05幅に合わせた自動短縮

<main class="stage">
  <div class="at is-demo">
    <div class="at__frame" id="at-frame">
      <div class="at__panel" id="at-panel">
        <nav class="at__nav" aria-label="パンくずリスト" id="at-nav">
          <ol class="at__list" id="at-list">
            <li class="at__item">
              <a class="at__crumb" href="#">ホーム</a>
              <span class="at__sep" aria-hidden="true"><svg viewBox="0 0 256 256" width="12" height="12" aria-hidden="true"><g fill="currentColor"><path d="m176 128l-80 80V48Z" opacity=".2"/><path d="m181.66 122.34l-80-80A8 8 0 0 0 88 48v160a8 8 0 0 0 13.66 5.66l80-80a8 8 0 0 0 0-11.32M104 188.69V67.31L164.69 128Z"/></g></svg></span>
            </li>
            <li class="at__item" id="at-dots" hidden>
              <span class="at__crumb at__crumb--dots" aria-label="隠れた階層"><svg viewBox="0 0 256 256" width="16" height="16" aria-hidden="true"><g fill="currentColor"><path d="M240 96v64a16 16 0 0 1-16 16H32a16 16 0 0 1-16-16V96a16 16 0 0 1 16-16h192a16 16 0 0 1 16 16" opacity=".2"/><path d="M140 128a12 12 0 1 1-12-12a12 12 0 0 1 12 12m56-12a12 12 0 1 0 12 12a12 12 0 0 0-12-12m-136 0a12 12 0 1 0 12 12a12 12 0 0 0-12-12"/></g></svg></span>
              <span class="at__sep" aria-hidden="true"><svg viewBox="0 0 256 256" width="12" height="12" aria-hidden="true"><g fill="currentColor"><path d="m176 128l-80 80V48Z" opacity=".2"/><path d="m181.66 122.34l-80-80A8 8 0 0 0 88 48v160a8 8 0 0 0 13.66 5.66l80-80a8 8 0 0 0 0-11.32M104 188.69V67.31L164.69 128Z"/></g></svg></span>
            </li>
            <li class="at__item" data-hide>
              <a class="at__crumb" href="#">電子機器</a>
              <span class="at__sep" aria-hidden="true"><svg viewBox="0 0 256 256" width="12" height="12" aria-hidden="true"><g fill="currentColor"><path d="m176 128l-80 80V48Z" opacity=".2"/><path d="m181.66 122.34l-80-80A8 8 0 0 0 88 48v160a8 8 0 0 0 13.66 5.66l80-80a8 8 0 0 0 0-11.32M104 188.69V67.31L164.69 128Z"/></g></svg></span>
            </li>
            <li class="at__item" data-hide>
              <a class="at__crumb" href="#">コンピューター</a>
              <span class="at__sep" aria-hidden="true"><svg viewBox="0 0 256 256" width="12" height="12" aria-hidden="true"><g fill="currentColor"><path d="m176 128l-80 80V48Z" opacity=".2"/><path d="m181.66 122.34l-80-80A8 8 0 0 0 88 48v160a8 8 0 0 0 13.66 5.66l80-80a8 8 0 0 0 0-11.32M104 188.69V67.31L164.69 128Z"/></g></svg></span>
            </li>
            <li class="at__item" data-hide>
              <a class="at__crumb" href="#">ノートPC</a>
              <span class="at__sep" aria-hidden="true"><svg viewBox="0 0 256 256" width="12" height="12" aria-hidden="true"><g fill="currentColor"><path d="m176 128l-80 80V48Z" opacity=".2"/><path d="m181.66 122.34l-80-80A8 8 0 0 0 88 48v160a8 8 0 0 0 13.66 5.66l80-80a8 8 0 0 0 0-11.32M104 188.69V67.31L164.69 128Z"/></g></svg></span>
            </li>
            <li class="at__item">
              <span class="at__crumb at__crumb--now" aria-current="page">13インチ ゲーミング</span>
            </li>
          </ol>
        </nav>
        <span class="at__handle" id="at-handle" role="separator" aria-orientation="vertical" aria-label="幅を調節" tabindex="0"></span>
      </div>
    </div>
    <p class="at__cap">ハンドルを引くと前の階層から隠れます</p>
  </div>
</main>

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

$duration: $dur-base;
$easing: $ease-spring;
$color: $subject-blue;

@include stage($stage-ink);

// flex 자식에는 hidden 이 안 먹는 경우가 있다 — 직접 못 박는다
[hidden] { display: none !important; }

.at {
  display: flex;
  flex-direction: column;
  align-items: center;
  width: min(432px, 88vw);
  color: $subject-cream;
  font-size: clamp(11px, 3vw, 13px);
  line-height: 18px;
  user-select: none;
  -webkit-user-select: none;
}

