01Buffering Overlay on a Frozen Frame

<main class="stage">
<div class="player is-demo" id="player">
  <div class="frame" id="frame" aria-hidden="true">
    <span class="frameDot"></span>
    <span class="frameDot"></span>
    <span class="frameDot"></span>
  </div>
  <div class="overlay" id="overlay">
    <span class="ring" id="ring"></span>
  </div>
  <button class="toggleBtn" id="toggleBtn" type="button" aria-pressed="false">Try stalling buffering now</button>
  <p class="status" id="status" aria-live="polite">Buffering</p>
</div>
</main>

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

// 변수 3개
$duration: $dur-loop;
$easing: linear;
$color: $subject-blue-light;

// 계산 겹: index.html 의 tick() 이 정지 경과 시간(phase)으로 스피너 회전 속도(--spin-duration)와
// 오버레이 흐림량(--blur)·불투명도를 매 틱 산술로 갱신한다 — 고정 트윈이 아니다.
@include stage($stage-ink);

.player {
  position: relative;
  width: 300px;
  height: 168px;
  border-radius: $r-card;
  overflow: hidden;
  box-shadow: $shadow-raised;
}

.frame {
  position: absolute;
  inset: 0;
  background: linear-gradient(135deg, #2a2740, $stage-ink 70%);
  display: flex;
  align-items: center;
  justify-content: center;
  gap: $sp-2;
}

.frameDot {
  width: 10px;
  height: 10px;
  border-radius: 50%;
  background: rgba($subject-cream, .25);
}

.overlay {
  position: absolute;
  inset: 0;
  display: grid;
  place-items: center;
  background: rgba(#0a0812, .55);
  backdrop-filter: blur(var(--blur, 6px));
  -webkit-backdrop-filter: blur(var(--blur, 6px));
  opacity: 0;
  transition: opacity $dur-quick $ease-out;
}

.ring {
  --spin-duration: 900ms;
  width: 44px;
  height: 44px;
  border-radius: 50%;
  border: 4px solid rgba($subject-cream, .22);
  border-top-color: $color;
  transform-origin: center;
  animation: spin var(--spin-duration) linear infinite;
}

@keyframes spin {
  from { transform: rotate(0deg); }
  to { transform: rotate(360deg); }
}

.toggleBtn {
  position: absolute;
  left: 50%;
  bottom: $sp-3;
  transform: translateX(-50%);
  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, .9);
  cursor: pointer;

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

.status {
  position: absolute;
  top: $sp-2;
  left: $sp-2;
  margin: 0;
  padding: $sp-1 $sp-2;
  border-radius: $r-sm;
  font-size: 11px;
  font-weight: 600;
  color: $subject-cream;
  background: rgba(#000, .35);
}

@media (max-width: 340px) {
  .player { width: 220px; height: 140px; }
  .ring { width: 34px; height: 34px; border-width: 3px; }
  .toggleBtn { font-size: 10px; padding: $sp-1 $sp-2; bottom: $sp-2; }
  .status { font-size: 10px; }
}

// reduce: 실사용 경로 적용 — 스피너 회전(장식)만 멈춘다. 오버레이 존재·상태 문구(aria-live)는 그대로 갱신된다
@media (prefers-reduced-motion: reduce) {
  .ring { animation: none; }
  .overlay { 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);
}

.player {
  position: relative;
  width: 300px;
  height: 168px;
  border-radius: 16px;
  overflow: hidden;
  box-shadow: 0 14px 24px rgba(23, 20, 26, 0.32);
}

.frame {
  position: absolute;
  inset: 0;
  background: linear-gradient(135deg, #2a2740, #17141a 70%);
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 8px;
}

.frameDot {
  width: 10px;
  height: 10px;
  border-radius: 50%;
  background: rgba(255, 247, 230, 0.25);
}

.overlay {
  position: absolute;
  inset: 0;
  display: grid;
  place-items: center;
  background: rgba(10, 8, 18, 0.55);
  backdrop-filter: blur(var(--blur, 6px));
  -webkit-backdrop-filter: blur(var(--blur, 6px));
  opacity: 0;
  transition: opacity 220ms ease-out;
}

.ring {
  --spin-duration: 900ms;
  width: 44px;
  height: 44px;
  border-radius: 50%;
  border: 4px solid rgba(255, 247, 230, 0.22);
  border-top-color: #5b8cf8;
  transform-origin: center;
  animation: spin var(--spin-duration) linear infinite;
}

