06ETA Recalculated From Remaining Size and Speed

<main class="stage">
<div class="etaCard is-demo" id="etaCard">
  <div class="track" id="track" role="progressbar" aria-label="Downloaded" aria-valuemin="0" aria-valuemax="100" aria-valuenow="0">
    <div class="fill" id="fill"></div>
  </div>
  <p class="eta" id="eta" aria-live="polite">Calculating</p>
  <p class="detail" id="detail">0.0MB / 48.0MB · 0.0MB/s</p>
  <button class="pauseBtn" id="pauseBtn" type="button" aria-pressed="false">Pause</button>
</div>
</main>

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

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

// 계산 겹: index.html 의 instSpeed() 가 합성파로 순간 속도를 만들고, tick() 이
// "남은 용량 ÷ 그 순간 속도" 를 매 틱 다시 나눠 ETA 문구를 새로 계산한다 — 저장된 카운트다운이 아니다.
@include stage($stage-paper);

.etaCard {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: $sp-2;
  width: 240px;
}

.track {
  position: relative;
  width: 100%;
  height: 10px;
  border-radius: $r-pill;
  background: rgba($subject-ink, .1);
  overflow: hidden;
}

.fill {
  --fill-pct: 0%;
  position: absolute;
  inset: 0;
  width: var(--fill-pct);
  border-radius: $r-pill;
  background: $color;
  transition: width $duration $easing;
}

.eta {
  margin: 0;
  font-size: 14px;
  font-weight: 700;
  color: $subject-ink;
}

.detail {
  margin: 0;
  font-size: 11px;
  color: rgba($subject-ink, .6);
}

.pauseBtn {
  appearance: none;
  border: none;
  margin-top: $sp-1;
  border-radius: $r-pill;
  padding: $sp-1 $sp-3;
  font-size: 11px;
  font-weight: 600;
  color: $subject-cream;
  background: $subject-ink;
  cursor: pointer;

  &:focus-visible { outline: 2px solid $subject-blue-deep; outline-offset: 2px; }
  &[aria-pressed="true"] { background: $subject-orange-deep; }
}

@media (max-width: 340px) {
  .etaCard { width: 190px; }
  .eta { font-size: 12px; }
  .detail, .pauseBtn { font-size: 10px; }
}

// reduce: 실사용 경로 적용 — 채움 막대 너비 전환만 끈다. ETA 문구는 값이 곧 정보라 계속 갱신돼야 한다
@media (prefers-reduced-motion: reduce) {
  .fill { transition: none; }
}

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

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

.etaCard {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 8px;
  width: 240px;
}

.track {
  position: relative;
  width: 100%;
  height: 10px;
  border-radius: 999px;
  background: rgba(23, 20, 26, 0.1);
  overflow: hidden;
}

.fill {
  --fill-pct: 0%;
  position: absolute;
  inset: 0;
  width: var(--fill-pct);
  border-radius: 999px;
  background: #4cd4a6;
  transition: width 300ms ease-out;
}

.eta {
  margin: 0;
  font-size: 14px;
  font-weight: 700;
  color: #17141a;
}

.detail {
  margin: 0;
  font-size: 11px;
  color: rgba(23, 20, 26, 0.6);
}

.pauseBtn {
  appearance: none;
  border: none;
  margin-top: 4px;
  border-radius: 999px;
  padding: 4px 12px;
  font-size: 11px;
  font-weight: 600;
  color: #fff7e6;
  background: #17141a;
  cursor: pointer;
}
.pauseBtn:focus-visible {
  outline: 2px solid #0a4fe8;
  outline-offset: 2px;
}
.pauseBtn[aria-pressed=true] {
  background: #c93000;
}

@media (max-width: 340px) {
  .etaCard {
    width: 190px;
  }
  .eta {
    font-size: 12px;
  }
  .detail, .pauseBtn {
    font-size: 10px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .fill {
    transition: none;
  }
}

