08Next-Only Cursor Pager with a Trail

<main class="stage">
<div class="pg is-demo" id="pgRoot">
  <div class="pg__card is-mint" id="pgCard" aria-hidden="true">
    <b class="pg__no" id="pgNo">1</b>
    <span class="pg__cursor" id="pgCursor">0000</span>
  </div>
  <nav class="pg__nav" aria-label="Page navigation">
    <button type="button" class="pg__next" id="pgNext">Next</button>
  </nav>
  <div class="pg__trail" id="pgTrail" aria-label="Pages visited">
    <i class="pg__line" id="pgLine" aria-hidden="true"></i>
  </div>
  <p class="pg__sr" id="pgSr" aria-live="polite"></p>
</div>
</main>

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

// 핵심: 전체 쪽수를 모르니 다음 커서만 받는다. 지나온 쪽은 점으로 남고, 점이 늘면 간격이 줄어 길이는 TRAIL_W 로 일정하다.

$trail-w: 232px;
$dot: 12px;

@include stage($stage-ink);

.pg { display: grid; gap: $sp-4; justify-items: center; color: $stage-paper; width: 264px; max-width: 100%; }

.pg__card { display: flex; align-items: center; justify-content: space-between; box-sizing: border-box; width: 100%; height: 56px; padding: $sp-2 $sp-4; border-radius: $r-card; }
.pg__card.is-mint { background: rgba($subject-mint, .4); }
.pg__card.is-lilac { background: rgba($subject-lilac, .44); }
.pg__card.is-pink { background: rgba($subject-pink, .42); }
.pg__card.is-sky { background: rgba($subject-sky, .42); }
.pg__no { font-size: 24px; line-height: 28px; font-weight: 700; color: $stage-paper; font-variant-numeric: tabular-nums; }
.pg__cursor { font-family: ui-monospace, "SFMono-Regular", Menlo, Consolas, monospace; font-size: 12px; line-height: 16px; padding: $sp-1 $sp-2; border-radius: $r-xs; background: rgba($stage-ink, .6); color: $stage-paper; }

.pg__next {
  box-sizing: border-box;
  min-width: 96px;
  height: 40px;
  padding: 0 $sp-5;
  border: 0;
  border-radius: $r-pill;
  background: $subject-lilac;
  color: $subject-ink;
  font-family: inherit;
  font-size: 14px;
  line-height: 20px;
  font-weight: 700;
  cursor: pointer;
}
.pg__next.is-end { opacity: .55; cursor: default; }
.pg__next:focus-visible, .pg__dot:focus-visible { outline: 2px solid $subject-sky; outline-offset: 2px; }

.pg__trail { position: relative; width: $trail-w; height: $dot; }
.pg__line { position: absolute; left: 0; top: 4px; width: $trail-w; height: 4px; border-radius: $r-xs; background: rgba($subject-pink, .8); transform-origin: 0 50%; transform: scaleX(0); }
.pg__dot {
  position: absolute;
  left: 0;
  top: 0;
  box-sizing: border-box;
  width: $dot;
  height: $dot;
  padding: 0;
  border: 0;
  border-radius: $r-pill;
  background: rgba($stage-paper, .86);
  transform: scale(0);
  will-change: transform;
}
.pg__dot.is-cur { background: $subject-pink; }

.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__next { min-width: 88px; }
}

@media (prefers-reduced-motion: reduce) {
  .pg__dot { 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: 16px;
  justify-items: center;
  color: #ffffff;
  width: 264px;
  max-width: 100%;
}

.pg__card {
  display: flex;
  align-items: center;
  justify-content: space-between;
  box-sizing: border-box;
  width: 100%;
  height: 56px;
  padding: 8px 16px;
  border-radius: 16px;
}

.pg__card.is-mint {
  background: rgba(76, 212, 166, 0.4);
}

.pg__card.is-lilac {
  background: rgba(185, 160, 255, 0.44);
}

.pg__card.is-pink {
  background: rgba(255, 158, 187, 0.42);
}

.pg__card.is-sky {
  background: rgba(110, 200, 255, 0.42);
}

.pg__no {
  font-size: 24px;
  line-height: 28px;
  font-weight: 700;
  color: #ffffff;
  font-variant-numeric: tabular-nums;
}

