04Numbers That Flash in Turn on a Long Jump

<main class="stage">
<div class="pg is-demo" id="pgRoot">
  <nav class="pg__nav" id="pgNav" aria-label="Page navigation"></nav>
  <div class="pg__track" aria-hidden="true"><i class="pg__dot" id="pgDot"></i></div>
  <div class="pg__read">
    <b id="pgFrom">1</b><span class="pg__arrow">→</span><b id="pgTo">1</b>
    <span class="pg__k">Span</span><b id="pgSpan">0</b>
  </div>
  <p class="pg__sr" id="pgSr" aria-live="polite"></p>
</div>
</main>

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

// 핵심: 칩마다 (출발과의 쪽수 차 x STAGGER_STEP) ms 늦게 번쩍인다 — 멀리 뛸수록 궤적이 길다.

$chip-w: 28px;
$chip-gap: 4px;

@include stage($stage-ink);

.pg { display: grid; gap: $sp-3; justify-items: center; color: $stage-paper; }

.pg__nav { display: flex; gap: $chip-gap; }

.pg__b {
  box-sizing: border-box;
  width: $chip-w;
  height: 48px;
  padding: 0;
  border: 1px solid rgba($stage-paper, .28);
  border-radius: $r-sm;
  background: rgba($stage-paper, .08);
  color: $stage-paper;
  font-family: inherit;
  font-size: 12px;
  line-height: 16px;
  font-weight: 600;
  font-variant-numeric: tabular-nums;
  cursor: pointer;
  will-change: transform;
}

.pg__b.is-lit { background: $subject-lilac; border-color: $subject-lilac; color: $subject-ink; }
.pg__b.is-cur { background: $subject-mint; border-color: $subject-mint; color: $subject-ink; }
.pg__b:focus-visible { outline: 2px solid $subject-sky; outline-offset: 2px; }

.pg__track { position: relative; height: 4px; border-radius: $r-xs; background: rgba($stage-paper, .14); width: 8 * ($chip-w + $chip-gap) + $chip-w; }
.pg__dot { position: absolute; left: 0; top: -4px; width: $chip-w; height: 12px; border-radius: $r-pill; background: $subject-pink; will-change: transform; }

.pg__read { display: flex; align-items: baseline; gap: $sp-2; font-size: 12px; line-height: 16px; }
.pg__read b { color: $subject-sky; font-variant-numeric: tabular-nums; }
.pg__arrow, .pg__k { color: rgba($stage-paper, .82); }

.pg__sr {
  position: absolute;
  width: 1px;
  height: 1px;
  margin: 0;
  overflow: hidden;
  clip: rect(0 0 0 0);
  white-space: nowrap;
}

@media (max-width: 340px) {
  .pg__b { font-size: 11px; }
}

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

.pg {
  display: grid;
  gap: 12px;
  justify-items: center;
  color: #ffffff;
}

.pg__nav {
  display: flex;
  gap: 4px;
}

.pg__b {
  box-sizing: border-box;
  width: 28px;
  height: 48px;
  padding: 0;
  border: 1px solid rgba(255, 255, 255, 0.28);
  border-radius: 8px;
  background: rgba(255, 255, 255, 0.08);
  color: #ffffff;
  font-family: inherit;
  font-size: 12px;
  line-height: 16px;
  font-weight: 600;
  font-variant-numeric: tabular-nums;
  cursor: pointer;
  will-change: transform;
}

.pg__b.is-lit {
  background: #b9a0ff;
  border-color: #b9a0ff;
  color: #17141a;
}

.pg__b.is-cur {
  background: #4cd4a6;
  border-color: #4cd4a6;
  color: #17141a;
}

.pg__b:focus-visible {
  outline: 2px solid #6ec8ff;
  outline-offset: 2px;
}

.pg__track {
  position: relative;
  height: 4px;
  border-radius: 4px;
  background: rgba(255, 255, 255, 0.14);
  width: 284px;
}

