05Today-marker value toggle — a ring around the cell holding today's value periodically grows while fading

<main class="stage">
<div class="tb is-demo" id="tb">
  <div class="tb__head"><span class="tb__label">March 2026</span></div>
  <div class="tb__weekday" aria-hidden="true">
    <span>Sun</span><span>Mon</span><span>Tue</span><span>Wed</span><span>Thu</span><span>Fri</span><span>Sat</span>
  </div>
  <div class="tb__grid" id="tbGrid"></div>
</div>
</main>

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

// 계산 겹: index.html loop() 이 감쇠 진동(지수 감쇠 x 코사인) 공식으로
// 배지 스케일과 링 확장/투명도를 매 프레임 계산한다 — 키프레임 반복이 아니다.
@include stage($stage-ink);

.tb { width: 100%; max-width: 220px; background: $subject-cream; border-radius: $r-card; padding: $sp-2; box-shadow: $shadow-raised; box-sizing: border-box; }
.tb__head { text-align: center; margin-bottom: $sp-1; }
.tb__label { font-size: 11px; font-weight: 700; color: $subject-ink; }
.tb__weekday, .tb__grid { display: grid; grid-template-columns: repeat(7, 1fr); }
.tb__weekday span { font-size: 9px; text-align: center; color: rgba($subject-ink, .72); padding-bottom: $sp-1; }
.tb__cellWrap { position: relative; display: grid; place-items: center; height: 21px; }
.tb__cell { display: grid; place-items: center; width: 100%; height: 100%; font-size: 11px; color: $subject-ink; border-radius: $r-xs; position: relative; z-index: 2; border: none; background: transparent; }
.tb__cell--out { visibility: hidden; }
.tb__cell--today { background: $subject-blue-deep; color: $subject-cream; font-weight: 700; }
.tb__ring {
  position: absolute;
  z-index: 1;
  width: 100%;
  height: 100%;
  border-radius: $r-xs;
  background: $subject-blue-deep;
  pointer-events: none;
  opacity: 0;
  will-change: transform, opacity;
}
.tb__badge { position: relative; z-index: 2; }

@media (max-width: 340px) {
  .tb { max-width: 180px; }
  .tb__cellWrap { height: 17px; }
  .tb__cell { font-size: 10px; }
  .tb__weekday span { font-size: 8px; padding-bottom: 0; }
}

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

.tb {
  width: 100%;
  max-width: 220px;
  background: #fff7e6;
  border-radius: 16px;
  padding: 8px;
  box-shadow: 0 14px 24px rgba(23, 20, 26, 0.32);
  box-sizing: border-box;
}

.tb__head {
  text-align: center;
  margin-bottom: 4px;
}

.tb__label {
  font-size: 11px;
  font-weight: 700;
  color: #17141a;
}

.tb__weekday, .tb__grid {
  display: grid;
  grid-template-columns: repeat(7, 1fr);
}

.tb__weekday span {
  font-size: 9px;
  text-align: center;
  color: rgba(23, 20, 26, 0.72);
  padding-bottom: 4px;
}

.tb__cellWrap {
  position: relative;
  display: grid;
  place-items: center;
  height: 21px;
}

.tb__cell {
  display: grid;
  place-items: center;
  width: 100%;
  height: 100%;
  font-size: 11px;
  color: #17141a;
  border-radius: 4px;
  position: relative;
  z-index: 2;
  border: none;
  background: transparent;
}

.tb__cell--out {
  visibility: hidden;
}

.tb__cell--today {
  background: #0a4fe8;
  color: #fff7e6;
  font-weight: 700;
}

.tb__ring {
  position: absolute;
  z-index: 1;
  width: 100%;
  height: 100%;
  border-radius: 4px;
  background: #0a4fe8;
  pointer-events: none;
  opacity: 0;
  will-change: transform, opacity;
}

.tb__badge {
  position: relative;
  z-index: 2;
}

@media (max-width: 340px) {
  .tb {
    max-width: 180px;
  }
  .tb__cellWrap {
    height: 17px;
  }
  .tb__cell {
    font-size: 10px;
  }
  .tb__weekday span {
    font-size: 8px;
    padding-bottom: 0;
  }
}
@media (prefers-reduced-motion: reduce) {
  .tb__ring {
    display: none;
  }
}