.pg__cursor {
  font-family: ui-monospace, "SFMono-Regular", Menlo, Consolas, monospace;
  font-size: 12px;
  line-height: 16px;
  padding: 4px 8px;
  border-radius: 4px;
  background: rgba(23, 20, 26, 0.6);
  color: #ffffff;
}

.pg__next {
  box-sizing: border-box;
  min-width: 96px;
  height: 40px;
  padding: 0 20px;
  border: 0;
  border-radius: 999px;
  background: #b9a0ff;
  color: #17141a;
  font-family: inherit;
  font-size: 14px;
  line-height: 20px;
  font-weight: 700;
  cursor: pointer;
}

.pg__next.is-end {
  opacity: 0.55;
  cursor: default;
}

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

.pg__trail {
  position: relative;
  width: 232px;
  height: 12px;
}

.pg__line {
  position: absolute;
  left: 0;
  top: 4px;
  width: 232px;
  height: 4px;
  border-radius: 4px;
  background: rgba(255, 158, 187, 0.8);
  transform-origin: 0 50%;
  transform: scaleX(0);
}

.pg__dot {
  position: absolute;
  left: 0;
  top: 0;
  box-sizing: border-box;
  width: 12px;
  height: 12px;
  padding: 0;
  border: 0;
  border-radius: 999px;
  background: rgba(255, 255, 255, 0.86);
  transform: scale(0);
  will-change: transform;
}

.pg__dot.is-cur {
  background: #ff9ebb;
}

.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__next {
    min-width: 88px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .pg__dot {
    transition: none;
  }
}

(function () {
  // 기법: Total 쪽수를 모르는 목록은 Next 커서만 받는다. 지나온 쪽을 점으로 남기고,
  // 점이 늘어날수록 간격을 TRAIL_W / (Dots 수 - 1) 로 줄여 길이가 일정하게 유지된다. 새 점은 스프링으로 튄다.
  var END_AT = 9;
  var TRAIL_W = 232;
  var MAX_GAP = 36;
  var DOT_SIZE = 12;
  var GAP_RATE = 12;
  var POP_MS = 420;
  var CYCLE_MS = 2700;
  var PRESS_START = 140;
  var PRESS_EVERY = 180;
  var BACK_AT = 1980;
  var BACK_TO = 3;
  var TONES = ['is-mint', 'is-lilac', 'is-pink', 'is-sky'];

  var root = document.getElementById('pgRoot');
  var trail = document.getElementById('pgTrail');
  var line = document.getElementById('pgLine');
  var nextBtn = document.getElementById('pgNext');
  var card = document.getElementById('pgCard');
  var noEl = document.getElementById('pgNo');
  var cursorEl = document.getElementById('pgCursor');
  var sr = document.getElementById('pgSr');
  var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;

  function cursorOf(n) { return (Math.imul(n, 2654435761) >>> 0).toString(16).slice(-4); }

  var dots = [];
  var born = [];
  for (var i = 0; i < END_AT; i += 1) {
    var d = document.createElement('button');
    d.type = 'button';
    d.className = 'pg__dot';
    d.setAttribute('aria-label', String(i + 1));
    d.tabIndex = -1;
    trail.appendChild(d);
    dots.push(d);
    born.push(-1);
  }

  var cur = 1;
  var reached = 1;
  var gapShown = 0;
  var t0 = null;
  var lastTs = null;
  var cycleBase = 0;
  var pressed = 0;
  var wentBack = false;

  function perfNow() { return t0 === null ? 0 : performance.now() - t0; }

  function sync(now, announce) {
    noEl.textContent = String(cur);
    cursorEl.textContent = cursorOf(cur);
    card.className = 'pg__card ' + TONES[cur % TONES.length];
    var atEnd = cur === END_AT;
    nextBtn.setAttribute('aria-disabled', atEnd ? 'true' : 'false');
    nextBtn.textContent = atEnd ? 'End' : 'Next';
    nextBtn.className = 'pg__next' + (atEnd ? ' is-end' : '');
    for (var s = 0; s < END_AT; s += 1) {
      var seen = s + 1 <= reached;
      dots[s].className = 'pg__dot' + (seen ? ' is-seen' : '') + (s + 1 === cur ? ' is-cur' : '');
      dots[s].tabIndex = seen ? 0 : -1;
      dots[s].setAttribute('aria-hidden', seen ? 'false' : 'true');
      if (s + 1 === cur) dots[s].setAttribute('aria-current', 'page'); else dots[s].removeAttribute('aria-current');
    }
    if (announce) sr.textContent = 'Page ' + cur;
  }