.pg__dot {
  position: absolute;
  left: 0;
  top: -4px;
  width: 28px;
  height: 12px;
  border-radius: 999px;
  background: #ff9ebb;
  will-change: transform;
}

.pg__read {
  display: flex;
  align-items: baseline;
  gap: 8px;
  font-size: 12px;
  line-height: 16px;
}

.pg__read b {
  color: #6ec8ff;
  font-variant-numeric: tabular-nums;
}

.pg__arrow, .pg__k {
  color: rgba(255, 255, 255, 0.82);
}

.pg__sr {
  position: absolute;
  width: 1px;
  height: 1px;
  margin: 0;
  overflow: hidden;
  clip: rect(0 0 0 0);
  white-space: nowrap;
}

@media (max-width: 340px) {
  .pg__b {
    font-size: 11px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .pg__b {
    transition: none;
  }
}

(function () {
  // 기법: 출발 쪽과 도착 쪽 사이를 칩 아홉 개로 나눠 보여 주고, 칩마다 (출발과의 쪽수 차 x STAGGER_STEP) 만큼 늦게 번쩍인다.
  // 멀리 뛸수록 Total 궤적이 길어지고, 번쩍임은 attack 후 지수로 꺼지는 곡선이다.
  var CHIP_COUNT = 9;
  var TOTAL_PAGES = 40;
  var STAGGER_STEP = 11;
  var ATTACK_MS = 50;
  var DECAY_MS = 220;
  var SETTLE_MS = 160;
  var START_MS = 100;
  var DEMO_PAGES = [1, 40, 12, 33, 2, 25, 40];

  var root = document.getElementById('pgRoot');
  var nav = document.getElementById('pgNav');
  var dot = document.getElementById('pgDot');
  var fromEl = document.getElementById('pgFrom');
  var toEl = document.getElementById('pgTo');
  var spanEl = document.getElementById('pgSpan');
  var sr = document.getElementById('pgSr');
  var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;
  var CHIP_W = 28;
  var CHIP_GAP = 4;

  var chips = [];
  for (var i = 0; i < CHIP_COUNT; i += 1) {
    var c = document.createElement('button');
    c.type = 'button';
    c.className = 'pg__b';
    nav.appendChild(c);
    chips.push(c);
  }

  var cur = 1;
  var from = 1;
  var to = 1;
  var labels = [];
  var delays = [];
  var tStart = 0;
  var totalMs = 0;
  var running = false;
  var t0 = null;
  var demoIdx = 0;
  var nextAt = START_MS;

  function setLabels(a, b) {
    labels = [];
    delays = [];
    for (var s = 0; s < CHIP_COUNT; s += 1) {
      var page = Math.round(a + ((b - a) * s) / (CHIP_COUNT - 1));
      labels.push(page);
      delays.push(Math.abs(page - a) * STAGGER_STEP);
      chips[s].textContent = String(page);
    }
    totalMs = Math.abs(b - a) * STAGGER_STEP + ATTACK_MS + DECAY_MS;
  }

  function paintRest() {
    for (var s = 0; s < CHIP_COUNT; s += 1) {
      var on = labels[s] === cur && (s === CHIP_COUNT - 1 || s === 0);
      chips[s].className = 'pg__b' + (on ? ' is-cur' : '');
      chips[s].style.transform = '';
      if (on) chips[s].setAttribute('aria-current', 'page'); else chips[s].removeAttribute('aria-current');
    }
    fromEl.textContent = String(from);
    toEl.textContent = String(to);
    spanEl.textContent = String(Math.abs(to - from));
  }

