05ボタン自身が進捗バーになる

<main class="stage">
  <div class="dl is-demo">
    <button class="dl__btn" id="dl-btn" type="button" data-state="idle" role="progressbar" aria-valuemin="0" aria-valuemax="100" aria-valuenow="0">
      <span class="dl__fill" aria-hidden="true"></span>
      <span class="dl__face" data-face="idle">
        <span class="dl__ic" aria-hidden="true"><svg viewBox="0 0 256 256" width="20" height="20"><g fill="currentColor"><path d="M216 48v160H40V48a16 16 0 0 1 16-16h144a16 16 0 0 1 16 16" opacity=".2"/><path d="M224 144v64a8 8 0 0 1-8 8H40a8 8 0 0 1-8-8v-64a8 8 0 0 1 16 0v56h160v-56a8 8 0 0 1 16 0m-101.66 5.66a8 8 0 0 0 11.32 0l40-40a8 8 0 0 0-11.32-11.32L136 124.69V32a8 8 0 0 0-16 0v92.69L93.66 98.34a8 8 0 0 0-11.32 11.32Z"/></g></svg></span>
        <span class="dl__t">ダウンロード</span>
      </span>
      <span class="dl__face" data-face="busy">
        <span class="dl__pct"></span>
      </span>
      <span class="dl__face" data-face="done">
        <span class="dl__ic" aria-hidden="true"><svg viewBox="0 0 256 256" width="20" height="20"><g fill="currentColor"><path d="M224 128a96 96 0 1 1-96-96a96 96 0 0 1 96 96" opacity=".2"/><path d="M173.66 98.34a8 8 0 0 1 0 11.32l-56 56a8 8 0 0 1-11.32 0l-24-24a8 8 0 0 1 11.32-11.32L112 148.69l50.34-50.35a8 8 0 0 1 11.32 0M232 128A104 104 0 1 1 128 24a104.11 104.11 0 0 1 104 104m-16 0a88 88 0 1 0-88 88a88.1 88.1 0 0 0 88-88"/></g></svg></span>
        <span class="dl__t">完了しました</span>
      </span>
    </button>
    <p class="dl__note">ボタンの内側がそのまま進捗バーです</p>
  </div>
</main>

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

$duration: $dur-base;
$easing: $ease-out;
$color: $subject-blue;

@include stage($stage-ink);

// 등록하지 않은 커스텀 속성은 브라우저가 글자로만 보고 보간하지 않는다 — 숫자로 등록해야 0 에서 100 으로 흐른다
@property --p {
  syntax: "<integer>";
  inherits: true;
  initial-value: 0;
}

.dl {
  box-sizing: border-box;
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: $sp-3;
  width: min(280px, 86vw);
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
}

.dl__btn {
  position: relative;
  box-sizing: border-box;
  margin: 0;
  padding: 0;
  width: 100%;
  height: 48px;
  overflow: hidden;
  border: 0;
  border-radius: $r-control;
  background-color: $subject-cream;
  color: $subject-ink;
  cursor: pointer;
  box-shadow: $shadow-raised;
}
.dl__btn:focus-visible { outline: 3px solid $color; outline-offset: 3px; }

// 채움 — 단일 변수 --p 가 그라디언트의 색 경계 자리를 정한다
.dl__fill {
  position: absolute;
  left: 0;
  right: 0;
  top: 0;
  bottom: 0;
  background-image: linear-gradient(90deg, $color 0 calc(var(--p) * 1%), transparent calc(var(--p) * 1%) 100%);
}

.dl__face {
  position: absolute;
  left: 0;
  right: 0;
  top: 0;
  bottom: 0;
  display: flex;
  align-items: center;
  justify-content: center;
  gap: $sp-2;
  opacity: 0;
}
.dl__ic { display: inline-flex; flex: 0 0 auto; }
.dl__ic svg { display: block; }
.dl__t {
  font-size: 15px;
  line-height: 20px;
  font-weight: 700;
  white-space: nowrap;
}
// 같은 변수를 숫자로도 읽는다 — 카운터에 넣으면 글자가 된다
.dl__pct::after {
  counter-reset: p var(--p);
  content: counter(p) "%";
  font-size: 15px;
  line-height: 20px;
  font-weight: 700;
  font-variant-numeric: tabular-nums;
}

