08실패하고 감쇠하며 다시 시도하는 버튼

<main class="stage">
<div class="rt is-demo" id="rtRoot">
  <div class="rt__wrap" id="rtBar" role="progressbar" aria-labelledby="rtLabel" aria-valuemin="0" aria-valuemax="100" aria-valuenow="0" aria-valuetext="0%">
    <svg class="rt__svg" viewBox="0 0 232 96" aria-hidden="true">
      <rect class="rt__ring" id="rtRing" x="3" y="3" width="226" height="90" rx="16" pathLength="100"/>
    </svg>
    <button class="rt__btn" id="rtBtn" type="button">
      <svg class="rt__icon" viewBox="0 0 24 24" aria-hidden="true"><path id="rtGlyph" d="M12 4v11M6.5 10.5 12 16l5.5-5.5"/></svg>
      <span id="rtLabel">내려받기</span>
    </button>
  </div>
  <p class="rt__meta"><span class="rt__tag">X</span> <b id="rtX">0.0</b> <span class="rt__tag">P</span> <b id="rtP">0</b></p>
  <p class="rt__sr" id="rtStatus" role="status"></p>
</div>
</main>

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

// 핵심: 흔들림 진폭은 지수 감쇠 함수로, 링 되감기는 보간 곡선으로 JS 가 계산한다. 실패색(--e)은 글자와 아이콘으로도 구분된다.

$rt-face: $subject-lilac;
$rt-fail: $error-soft;

@include stage($stage-ink);

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

.rt__wrap {
  --e: 0;
  position: relative;
  width: 232px;
  max-width: 100%;
  aspect-ratio: 232 / 96;
}
.rt__svg {
  position: absolute;
  inset: 0;
  width: 100%;
  height: 100%;
}
.rt__ring {
  fill: none;
  stroke: color-mix(in srgb, #{$subject-mint}, #{$tick-down} calc(var(--e) * 100%));
  stroke-width: 5;
  stroke-dasharray: 100 100;
  stroke-dashoffset: 100;
  stroke-linecap: round;
}

.rt__btn {
  position: absolute;
  left: 7%;
  right: 7%;
  top: 21%;
  bottom: 21%;
  box-sizing: border-box;
  display: flex;
  align-items: center;
  justify-content: center;
  gap: $sp-3;
  border: 0;
  border-radius: $r-control;
  background: color-mix(in srgb, #{$rt-face}, #{$rt-fail} calc(var(--e) * 100%));
  color: $subject-ink;
  font-family: inherit;
  font-size: 16px;
  font-weight: 700;
  line-height: 24px;
  cursor: pointer;
}
.rt__btn:focus-visible { outline: 3px solid $stage-paper; outline-offset: 4px; }
.rt__icon {
  width: 24px;
  height: 24px;
  fill: none;
  stroke: currentColor;
  stroke-width: 2.5;
  stroke-linecap: round;
  stroke-linejoin: round;
}

.rt__meta {
  margin: 0;
  display: flex;
  align-items: baseline;
  gap: $sp-2;
  font-size: 12px;
  line-height: 16px;
  color: $stage-paper;
}
.rt__tag { font-weight: 700; letter-spacing: .08em; }
.rt__meta b { min-width: 4ch; text-align: right; font-variant-numeric: tabular-nums; }

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

@media (prefers-reduced-motion: reduce) {
  .rt__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: #17141a;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  padding: clamp(8px, 4vw, 24px);
}

.rt {
  position: relative;
  width: min(100%, 280px);
  display: grid;
  gap: 12px;
  justify-items: center;
}

.rt__wrap {
  --e: 0;
  position: relative;
  width: 232px;
  max-width: 100%;
  aspect-ratio: 232/96;
}

.rt__svg {
  position: absolute;
  inset: 0;
  width: 100%;
  height: 100%;
}

.rt__ring {
  fill: none;
  stroke: color-mix(in srgb, #4cd4a6, #ff7a5e calc(var(--e) * 100%));
  stroke-width: 5;
  stroke-dasharray: 100 100;
  stroke-dashoffset: 100;
  stroke-linecap: round;
}