@keyframes spin {
  from {
    transform: rotate(0deg);
  }
  to {
    transform: rotate(360deg);
  }
}
.toggleBtn {
  position: absolute;
  left: 50%;
  bottom: 12px;
  transform: translateX(-50%);
  appearance: none;
  border: none;
  border-radius: 999px;
  padding: 4px 12px;
  font-size: 11px;
  font-weight: 600;
  color: #17141a;
  background: rgba(255, 247, 230, 0.9);
  cursor: pointer;
}
.toggleBtn:focus-visible {
  outline: 2px solid #5b8cf8;
  outline-offset: 2px;
}

.status {
  position: absolute;
  top: 8px;
  left: 8px;
  margin: 0;
  padding: 4px 8px;
  border-radius: 8px;
  font-size: 11px;
  font-weight: 600;
  color: #fff7e6;
  background: rgba(0, 0, 0, 0.35);
}

@media (max-width: 340px) {
  .player {
    width: 220px;
    height: 140px;
  }
  .ring {
    width: 34px;
    height: 34px;
    border-width: 3px;
  }
  .toggleBtn {
    font-size: 10px;
    padding: 4px 8px;
    bottom: 8px;
  }
  .status {
    font-size: 10px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .ring {
    animation: none;
  }
  .overlay {
    transition: none;
  }
}

(function () {
  var STALL_CYCLE_MS = 2000; // 정지→회복 한 사이클 — 캡처 창(2초)의 약수
  var STALL_PORTION = 0.72; // 한 사이클 중 정지 상태가 차지하는 비율
  var TICK_MS = 60; // 계산 갱신 간격
  var SPIN_MS_STALL_START = 1500; // 정지 시작 시 스피너 한 바퀴 시간(느림)
  var SPIN_MS_STALL_END = 550; // 정지가 길어질수록 빨라지는 하한

  var overlay = document.getElementById('overlay');
  var ring = document.getElementById('ring');
  var status = document.getElementById('status');
  var toggleBtn = document.getElementById('toggleBtn');
  var player = document.getElementById('player');
  var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;

  function clamp(v, lo, hi) { return Math.min(hi, Math.max(lo, v)); }

  // 정지 경과 시간과 사이클 위상만으로 스피너 속도·오버레이 흐림 정도를 계산한다 — 값 자체는 CSS 트윈이 아니라 산술이다
  function tick(elapsedMs) {
    var phase = elapsedMs % STALL_CYCLE_MS;
    var stallSpan = STALL_CYCLE_MS * STALL_PORTION;
    var stalling = phase < stallSpan;
    if (stalling) {
      var stallFrac = clamp(phase / stallSpan, 0, 1);
      var spinMs = SPIN_MS_STALL_START - (SPIN_MS_STALL_START - SPIN_MS_STALL_END) * stallFrac;
      // 합성파 두 개로 네트워크 흔들림을 흉내낸다 — Math.random 은 렌더마다 프레임이 달라져 측정을 어지럽힌다
      var jitter = 0.5 + 0.28 * Math.sin(elapsedMs / 190) + 0.14 * Math.sin(elapsedMs / 61);
      jitter = clamp(jitter, 0, 1);
      ring.style.setProperty('--spin-duration', spinMs.toFixed(0) + 'ms');
      overlay.style.setProperty('--blur', (4 + jitter * 7).toFixed(2) + 'px');
      overlay.style.opacity = (0.5 + jitter * 0.28).toFixed(2);
      if (status.textContent !== 'Buffering') status.textContent = 'Buffering';
    } else {
      overlay.style.opacity = '0';
      if (status.textContent !== 'Playback resumed') status.textContent = 'Playback resumed';
    }
  }

  var timer = null;
  var start = 0;
  function loop() {
    tick(performance.now() - start);
  }

  function human() {
    if (player.classList.contains('is-demo')) {
      player.classList.remove('is-demo');
      window.clearInterval(timer);
      timer = null;
    }
  }

  toggleBtn.addEventListener('click', function () {
    human();
    var manualStall = overlay.style.opacity !== '1';
    overlay.style.opacity = manualStall ? '1' : '0';
    overlay.style.setProperty('--blur', '8px');
    ring.style.setProperty('--spin-duration', '900ms');
    status.textContent = manualStall ? 'Buffering' : 'Playback resumed';
    toggleBtn.setAttribute('aria-pressed', manualStall ? 'true' : 'false');
    toggleBtn.textContent = manualStall ? 'Resume playback' : 'Try stalling buffering now';
  });

  if (!reduce) {
    start = performance.now();
    tick(0);
    timer = window.setInterval(loop, TICK_MS);
  } else {
    // reduce: 실사용 경로 — 회전·흐림 변화는 멈추고 정지된 오버레이 상태 하나만 고정으로 보여준다
    overlay.style.opacity = '0.6';
    overlay.style.setProperty('--blur', '6px');
    status.textContent = 'Buffering';
  }
})();

