01枠の数が固定のページ窓

<main class="stage">
<div class="pg is-demo" id="pgRoot">
  <nav class="pg__nav" id="pgNav" aria-label="ページ移動"></nav>
  <div class="pg__kinds" id="pgKinds" aria-hidden="true"></div>
  <div class="pg__read">
    <span class="pg__k">現在</span><b id="pgCur">1</b>
    <span class="pg__k">全体</span><b id="pgTotal">40</b>
    <span class="pg__k">枠</span><b id="pgSlots">7</b>
  </div>
  <p class="pg__sr" id="pgSr" aria-live="polite"></p>
</div>
</main>

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

// 핵심: 칸 수(SLOT_COUNT)는 고정이고, 어느 쪽에서도 버튼 줄의 너비가 같다.
// 숫자가 바뀐 칸만 JS 가 transform 으로 살짝 튕긴다.

$slot-w: 32px;
$slot-gap: 4px;

@include stage($stage-ink);

.pg {
  display: grid;
  gap: $sp-3;
  justify-items: center;
  width: 100%;
  max-width: 320px;
  color: $stage-paper;
}

.pg__nav, .pg__kinds { display: flex; justify-content: center; gap: $slot-gap; width: 100%; }

.pg__b {
  box-sizing: border-box;
  flex: 0 1 $slot-w;
  min-width: 0;
  height: $slot-w;
  padding: 0;
  border: 1px solid rgba($stage-paper, .28);
  border-radius: $r-control;
  background: rgba($stage-paper, .08);
  color: $stage-paper;
  font-family: inherit;
  font-size: 13px;
  line-height: 16px;
  font-weight: 600;
  font-variant-numeric: tabular-nums;
  cursor: pointer;
}

.pg__b.is-cur { background: $subject-mint; border-color: $subject-mint; color: $subject-ink; }
.pg__b.is-gap { border-color: transparent; background: transparent; color: rgba($stage-paper, .72); cursor: default; }
.pg__b:focus-visible { outline: 2px solid $subject-sky; outline-offset: 2px; }

.pg__kind { flex: 0 1 $slot-w; min-width: 0; height: 4px; border-radius: $r-xs; background: rgba($stage-paper, .24); }
.pg__kind.is-win { background: rgba($subject-mint, .72); }
.pg__kind.is-edge { background: rgba($subject-lilac, .82); }

.pg__read {
  display: flex;
  align-items: baseline;
  gap: $sp-2;
  font-size: 12px;
  line-height: 16px;
}

.pg__k { color: rgba($stage-paper, .82); }
.pg__read b { color: $subject-sky; font-variant-numeric: tabular-nums; margin-right: $sp-2; }

.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: 12px; }
}

@media (prefers-reduced-motion: reduce) {
  .pg__b { transform: 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;
  width: 100%;
  max-width: 320px;
  color: #ffffff;
}

.pg__nav, .pg__kinds {
  display: flex;
  justify-content: center;
  gap: 4px;
  width: 100%;
}

.pg__b {
  box-sizing: border-box;
  flex: 0 1 32px;
  min-width: 0;
  height: 32px;
  padding: 0;
  border: 1px solid rgba(255, 255, 255, 0.28);
  border-radius: 12px;
  background: rgba(255, 255, 255, 0.08);
  color: #ffffff;
  font-family: inherit;
  font-size: 13px;
  line-height: 16px;
  font-weight: 600;
  font-variant-numeric: tabular-nums;
  cursor: pointer;
}

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

.pg__b.is-gap {
  border-color: transparent;
  background: transparent;
  color: rgba(255, 255, 255, 0.72);
  cursor: default;
}

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

.pg__kind {
  flex: 0 1 32px;
  min-width: 0;
  height: 4px;
  border-radius: 4px;
  background: rgba(255, 255, 255, 0.24);
}

.pg__kind.is-win {
  background: rgba(76, 212, 166, 0.72);
}

.pg__kind.is-edge {
  background: rgba(185, 160, 255, 0.82);
}

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

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

.pg__read b {
  color: #6ec8ff;
  font-variant-numeric: tabular-nums;
  margin-right: 8px;
}

.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: 12px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .pg__b {
    transform: none;
  }
}