.rt__btn {
  position: absolute;
  left: 7%;
  right: 7%;
  top: 21%;
  bottom: 21%;
  box-sizing: border-box;
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 12px;
  border: 0;
  border-radius: 12px;
  background: color-mix(in srgb, #b9a0ff, #ffe0d8 calc(var(--e) * 100%));
  color: #17141a;
  font-family: inherit;
  font-size: 16px;
  font-weight: 700;
  line-height: 24px;
  cursor: pointer;
}

.rt__btn:focus-visible {
  outline: 3px solid #ffffff;
  outline-offset: 4px;
}

.rt__icon {
  width: 24px;
  height: 24px;
  fill: none;
  stroke: currentColor;
  stroke-width: 2.5;
  stroke-linecap: round;
  stroke-linejoin: round;
}

.rt__meta {
  margin: 0;
  display: flex;
  align-items: baseline;
  gap: 8px;
  font-size: 12px;
  line-height: 16px;
  color: #ffffff;
}

.rt__tag {
  font-weight: 700;
  letter-spacing: 0.08em;
}

.rt__meta b {
  min-width: 4ch;
  text-align: right;
  font-variant-numeric: tabular-nums;
}

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

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

(function () {
  // 기법: 실패 순간부터 흔들림 x = SHAKE_AMP x e^(-SHAKE_DECAY x t) x sin(2 pi f t) 로 진폭이 지수로 줄고,
  // 링은 실패한 길이에서 처음으로 REWIND_MS 동안 되감긴다. 두 번째 시도는 끝까지 간다.
  var SHAKE_AMP = 14;
  var SHAKE_DECAY = 5;
  var REWIND_MS = 500;
  var SHAKE_HZ = 4.5;
  var FAIL_AT = 0.62;
  var RUN_MS = 700;
  var REWIND_DELAY = 150;
  var START_MS = 200;
  var CYCLE_MS = 2000;

  var root = document.getElementById('rtRoot');
  var bar = document.getElementById('rtBar');
  var btn = document.getElementById('rtBtn');
  var ring = document.getElementById('rtRing');
  var labelEl = document.getElementById('rtLabel');
  var glyph = document.getElementById('rtGlyph');
  var xEl = document.getElementById('rtX');
  var pEl = document.getElementById('rtP');
  var statusEl = document.getElementById('rtStatus');
  var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;

  var ARROW = 'M12 4v11M6.5 10.5 12 16l5.5-5.5';
  var BANG = 'M12 5v9M12 19v.5';
  var clock = 0;
  var runStart = null;
  var outcome = 'fail';
  var attempts = 0;
  var settled = null;
  var lastNote = '';
  var t0 = null;

  function clamp(v, lo, hi) { return Math.max(lo, Math.min(hi, v)); }
  function stopDemo() { root.classList.remove('is-demo'); }
  function outQuad(t) { return 1 - (1 - t) * (1 - t); }
  function inOut(t) { return t < 0.5 ? 2 * t * t : 1 - Math.pow(-2 * t + 2, 2) / 2; }
  function busy(now) { return runStart !== null && now - runStart < RUN_MS + REWIND_DELAY + REWIND_MS; }

  function frame(now) {
    var s;
    var res = outcome;
    if (root.classList.contains('is-demo')) {
      s = now < START_MS ? null : START_MS + Math.floor((now - START_MS) / CYCLE_MS) * CYCLE_MS;
      res = 'fail';
    } else {
      s = runStart;
    }
    if (settled) return settled;
    if (s === null) return { p: 0, x: 0, e: 0, label: '내려받기', glyph: ARROW, note: '' };
    var t = now - s;
    if (t < RUN_MS) {
      var u = outQuad(t / RUN_MS);
      return { p: res === 'fail' ? FAIL_AT * u : u, x: 0, e: 0, label: '받는 중', glyph: ARROW, note: '' };
    }
    if (res === 'ok') return { p: 1, x: 0, e: 0, label: '완료', glyph: ARROW, note: '받기 완료' };
    var tau = (t - RUN_MS) / 1000;
    var rw = clamp((t - RUN_MS - REWIND_DELAY) / REWIND_MS, 0, 1);
    return {
      p: FAIL_AT * (1 - inOut(rw)),
      x: SHAKE_AMP * Math.exp(-SHAKE_DECAY * tau) * Math.sin(2 * Math.PI * SHAKE_HZ * tau),
      e: 1,
      label: rw >= 1 ? '다시 시도' : '실패',
      glyph: BANG,
      note: '받기가 끊겼어요'
    };
  }

