; }
}

.closeBtn {
  position: absolute;
  top: $sp-2;
  right: $sp-2;
  appearance: none;
  border: none;
  border-radius: $r-pill;
  padding: $sp-1 $sp-3;
  font-size: 11px;
  font-weight: 600;
  color: $subject-ink;
  background: rgba($subject-cream, .92);
  cursor: pointer;
}

.focusRing {
  position: absolute;
  top: 0;
  left: 0;
  border-radius: $r-pill;
  border: 2px solid $color;
  box-shadow: 0 0 0 3px rgba($subject-sky, .32);
  opacity: 0;
  pointer-events: none;
  will-change: transform;
}

@media (max-width: 340px) {
  .scene { width: 220px; height: 124px; }
  .fullImg { width: 140px; height: 80px; }
  .ctrlBtn { font-size: 10px; padding: $sp-1 $sp-2; }
}

@media (prefers-reduced-motion: reduce) {
  // 실사용 경로 적용 — 링 이동은 index.html 의 animate() 가 reduce 시 즉시 최종 위치로 처리한다.
  .closeBtn, .ctrlBtn, .thumb { transition: none; }
}

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

.stage {
  box-sizing: border-box;
  min-height: 100vh;
  display: grid;
  place-items: center;
  margin: 0;
  background: #ff4d1f;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  padding: clamp(8px, 4vw, 24px);
}

.scene {
  position: relative;
  width: 320px;
  height: 180px;
  border-radius: 16px;
  overflow: hidden;
  box-shadow: 0 14px 24px rgba(23, 20, 26, 0.32);
  background: linear-gradient(160deg, #ffe3b0, #ff4d1f 85%);
}

.grid {
  position: absolute;
  inset: 0;
  margin: 0;
  padding: 0;
  list-style: none;
  display: flex;
  align-items: center;
  justify-content: center;
}

.thumb {
  appearance: none;
  border: none;
  background: none;
  padding: 0;
  cursor: pointer;
}
.thumb:focus-visible .thumbImg {
  outline: 2px solid #6ec8ff;
  outline-offset: 2px;
}

.thumbImg {
  display: block;
  width: 72px;
  height: 72px;
  border-radius: 8px;
  box-shadow: 0 6px 12px rgba(23, 20, 26, 0.32);
  background: linear-gradient(135deg, #2f6df6, #6ec8ff);
}

.backdrop {
  position: absolute;
  inset: 0;
  background: #17141a;
  opacity: 0;
  visibility: hidden;
  pointer-events: none;
}

.lightbox {
  position: absolute;
  inset: 0;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  gap: 12px;
  visibility: hidden;
}

.fullImg {
  display: block;
  width: 190px;
  height: 108px;
  border-radius: 16px;
  background: linear-gradient(135deg, #2f6df6, #6ec8ff 60%, #4cd4a6);
}

.toolbar {
  display: flex;
  gap: 8px;
}

.ctrlBtn {
  appearance: none;
  border: none;
  border-radius: 999px;
  padding: 4px 12px;
  font-size: 11px;
  font-weight: 600;
  color: #17141a;
  background: rgba(255, 247, 230, 0.92);
  cursor: pointer;
  position: relative;
}
.ctrlBtn--primary {
  background: #6ec8ff;
  color: #17141a;
}

.closeBtn {
  position: absolute;
  top: 8px;
  right: 8px;
  appearance: none;
  border: none;
  border-radius: 999px;
  padding: 4px 12px;
  font-size: 11px;
  font-weight: 600;
  color: #17141a;
  background: rgba(255, 247, 230, 0.92);
  cursor: pointer;
}

.focusRing {
  position: absolute;
  top: 0;
  left: 0;
  border-radius: 999px;
  border: 2px solid #6ec8ff;
  box-shadow: 0 0 0 3px rgba(110, 200, 255, 0.32);
  opacity: 0;
  pointer-events: none;
  will-change: transform;
}

@media (max-width: 340px) {
  .scene {
    width: 220px;
    height: 124px;
  }
  .fullImg {
    width: 140px;
    height: 80px;
  }
  .ctrlBtn {
    font-size: 10px;
    padding: 4px 8px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .closeBtn, .ctrlBtn, .thumb {
    transition: none;
  }
}

(function () {
  var LIGHTBOX_FOCUS_RING_MS = 220; // 포커스 링이 Next 요소로 미끄러지는 시간
  var STEP_HOLD_MS = 260;
  var LOOP_MS = 2000;

  var scene = document.getElementById('scene');
  var backdrop = document.getElementById('backdrop');
  var lightbox = document.getElementById('lightbox');
  var closeBtn = document.getElementById('closeBtn');
  var prevBtn = document.getElementById('prevBtn');
  var infoBtn = document.getElementById('infoBtn');
  var nextBtn = document.getElementById('nextBtn');
  var focusRing = document.getElementById('focusRing');
  var thumb = document.getElementById('thumb0');
  var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;