(function () {
  // 기법: 어느 쪽에서도 버튼 枠 수(SLOT_COUNT)가 같도록 보이는 번호를 계산한다.
  // 양끝(첫·最後 쪽)은 항상 남기고, 現在 쪽이 한쪽 最後 가까이면 말줄임 하나만, 가운데면 말줄임 둘을 둔다.
  var SLOT_COUNT = 7;
  var TOTAL_PAGES = 40;
  var GAP = -1;
  var STEP_MS = 230;
  var START_MS = 120;
  var DEMO_PAGES = [1, 2, 4, 5, 9, 17, 26, 35, 37, 40, 36, 21, 3];

  function windowSlots(cur, total, slots) {
    var out = [];
    var i;
    if (total <= slots) {
      for (i = 1; i <= total; i += 1) out.push(i);
      return out;
    }
    var inner = slots - 4;
    if (cur <= slots - 3) {
      for (i = 1; i <= slots - 2; i += 1) out.push(i);
      out.push(GAP, total);
      return out;
    }
    if (cur >= total - slots + 4) {
      out.push(1, GAP);
      for (i = total - slots + 3; i <= total; i += 1) out.push(i);
      return out;
    }
    var lo = cur - Math.floor((inner - 1) / 2);
    out.push(1, GAP);
    for (i = 0; i < inner; i += 1) out.push(lo + i);
    out.push(GAP, total);
    return out;
  }

  var root = document.getElementById('pgRoot');
  var nav = document.getElementById('pgNav');
  var kindsEl = document.getElementById('pgKinds');
  var curEl = document.getElementById('pgCur');
  var sr = document.getElementById('pgSr');
  var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;

  var btns = [];
  var kinds = [];
  var pulse = [];
  var jump = [];
  for (var i = 0; i < SLOT_COUNT; i += 1) {
    var b = document.createElement('button');
    b.type = 'button';
    b.className = 'pg__b';
    nav.appendChild(b);
    btns.push(b);
    var k = document.createElement('span');
    k.className = 'pg__kind';
    kindsEl.appendChild(k);
    kinds.push(k);
    pulse.push(-1);
    jump.push(1);
  }

  document.getElementById('pgTotal').textContent = String(TOTAL_PAGES);
  document.getElementById('pgSlots').textContent = String(SLOT_COUNT);
  var cur = 1;
  var t0 = null;
  var lastStep = -1;
  var wantFocus = false;
  function perfNow() { return t0 === null ? 0 : performance.now() - t0; }

  function render(now) {
    var arr = windowSlots(cur, TOTAL_PAGES, SLOT_COUNT);
    for (var s = 0; s < SLOT_COUNT; s += 1) {
      var v = arr[s];
      var el = btns[s];
      var isGap = v === GAP;
      var txt = isGap ? '…' : String(v);
      if (el.textContent !== txt) {
        el.textContent = txt;
        if (!reduce) pulse[s] = now;
      }
      el.className = 'pg__b' + (isGap ? ' is-gap' : '') + (v === cur ? ' is-cur' : '');
      if (v === cur) { el.setAttribute('aria-current', 'page'); } else { el.removeAttribute('aria-current'); }
      el.setAttribute('aria-hidden', isGap ? 'true' : 'false');
      el.tabIndex = isGap ? -1 : 0;
      jump[s] = isGap ? Math.round((arr[s - 1] + arr[s + 1]) / 2) : v;
      kinds[s].className = 'pg__kind ' + (isGap ? 'is-gap' : (v === 1 || v === TOTAL_PAGES) ? 'is-edge' : 'is-win');
      if (v === cur && wantFocus) { el.focus({ preventScroll: true }); wantFocus = false; }
    }
    curEl.textContent = String(cur);
  }

  function go(n, byUser) {
    var next = Math.max(1, Math.min(TOTAL_PAGES, n));
    if (byUser) root.classList.remove('is-demo');
    if (next === cur) return;
    cur = next;
    render(perfNow());
    if (byUser) sr.textContent = '現在 ' + cur + ' / ' + TOTAL_PAGES;
  }

  nav.addEventListener('click', function (e) {
    var el = e.target;
    var idx = btns.indexOf(el);
    if (idx < 0) return;
    go(jump[idx], true);
  });
  nav.addEventListener('keydown', function (e) {
    var key = e.key;
    var to = null;
    if (key === 'ArrowRight') to = cur + 1;
    else if (key === 'ArrowLeft') to = cur - 1;
    else if (key === 'Home') to = 1;
    else if (key === 'End') to = TOTAL_PAGES;
    if (to === null) return;
    e.preventDefault();
    wantFocus = true;
    go(to, true);
    wantFocus = false;
  });