  function jumpTo(page, byUser, now) {
    if (byUser) root.classList.remove('is-demo');
    if (page === cur || page < 1 || page > TOTAL_PAGES) return;
    from = cur;
    to = page;
    setLabels(from, to);
    cur = page;
    fromEl.textContent = String(from);
    toEl.textContent = String(to);
    spanEl.textContent = String(Math.abs(to - from));
    if (byUser) sr.textContent = 'Page ' + cur + ' / ' + TOTAL_PAGES;
    if (reduce) { setLabels(cur, cur); paintRest(); return; }
    tStart = now;
    running = true;
  }

  function pulseAt(age) {
    if (age < 0) return 0;
    if (age < ATTACK_MS) return age / ATTACK_MS;
    return Math.exp(-(age - ATTACK_MS) / (DECAY_MS * 0.45));
  }

  function tick(ts) {
    if (t0 === null) t0 = ts;
    var now = ts - t0;
    if (root.classList.contains('is-demo') && now >= nextAt && !running) {
      demoIdx = (demoIdx + 1) % DEMO_PAGES.length;
      jumpTo(DEMO_PAGES[demoIdx], false, now);
      nextAt = now + 1e9;
    }
    if (running) {
      var elapsed = now - tStart;
      for (var s = 0; s < CHIP_COUNT; s += 1) {
        var p = pulseAt(elapsed - delays[s]);
        var on = elapsed - delays[s] >= 0;
        chips[s].className = 'pg__b' + (p > 0.02 ? ' is-lit' : '') + (on && s === CHIP_COUNT - 1 ? ' is-cur' : '');
        chips[s].style.transform = p > 0.02 ? 'translateY(' + (-8 * p).toFixed(2) + 'px) scale(' + (1 + 0.22 * p).toFixed(3) + ')' : '';
        chips[s].style.opacity = p > 0.02 ? '1' : (on ? '0.9' : '0.72');
      }
      var head = Math.min(1, elapsed / Math.max(1, totalMs - DECAY_MS));
      dot.style.transform = 'translateX(' + (head * (CHIP_COUNT - 1) * (CHIP_W + CHIP_GAP)).toFixed(1) + 'px)';
      if (elapsed >= totalMs + SETTLE_MS) {
        running = false;
        setLabels(cur, cur);
        for (var q = 0; q < CHIP_COUNT; q += 1) chips[q].style.opacity = '';
        dot.style.transform = 'translateX(0)';
        paintRest();
        if (root.classList.contains('is-demo')) nextAt = now + SETTLE_MS;
      }
    }
    requestAnimationFrame(tick);
  }

  nav.addEventListener('click', function (e) {
    var idx = chips.indexOf(e.target);
    if (idx >= 0 && !running) jumpTo(labels[idx], true, t0 === null ? 0 : performance.now() - t0);
  });
  nav.addEventListener('keydown', function (e) {
    var step = 0;
    if (e.key === 'ArrowRight') step = 1;
    else if (e.key === 'ArrowLeft') step = -1;
    else if (e.key === 'PageDown') step = 10;
    else if (e.key === 'PageUp') step = -10;
    if (!step || running) return;
    e.preventDefault();
    jumpTo(Math.max(1, Math.min(TOTAL_PAGES, cur + step)), true, t0 === null ? 0 : performance.now() - t0);
  });

  setLabels(1, 1);
  paintRest();
  if (reduce) {
    root.classList.remove('is-demo');
    from = 1;
    jumpTo(40, true, 0);
  } else {
    requestAnimationFrame(tick);
  }
})();

// JumpTrailPager — vanilla 판(04-pager-long-jump-stagger-trail-ripple) 의 React 포트.
// 출발·도착 사이를 칩 아홉 개로 나누고, 칩마다 (출발과의 쪽수 차 x STAGGER_STEP) ms 늦게 번쩍인다.
import { useEffect, useRef } from "react";
import styles from "./JumpTrailPager.module.scss";