  // 실제 tab 순서 — 이 배열이 곧 트랩의 앞뒤 경계다
  var order = [closeBtn, prevBtn, infoBtn, nextBtn];

  var open = false;
  var timers = [];
  var lastRingRect = null;

  function clamp(v, lo, hi) { return Math.min(hi, Math.max(lo, v)); }
  function easeOutCubic(t) { return 1 - Math.pow(1 - t, 3); }

  function animate(duration, onFrame, onDone) {
    if (reduce) { onFrame(1); if (onDone) onDone(); return; }
    var start = performance.now();
    function frame(now) {
      var p = clamp((now - start) / duration, 0, 1);
      onFrame(easeOutCubic(p));
      if (p < 1) requestAnimationFrame(frame);
      else if (onDone) onDone();
    }
    requestAnimationFrame(frame);
  }

  // FLIP: 링의 지금 실제 위치와 목표 요소의 실제 위치를 측정해 그 차만큼 되돌렸다가 0 으로 애니메이션한다
  function glideRingTo(el) {
    var boxRect = lightbox.getBoundingClientRect();
    var toRect = el.getBoundingClientRect();
    var toX = toRect.left - boxRect.left;
    var toY = toRect.top - boxRect.top;
    var toW = toRect.width;
    var toH = toRect.height;
    var fromRect = lastRingRect || { x: toX, y: toY, w: toW, h: toH };
    focusRing.style.width = toW + 'px';
    focusRing.style.height = toH + 'px';
    focusRing.style.transform = 'translate(' + toX + 'px,' + toY + 'px)';
    var dx = fromRect.x - toX;
    var dy = fromRect.y - toY;
    var sx = fromRect.w / toW;
    var sy = fromRect.h / toH;
    focusRing.style.opacity = '1';
    animate(LIGHTBOX_FOCUS_RING_MS, function (e) {
      var ix = dx * (1 - e);
      var iy = dy * (1 - e);
      var isx = sx + (1 - sx) * e;
      var isy = sy + (1 - sy) * e;
      focusRing.style.transform = 'translate(' + (toX + ix).toFixed(2) + 'px,' + (toY + iy).toFixed(2) + 'px) scale(' + isx.toFixed(4) + ',' + isy.toFixed(4) + ')';
    }, function () {
      lastRingRect = { x: toX, y: toY, w: toW, h: toH };
    });
  }

  order.forEach(function (el) {
    el.addEventListener('focus', function () { glideRingTo(el); });
  });

  function openFrom() {
    if (open) return;
    open = true;
    lastRingRect = null;
    focusRing.style.opacity = '0';
    lightbox.style.visibility = 'visible';
    lightbox.setAttribute('aria-hidden', 'false');
    backdrop.style.visibility = 'visible';
    animate(220, function (e) { backdrop.style.opacity = (e * 0.78).toFixed(3); }, function () {
      closeBtn.focus({ preventScroll: true });
    });
  }

  function closeLightbox() {
    if (!open) return;
    animate(200, function (e) { backdrop.style.opacity = (0.78 * (1 - e)).toFixed(3); }, function () {
      lightbox.style.visibility = 'hidden';
      lightbox.setAttribute('aria-hidden', 'true');
      backdrop.style.visibility = 'hidden';
      focusRing.style.opacity = '0';
      open = false;
      thumb.focus({ preventScroll: true });
    });
  }

  function human() {
    if (scene.classList.contains('is-demo')) {
      scene.classList.remove('is-demo');
      timers.forEach(function (id) { clearTimeout(id); clearInterval(id); });
      timers = [];
    }
  }

  thumb.addEventListener('click', function () { human(); openFrom(); });
  closeBtn.addEventListener('click', function () { human(); closeLightbox(); });
  backdrop.addEventListener('click', function () { human(); closeLightbox(); });

  // 진짜 포커스 트랩: 끝에서 Tab 하면 처음으로, 처음에서 Shift+Tab 하면 끝으로 감긴다
  lightbox.addEventListener('keydown', function (e) {
    if (!open) return;
    if (e.key === 'Escape') { human(); closeLightbox(); return; }
    if (e.key !== 'Tab') return;
    var i = order.indexOf(document.activeElement);
    if (i === -1) return;
    if (e.shiftKey && i === 0) {
      e.preventDefault();
      human();
      order[order.length - 1].focus({ preventScroll: true });
    } else if (!e.shiftKey && i === order.length - 1) {
      e.preventDefault();
      human();
      order[0].focus({ preventScroll: true });
    }
  });

  function cycle() {
    openFrom();
    var i = 0;
    function step() {
      if (i >= order.length) {
        // 끝에서 다시 처음으로 — 실제 트랩과 같은 감김을 시연
        order[0].focus({ preventScroll: true });
        timers.push(setTimeout(closeLightbox, STEP_HOLD_MS));
        return;
      }
      order[i].focus({ preventScroll: true });
      i += 1;
      timers.push(setTimeout(step, STEP_HOLD_MS));
    }
    timers.push(setTimeout(step, 260));
  }

  if (!reduce) {
    cycle();
    timers.push(setInterval(function () {
      if (scene.classList.contains('is-demo')) cycle();
    }, LOOP_MS));
  }
})();