  function tick(ts) {
    if (t0 === null) t0 = ts;
    var now = ts - t0;
    if (root.classList.contains('is-demo')) {
      var step = now < START_MS ? 0 : Math.floor((now - START_MS) / STEP_MS) % DEMO_PAGES.length;
      if (step !== lastStep) {
        lastStep = step;
        cur = DEMO_PAGES[step];
        render(now);
      }
    }
    for (var s = 0; s < SLOT_COUNT; s += 1) {
      if (pulse[s] < 0) continue;
      var age = now - pulse[s];
      var sc = age >= 420 ? 1 : 1 - 0.5 * Math.exp(-age / 80) * Math.cos(age / 60);
      btns[s].style.transform = sc === 1 ? '' : 'scale(' + sc.toFixed(3) + ')';
      if (sc === 1) pulse[s] = -1;
    }
    requestAnimationFrame(tick);
  }

  if (reduce) {
    root.classList.remove('is-demo');
    cur = 17;
    render(0);
  } else {
    cur = DEMO_PAGES[0];
    render(0);
    requestAnimationFrame(tick);
  }
})();

// FixedSlotPager — vanilla 판(01-pager-fixed-slot-window-ellipsis-collapse) 의 React 포트.
// 어느 쪽에서도 버튼 칸 수(SLOT_COUNT)가 같도록 보이는 번호를 계산한다. 숫자가 바뀐 칸만 transform 으로 튕긴다.
import { useEffect, useRef } from "react";
import styles from "./FixedSlotPager.module.scss";

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

const SLOT_COUNT = 7;
const TOTAL_PAGES = 40;
const GAP = -1;
const STEP_MS = 230;
const START_MS = 120;
const DEMO_PAGES = [1, 2, 4, 5, 9, 17, 26, 35, 37, 40, 36, 21, 3];

function windowSlots(cur: number, total: number, slots: number): number[] {
  const out: number[] = [];
  if (total <= slots) {
    for (let i = 1; i <= total; i += 1) out.push(i);
    return out;
  }
  const inner = slots - 4;
  if (cur <= slots - 3) {
    for (let i = 1; i <= slots - 2; i += 1) out.push(i);
    out.push(GAP, total);
    return out;
  }
  if (cur >= total - slots + 4) {
    out.push(1, GAP);
    for (let i = total - slots + 3; i <= total; i += 1) out.push(i);
    return out;
  }
  const lo = cur - Math.floor((inner - 1) / 2);
  out.push(1, GAP);
  for (let i = 0; i < inner; i += 1) out.push(lo + i);
  out.push(GAP, total);
  return out;
}

export default function FixedSlotPager() {
  const navRef = useRef<HTMLElement | null>(null) as Box<HTMLElement | null>;
  const curRef = useRef<HTMLElement | null>(null) as Box<HTMLElement | null>;
  const srRef = useRef<HTMLParagraphElement | null>(null) as Box<HTMLParagraphElement | null>;
  const btnRefs = useRef<Array<HTMLButtonElement | null>>([]) as Box<Array<HTMLButtonElement | null>>;
  const kindRefs = useRef<Array<HTMLSpanElement | null>>([]) as Box<Array<HTMLSpanElement | null>>;

  useEffect(() => {
    const nav = navRef.current;
    const curEl = curRef.current;
    const sr = srRef.current;
    if (!nav || !curEl || !sr) return;
    const btns = btnRefs.current;
    const kinds = kindRefs.current;
    const reduce = window.matchMedia("(prefers-reduced-motion: reduce)").matches;
    const pulse: number[] = [];
    const jump: number[] = [];
    for (let i = 0; i < SLOT_COUNT; i += 1) { pulse.push(-1); jump.push(1); }

    let demo = true;
    let cur = 1;
    let t0: number | null = null;
    let lastStep = -1;
    let wantFocus = false;
    let raf = 0;
    const perfNow = (): number => (t0 === null ? 0 : performance.now() - t0);