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

const CHIP_COUNT = 9;
const TOTAL_PAGES = 40;
const STAGGER_STEP = 11;
const ATTACK_MS = 50;
const DECAY_MS = 220;
const SETTLE_MS = 160;
const START_MS = 100;
const CHIP_W = 28;
const CHIP_GAP = 4;
const DEMO_PAGES = [1, 40, 12, 33, 2, 25, 40];

export default function JumpTrailPager() {
  const rootRef = useRef<HTMLDivElement | null>(null) as Box<HTMLDivElement | null>;
  const navRef = useRef<HTMLElement | null>(null) as Box<HTMLElement | null>;
  const dotRef = useRef<HTMLElement | null>(null) as Box<HTMLElement | null>;
  const fromRef = useRef<HTMLElement | null>(null) as Box<HTMLElement | null>;
  const toRef = useRef<HTMLElement | null>(null) as Box<HTMLElement | null>;
  const spanRef = useRef<HTMLElement | null>(null) as Box<HTMLElement | null>;
  const srRef = useRef<HTMLParagraphElement | null>(null) as Box<HTMLParagraphElement | null>;
  const chipRefs = useRef<Array<HTMLButtonElement | null>>([]) as Box<Array<HTMLButtonElement | null>>;

  useEffect(() => {
    const nav = navRef.current;
    const dot = dotRef.current;
    const fromEl = fromRef.current;
    const toEl = toRef.current;
    const spanEl = spanRef.current;
    const sr = srRef.current;
    if (!nav || !dot || !fromEl || !toEl || !spanEl || !sr) return;
    const chips = chipRefs.current;
    const reduce = window.matchMedia("(prefers-reduced-motion: reduce)").matches;

    let demo = true;
    let cur = 1;
    let from = 1;
    let to = 1;
    let labels: number[] = [];
    let delays: number[] = [];
    let tStart = 0;
    let totalMs = 0;
    let running = false;
    let t0: number | null = null;
    let demoIdx = 0;
    let nextAt = START_MS;
    let raf = 0;
    const perfNow = (): number => (t0 === null ? 0 : performance.now() - t0);

    function setLabels(a: number, b: number): void {
      labels = [];
      delays = [];
      for (let s = 0; s < CHIP_COUNT; s += 1) {
        const page = Math.round(a + ((b - a) * s) / (CHIP_COUNT - 1));
        labels.push(page);
        delays.push(Math.abs(page - a) * STAGGER_STEP);
        const chip = chips[s];
        if (chip) chip.textContent = String(page);
      }
      totalMs = Math.abs(b - a) * STAGGER_STEP + ATTACK_MS + DECAY_MS;
    }

    function paintRest(): void {
      for (let s = 0; s < CHIP_COUNT; s += 1) {
        const chip = chips[s];
        if (!chip) continue;
        const on = labels[s] === cur && (s === CHIP_COUNT - 1 || s === 0);
        chip.className = [styles.pg__b, on ? styles["is-cur"] : ""].join(" ");
        chip.style.transform = "";
        if (on) chip.setAttribute("aria-current", "page"); else chip.removeAttribute("aria-current");
      }
      fromEl!.textContent = String(from);
      toEl!.textContent = String(to);
      spanEl!.textContent = String(Math.abs(to - from));
    }

    function jumpTo(page: number, byUser: boolean, now: number): void {
      if (byUser) demo = false;
      if (page === cur || page < 1 || page > TOTAL_PAGES) return;
      from = cur;
      to = page;
      setLabels(from, to);
      cur = page;
      fromEl!.textContent = String(from);
      toEl!.textContent = String(to);
      spanEl!.textContent = String(Math.abs(to - from));
      if (byUser) sr!.textContent = "현재 " + cur + " / " + TOTAL_PAGES;
      if (reduce) { setLabels(cur, cur); paintRest(); return; }
      tStart = now;
      running = true;
    }

    function pulseAt(age: number): number {
      if (age < 0) return 0;
      if (age < ATTACK_MS) return age / ATTACK_MS;
      return Math.exp(-(age - ATTACK_MS) / (DECAY_MS * 0.45));
    }