// 바깥 틀은 고정, 안쪽 패널만 폭이 변한다
.at__frame { width: 100%; }
.at__panel {
  box-sizing: border-box;
  display: flex;
  align-items: center;
  gap: $sp-2;
  width: 100%;
  padding: $sp-2;
  border: 1px solid rgba($subject-cream, .24);
  border-radius: $r-card;
  background: rgba($subject-cream, .10);
}

.at__nav {
  flex: 1 1 auto;
  min-width: 0;
  overflow: hidden;
}
// 자연 폭(max-content)으로 두되 칸 자리가 다 떨어지면 마지막 칸만 말줄임으로 줄어든다.
// JS 는 재는 순간에만 max-width 를 풀어 "진짜 넘치는가" 를 본다
.at__list {
  display: flex;
  align-items: center;
  width: max-content;
  max-width: 100%;
  margin: 0;
  padding: 0;
  list-style: none;
}
.at__item {
  flex: 0 0 auto;
  display: flex;
  align-items: center;
  white-space: nowrap;
}
.at__item:last-child { flex: 0 1 auto; min-width: 0; }
.at__sep {
  display: inline-flex;
  margin: 0 $sp-1;
  color: rgba($subject-cream, .42);
}
.at__sep svg { display: block; }

.at__crumb {
  display: inline-flex;
  align-items: center;
  padding: $sp-1 $sp-2;
  border-radius: $r-sm;
  background: rgba($subject-cream, .12);
  color: rgba($subject-cream, .82);
  font-weight: 600;
  line-height: 18px;
  text-decoration: none;
  white-space: nowrap;
}
.at__crumb:hover { background: rgba($subject-cream, .24); color: $subject-cream; }
.at__crumb:focus-visible { outline: 2px solid $subject-cream; outline-offset: 2px; }
.at__crumb--dots {
  padding: $sp-1;
  color: $subject-cream;
}
.at__crumb--dots svg { display: block; }
.at__crumb--now {
  display: block;
  min-width: 0;
  overflow: hidden;
  text-overflow: ellipsis;
  background: $subject-blue-deep;
  color: $subject-cream;
  font-weight: 800;
}
.at__crumb--now:hover { background: $subject-blue-deep; }

.at__handle {
  flex: 0 0 auto;
  width: 8px;
  height: 24px;
  border-radius: $r-pill;
  background: rgba($subject-cream, .62);
  cursor: col-resize;
  touch-action: none;
}
.at__handle:hover { background: $subject-cream; }
.at__handle:focus-visible { outline: 2px solid $color; outline-offset: 2px; }

.at__cap {
  margin: $sp-2 0 0;
  font-size: 11px;
  line-height: 14px;
  font-weight: 600;
  color: rgba($subject-cream, .58);
  text-align: center;
}

// ── 자동 루프(2초): 폭 100% → 46% → 100%. 진짜 ResizeObserver 가 반응해 칸이 사라졌다 돌아온다 ──
// 여기만 width 를 애니메이션한다 — 폭 변화 자체가 주제이고, 레이아웃이 다시 계산돼야 콜백이 돈다
.at.is-demo .at__panel {
  animation-name: at-squeeze;
  animation-duration: $dur-loop;
  animation-timing-function: $easing;
  animation-iteration-count: infinite;
}
@keyframes at-squeeze {
  0%, 8%    { width: 100%; }
  44%, 56%  { width: 46%; }
  86%, 100% { width: 100%; }
}

@media (prefers-reduced-motion: reduce) {
  .at.is-demo .at__panel { animation: none !important; width: 100%; }
  .at__crumb, .at__handle { transition: none; }
}

@media (max-width: 340px) {
  .at__panel { padding: $sp-1; }
  .at__crumb { padding: $sp-1; }
  .at__cap { margin-top: $sp-1; }
}

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);
}

[hidden] {
  display: none !important;
}

.at {
  display: flex;
  flex-direction: column;
  align-items: center;
  width: min(432px, 88vw);
  color: #fff7e6;
  font-size: clamp(11px, 3vw, 13px);
  line-height: 18px;
  user-select: none;
  -webkit-user-select: none;
}

.at__frame {
  width: 100%;
}

.at__panel {
  box-sizing: border-box;
  display: flex;
  align-items: center;
  gap: 8px;
  width: 100%;
  padding: 8px;
  border: 1px solid rgba(255, 247, 230, 0.24);
  border-radius: 16px;
  background: rgba(255, 247, 230, 0.1);
}

