02A Border Ring Filled by a Progress Curve

<main class="stage">
<div class="rg is-demo" id="rgRoot">
  <div class="rg__wrap" id="rgBar" role="progressbar" aria-labelledby="rgLabel" aria-valuemin="0" aria-valuemax="100" aria-valuenow="0" aria-valuetext="0%">
    <svg class="rg__svg" viewBox="0 0 232 96" aria-hidden="true">
      <rect class="rg__ghost" id="rgGhost" x="11" y="11" width="210" height="74" pathLength="100"/>
      <rect class="rg__ring" id="rgRing" x="3" y="3" width="226" height="90" pathLength="100"/>
    </svg>
    <button class="rg__btn" id="rgBtn" type="button"><span id="rgLabel">Download</span><b id="rgPct">0%</b></button>
  </div>
  <p class="rg__meta"><span class="rg__tag">POW</span> <b id="rgPow">2</b> <span class="rg__tag">LEAD</span> <b id="rgLead">0</b></p>
</div>
</main>

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

// 핵심: 링 길이는 SVG stroke-dashoffset, 값은 JS 가 곡선으로 계산한다. 버튼 안 채움도 같은 진행률(--f)을 쓴다.

$ring-face: $subject-sky;
$ring-fill: $subject-mint;

@include stage($stage-ink);

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

.rg__wrap {
  position: relative;
  width: 232px;
  max-width: 100%;
  aspect-ratio: 232 / 96;
}
.rg__svg {
  position: absolute;
  inset: 0;
  width: 100%;
  height: 100%;
}
.rg__ring, .rg__ghost {
  fill: none;
  stroke-dasharray: 100 100;
  stroke-dashoffset: 100;
  stroke-linecap: round;
}
.rg__ring { stroke: $subject-mint; stroke-width: 5; }
.rg__ghost { stroke: $stage-paper; stroke-width: 2; }

.rg__btn {
  --f: 0;
  position: absolute;
  left: 7%;
  right: 7%;
  top: 21%;
  bottom: 21%;
  box-sizing: border-box;
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 0 $sp-4;
  border: 0;
  border-radius: $r-control;
  background: linear-gradient(90deg, #{$ring-fill} calc(var(--f) * 100%), #{$ring-face} calc(var(--f) * 100%));
  color: $subject-ink;
  font-family: inherit;
  font-size: 16px;
  font-weight: 700;
  line-height: 24px;
  cursor: pointer;
}
.rg__btn:focus-visible { outline: 3px solid $stage-paper; outline-offset: 4px; }
.rg__btn b { font-variant-numeric: tabular-nums; }

.rg__meta {
  margin: 0;
  display: flex;
  align-items: baseline;
  gap: $sp-2;
  font-size: 12px;
  line-height: 16px;
  color: $stage-paper;
}
.rg__tag { font-weight: 700; letter-spacing: .08em; }
.rg__meta b { min-width: 3ch; text-align: right; font-variant-numeric: tabular-nums; }

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

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

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

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

.rg__ring, .rg__ghost {
  fill: none;
  stroke-dasharray: 100 100;
  stroke-dashoffset: 100;
  stroke-linecap: round;
}

.rg__ring {
  stroke: #4cd4a6;
  stroke-width: 5;
}

.rg__ghost {
  stroke: #ffffff;
  stroke-width: 2;
}

.rg__btn {
  --f: 0;
  position: absolute;
  left: 7%;
  right: 7%;
  top: 21%;
  bottom: 21%;
  box-sizing: border-box;
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 0 16px;
  border: 0;
  border-radius: 12px;
  background: linear-gradient(90deg, #4cd4a6 calc(var(--f) * 100%), #6ec8ff calc(var(--f) * 100%));
  color: #17141a;
  font-family: inherit;
  font-size: 16px;
  font-weight: 700;
  line-height: 24px;
  cursor: pointer;
}

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

.rg__btn b {
  font-variant-numeric: tabular-nums;
}

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

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

.rg__meta b {
  min-width: 3ch;
  text-align: right;
  font-variant-numeric: tabular-nums;
}

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

(function () {
  // 기법: 진행률을 시간에 비례시키지 않고 곡선 p = 1 - (1 - u)^CURVE_POW 로 계산한다 (u 는 시간 비율).
  // 굵은 링 = 곡선 진행률, 가는 안쪽 링 = 같은 시간의 균일 진행률. 둘의 차이(LEAD)가 곡선이 앞서는 만큼이다.
  var CURVE_POW = 2;
  var RING_R = 16;
  var RUN_MS = 1400;
  var START_MS = 200;
  var CYCLE_MS = 2000;

  var root = document.getElementById('rgRoot');
  var bar = document.getElementById('rgBar');
  var btn = document.getElementById('rgBtn');
  var ring = document.getElementById('rgRing');
  var ghost = document.getElementById('rgGhost');
  var labelEl = document.getElementById('rgLabel');
  var pctEl = document.getElementById('rgPct');
  var powEl = document.getElementById('rgPow');
  var leadEl = document.getElementById('rgLead');
  var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;

  var clock = 0;
  var runStart = null;
  var t0 = null;
  var lastTs = null;

  function ringCurve(u) { return 1 - Math.pow(1 - u, CURVE_POW); }
  function stopDemo() { root.classList.remove('is-demo'); }

  ring.setAttribute('rx', String(RING_R));
  ghost.setAttribute('rx', String(RING_R - 6));
  powEl.textContent = String(CURVE_POW);