  function paint(f) {
    var pct = Math.round(f.p * 100);
    ring.style.strokeDashoffset = String((100 - f.p * 100).toFixed(2));
    ring.style.opacity = f.p < 0.004 ? '0' : '1';
    bar.style.setProperty('--e', String(f.e));
    bar.style.transform = 'translateX(' + f.x.toFixed(2) + 'px)';
    labelEl.textContent = f.label;
    glyph.setAttribute('d', f.glyph);
    xEl.textContent = f.x.toFixed(1);
    pEl.textContent = String(pct);
    bar.setAttribute('aria-valuenow', String(pct));
    bar.setAttribute('aria-valuetext', pct + '%');
    if (f.note !== lastNote) { lastNote = f.note; statusEl.textContent = f.note; }
  }

  btn.addEventListener('click', function () {
    stopDemo();
    if (busy(clock)) return;
    outcome = attempts % 2 === 0 ? 'fail' : 'ok';
    attempts += 1;
    if (reduce) {
      settled = outcome === 'ok'
        ? { p: 1, x: 0, e: 0, label: '완료', glyph: ARROW, note: '받기 완료' }
        : { p: 0, x: 0, e: 1, label: '다시 시도', glyph: BANG, note: '받기가 끊겼어요' };
      paint(settled);
      settled = null;
      runStart = null;
      return;
    }
    runStart = clock;
  });

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

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

// RetryDecayButton — vanilla 판(08-dlbtn-error-retry-decay) 의 React 포트.
// 실패 순간부터 흔들림 진폭이 지수로 줄고, 링은 실패한 길이에서 처음으로 REWIND_MS 동안 되감긴다. 두 번째 시도는 끝까지 간다.
import { useEffect, useRef } from "react";
import styles from "./RetryDecayButton.module.scss";

const SHAKE_AMP = 14;
const SHAKE_DECAY = 5;
const REWIND_MS = 500;
const SHAKE_HZ = 4.5;
const FAIL_AT = 0.62;
const RUN_MS = 700;
const REWIND_DELAY = 150;
const START_MS = 200;
const CYCLE_MS = 2000;
const ARROW = "M12 4v11M6.5 10.5 12 16l5.5-5.5";
const BANG = "M12 5v9M12 19v.5";

type Frame = { p: number; x: number; e: number; label: string; glyph: string; note: string };
type Outcome = "fail" | "ok";

function clamp(v: number, lo: number, hi: number): number {
  return Math.max(lo, Math.min(hi, v));
}
function outQuad(t: number): number {
  return 1 - (1 - t) * (1 - t);
}
function inOut(t: number): number {
  return t < 0.5 ? 2 * t * t : 1 - Math.pow(-2 * t + 2, 2) / 2;
}

export default function RetryDecayButton() {
  const rootRef = useRef<HTMLDivElement | null>(null);
  const barRef = useRef<HTMLDivElement | null>(null);
  const btnRef = useRef<HTMLButtonElement | null>(null);
  const ringRef = useRef<SVGRectElement | null>(null);
  const labelRef = useRef<HTMLSpanElement | null>(null);
  const glyphRef = useRef<SVGPathElement | null>(null);
  const xRef = useRef<HTMLElement | null>(null);
  const pRef = useRef<HTMLElement | null>(null);
  const statusRef = useRef<HTMLParagraphElement | null>(null);

  useEffect(() => {
    const bar = barRef.current;
    const btn = btnRef.current;
    const ring = ringRef.current;
    const labelEl = labelRef.current;
    const glyph = glyphRef.current;
    const xEl = xRef.current;
    const pEl = pRef.current;
    const statusEl = statusRef.current;
    if (!bar || !btn || !ring || !labelEl || !glyph || !xEl || !pEl || !statusEl) return;
    const reduce = window.matchMedia("(prefers-reduced-motion: reduce)").matches;
    let demo = !reduce;
    let clock = 0;
    let runStart: number | null = null;
    let outcome: Outcome = "fail";
    let attempts = 0;
    let lastNote = "";
    let t0: number | null = null;
    let raf = 0;