    function tick(ts: number): void {
      if (t0 === null) t0 = ts;
      const now = ts - t0;
      if (demo && now >= nextAt && !running) {
        demoIdx = (demoIdx + 1) % DEMO_PAGES.length;
        jumpTo(DEMO_PAGES[demoIdx], false, now);
        nextAt = now + 1e9;
      }
      if (running) {
        const elapsed = now - tStart;
        for (let s = 0; s < CHIP_COUNT; s += 1) {
          const chip = chips[s];
          if (!chip) continue;
          const p = pulseAt(elapsed - delays[s]);
          const on = elapsed - delays[s] >= 0;
          chip.className = [styles.pg__b, p > 0.02 ? styles["is-lit"] : "", on && s === CHIP_COUNT - 1 ? styles["is-cur"] : ""].join(" ");
          chip.style.transform = p > 0.02 ? "translateY(" + (-8 * p).toFixed(2) + "px) scale(" + (1 + 0.22 * p).toFixed(3) + ")" : "";
          chip.style.opacity = p > 0.02 ? "1" : on ? "0.9" : "0.72";
        }
        const head = Math.min(1, elapsed / Math.max(1, totalMs - DECAY_MS));
        dot!.style.transform = "translateX(" + (head * (CHIP_COUNT - 1) * (CHIP_W + CHIP_GAP)).toFixed(1) + "px)";
        if (elapsed >= totalMs + SETTLE_MS) {
          running = false;
          setLabels(cur, cur);
          for (let q = 0; q < CHIP_COUNT; q += 1) {
            const chip = chips[q];
            if (chip) chip.style.opacity = "";
          }
          dot!.style.transform = "translateX(0)";
          paintRest();
          if (demo) nextAt = now + SETTLE_MS;
        }
      }
      raf = requestAnimationFrame(tick);
    }

    const onClick = (e: MouseEvent): void => {
      const idx = chips.indexOf(e.target as HTMLButtonElement);
      if (idx >= 0 && !running) jumpTo(labels[idx], true, perfNow());
    };
    const onKey = (e: KeyboardEvent): void => {
      let step = 0;
      if (e.key === "ArrowRight") step = 1;
      else if (e.key === "ArrowLeft") step = -1;
      else if (e.key === "PageDown") step = 10;
      else if (e.key === "PageUp") step = -10;
      if (!step || running) return;
      e.preventDefault();
      jumpTo(Math.max(1, Math.min(TOTAL_PAGES, cur + step)), true, perfNow());
    };
    nav.addEventListener("click", onClick);
    nav.addEventListener("keydown", onKey);

    setLabels(1, 1);
    paintRest();
    if (reduce) {
      demo = false;
      from = 1;
      jumpTo(40, true, 0);
    } else {
      raf = requestAnimationFrame(tick);
    }
    return () => {
      cancelAnimationFrame(raf);
      nav.removeEventListener("click", onClick);
      nav.removeEventListener("keydown", onKey);
    };
  }, []);

  return (
    <main className={styles.stage}>
      <div className={styles.pg} ref={rootRef}>
        <nav className={styles.pg__nav} ref={navRef} aria-label="페이지 이동">
          {Array.from({ length: CHIP_COUNT }, (_, i) => (
            <button type="button" className={styles.pg__b} key={i} ref={(el: HTMLButtonElement | null) => { chipRefs.current[i] = el; }}></button>
          ))}
        </nav>
        <div className={styles.pg__track} aria-hidden="true"><i className={styles.pg__dot} ref={dotRef}></i></div>
        <div className={styles.pg__read}>
          <b ref={fromRef}>1</b><span className={styles.pg__arrow}>→</span><b ref={toRef}>1</b>
          <span className={styles.pg__k}>간격</span><b ref={spanRef}>0</b>
        </div>
        <p className={styles.pg__sr} ref={srRef} aria-live="polite"></p>
      </div>
    </main>
  );
}