04A Chip That Counts Up the Received Size

<main class="stage">
<div class="sz is-demo" id="szRoot">
  <button class="sz__btn" id="szBtn" type="button"><span id="szLabel">Download</span></button>
  <div class="sz__chips">
    <p class="sz__chip"><span class="sz__tag">MB</span> <b id="szGot">0.0</b><span class="sz__of">/ 48</span></p>
    <p class="sz__chip"><span class="sz__tag">ETA</span> <b id="szEta">--:--</b></p>
  </div>
  <p class="sz__sr" id="szStatus" role="status"></p>
</div>
</main>

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

// 핵심: 숫자 두 개(받은 크기 · 남은 시간)와 버튼 안 채움이 같은 계산값 하나에서 나온다.

$sz-face: $subject-lilac;
$sz-fill: $subject-mint;

@include stage($stage-orange);

.sz {
  --f: 0;
  width: min(100%, 280px);
  display: grid;
  gap: $sp-3;
  justify-items: center;
}

.sz__btn {
  box-sizing: border-box;
  width: 240px;
  max-width: 100%;
  height: 64px;
  border: 0;
  border-radius: $r-control;
  background: linear-gradient(90deg, #{$sz-fill} calc(var(--f) * 100%), #{$sz-face} calc(var(--f) * 100%));
  box-shadow: $shadow-press;
  color: $subject-ink;
  font-family: inherit;
  font-size: 20px;
  font-weight: 700;
  line-height: 24px;
  cursor: pointer;
}
.sz__btn:focus-visible { outline: 3px solid $subject-ink; outline-offset: 3px; }

.sz__chips {
  width: 100%;
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: $sp-2;
}
.sz__chip {
  margin: 0;
  box-sizing: border-box;
  display: flex;
  align-items: baseline;
  gap: $sp-1;
  padding: $sp-2;
  border-radius: $r-sm;
  background: color-mix(in srgb, #{$subject-cream}, #{$sz-fill} calc(var(--f) * 100%));
  color: $subject-ink;
  font-size: 14px;
  line-height: 24px;
}
.sz__tag { font-size: 12px; font-weight: 700; letter-spacing: .08em; }
.sz__chip b { min-width: 4ch; font-size: 20px; text-align: right; font-variant-numeric: tabular-nums; }
.sz__of { font-size: 12px; }

.sz__sr {
  position: absolute;
  width: 1px;
  height: 1px;
  margin: -1px;
  overflow: hidden;
  clip-path: inset(50%);
  white-space: nowrap;
}

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

.sz {
  --f: 0;
  width: min(100%, 280px);
  display: grid;
  gap: 12px;
  justify-items: center;
}

.sz__btn {
  box-sizing: border-box;
  width: 240px;
  max-width: 100%;
  height: 64px;
  border: 0;
  border-radius: 12px;
  background: linear-gradient(90deg, #4cd4a6 calc(var(--f) * 100%), #b9a0ff calc(var(--f) * 100%));
  box-shadow: 0 6px 12px rgba(23, 20, 26, 0.32);
  color: #17141a;
  font-family: inherit;
  font-size: 20px;
  font-weight: 700;
  line-height: 24px;
  cursor: pointer;
}

.sz__btn:focus-visible {
  outline: 3px solid #17141a;
  outline-offset: 3px;
}

.sz__chips {
  width: 100%;
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 8px;
}

.sz__chip {
  margin: 0;
  box-sizing: border-box;
  display: flex;
  align-items: baseline;
  gap: 4px;
  padding: 8px;
  border-radius: 8px;
  background: color-mix(in srgb, #fff7e6, #4cd4a6 calc(var(--f) * 100%));
  color: #17141a;
  font-size: 14px;
  line-height: 24px;
}

.sz__tag {
  font-size: 12px;
  font-weight: 700;
  letter-spacing: 0.08em;
}

.sz__chip b {
  min-width: 4ch;
  font-size: 20px;
  text-align: right;
  font-variant-numeric: tabular-nums;
}

.sz__of {
  font-size: 12px;
}

.sz__sr {
  position: absolute;
  width: 1px;
  height: 1px;
  margin: -1px;
  overflow: hidden;
  clip-path: inset(50%);
  white-space: nowrap;
}

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

(function () {
  // 기법: 받은 크기 = TARGET_MB x (1 - (1 - u)^COUNT_EASE) 로 감속하며 올라간다 (u 는 시간 비율).
  // 남은 시간 = 남은 양 / 지금까지의 평균 속도. 평균 속도가 시간에 따라 변하므로 ETA 는 시작 때 가장 크고 끝에서 0 이 된다.
  var TARGET_MB = 48;
  var ETA_MIN = 2;
  var COUNT_EASE = 3;
  var RUN_MS = 1500;
  var START_MS = 200;
  var CYCLE_MS = 2000;

  var root = document.getElementById('szRoot');
  var btn = document.getElementById('szBtn');
  var labelEl = document.getElementById('szLabel');
  var gotEl = document.getElementById('szGot');
  var etaEl = document.getElementById('szEta');
  var statusEl = document.getElementById('szStatus');
  var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;

  var clock = 0;
  var runStart = null;
  var finished = false;
  var announced = false;
  var t0 = null;

  function stopDemo() { root.classList.remove('is-demo'); }
  function two(n) { return n < 10 ? '0' + n : String(n); }

  function startOf(now) {
    if (root.classList.contains('is-demo')) {
      return now < START_MS ? null : START_MS + Math.floor((now - START_MS) / CYCLE_MS) * CYCLE_MS;
    }
    return runStart;
  }