// 사람이 실제로 누른 경로
.dl:not(.is-demo) .dl__btn[data-state="idle"] .dl__face[data-face="idle"],
.dl:not(.is-demo) .dl__btn[data-state="busy"] .dl__face[data-face="busy"],
.dl:not(.is-demo) .dl__btn[data-state="done"] .dl__face[data-face="done"] { opacity: 1; }
.dl:not(.is-demo) .dl__btn[data-state="busy"] .dl__face[data-face="busy"] { color: $subject-cream; }
.dl:not(.is-demo) .dl__btn[data-state="done"] .dl__fill { background-image: none; background-color: $subject-mint; }

.dl__note {
  margin: 0;
  font-size: 12px;
  line-height: 18px;
  font-weight: 500;
  color: $subject-cream;
}

// ── 자동 루프: 12% 에 시작해 78% 에 100% 를 채우고 82% 에 완료로 끊었다가 88% 에 원복 ──
// --p 는 등속으로 흐르고, 완료 색은 한 프레임에 끊는다 — 한 요소에 두 애니메이션을 겹쳐 건다
.dl.is-demo .dl__btn {
  animation-name: dl-p, dl-skin;
  animation-duration: $dur-loop, $dur-loop;
  animation-timing-function: linear, steps(1, end);
  animation-iteration-count: infinite, infinite;
}
@keyframes dl-p {
  0%   { --p: 0; }
  12%  { --p: 0; }
  78%  { --p: 100; }
  100% { --p: 100; }
}
@keyframes dl-skin {
  0%   { background-color: $subject-cream; }
  82%  { background-color: $subject-mint; }
  88%  { background-color: $subject-cream; }
  100% { background-color: $subject-cream; }
}

.dl.is-demo .dl__face {
  animation-duration: $dur-loop;
  animation-timing-function: steps(1, end);
  animation-iteration-count: infinite;
}
.dl.is-demo .dl__face[data-face="idle"] { animation-name: dl-idle; }
.dl.is-demo .dl__face[data-face="busy"] { animation-name: dl-busy; }
.dl.is-demo .dl__face[data-face="done"] { animation-name: dl-done; }
@keyframes dl-idle {
  0%   { opacity: 1; }
  12%  { opacity: 0; }
  88%  { opacity: 1; }
  100% { opacity: 1; }
}
@keyframes dl-busy {
  0%   { opacity: 0; color: $subject-ink; }
  12%  { opacity: 1; color: $subject-ink; }
  40%  { opacity: 1; color: $subject-cream; }
  82%  { opacity: 0; color: $subject-cream; }
  100% { opacity: 0; color: $subject-cream; }
}
@keyframes dl-done {
  0%   { opacity: 0; }
  82%  { opacity: 1; }
  88%  { opacity: 0; }
  100% { opacity: 0; }
}

// 완료로 끊는 동안은 채움 띠를 걷어 버튼 자체 색이 그대로 보이게 한다
.dl.is-demo .dl__fill {
  animation-name: dl-veil;
  animation-duration: $dur-loop;
  animation-timing-function: steps(1, end);
  animation-iteration-count: infinite;
}
@keyframes dl-veil {
  0%   { opacity: 1; }
  82%  { opacity: 0; }
  88%  { opacity: 1; }
  100% { opacity: 1; }
}

@media (max-width: 340px) {
  .dl { gap: $sp-2; }
  .dl__btn { height: 44px; }
  .dl__t { font-size: 13px; line-height: 18px; }
  .dl__note { font-size: 11px; line-height: 16px; }
}

@media (prefers-reduced-motion: reduce) {
  .dl.is-demo .dl__btn,
  .dl.is-demo .dl__face,
  .dl.is-demo .dl__fill { animation: none !important; }
  .dl.is-demo .dl__face[data-face="idle"] { opacity: 1; }
}

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);
}

@property --p {
  syntax: "<integer>";
  inherits: true;
  initial-value: 0;
}
.dl {
  box-sizing: border-box;
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 12px;
  width: min(280px, 86vw);
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
}

.dl__btn {
  position: relative;
  box-sizing: border-box;
  margin: 0;
  padding: 0;
  width: 100%;
  height: 48px;
  overflow: hidden;
  border: 0;
  border-radius: 12px;
  background-color: #fff7e6;
  color: #17141a;
  cursor: pointer;
  box-shadow: 0 14px 24px rgba(23, 20, 26, 0.32);
}

.dl__btn:focus-visible {
  outline: 3px solid #2f6df6;
  outline-offset: 3px;
}

.dl__fill {
  position: absolute;
  left: 0;
  right: 0;
  top: 0;
  bottom: 0;
  background-image: linear-gradient(90deg, #2f6df6 0 calc(var(--p) * 1%), transparent calc(var(--p) * 1%) 100%);
}

