06Group chat cycle — a label redrawing width from remaining time as typers change

<main class="stage">
<section class="panel">
  <div class="row" role="status" aria-live="polite" aria-label="Group chat typing indicator">
    <span class="who" id="who">A</span>
    <span class="track"><span class="fill" id="fill"></span></span>
  </div>
</section>
</main>

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

@include stage($stage-yellow);

.panel { display: flex; align-items: center; }
.row {
  display: flex;
  align-items: center;
  gap: $sp-3;
  padding: $sp-3 $sp-4;
  border-radius: $r-card;
  background: $subject-ink;
}

.who {
  color: $subject-cream;
  font-size: 14px;
  font-weight: 600;
  width: 18px;
}

.track {
  position: relative;
  width: 96px;
  height: 4px;
  border-radius: $r-xs;
  background: rgba($subject-cream, .28);
  overflow: hidden;
}

.fill {
  position: absolute;
  inset: 0;
  border-radius: $r-xs;
  background: $subject-cream;
  transform-origin: left center;
}

@media (max-width: 340px) {
  .track { width: 72px; }
}

@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: #ffd23f;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  padding: clamp(8px, 4vw, 24px);
}

.panel {
  display: flex;
  align-items: center;
}

.row {
  display: flex;
  align-items: center;
  gap: 12px;
  padding: 12px 16px;
  border-radius: 16px;
  background: #17141a;
}

.who {
  color: #fff7e6;
  font-size: 14px;
  font-weight: 600;
  width: 18px;
}

.track {
  position: relative;
  width: 96px;
  height: 4px;
  border-radius: 4px;
  background: rgba(255, 247, 230, 0.28);
  overflow: hidden;
}

.fill {
  position: absolute;
  inset: 0;
  border-radius: 4px;
  background: #fff7e6;
  transform-origin: left center;
}

@media (max-width: 340px) {
  .track {
    width: 72px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .fill {
    transition: none;
  }
}

// 그룹 채팅 순환 — 입력자가 바뀔 때마다 이전 이름이 남아 있을 시간 값을 세어 그 값만큼 막대를 줄인다.
// 계산 겹: 남은 시간 비율 재계산 → scaleX 로 반영, 다음 입력자로 교체. 자동 재생만, 실사용자 리스너 없음.
(function () {
  var who = document.getElementById('who');
  var fill = document.getElementById('fill');
  if (!who || !fill) return;

  var NAMES = ['A', 'B', 'C'];
  var HOLD_MS = 640;
  var CYCLE_MS = HOLD_MS * NAMES.length;

  function apply(t) {
    var idx = Math.floor(t / HOLD_MS) % NAMES.length;
    var phaseT = t % HOLD_MS;
    var remain = 1 - phaseT / HOLD_MS;
    who.textContent = NAMES[idx];
    fill.style.transform = 'scaleX(' + remain.toFixed(3) + ')';
  }

  apply(0);
  var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;
  if (reduce) { fill.style.transform = 'scaleX(1)'; return; }
  var start = null;
  function loop(ts) {
    if (start === null) start = ts;
    var t = (ts - start) % CYCLE_MS;
    apply(t);
    requestAnimationFrame(loop);
  }
  requestAnimationFrame(loop);
})();

import { useEffect, useRef } from "react";
import styles from "./TypingGroupChatCycle.module.scss";

// 그룹 채팅 순환 — 입력자가 바뀔 때마다 이전 이름이 남아 있을 시간 값을 세어 그 값만큼 막대를 줄인다.
// 계산 겹: 남은 시간 비율 재계산 → scaleX 로 반영, 다음 입력자로 교체. 자동 재생만, 실사용자 리스너 없음.
const NAMES = ["A", "B", "C"];
const HOLD_MS = 640;

export default function TypingGroupChatCycle() {
  const whoRef = useRef<HTMLSpanElement>(null);
  const fillRef = useRef<HTMLSpanElement>(null);

  useEffect(() => {
    const who = whoRef.current;
    const fill = fillRef.current;
    if (!who || !fill) return;

    function apply(t: number) {
      const idx = Math.floor(t / HOLD_MS) % NAMES.length;
      const phaseT = t % HOLD_MS;
      const remain = 1 - phaseT / HOLD_MS;
      who!.textContent = NAMES[idx];
      fill!.style.transform = "scaleX(" + remain.toFixed(3) + ")";
    }

    apply(0);
    const reduce = window.matchMedia("(prefers-reduced-motion: reduce)").matches;
    if (reduce) {
      fill.style.transform = "scaleX(1)";
      return;
    }
    let start: number | null = null;
    let raf = 0;
    const CYCLE_MS = HOLD_MS * NAMES.length;
    function loop(ts: number) {
      if (start === null) start = ts;
      const t = (ts - start) % CYCLE_MS;
      apply(t);
      raf = requestAnimationFrame(loop);
    }
    raf = requestAnimationFrame(loop);
    return () => cancelAnimationFrame(raf);
  }, []);

  return (
    <div className={styles.stage}>
      <section className={styles.panel}>
        <div className={styles.row} role="status" aria-live="polite" aria-label="그룹 채팅 입력 표시">
          <span ref={whoRef} className={styles.who}>A</span>
          <span className={styles.track}>
            <span ref={fillRef} className={styles.fill} />
          </span>
        </div>
      </section>
    </div>
  );
}