  function goNext(byUser, now) {
    if (byUser) root.classList.remove('is-demo');
    if (cur >= END_AT) return;
    cur += 1;
    if (cur > reached) { reached = cur; if (!reduce) born[cur - 1] = now; }
    sync(now, byUser);
  }

  function goBack(page, byUser, now) {
    if (byUser) root.classList.remove('is-demo');
    if (page < 1 || page > reached || page === cur) return;
    cur = page;
    sync(now, byUser);
  }

  nextBtn.addEventListener('click', function () { goNext(true, perfNow()); });
  trail.addEventListener('click', function (e) { var idx = dots.indexOf(e.target); if (idx >= 0) goBack(idx + 1, true, perfNow()); });
  root.addEventListener('keydown', function (e) {
    if (e.key === 'ArrowRight') { e.preventDefault(); goNext(true, perfNow()); }
    else if (e.key === 'ArrowLeft') { e.preventDefault(); goBack(cur - 1, true, perfNow()); }
  });

  function popScale(age) {
    if (age < 0 || age >= POP_MS) return 1;
    return 1 - Math.exp(-age / 65) * Math.cos(age / 50);
  }

  function paint(now, dt) {
    var n = Math.max(2, reached);
    var targetGap = Math.min(MAX_GAP, TRAIL_W / (n - 1));
    gapShown = reduce ? targetGap : gapShown + (targetGap - gapShown) * (1 - Math.exp(-dt * GAP_RATE));
    for (var s = 0; s < END_AT; s += 1) {
      var seen = s + 1 <= reached;
      var sc = seen ? popScale(now - born[s]) : 0;
      if (seen && sc === 1) born[s] = -1;
      dots[s].style.opacity = seen ? '1' : '0';
      dots[s].style.transform = 'translateX(' + (s * gapShown).toFixed(2) + 'px) scale(' + sc.toFixed(3) + ')';
    }
    line.style.transform = 'scaleX(' + (((reached - 1) * gapShown) / TRAIL_W).toFixed(4) + ')';
  }

  function tick(ts) {
    if (t0 === null) t0 = ts;
    var now = ts - t0;
    var dt = lastTs === null ? 0.016 : Math.min(0.05, (ts - lastTs) / 1000);
    lastTs = ts;
    if (root.classList.contains('is-demo')) {
      var t = now - cycleBase;
      while (pressed < END_AT - 1 && t >= PRESS_START + pressed * PRESS_EVERY) { goNext(false, now); pressed += 1; }
      if (!wentBack && t >= BACK_AT) { wentBack = true; goBack(BACK_TO, false, now); }
      if (t >= CYCLE_MS) {
        cycleBase = now; pressed = 0; wentBack = false;
        cur = 1; reached = 1; gapShown = 0;
        for (var q = 0; q < END_AT; q += 1) born[q] = -1;
        sync(now, false);
      }
    }
    paint(now, dt);
    requestAnimationFrame(tick);
  }

  sync(0, false);
  if (reduce) {
    root.classList.remove('is-demo');
    paint(0, 1);
  } else {
    requestAnimationFrame(tick);
  }
  if (reduce) {
    nextBtn.addEventListener('click', function () { paint(0, 1); });
    trail.addEventListener('click', function () { paint(0, 1); });
  }
})();

// CursorTrailPager — vanilla 판(08-pager-cursor-next-only-breadcrumb-trail) 의 React 포트.
// 전체 쪽수를 모르는 목록은 다음 커서만 받는다. 지나온 쪽은 점으로 남고, 점이 늘면 간격이 줄어 길이가 일정하다.
import { useEffect, useRef } from "react";
import styles from "./CursorTrailPager.module.scss";