(function () {
  var BASE = { y: 2026, m: 3, d: 14 }; // 계산 겹 상수: 고정 오늘, new Date() 미사용
  var CELL_TOTAL = 42;
  var CYCLE = 1500; // ms, 자동재생이 펄스를 다시 트는 간격
  var DUR = 1100; // ms, 감쇠 진동 한 회가 잦아드는 데 걸리는 시간
  var FREQ = 2 * Math.PI * 2.3 / DUR; // 계산 겹: 진동 각속도
  var ZETA = 4.2; // 계산 겹: 감쇠 상수 — 클수록 빨리 잦아든다

  function isLeap(y) { return (y % 4 === 0 && y % 100 !== 0) || y % 400 === 0; }
  function daysInMonth(y, m) {
    var t = [31, isLeap(y) ? 29 : 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31];
    return t[m - 1];
  }
  function dow(y, m, d) { // Zeller 합동식 — 0=Sun ~ 6=Sat
    var yy = y, mm = m;
    if (mm < 3) { yy -= 1; mm += 12; }
    var K = yy % 100, J = Math.floor(yy / 100);
    var h = (d + Math.floor(13 * (mm + 1) / 5) + K + Math.floor(K / 4) + Math.floor(J / 4) - 2 * J) % 7;
    h = ((h % 7) + 7) % 7;
    return (h + 6) % 7;
  }

  var tb = document.getElementById('tb');
  var grid = document.getElementById('tbGrid');
  var n = daysInMonth(BASE.y, BASE.m);
  var lead = dow(BASE.y, BASE.m, 1);
  var trail = CELL_TOTAL - lead - n;
  var i, wrap, cell;
  var ring = null, badgeCell = null;

  for (i = 0; i < lead; i++) {
    wrap = document.createElement('span');
    wrap.className = 'tb__cellWrap';
    cell = document.createElement('span');
    cell.className = 'tb__cell tb__cell--out';
    wrap.appendChild(cell);
    grid.appendChild(wrap);
  }
  for (var d = 1; d <= n; d++) {
    wrap = document.createElement('span');
    wrap.className = 'tb__cellWrap';
    if (d === BASE.d) {
      ring = document.createElement('span');
      ring.className = 'tb__ring';
      wrap.appendChild(ring);
      cell = document.createElement('button');
      cell.type = 'button';
      cell.className = 'tb__cell tb__cell--today tb__badge';
      cell.textContent = String(d);
      wrap.appendChild(cell);
      badgeCell = cell;
    } else {
      cell = document.createElement('span');
      cell.className = 'tb__cell';
      cell.textContent = String(d);
      wrap.appendChild(cell);
    }
    grid.appendChild(wrap);
  }
  for (i = 0; i < trail; i++) {
    wrap = document.createElement('span');
    wrap.className = 'tb__cellWrap';
    cell = document.createElement('span');
    cell.className = 'tb__cell tb__cell--out';
    wrap.appendChild(cell);
    grid.appendChild(wrap);
  }

  var isDemo = true;
  var triggerTime = 0;
  var rafId = null;
  var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;

  function pulseAt(t) {
    // 계산 겹: 지수 감쇠 x 코사인 진동 — 스프링이 잦아드는 물리량을 그대로 계산한다
    if (t < 0 || t > DUR) return { ring: 0, ringAlpha: 0, badge: 1 };
    var x = t / DUR;
    var amp = Math.exp(-ZETA * x);
    var osc = Math.cos(FREQ * t);
    var ringScale = 1 + 1.9 * (1 - amp);
    var ringAlpha = Math.max(0, amp * .55);
    var badgeScale = 1 + .16 * amp * osc;
    return { ring: ringScale, ringAlpha: ringAlpha, badge: badgeScale };
  }

  function human() {
    tb.classList.remove('is-demo');
    isDemo = false;
  }

  function trigger(ts) {
    triggerTime = ts;
  }

  function loop(ts) {
    if (!triggerTime) triggerTime = ts;
    var elapsed = ts - triggerTime;
    if (isDemo && !reduce && elapsed > CYCLE) {
      triggerTime = ts;
      elapsed = 0;
    }
    var p = pulseAt(elapsed);
    if (ring) {
      ring.style.transform = 'scale(' + p.ring.toFixed(3) + ')';
      ring.style.opacity = String(p.ringAlpha.toFixed(3));
    }
    if (badgeCell) {
      badgeCell.style.transform = 'scale(' + p.badge.toFixed(3) + ')';
    }
    rafId = requestAnimationFrame(loop);
  }

  badgeCell.addEventListener('click', function (ev) {
    human();
    trigger(performance.now());
  });
  badgeCell.addEventListener('keydown', function (ev) {
    if (ev.key !== 'Enter' && ev.key !== ' ') return;
    ev.preventDefault();
    human();
    trigger(performance.now());
  });

  if (!reduce) {
    rafId = requestAnimationFrame(loop);
  } else if (ring) {
    ring.style.display = 'none';
  }
})();

import { useEffect, useRef, useState } from 'react';
import styles from './DatePickerTodayPulse.module.scss';

type Box<T> = { current: T };

const BASE = { y: 2026, m: 3, d: 14 }; // 계산 겹 상수: 고정 오늘, new Date() 미사용
const CELL_TOTAL = 42;
const CYCLE = 1500; // ms, 자동재생이 펄스를 다시 트는 간격
const DUR = 1100; // ms, 감쇠 진동 한 회가 잦아드는 데 걸리는 시간
const FREQ = (2 * Math.PI * 2.3) / DUR; // 계산 겹: 진동 각속도
const ZETA = 4.2; // 계산 겹: 감쇠 상수 — 클수록 빨리 잦아든다
const WEEKDAY = ['일', '월', '화', '수', '목', '금', '토'];