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

const LIGHTBOX_FOCUS_RING_MS = 220; // 포커스 링이 다음 요소로 미끄러지는 시간
const STEP_HOLD_MS = 260;
const LOOP_MS = 2000;

type RingRect = { x: number; y: number; w: number; h: number };

export default function KeyboardFocusTrapRing() {
  const sceneRef = useRef<HTMLDivElement>(null);

  useEffect(() => {
    const scene0 = sceneRef.current;
    if (!scene0) return undefined;
    const backdrop0 = scene0.querySelector<HTMLDivElement>('.' + styles.backdrop);
    const lightbox0 = scene0.querySelector<HTMLDivElement>('.' + styles.lightbox);
    const closeBtn0 = scene0.querySelector<HTMLButtonElement>('.' + styles.closeBtn);
    const prevBtn0 = scene0.querySelector<HTMLButtonElement>('.' + styles.prevBtn);
    const infoBtn0 = scene0.querySelector<HTMLButtonElement>('.' + styles.infoBtn);
    const nextBtn0 = scene0.querySelector<HTMLButtonElement>('.' + styles.nextBtn);
    const focusRing0 = scene0.querySelector<HTMLSpanElement>('.' + styles.focusRing);
    const thumb0 = scene0.querySelector<HTMLButtonElement>('.' + styles.thumb);
    if (!backdrop0 || !lightbox0 || !closeBtn0 || !prevBtn0 || !infoBtn0 || !nextBtn0 || !focusRing0 || !thumb0) return undefined;
    const scene = scene0;
    const backdrop = backdrop0;
    const lightbox = lightbox0;
    const closeBtn = closeBtn0;
    const prevBtn = prevBtn0;
    const infoBtn = infoBtn0;
    const nextBtn = nextBtn0;
    const focusRing = focusRing0;
    const thumb = thumb0;

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

    // 실제 tab 순서 — 이 배열이 곧 트랩의 앞뒤 경계다
    const order = [closeBtn, prevBtn, infoBtn, nextBtn];

    let open = false;
    let timers: number[] = [];
    let lastRingRect: RingRect | null = null;

    function clamp(v: number, lo: number, hi: number) { return Math.min(hi, Math.max(lo, v)); }
    function easeOutCubic(t: number) { return 1 - Math.pow(1 - t, 3); }

    function animate(duration: number, onFrame: (e: number) => void, onDone?: () => void) {
      if (reduce) { onFrame(1); if (onDone) onDone(); return; }
      const start = performance.now();
      function frame(now: number) {
        const p = clamp((now - start) / duration, 0, 1);
        onFrame(easeOutCubic(p));
        if (p < 1) requestAnimationFrame(frame);
        else if (onDone) onDone();
      }
      requestAnimationFrame(frame);
    }

    // FLIP: 링의 지금 실제 위치와 목표 요소의 실제 위치를 측정해 그 차만큼 되돌렸다가 0 으로 애니메이션한다
    function glideRingTo(el: HTMLElement) {
      const boxRect = lightbox.getBoundingClientRect();
      const toRect = el.getBoundingClientRect();
      const toX = toRect.left - boxRect.left;
      const toY = toRect.top - boxRect.top;
      const toW = toRect.width;
      const toH = toRect.height;
      const fromRect: RingRect = lastRingRect || { x: toX, y: toY, w: toW, h: toH };
      focusRing.style.width = toW + 'px';
      focusRing.style.height = toH + 'px';
      focusRing.style.transform = 'translate(' + toX + 'px,' + toY + 'px)';
      const dx = fromRect.x - toX;
      const dy = fromRect.y - toY;
      const sx = fromRect.w / toW;
      const sy = fromRect.h / toH;
      focusRing.style.opacity = '1';
      animate(LIGHTBOX_FOCUS_RING_MS, (e) => {
        const ix = dx * (1 - e);
        const iy = dy * (1 - e);
        const isx = sx + (1 - sx) * e;
        const isy = sy + (1 - sy) * e;
        focusRing.style.transform = 'translate(' + (toX + ix).toFixed(2) + 'px,' + (toY + iy).toFixed(2) + 'px) scale(' + isx.toFixed(4) + ',' + isy.toFixed(4) + ')';
      }, () => {
        lastRingRect = { x: toX, y: toY, w: toW, h: toH };
      });
    }