  function render(now) {
    var s = startOf(now);
    var u = s === null ? 0 : Math.max(0, Math.min(1, (now - s) / RUN_MS));
    if (reduce && finished) u = 1;
    var got = TARGET_MB * (1 - Math.pow(1 - u, COUNT_EASE));
    var eta = '--:--';
    if (u > 0) {
      var elapsedSec = Math.max(u, 0.004) * ETA_MIN * 60;
      var avg = Math.max(got, 0.01) / elapsedSec;
      var left = Math.round((TARGET_MB - got) / avg);
      eta = Math.floor(left / 60) + ':' + two(left % 60);
    }
    root.style.setProperty('--f', (got / TARGET_MB).toFixed(3));
    gotEl.textContent = got.toFixed(1);
    etaEl.textContent = eta;
    labelEl.textContent = u >= 1 ? 'Done' : (u > 0 ? 'Receiving' : 'Download');
    if (u >= 1 && !announced) { announced = true; statusEl.textContent = 'Download complete'; }
    if (u < 1 && announced) { announced = false; statusEl.textContent = ''; }
  }

  function activate() {
    stopDemo();
    if (reduce) { finished = true; render(clock); return; }
    if (runStart !== null && clock - runStart < RUN_MS) return;
    runStart = clock;
  }
  btn.addEventListener('click', activate);

  function tick(ts) {
    if (t0 === null) t0 = ts;
    clock = ts - t0;
    render(clock);
    requestAnimationFrame(tick);
  }

  if (reduce) {
    stopDemo();
    render(0);
  } else {
    requestAnimationFrame(tick);
  }
})();

// SizeCountButton — vanilla 판(04-dlbtn-size-count-estimate) 의 React 포트.
// 받은 크기는 TARGET_MB x (1 - (1 - u)^COUNT_EASE) 로 감속하며 오르고, 남은 시간은 남은 양 / 평균 속도 로 계산한다.
import { useEffect, useRef } from "react";
import styles from "./SizeCountButton.module.scss";

const TARGET_MB = 48;
const ETA_MIN = 2;
const COUNT_EASE = 3;
const RUN_MS = 1500;
const START_MS = 200;
const CYCLE_MS = 2000;

function two(n: number): string {
  return n < 10 ? "0" + n : String(n);
}

export default function SizeCountButton() {
  const rootRef = useRef<HTMLDivElement | null>(null);
  const btnRef = useRef<HTMLButtonElement | null>(null);
  const labelRef = useRef<HTMLSpanElement | null>(null);
  const gotRef = useRef<HTMLElement | null>(null);
  const etaRef = useRef<HTMLElement | null>(null);
  const statusRef = useRef<HTMLParagraphElement | null>(null);

  useEffect(() => {
    const root = rootRef.current;
    const btn = btnRef.current;
    const labelEl = labelRef.current;
    const gotEl = gotRef.current;
    const etaEl = etaRef.current;
    const statusEl = statusRef.current;
    if (!root || !btn || !labelEl || !gotEl || !etaEl || !statusEl) return;
    const reduce = window.matchMedia("(prefers-reduced-motion: reduce)").matches;
    let demo = !reduce;
    let clock = 0;
    let runStart: number | null = null;
    let finished = false;
    let announced = false;
    let t0: number | null = null;
    let raf = 0;

    const startOf = (now: number): number | null => {
      if (demo) return now < START_MS ? null : START_MS + Math.floor((now - START_MS) / CYCLE_MS) * CYCLE_MS;
      return runStart;
    };
    const render = (now: number): void => {
      const s = startOf(now);
      let u = s === null ? 0 : Math.max(0, Math.min(1, (now - s) / RUN_MS));
      if (reduce && finished) u = 1;
      const got = TARGET_MB * (1 - Math.pow(1 - u, COUNT_EASE));
      let eta = "--:--";
      if (u > 0) {
        const elapsedSec = Math.max(u, 0.004) * ETA_MIN * 60;
        const avg = Math.max(got, 0.01) / elapsedSec;
        const left = Math.round((TARGET_MB - got) / avg);
        eta = Math.floor(left / 60) + ":" + two(left % 60);
      }
      root.style.setProperty("--f", (got / TARGET_MB).toFixed(3));
      gotEl.textContent = got.toFixed(1);
      etaEl.textContent = eta;
      labelEl.textContent = u >= 1 ? "완료" : u > 0 ? "받는 중" : "내려받기";
      if (u >= 1 && !announced) { announced = true; statusEl.textContent = "받기 완료"; }
      if (u < 1 && announced) { announced = false; statusEl.textContent = ""; }
    };
    const activate = (): void => {
      demo = false;
      if (reduce) { finished = true; render(clock); return; }
      if (runStart !== null && clock - runStart < RUN_MS) return;
      runStart = clock;
    };
    btn.addEventListener("click", activate);

    function tick(ts: number): void {
      if (t0 === null) t0 = ts;
      clock = ts - t0;
      render(clock);
      raf = requestAnimationFrame(tick);
    }

    if (reduce) render(0);
    else raf = requestAnimationFrame(tick);
    return () => {
      cancelAnimationFrame(raf);
      btn.removeEventListener("click", activate);
    };
  }, []);

  return (
    <main className={styles.stage}>
      <div className={styles.sz} ref={rootRef}>
        <button className={styles.sz__btn} type="button" ref={btnRef}>
          <span ref={labelRef}>내려받기</span>
        </button>
        <div className={styles.sz__chips}>
          <p className={styles.sz__chip}>
            <span className={styles.sz__tag}>MB</span> <b ref={gotRef}>0.0</b>
            <span className={styles.sz__of}>/ {TARGET_MB}</span>
          </p>
          <p className={styles.sz__chip}>
            <span className={styles.sz__tag}>ETA</span> <b ref={etaRef}>--:--</b>
          </p>
        </div>
        <p className={styles.sz__sr} role="status" ref={statusRef} />
      </div>
    </main>
  );
}