(function () {
  var TOTAL_MB = 48;
  var LOOP_MS = 7000; // 이 시간 안에 전체를 받는 기준 사이클
  var TICK_MS = 120;
  var BASE_SPEED_MBPS = TOTAL_MB / (LOOP_MS / 1000);
  var SPEED_VARIANCE = 0.55; // 속도 흔들림 비율

  var etaCard = document.getElementById('etaCard');
  var track = document.getElementById('track');
  var fill = document.getElementById('fill');
  var etaEl = document.getElementById('eta');
  var detail = document.getElementById('detail');
  var pauseBtn = document.getElementById('pauseBtn');
  var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;

  var loadedMb = 0;
  var lastMs = 0;
  var paused = false;

  // 결정론적 합성파로 순간 전송 속도를 흉내낸다 — 매 틱 다른 속도라 ETA 가 매번 다시 계산된다
  function instSpeed(ms) {
    var w = 1 + SPEED_VARIANCE * Math.sin(ms / 480) + 0.2 * Math.sin(ms / 133);
    return Math.max(0.15, BASE_SPEED_MBPS * w);
  }

  function paint(speed) {
    var pct = Math.min(100, (loadedMb / TOTAL_MB) * 100);
    fill.style.setProperty('--fill-pct', pct.toFixed(1) + '%');
    track.setAttribute('aria-valuenow', String(Math.round(pct)));
    detail.textContent = loadedMb.toFixed(1) + 'MB / ' + TOTAL_MB.toFixed(1) + 'MB · ' + speed.toFixed(1) + 'MB/s';
    if (paused) {
      etaEl.textContent = 'Paused';
    } else if (loadedMb >= TOTAL_MB) {
      etaEl.textContent = 'Download complete';
    } else {
      // 남은 용량 ÷ 지금 속도 = 예상 시간 — 저장해 둔 카운트다운이 아니라 매 틱 새로 나눈 값
      var remaining = TOTAL_MB - loadedMb;
      var etaSec = remaining / speed;
      etaEl.textContent = 'About ' + Math.ceil(etaSec) + 'sec left';
    }
  }

  function tick(nowMs) {
    var dtMs = lastMs === 0 ? 0 : nowMs - lastMs;
    lastMs = nowMs;
    var speed = instSpeed(nowMs);
    if (!paused && loadedMb < TOTAL_MB) {
      loadedMb = Math.min(TOTAL_MB, loadedMb + speed * (dtMs / 1000));
    }
    if (loadedMb >= TOTAL_MB && !paused) {
      loadedMb = 0; // 데모 루프 — 완료 뒤 처음부터 다시
    }
    paint(speed);
  }

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

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

  pauseBtn.addEventListener('click', function () {
    human();
    paused = !paused;
    pauseBtn.setAttribute('aria-pressed', paused ? 'true' : 'false');
    pauseBtn.textContent = paused ? 'Resume download' : 'Pause';
    paint(instSpeed(performance.now() - start));
    if (!timer) {
      lastMs = performance.now() - start;
      timer = window.setInterval(loop, TICK_MS);
    }
  });

  if (!reduce) {
    start = performance.now();
    tick(0);
    timer = window.setInterval(loop, TICK_MS);
  } else {
    // reduce: 실사용 경로 적용 — 채움 막대 전환만 멈추고 남은 시간 문구는 한 값으로 고정해 보여준다
    loadedMb = TOTAL_MB * 0.4;
    paint(BASE_SPEED_MBPS);
  }
})();

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

const TOTAL_MB = 48;
const LOOP_MS = 7000; // 이 시간 안에 전체를 받는 기준 사이클
const TICK_MS = 120;
const BASE_SPEED_MBPS = TOTAL_MB / (LOOP_MS / 1000);
const SPEED_VARIANCE = 0.55; // 속도 흔들림 비율