function isLeap(y: number) {
  return (y % 4 === 0 && y % 100 !== 0) || y % 400 === 0;
}
function daysInMonth(y: number, m: number) {
  const t = [31, isLeap(y) ? 29 : 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31];
  return t[m - 1];
}
function dow(y: number, m: number, d: number) { // Zeller 합동식 — 0=일 ~ 6=토
  let yy = y;
  let mm = m;
  if (mm < 3) { yy -= 1; mm += 12; }
  const K = yy % 100;
  const J = Math.floor(yy / 100);
  let h = (d + Math.floor((13 * (mm + 1)) / 5) + K + Math.floor(K / 4) + Math.floor(J / 4) - 2 * J) % 7;
  h = ((h % 7) + 7) % 7;
  return (h + 6) % 7;
}

const N_DAYS = daysInMonth(BASE.y, BASE.m);
const LEAD = dow(BASE.y, BASE.m, 1);
const TRAIL = CELL_TOTAL - LEAD - N_DAYS;

function pulseAt(t: number) {
  // 계산 겹: 지수 감쇠 x 코사인 진동 — 스프링이 잦아드는 물리량을 그대로 계산한다
  if (t < 0 || t > DUR) return { ring: 0, ringAlpha: 0, badge: 1 };
  const x = t / DUR;
  const amp = Math.exp(-ZETA * x);
  const osc = Math.cos(FREQ * t);
  const ringScale = 1 + 1.9 * (1 - amp);
  const ringAlpha = Math.max(0, amp * .55);
  const badgeScale = 1 + .16 * amp * osc;
  return { ring: ringScale, ringAlpha, badge: badgeScale };
}

export default function DatePickerTodayPulse() {
  const ringRef = useRef(null) as unknown as Box<HTMLSpanElement>;
  const badgeRef = useRef(null) as unknown as Box<HTMLButtonElement>;
  const isDemoRef = useRef(true) as unknown as Box<boolean>;
  const triggerRef = useRef(0) as unknown as Box<number>;
  const [isDemo, setIsDemo] = useState(true);

  function human() {
    isDemoRef.current = false;
    setIsDemo(false);
  }

  useEffect(() => {
    const reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;
    if (reduce) return;
    let rafId = 0;
    function loop(ts: number) {
      if (!triggerRef.current) triggerRef.current = ts;
      let elapsed = ts - triggerRef.current;
      if (isDemoRef.current && elapsed > CYCLE) {
        triggerRef.current = ts;
        elapsed = 0;
      }
      const p = pulseAt(elapsed);
      const ring = ringRef.current;
      const badge = badgeRef.current;
      if (ring) {
        ring.style.transform = 'scale(' + p.ring.toFixed(3) + ')';
        ring.style.opacity = String(p.ringAlpha.toFixed(3));
      }
      if (badge) {
        badge.style.transform = 'scale(' + p.badge.toFixed(3) + ')';
      }
      rafId = requestAnimationFrame(loop);
    }
    rafId = requestAnimationFrame(loop);
    return () => cancelAnimationFrame(rafId);
  }, []);

  function retrigger() {
    human();
    triggerRef.current = performance.now();
  }

  function onKeyDown(e: { key: string; preventDefault: () => void }) {
    if (e.key !== 'Enter' && e.key !== ' ') return;
    e.preventDefault();
    retrigger();
  }

  const lead = Array.from({ length: LEAD }, (_, i) => (
    <span className={styles.tbCellWrap} key={'l' + i}><span className={styles.tbCell} /></span>
  ));
  const days = Array.from({ length: N_DAYS }, (_, i) => {
    const d = i + 1;
    if (d === BASE.d) {
      return (
        <span className={styles.tbCellWrap} key={'d' + d}>
          <span className={styles.tbRing} ref={ringRef} />
          <button
            type="button"
            className={`${styles.tbCell} ${styles.tbCellToday} ${styles.tbBadge}`}
            ref={badgeRef}
            onClick={retrigger}
            onKeyDown={onKeyDown}
          >
            {d}
          </button>
        </span>
      );
    }
    return (
      <span className={styles.tbCellWrap} key={'d' + d}><span className={styles.tbCell}>{d}</span></span>
    );
  });
  const trail = Array.from({ length: TRAIL }, (_, i) => (
    <span className={styles.tbCellWrap} key={'t' + i}><span className={styles.tbCell} /></span>
  ));

  return (
    <div className={`${styles.tb} ${isDemo ? styles.isDemo : ''}`}>
      <div className={styles.tbHead}><span className={styles.tbLabel}>2026년 3월</span></div>
      <div className={styles.tbWeekday} aria-hidden="true">
        {WEEKDAY.map((w) => <span key={w}>{w}</span>)}
      </div>
      <div className={styles.tbGrid}>{lead}{days}{trail}</div>
    </div>
  );
}