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

const END_AT = 9;
const TRAIL_W = 232;
const MAX_GAP = 36;
const GAP_RATE = 12;
const POP_MS = 420;
const CYCLE_MS = 2700;
const PRESS_START = 140;
const PRESS_EVERY = 180;
const BACK_AT = 1980;
const BACK_TO = 3;
const TONES = ["is-mint", "is-lilac", "is-pink", "is-sky"];

const cursorOf = (n: number): string => (Math.imul(n, 2654435761) >>> 0).toString(16).slice(-4);

export default function CursorTrailPager() {
  const rootRef = useRef<HTMLDivElement | null>(null) as Box<HTMLDivElement | null>;
  const trailRef = useRef<HTMLDivElement | null>(null) as Box<HTMLDivElement | null>;
  const lineRef = useRef<HTMLElement | null>(null) as Box<HTMLElement | null>;
  const nextRef = useRef<HTMLButtonElement | null>(null) as Box<HTMLButtonElement | null>;
  const cardRef = useRef<HTMLDivElement | null>(null) as Box<HTMLDivElement | null>;
  const noRef = useRef<HTMLElement | null>(null) as Box<HTMLElement | null>;
  const cursorRef = useRef<HTMLSpanElement | null>(null) as Box<HTMLSpanElement | null>;
  const srRef = useRef<HTMLParagraphElement | null>(null) as Box<HTMLParagraphElement | null>;
  const dotRefs = useRef<Array<HTMLButtonElement | null>>([]) as Box<Array<HTMLButtonElement | null>>;

  useEffect(() => {
    const root = rootRef.current;
    const trail = trailRef.current;
    const line = lineRef.current;
    const nextBtn = nextRef.current;
    const card = cardRef.current;
    const noEl = noRef.current;
    const cursorEl = cursorRef.current;
    const sr = srRef.current;
    if (!root || !trail || !line || !nextBtn || !card || !noEl || !cursorEl || !sr) return;
    const dots = dotRefs.current;
    const reduce = window.matchMedia("(prefers-reduced-motion: reduce)").matches;
    const born: number[] = [];
    for (let i = 0; i < END_AT; i += 1) born.push(-1);

    let demo = true;
    let cur = 1;
    let reached = 1;
    let gapShown = 0;
    let t0: number | null = null;
    let lastTs: number | null = null;
    let cycleBase = 0;
    let pressed = 0;
    let wentBack = false;
    let raf = 0;
    const perfNow = (): number => (t0 === null ? 0 : performance.now() - t0);

    function sync(announce: boolean): void {
      noEl!.textContent = String(cur);
      cursorEl!.textContent = cursorOf(cur);
      card!.className = [styles.pg__card, styles[TONES[cur % TONES.length]]].join(" ");
      const atEnd = cur === END_AT;
      nextBtn!.setAttribute("aria-disabled", atEnd ? "true" : "false");
      nextBtn!.textContent = atEnd ? "끝" : "다음";
      nextBtn!.className = [styles.pg__next, atEnd ? styles["is-end"] : ""].join(" ");
      for (let s = 0; s < END_AT; s += 1) {
        const el = dots[s];
        if (!el) continue;
        const seen = s + 1 <= reached;
        el.className = [styles.pg__dot, seen ? styles["is-seen"] : "", s + 1 === cur ? styles["is-cur"] : ""].join(" ");
        el.tabIndex = seen ? 0 : -1;
        el.setAttribute("aria-hidden", seen ? "false" : "true");
        if (s + 1 === cur) el.setAttribute("aria-current", "page"); else el.removeAttribute("aria-current");
      }
      if (announce) sr!.textContent = "현재 " + cur;
    }

    function goNext(byUser: boolean, now: number): void {
      if (byUser) demo = false;
      if (cur >= END_AT) return;
      cur += 1;
      if (cur > reached) { reached = cur; if (!reduce) born[cur - 1] = now; }
      sync(byUser);
    }

    function goBack(p: number, byUser: boolean): void {
      if (byUser) demo = false;
      if (p < 1 || p > reached || p === cur) return;
      cur = p;
      sync(byUser);
    }

    const popScale = (age: number): number => (age < 0 || age >= POP_MS ? 1 : 1 - Math.exp(-age / 65) * Math.cos(age / 50));