.dl__face {
  position: absolute;
  left: 0;
  right: 0;
  top: 0;
  bottom: 0;
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 8px;
  opacity: 0;
}

.dl__ic {
  display: inline-flex;
  flex: 0 0 auto;
}

.dl__ic svg {
  display: block;
}

.dl__t {
  font-size: 15px;
  line-height: 20px;
  font-weight: 700;
  white-space: nowrap;
}

.dl__pct::after {
  counter-reset: p var(--p);
  content: counter(p) "%";
  font-size: 15px;
  line-height: 20px;
  font-weight: 700;
  font-variant-numeric: tabular-nums;
}

.dl:not(.is-demo) .dl__btn[data-state=idle] .dl__face[data-face=idle],
.dl:not(.is-demo) .dl__btn[data-state=busy] .dl__face[data-face=busy],
.dl:not(.is-demo) .dl__btn[data-state=done] .dl__face[data-face=done] {
  opacity: 1;
}

.dl:not(.is-demo) .dl__btn[data-state=busy] .dl__face[data-face=busy] {
  color: #fff7e6;
}

.dl:not(.is-demo) .dl__btn[data-state=done] .dl__fill {
  background-image: none;
  background-color: #4cd4a6;
}

.dl__note {
  margin: 0;
  font-size: 12px;
  line-height: 18px;
  font-weight: 500;
  color: #fff7e6;
}

.dl.is-demo .dl__btn {
  animation-name: dl-p, dl-skin;
  animation-duration: 2s, 2s;
  animation-timing-function: linear, steps(1, end);
  animation-iteration-count: infinite, infinite;
}

@keyframes dl-p {
  0% {
    --p: 0;
  }
  12% {
    --p: 0;
  }
  78% {
    --p: 100;
  }
  100% {
    --p: 100;
  }
}
@keyframes dl-skin {
  0% {
    background-color: #fff7e6;
  }
  82% {
    background-color: #4cd4a6;
  }
  88% {
    background-color: #fff7e6;
  }
  100% {
    background-color: #fff7e6;
  }
}
.dl.is-demo .dl__face {
  animation-duration: 2s;
  animation-timing-function: steps(1, end);
  animation-iteration-count: infinite;
}

.dl.is-demo .dl__face[data-face=idle] {
  animation-name: dl-idle;
}

.dl.is-demo .dl__face[data-face=busy] {
  animation-name: dl-busy;
}

.dl.is-demo .dl__face[data-face=done] {
  animation-name: dl-done;
}

@keyframes dl-idle {
  0% {
    opacity: 1;
  }
  12% {
    opacity: 0;
  }
  88% {
    opacity: 1;
  }
  100% {
    opacity: 1;
  }
}
@keyframes dl-busy {
  0% {
    opacity: 0;
    color: #17141a;
  }
  12% {
    opacity: 1;
    color: #17141a;
  }
  40% {
    opacity: 1;
    color: #fff7e6;
  }
  82% {
    opacity: 0;
    color: #fff7e6;
  }
  100% {
    opacity: 0;
    color: #fff7e6;
  }
}
@keyframes dl-done {
  0% {
    opacity: 0;
  }
  82% {
    opacity: 1;
  }
  88% {
    opacity: 0;
  }
  100% {
    opacity: 0;
  }
}
.dl.is-demo .dl__fill {
  animation-name: dl-veil;
  animation-duration: 2s;
  animation-timing-function: steps(1, end);
  animation-iteration-count: infinite;
}

@keyframes dl-veil {
  0% {
    opacity: 1;
  }
  82% {
    opacity: 0;
  }
  88% {
    opacity: 1;
  }
  100% {
    opacity: 1;
  }
}
@media (max-width: 340px) {
  .dl {
    gap: 8px;
  }
  .dl__btn {
    height: 44px;
  }
  .dl__t {
    font-size: 13px;
    line-height: 18px;
  }
  .dl__note {
    font-size: 11px;
    line-height: 16px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .dl.is-demo .dl__btn,
  .dl.is-demo .dl__face,
  .dl.is-demo .dl__fill {
    animation: none !important;
  }
  .dl.is-demo .dl__face[data-face=idle] {
    opacity: 1;
  }
}