    function render(now: number): void {
      const arr = windowSlots(cur, TOTAL_PAGES, SLOT_COUNT);
      for (let s = 0; s < SLOT_COUNT; s += 1) {
        const v = arr[s];
        const el = btns[s];
        const kind = kinds[s];
        if (!el || !kind) continue;
        const isGap = v === GAP;
        const txt = isGap ? "…" : String(v);
        if (el.textContent !== txt) {
          el.textContent = txt;
          if (!reduce) pulse[s] = now;
        }
        el.className = [styles.pg__b, isGap ? styles["is-gap"] : "", v === cur ? styles["is-cur"] : ""].join(" ");
        if (v === cur) el.setAttribute("aria-current", "page"); else el.removeAttribute("aria-current");
        el.setAttribute("aria-hidden", isGap ? "true" : "false");
        el.tabIndex = isGap ? -1 : 0;
        jump[s] = isGap ? Math.round((arr[s - 1] + arr[s + 1]) / 2) : v;
        const kindClass = isGap ? styles["is-gap"] : v === 1 || v === TOTAL_PAGES ? styles["is-edge"] : styles["is-win"];
        kind.className = [styles.pg__kind, kindClass].join(" ");
        if (v === cur && wantFocus) { el.focus({ preventScroll: true }); wantFocus = false; }
      }
      curEl!.textContent = String(cur);
    }

    function go(n: number, byUser: boolean): void {
      const next = Math.max(1, Math.min(TOTAL_PAGES, n));
      if (byUser) demo = false;
      if (next === cur) return;
      cur = next;
      render(perfNow());
      if (byUser) sr!.textContent = "현재 " + cur + " / " + TOTAL_PAGES;
    }

    const onClick = (e: MouseEvent): void => {
      const idx = btns.indexOf(e.target as HTMLButtonElement);
      if (idx >= 0) go(jump[idx], true);
    };
    const onKey = (e: KeyboardEvent): void => {
      let to: number | null = null;
      if (e.key === "ArrowRight") to = cur + 1;
      else if (e.key === "ArrowLeft") to = cur - 1;
      else if (e.key === "Home") to = 1;
      else if (e.key === "End") to = TOTAL_PAGES;
      if (to === null) return;
      e.preventDefault();
      wantFocus = true;
      go(to, true);
      wantFocus = false;
    };
    nav.addEventListener("click", onClick);
    nav.addEventListener("keydown", onKey);

    function tick(ts: number): void {
      if (t0 === null) t0 = ts;
      const now = ts - t0;
      if (demo) {
        const step = now < START_MS ? 0 : Math.floor((now - START_MS) / STEP_MS) % DEMO_PAGES.length;
        if (step !== lastStep) {
          lastStep = step;
          cur = DEMO_PAGES[step];
          render(now);
        }
      }
      for (let s = 0; s < SLOT_COUNT; s += 1) {
        if (pulse[s] < 0) continue;
        const age = now - pulse[s];
        const sc = age >= 420 ? 1 : 1 - 0.5 * Math.exp(-age / 80) * Math.cos(age / 60);
        const el = btns[s];
        if (el) el.style.transform = sc === 1 ? "" : "scale(" + sc.toFixed(3) + ")";
        if (sc === 1) pulse[s] = -1;
      }
      raf = requestAnimationFrame(tick);
    }

    if (reduce) {
      demo = false;
      cur = 17;
      render(0);
    } else {
      cur = DEMO_PAGES[0];
      render(0);
      raf = requestAnimationFrame(tick);
    }
    return () => {
      cancelAnimationFrame(raf);
      nav.removeEventListener("click", onClick);
      nav.removeEventListener("keydown", onKey);
    };
  }, []);

  return (
    <main className={styles.stage}>
      <div className={styles.pg}>
        <nav className={styles.pg__nav} ref={navRef} aria-label="페이지 이동">
          {Array.from({ length: SLOT_COUNT }, (_, i) => (
            <button type="button" className={styles.pg__b} key={i} ref={(el: HTMLButtonElement | null) => { btnRefs.current[i] = el; }}></button>
          ))}
        </nav>
        <div className={styles.pg__kinds} aria-hidden="true">
          {Array.from({ length: SLOT_COUNT }, (_, i) => (
            <span className={styles.pg__kind} key={i} ref={(el: HTMLSpanElement | null) => { kindRefs.current[i] = el; }}></span>
          ))}
        </div>
        <div className={styles.pg__read}>
          <span className={styles.pg__k}>현재</span><b ref={curRef}>1</b>
          <span className={styles.pg__k}>전체</span><b>{TOTAL_PAGES}</b>
          <span className={styles.pg__k}>칸</span><b>{SLOT_COUNT}</b>
        </div>
        <p className={styles.pg__sr} ref={srRef} aria-live="polite"></p>
      </div>
    </main>
  );
}