    function paint(now: number, dt: number): void {
      const n = Math.max(2, reached);
      const targetGap = Math.min(MAX_GAP, TRAIL_W / (n - 1));
      gapShown = reduce ? targetGap : gapShown + (targetGap - gapShown) * (1 - Math.exp(-dt * GAP_RATE));
      for (let s = 0; s < END_AT; s += 1) {
        const el = dots[s];
        if (!el) continue;
        const seen = s + 1 <= reached;
        const sc = seen ? popScale(now - born[s]) : 0;
        if (seen && sc === 1) born[s] = -1;
        el.style.opacity = seen ? "1" : "0";
        el.style.transform = "translateX(" + (s * gapShown).toFixed(2) + "px) scale(" + sc.toFixed(3) + ")";
      }
      line!.style.transform = "scaleX(" + (((reached - 1) * gapShown) / TRAIL_W).toFixed(4) + ")";
    }

    const onNext = (): void => goNext(true, perfNow());
    const onTrail = (e: MouseEvent): void => {
      const idx = dots.indexOf(e.target as HTMLButtonElement);
      if (idx >= 0) goBack(idx + 1, true);
    };
    const onKey = (e: KeyboardEvent): void => {
      if (e.key === "ArrowRight") { e.preventDefault(); goNext(true, perfNow()); }
      else if (e.key === "ArrowLeft") { e.preventDefault(); goBack(cur - 1, true); }
    };
    const onReduceClick = (): void => paint(0, 1);
    nextBtn.addEventListener("click", onNext);
    trail.addEventListener("click", onTrail);
    root.addEventListener("keydown", onKey);

    function tick(ts: number): void {
      if (t0 === null) t0 = ts;
      const now = ts - t0;
      const dt = lastTs === null ? 0.016 : Math.min(0.05, (ts - lastTs) / 1000);
      lastTs = ts;
      if (demo) {
        const t = now - cycleBase;
        while (pressed < END_AT - 1 && t >= PRESS_START + pressed * PRESS_EVERY) { goNext(false, now); pressed += 1; }
        if (!wentBack && t >= BACK_AT) { wentBack = true; goBack(BACK_TO, false); }
        if (t >= CYCLE_MS) {
          cycleBase = now; pressed = 0; wentBack = false;
          cur = 1; reached = 1; gapShown = 0;
          for (let q = 0; q < END_AT; q += 1) born[q] = -1;
          sync(false);
        }
      }
      paint(now, dt);
      raf = requestAnimationFrame(tick);
    }

    sync(false);
    if (reduce) {
      demo = false;
      paint(0, 1);
      nextBtn.addEventListener("click", onReduceClick);
      trail.addEventListener("click", onReduceClick);
    } else {
      raf = requestAnimationFrame(tick);
    }
    return () => {
      cancelAnimationFrame(raf);
      nextBtn.removeEventListener("click", onNext);
      trail.removeEventListener("click", onTrail);
      root.removeEventListener("keydown", onKey);
      nextBtn.removeEventListener("click", onReduceClick);
      trail.removeEventListener("click", onReduceClick);
    };
  }, []);

  return (
    <main className={styles.stage}>
      <div className={styles.pg} ref={rootRef}>
        <div className={[styles.pg__card, styles["is-mint"]].join(" ")} ref={cardRef} aria-hidden="true">
          <b className={styles.pg__no} ref={noRef}>1</b>
          <span className={styles.pg__cursor} ref={cursorRef}>0000</span>
        </div>
        <nav className={styles.pg__nav} aria-label="페이지 이동">
          <button type="button" className={styles.pg__next} ref={nextRef}>다음</button>
        </nav>
        <div className={styles.pg__trail} ref={trailRef} aria-label="지나온 쪽">
          <i className={styles.pg__line} ref={lineRef} aria-hidden="true"></i>
          {Array.from({ length: END_AT }, (_, i) => (
            <button type="button" className={styles.pg__dot} key={i} tabIndex={-1} aria-label={String(i + 1)} ref={(el: HTMLButtonElement | null) => { dotRefs.current[i] = el; }}></button>
          ))}
        </div>
        <p className={styles.pg__sr} ref={srRef} aria-live="polite"></p>
      </div>
    </main>
  );
}