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

const STALL_CYCLE_MS = 2000;
const STALL_PORTION = 0.72;
const TICK_MS = 60;
const SPIN_MS_STALL_START = 1500;
const SPIN_MS_STALL_END = 550;

function clamp(v: number, lo: number, hi: number) {
  return Math.min(hi, Math.max(lo, v));
}

export default function BufferingSpinnerOverlay() {
  const playerRef = useRef<HTMLDivElement>(null);
  const overlayRef = useRef<HTMLDivElement>(null);
  const ringRef = useRef<HTMLSpanElement>(null);
  const statusRef = useRef<HTMLParagraphElement>(null);
  const toggleBtnRef = useRef<HTMLButtonElement>(null);

  useEffect(() => {
    const player = playerRef.current;
    const overlay = overlayRef.current;
    const ring = ringRef.current;
    const status = statusRef.current;
    const toggleBtn = toggleBtnRef.current;
    if (!player || !overlay || !ring || !status || !toggleBtn) return undefined;
    const reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;

    function tick(elapsedMs: number) {
      if (!overlay || !ring || !status) return;
      const phase = elapsedMs % STALL_CYCLE_MS;
      const stallSpan = STALL_CYCLE_MS * STALL_PORTION;
      const stalling = phase < stallSpan;
      if (stalling) {
        const stallFrac = clamp(phase / stallSpan, 0, 1);
        const spinMs = SPIN_MS_STALL_START - (SPIN_MS_STALL_START - SPIN_MS_STALL_END) * stallFrac;
        const jitter = clamp(0.5 + 0.28 * Math.sin(elapsedMs / 190) + 0.14 * Math.sin(elapsedMs / 61), 0, 1);
        ring.style.setProperty('--spin-duration', spinMs.toFixed(0) + 'ms');
        overlay.style.setProperty('--blur', (4 + jitter * 7).toFixed(2) + 'px');
        overlay.style.opacity = (0.5 + jitter * 0.28).toFixed(2);
        if (status.textContent !== '버퍼링 중') status.textContent = '버퍼링 중';
      } else {
        overlay.style.opacity = '0';
        if (status.textContent !== '재생 재개') status.textContent = '재생 재개';
      }
    }

    let timer: ReturnType<typeof window.setInterval> | null = null;
    let start = 0;
    function loop() {
      tick(performance.now() - start);
    }

    function human() {
      if (player && player.classList.contains(styles['is-demo'])) {
        player.classList.remove(styles['is-demo']);
        if (timer !== null) window.clearInterval(timer);
        timer = null;
      }
    }

    function onToggle() {
      human();
      if (!overlay || !ring || !status || !toggleBtn) return;
      const manualStall = overlay.style.opacity !== '1';
      overlay.style.opacity = manualStall ? '1' : '0';
      overlay.style.setProperty('--blur', '8px');
      ring.style.setProperty('--spin-duration', '900ms');
      status.textContent = manualStall ? '버퍼링 중' : '재생 재개';
      toggleBtn.setAttribute('aria-pressed', manualStall ? 'true' : 'false');
      toggleBtn.textContent = manualStall ? '재생 다시 잇기' : '지금 버퍼링 멈춰보기';
    }

    toggleBtn.addEventListener('click', onToggle);

    if (!reduce) {
      start = performance.now();
      tick(0);
      timer = window.setInterval(loop, TICK_MS);
    } else {
      // reduce: 실사용 경로 적용 — 회전·흐림 변화는 멈추고 정지된 오버레이 상태 하나만 고정으로 보여준다
      overlay.style.opacity = '0.6';
      overlay.style.setProperty('--blur', '6px');
      status.textContent = '버퍼링 중';
    }

    return () => {
      if (timer !== null) window.clearInterval(timer);
      toggleBtn.removeEventListener('click', onToggle);
    };
  }, []);

  return (
    <div className={`${styles.player} ${styles['is-demo']}`} ref={playerRef}>
      <div className={styles.frame} aria-hidden="true">
        <span className={styles.frameDot} />
        <span className={styles.frameDot} />
        <span className={styles.frameDot} />
      </div>
      <div className={styles.overlay} ref={overlayRef}>
        <span className={styles.ring} ref={ringRef} />
      </div>
      <button className={styles.toggleBtn} ref={toggleBtnRef} type="button" aria-pressed="false">지금 버퍼링 멈춰보기</button>
      <p className={styles.status} ref={statusRef} aria-live="polite">버퍼링 중</p>
    </div>
  );
}