// 결정론적 합성파로 순간 전송 속도를 흉내낸다 — 매 틱 다른 속도라 ETA 가 매번 다시 계산된다
function instSpeed(ms: number) {
  const w = 1 + SPEED_VARIANCE * Math.sin(ms / 480) + 0.2 * Math.sin(ms / 133);
  return Math.max(0.15, BASE_SPEED_MBPS * w);
}

export default function BufferingCountdownEta() {
  const cardRef = useRef<HTMLDivElement>(null);
  const trackRef = useRef<HTMLDivElement>(null);
  const fillRef = useRef<HTMLDivElement>(null);
  const etaRef = useRef<HTMLParagraphElement>(null);
  const detailRef = useRef<HTMLParagraphElement>(null);
  const pauseBtnRef = useRef<HTMLButtonElement>(null);

  useEffect(() => {
    const card = cardRef.current;
    const track = trackRef.current;
    const fill = fillRef.current;
    const etaEl = etaRef.current;
    const detail = detailRef.current;
    const pauseBtn = pauseBtnRef.current;
    if (!card || !track || !fill || !etaEl || !detail || !pauseBtn) return undefined;
    const reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;

    let loadedMb = 0;
    let lastMs = 0;
    let paused = false;

    function paint(speed: number) {
      if (!fill || !track || !detail || !etaEl) return;
      const pct = Math.min(100, (loadedMb / TOTAL_MB) * 100);
      fill.style.setProperty('--fill-pct', pct.toFixed(1) + '%');
      track.setAttribute('aria-valuenow', String(Math.round(pct)));
      detail.textContent = loadedMb.toFixed(1) + 'MB / ' + TOTAL_MB.toFixed(1) + 'MB · ' + speed.toFixed(1) + 'MB/s';
      if (paused) {
        etaEl.textContent = '일시정지됨';
      } else if (loadedMb >= TOTAL_MB) {
        etaEl.textContent = '받기 완료';
      } else {
        // 남은 용량 ÷ 지금 속도 = 예상 시간 — 저장해 둔 카운트다운이 아니라 매 틱 새로 나눈 값
        const remaining = TOTAL_MB - loadedMb;
        const etaSec = remaining / speed;
        etaEl.textContent = '약 ' + Math.ceil(etaSec) + '초 남음';
      }
    }

    function tick(nowMs: number) {
      const dtMs = lastMs === 0 ? 0 : nowMs - lastMs;
      lastMs = nowMs;
      const speed = instSpeed(nowMs);
      if (!paused && loadedMb < TOTAL_MB) {
        loadedMb = Math.min(TOTAL_MB, loadedMb + speed * (dtMs / 1000));
      }
      if (loadedMb >= TOTAL_MB && !paused) {
        loadedMb = 0; // 데모 루프 — 완료 뒤 처음부터 다시
      }
      paint(speed);
    }

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

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

    function onPause() {
      human();
      if (!pauseBtn) return;
      paused = !paused;
      pauseBtn.setAttribute('aria-pressed', paused ? 'true' : 'false');
      pauseBtn.textContent = paused ? '이어받기' : '일시정지';
      paint(instSpeed(performance.now() - start));
      if (!timer) {
        lastMs = performance.now() - start;
        timer = window.setInterval(loop, TICK_MS);
      }
    }
    pauseBtn.addEventListener('click', onPause);

    if (!reduce) {
      start = performance.now();
      tick(0);
      timer = window.setInterval(loop, TICK_MS);
    } else {
      // reduce: 실사용 경로 적용 — 채움 막대 전환만 멈추고 남은 시간 문구는 한 값으로 고정해 보여준다
      loadedMb = TOTAL_MB * 0.4;
      paint(BASE_SPEED_MBPS);
    }

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

  return (
    <div className={`${styles.etaCard} ${styles['is-demo']}`} ref={cardRef}>
      <div
        className={styles.track}
        ref={trackRef}
        role="progressbar"
        aria-label="받은 용량"
        aria-valuemin={0}
        aria-valuemax={100}
        aria-valuenow={0}
      >
        <div className={styles.fill} ref={fillRef} />
      </div>
      <p className={styles.eta} ref={etaRef} aria-live="polite">계산 중</p>
      <p className={styles.detail} ref={detailRef}>0.0MB / 48.0MB · 0.0MB/s</p>
      <button className={styles.pauseBtn} ref={pauseBtnRef} type="button" aria-pressed="false">일시정지</button>
    </div>
  );
}