    const busy = (now: number): boolean =>
      runStart !== null && now - runStart < RUN_MS + REWIND_DELAY + REWIND_MS;

    const frame = (now: number): Frame => {
      let s: number | null;
      let res: Outcome = outcome;
      if (demo) {
        s = now < START_MS ? null : START_MS + Math.floor((now - START_MS) / CYCLE_MS) * CYCLE_MS;
        res = "fail";
      } else {
        s = runStart;
      }
      if (s === null) return { p: 0, x: 0, e: 0, label: "내려받기", glyph: ARROW, note: "" };
      const t = now - s;
      if (t < RUN_MS) {
        const u = outQuad(t / RUN_MS);
        return { p: res === "fail" ? FAIL_AT * u : u, x: 0, e: 0, label: "받는 중", glyph: ARROW, note: "" };
      }
      if (res === "ok") return { p: 1, x: 0, e: 0, label: "완료", glyph: ARROW, note: "받기 완료" };
      const tau = (t - RUN_MS) / 1000;
      const rw = clamp((t - RUN_MS - REWIND_DELAY) / REWIND_MS, 0, 1);
      return {
        p: FAIL_AT * (1 - inOut(rw)),
        x: SHAKE_AMP * Math.exp(-SHAKE_DECAY * tau) * Math.sin(2 * Math.PI * SHAKE_HZ * tau),
        e: 1,
        label: rw >= 1 ? "다시 시도" : "실패",
        glyph: BANG,
        note: "받기가 끊겼어요"
      };
    };
    const paint = (f: Frame): void => {
      const pct = Math.round(f.p * 100);
      ring.style.strokeDashoffset = (100 - f.p * 100).toFixed(2);
      ring.style.opacity = f.p < 0.004 ? "0" : "1";
      bar.style.setProperty("--e", String(f.e));
      bar.style.transform = `translateX(${f.x.toFixed(2)}px)`;
      labelEl.textContent = f.label;
      glyph.setAttribute("d", f.glyph);
      xEl.textContent = f.x.toFixed(1);
      pEl.textContent = String(pct);
      bar.setAttribute("aria-valuenow", String(pct));
      bar.setAttribute("aria-valuetext", pct + "%");
      if (f.note !== lastNote) { lastNote = f.note; statusEl.textContent = f.note; }
    };
    const onClick = (): void => {
      demo = false;
      if (busy(clock)) return;
      outcome = attempts % 2 === 0 ? "fail" : "ok";
      attempts += 1;
      if (reduce) {
        paint(outcome === "ok"
          ? { p: 1, x: 0, e: 0, label: "완료", glyph: ARROW, note: "받기 완료" }
          : { p: 0, x: 0, e: 1, label: "다시 시도", glyph: BANG, note: "받기가 끊겼어요" });
        runStart = null;
        return;
      }
      runStart = clock;
    };
    btn.addEventListener("click", onClick);

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

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

  return (
    <main className={styles.stage}>
      <div className={styles.rt} ref={rootRef}>
        <div className={styles.rt__wrap} ref={barRef} role="progressbar" aria-labelledby="rtLabel" aria-valuemin={0} aria-valuemax={100} aria-valuenow={0} aria-valuetext="0%">
          <svg className={styles.rt__svg} viewBox="0 0 232 96" aria-hidden="true">
            <rect className={styles.rt__ring} ref={ringRef} x="3" y="3" width="226" height="90" rx="16" pathLength="100" />
          </svg>
          <button className={styles.rt__btn} type="button" ref={btnRef}>
            <svg className={styles.rt__icon} viewBox="0 0 24 24" aria-hidden="true"><path d={ARROW} ref={glyphRef} /></svg>
            <span id="rtLabel" ref={labelRef}>내려받기</span>
          </button>
        </div>
        <p className={styles.rt__meta}>
          <span className={styles.rt__tag}>X</span> <b ref={xRef}>0.0</b> <span className={styles.rt__tag}>P</span> <b ref={pRef}>0</b>
        </p>
        <p className={styles.rt__sr} role="status" ref={statusRef} />
      </div>
    </main>
  );
}