  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 === 'done' ? null : 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 && runStart === 'done') u = 1;
    var p = ringCurve(u);
    var pct = Math.round(p * 100);
    ring.style.strokeDashoffset = String((100 - p * 100).toFixed(2));
    ghost.style.strokeDashoffset = String((100 - u * 100).toFixed(2));
    ring.style.opacity = p < 0.004 ? '0' : '1';
    ghost.style.opacity = u < 0.004 ? '0' : '1';
    btn.style.setProperty('--f', p.toFixed(3));
    pctEl.textContent = pct + '%';
    leadEl.textContent = String(Math.round((p - u) * 100));
    labelEl.textContent = u >= 1 ? 'Done' : (u > 0 ? 'Receiving' : 'Download');
    bar.setAttribute('aria-valuenow', String(pct));
    bar.setAttribute('aria-valuetext', pct + '%');
  }

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

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

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

// RingProgressButton — vanilla 판(02-dlbtn-ring-progress-curve) 의 React 포트.
// 진행률은 곡선 p = 1 - (1 - u)^CURVE_POW 로 계산한다. 굵은 링 = 곡선, 가는 링 = 같은 시간의 균일 진행률.
import { useEffect, useRef } from "react";
import styles from "./RingProgressButton.module.scss";

const CURVE_POW = 2;
const RING_R = 16;
const RUN_MS = 1400;
const START_MS = 200;
const CYCLE_MS = 2000;

type Start = number | "done" | null;

function ringCurve(u: number): number {
  return 1 - Math.pow(1 - u, CURVE_POW);
}

export default function RingProgressButton() {
  const barRef = useRef<HTMLDivElement | null>(null);
  const btnRef = useRef<HTMLButtonElement | null>(null);
  const ringRef = useRef<SVGRectElement | null>(null);
  const ghostRef = useRef<SVGRectElement | null>(null);
  const labelRef = useRef<HTMLSpanElement | null>(null);
  const pctRef = useRef<HTMLElement | null>(null);
  const leadRef = useRef<HTMLElement | null>(null);

  useEffect(() => {
    const bar = barRef.current;
    const btn = btnRef.current;
    const ring = ringRef.current;
    const ghost = ghostRef.current;
    const labelEl = labelRef.current;
    const pctEl = pctRef.current;
    const leadEl = leadRef.current;
    if (!bar || !btn || !ring || !ghost || !labelEl || !pctEl || !leadEl) return;
    const reduce = window.matchMedia("(prefers-reduced-motion: reduce)").matches;
    let demo = !reduce;
    let clock = 0;
    let runStart: Start = null;
    let t0: number | null = null;
    let raf = 0;

    ring.setAttribute("rx", String(RING_R));
    ghost.setAttribute("rx", String(RING_R - 6));

    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 === "done" ? null : 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 && runStart === "done") u = 1;
      const p = ringCurve(u);
      const pct = Math.round(p * 100);
      ring.style.strokeDashoffset = (100 - p * 100).toFixed(2);
      ghost.style.strokeDashoffset = (100 - u * 100).toFixed(2);
      ring.style.opacity = p < 0.004 ? "0" : "1";
      ghost.style.opacity = u < 0.004 ? "0" : "1";
      btn.style.setProperty("--f", p.toFixed(3));
      pctEl.textContent = pct + "%";
      leadEl.textContent = String(Math.round((p - u) * 100));
      labelEl.textContent = u >= 1 ? "완료" : u > 0 ? "받는 중" : "내려받기";
      bar.setAttribute("aria-valuenow", String(pct));
      bar.setAttribute("aria-valuetext", pct + "%");
    };
    const activate = (): void => {
      demo = false;
      if (reduce) { runStart = "done"; render(clock); return; }
      if (typeof runStart === "number" && 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.rg}>
        <div className={styles.rg__wrap} ref={barRef} role="progressbar" aria-labelledby="rgLabel" aria-valuemin={0} aria-valuemax={100} aria-valuenow={0} aria-valuetext="0%">
          <svg className={styles.rg__svg} viewBox="0 0 232 96" aria-hidden="true">
            <rect className={styles.rg__ghost} ref={ghostRef} x="11" y="11" width="210" height="74" pathLength="100" />
            <rect className={styles.rg__ring} ref={ringRef} x="3" y="3" width="226" height="90" pathLength="100" />
          </svg>
          <button className={styles.rg__btn} type="button" ref={btnRef}>
            <span id="rgLabel" ref={labelRef}>내려받기</span>
            <b ref={pctRef}>0%</b>
          </button>
        </div>
        <p className={styles.rg__meta}>
          <span className={styles.rg__tag}>POW</span> <b>{CURVE_POW}</b> <span className={styles.rg__tag}>LEAD</span> <b ref={leadRef}>0</b>
        </p>
      </div>
    </main>
  );
}