    const focusHandlers = order.map((el) => () => glideRingTo(el));
    order.forEach((el, i) => el.addEventListener('focus', focusHandlers[i]));

    function openFrom() {
      if (open) return;
      open = true;
      lastRingRect = null;
      focusRing.style.opacity = '0';
      lightbox.style.visibility = 'visible';
      lightbox.setAttribute('aria-hidden', 'false');
      backdrop.style.visibility = 'visible';
      animate(220, (e) => { backdrop.style.opacity = (e * 0.78).toFixed(3); }, () => {
        closeBtn.focus({ preventScroll: true });
      });
    }

    function closeLightbox() {
      if (!open) return;
      animate(200, (e) => { backdrop.style.opacity = (0.78 * (1 - e)).toFixed(3); }, () => {
        lightbox.style.visibility = 'hidden';
        lightbox.setAttribute('aria-hidden', 'true');
        backdrop.style.visibility = 'hidden';
        focusRing.style.opacity = '0';
        open = false;
        thumb.focus({ preventScroll: true });
      });
    }

    function human() {
      if (scene.classList.contains(styles['is-demo'])) {
        scene.classList.remove(styles['is-demo']);
        timers.forEach((id) => { window.clearTimeout(id); window.clearInterval(id); });
        timers = [];
      }
    }

    function onThumbClick() { human(); openFrom(); }
    function onCloseClick() { human(); closeLightbox(); }
    function onBackdropClick() { human(); closeLightbox(); }
    thumb.addEventListener('click', onThumbClick);
    closeBtn.addEventListener('click', onCloseClick);
    backdrop.addEventListener('click', onBackdropClick);

    // 진짜 포커스 트랩: 끝에서 Tab 하면 처음으로, 처음에서 Shift+Tab 하면 끝으로 감긴다
    function onLightboxKeydown(e: KeyboardEvent) {
      if (!open) return;
      if (e.key === 'Escape') { human(); closeLightbox(); return; }
      if (e.key !== 'Tab') return;
      const i = order.indexOf(document.activeElement as HTMLButtonElement);
      if (i === -1) return;
      if (e.shiftKey && i === 0) {
        e.preventDefault();
        human();
        order[order.length - 1].focus({ preventScroll: true });
      } else if (!e.shiftKey && i === order.length - 1) {
        e.preventDefault();
        human();
        order[0].focus({ preventScroll: true });
      }
    }
    lightbox.addEventListener('keydown', onLightboxKeydown);

    function cycle() {
      openFrom();
      let i = 0;
      function step() {
        if (i >= order.length) {
          // 끝에서 다시 처음으로 — 실제 트랩과 같은 감김을 시연
          order[0].focus({ preventScroll: true });
          timers.push(window.setTimeout(closeLightbox, STEP_HOLD_MS));
          return;
        }
        order[i].focus({ preventScroll: true });
        i += 1;
        timers.push(window.setTimeout(step, STEP_HOLD_MS));
      }
      timers.push(window.setTimeout(step, 260));
    }

    if (!reduce) {
      cycle();
      timers.push(window.setInterval(() => {
        if (scene.classList.contains(styles['is-demo'])) cycle();
      }, LOOP_MS));
    }

    return () => {
      timers.forEach((id) => { window.clearTimeout(id); window.clearInterval(id); });
      order.forEach((el, i) => el.removeEventListener('focus', focusHandlers[i]));
      thumb.removeEventListener('click', onThumbClick);
      closeBtn.removeEventListener('click', onCloseClick);
      backdrop.removeEventListener('click', onBackdropClick);
      lightbox.removeEventListener('keydown', onLightboxKeydown);
    };
  }, []);

  return (
    <div className={`${styles.scene} ${styles['is-demo']}`} ref={sceneRef}>
      <ul className={styles.grid}>
        <li><button className={styles.thumb} type="button" aria-haspopup="dialog"><span className={styles.thumbImg} /></button></li>
      </ul>
      <div className={styles.backdrop} />
      <div className={styles.lightbox} role="dialog" aria-modal="true" aria-hidden="true" aria-label="키보드로만 움직이는 라이트박스">
        <span className={styles.fullImg} />
        <div className={styles.toolbar}>
          <button className={styles.prevBtn + ' ' + styles.ctrlBtn} type="button">이전</button>
          <button className={styles.infoBtn + ' ' + styles.ctrlBtn} type="button">정보</button>
          <button className={`${styles.nextBtn} ${styles.ctrlBtn} ${styles['ctrlBtn--primary']}`} type="button">다음</button>
        </div>
        <button className={styles.closeBtn} type="button">닫기</button>
        <span className={styles.focusRing} aria-hidden="true" />
      </div>
    </div>
  );
}