// 실제 동작: 퍼센트를 CSS 변수 --p 하나에만 적는다. 채움 너비도 숫자도 그 변수에서 나온다
var root = document.querySelector('.dl');
var btn = document.getElementById('dl-btn');
var timer = 0;
btn.addEventListener('click', function () {
  root.classList.remove('is-demo');
  if (btn.getAttribute('data-state') === 'busy') return;
  var p = 0;
  btn.setAttribute('data-state', 'busy');
  clearInterval(timer);
  timer = setInterval(function () {
    p = Math.min(100, p + 4);
    btn.style.setProperty('--p', p);
    btn.setAttribute('aria-valuenow', String(p));
    if (p === 100) { clearInterval(timer); btn.setAttribute('data-state', 'done'); }
  }, 80);
});

import { useEffect, useState } from "react";
import type { CSSProperties } from "react";
import styles from "./DownloadProgressButton.module.scss";

export type DownloadProgressButtonProps = {
  label?: string;
  doneLabel?: string;
  note?: string;
  duration?: number;
  easing?: string;
  color?: string;
};

type Vars = CSSProperties & {
  "--duration"?: string;
  "--easing"?: string;
  "--color"?: string;
  "--p"?: string;
};
type State = "idle" | "busy" | "done";

const STEP = 4;   // 한 번에 올리는 퍼센트
const TICK = 80;  // 올리는 간격(ms)

export default function DownloadProgressButton({
  label = "Download",
  doneLabel = "Saved",
  note = "The inside of the button is the progress bar",
  duration = 300,
  easing = "ease-out",
  color = "#2f6df6",
}: DownloadProgressButtonProps) {
  const [demo, setDemo] = useState(true);
  const [state, setState] = useState<State>("idle");
  const [p, setP] = useState(0);

  // 퍼센트를 --p 하나에만 적는다 — 채움 너비도 숫자도 그 변수에서 나온다
  const vars: Vars = { "--duration": `${duration}ms`, "--easing": easing, "--color": color };
  const btnVars: Vars = demo ? {} : { "--p": String(p) };

  useEffect(() => {
    if (state !== "busy") return;
    let v = 0;
    setP(0);
    const id = setInterval(() => {
      v = Math.min(100, v + STEP);
      setP(v);
      if (v === 100) {
        clearInterval(id);
        setState("done");
      }
    }, TICK);
    return () => clearInterval(id);
  }, [state]);

  function start() {
    setDemo(false);
    if (state === "busy") return;
    setState("busy");
  }

  return (
    <div className={`${styles.dl} ${demo ? styles.isDemo : ""}`} style={vars}>
      <button
        className={styles.btn}
        type="button"
        style={btnVars}
        data-state={state}
        role="progressbar"
        aria-valuemin={0}
        aria-valuemax={100}
        aria-valuenow={demo ? 0 : p}
        onClick={start}
      >
        <span className={styles.fill} aria-hidden="true" />
        <span className={styles.face} data-face="idle">
          <span className={styles.ic} aria-hidden="true">
            <svg viewBox="0 0 256 256" width="20" height="20">
              <g fill="currentColor">
                <path d="M216 48v160H40V48a16 16 0 0 1 16-16h144a16 16 0 0 1 16 16" opacity=".2" />
                <path d="M224 144v64a8 8 0 0 1-8 8H40a8 8 0 0 1-8-8v-64a8 8 0 0 1 16 0v56h160v-56a8 8 0 0 1 16 0m-101.66 5.66a8 8 0 0 0 11.32 0l40-40a8 8 0 0 0-11.32-11.32L136 124.69V32a8 8 0 0 0-16 0v92.69L93.66 98.34a8 8 0 0 0-11.32 11.32Z" />
              </g>
            </svg>
          </span>
          <span className={styles.t}>{label}</span>
        </span>
        <span className={styles.face} data-face="busy">
          <span className={styles.pct} />
        </span>
        <span className={styles.face} data-face="done">
          <span className={styles.ic} aria-hidden="true">
            <svg viewBox="0 0 256 256" width="20" height="20">
              <g fill="currentColor">
                <path d="M224 128a96 96 0 1 1-96-96a96 96 0 0 1 96 96" opacity=".2" />
                <path d="M173.66 98.34a8 8 0 0 1 0 11.32l-56 56a8 8 0 0 1-11.32 0l-24-24a8 8 0 0 1 11.32-11.32L112 148.69l50.34-50.35a8 8 0 0 1 11.32 0M232 128A104 104 0 1 1 128 24a104.11 104.11 0 0 1 104 104m-16 0a88 88 0 1 0-88 88a88.1 88.1 0 0 0 88-88" />
              </g>
            </svg>
          </span>
          <span className={styles.t}>{doneLabel}</span>
        </span>
      </button>
      <p className={styles.note}>{note}</p>
    </div>
  );
}