.at__nav {
  flex: 1 1 auto;
  min-width: 0;
  overflow: hidden;
}

.at__list {
  display: flex;
  align-items: center;
  width: max-content;
  max-width: 100%;
  margin: 0;
  padding: 0;
  list-style: none;
}

.at__item {
  flex: 0 0 auto;
  display: flex;
  align-items: center;
  white-space: nowrap;
}

.at__item:last-child {
  flex: 0 1 auto;
  min-width: 0;
}

.at__sep {
  display: inline-flex;
  margin: 0 4px;
  color: rgba(255, 247, 230, 0.42);
}

.at__sep svg {
  display: block;
}

.at__crumb {
  display: inline-flex;
  align-items: center;
  padding: 4px 8px;
  border-radius: 8px;
  background: rgba(255, 247, 230, 0.12);
  color: rgba(255, 247, 230, 0.82);
  font-weight: 600;
  line-height: 18px;
  text-decoration: none;
  white-space: nowrap;
}

.at__crumb:hover {
  background: rgba(255, 247, 230, 0.24);
  color: #fff7e6;
}

.at__crumb:focus-visible {
  outline: 2px solid #fff7e6;
  outline-offset: 2px;
}

.at__crumb--dots {
  padding: 4px;
  color: #fff7e6;
}

.at__crumb--dots svg {
  display: block;
}

.at__crumb--now {
  display: block;
  min-width: 0;
  overflow: hidden;
  text-overflow: ellipsis;
  background: #0a4fe8;
  color: #fff7e6;
  font-weight: 800;
}

.at__crumb--now:hover {
  background: #0a4fe8;
}

.at__handle {
  flex: 0 0 auto;
  width: 8px;
  height: 24px;
  border-radius: 999px;
  background: rgba(255, 247, 230, 0.62);
  cursor: col-resize;
  touch-action: none;
}

.at__handle:hover {
  background: #fff7e6;
}

.at__handle:focus-visible {
  outline: 2px solid #2f6df6;
  outline-offset: 2px;
}

.at__cap {
  margin: 8px 0 0;
  font-size: 11px;
  line-height: 14px;
  font-weight: 600;
  color: rgba(255, 247, 230, 0.58);
  text-align: center;
}

.at.is-demo .at__panel {
  animation-name: at-squeeze;
  animation-duration: 2s;
  animation-timing-function: cubic-bezier(0.2, 0.8, 0.2, 1);
  animation-iteration-count: infinite;
}

@keyframes at-squeeze {
  0%, 8% {
    width: 100%;
  }
  44%, 56% {
    width: 46%;
  }
  86%, 100% {
    width: 100%;
  }
}
@media (prefers-reduced-motion: reduce) {
  .at.is-demo .at__panel {
    animation: none !important;
    width: 100%;
  }
  .at__crumb, .at__handle {
    transition: none;
  }
}
@media (max-width: 340px) {
  .at__panel {
    padding: 4px;
  }
  .at__crumb {
    padding: 4px;
  }
  .at__cap {
    margin-top: 4px;
  }
}

// 실동작: ResizeObserver 가 패널 폭을 보고, 목록의 scrollWidth 가 넘치면 앞 단계부터 hidden 을 붙인다
var root = document.querySelector('.at');
var frame = document.getElementById('at-frame');
var panel = document.getElementById('at-panel');
var nav = document.getElementById('at-nav');
var list = document.getElementById('at-list');
var dots = document.getElementById('at-dots');
var handle = document.getElementById('at-handle');
var hideables = [].slice.call(list.querySelectorAll('[data-hide]'));
function fit() {
  list.style.maxWidth = 'none';           // 재는 동안만 자연 폭으로
  hideables.forEach(function (el) { el.hidden = false; });
  dots.hidden = true;
  for (var i = 0; i < hideables.length && list.scrollWidth > nav.clientWidth; i++) {
    dots.hidden = false;
    hideables[i].hidden = true;
  }
  list.style.maxWidth = '';
}
new ResizeObserver(fit).observe(panel);
function setW(px) {
  var fw = frame.clientWidth;
  var w = Math.max(104, Math.min(px, fw));
  panel.style.width = (w / fw * 100) + '%';
}
var isDragging = false;
handle.addEventListener('pointerdown', function (e) {
  root.classList.remove('is-demo');
  handle.setPointerCapture(e.pointerId);
  isDragging = true;
  e.preventDefault();
});
handle.addEventListener('pointermove', function (e) {
  if (!isDragging) return;
  setW(e.clientX - frame.getBoundingClientRect().left + 8);
});
handle.addEventListener('pointerup', function () { isDragging = false; });
handle.addEventListener('pointercancel', function () { isDragging = false; });
handle.addEventListener('keydown', function (e) {
  if (e.key !== 'ArrowLeft' && e.key !== 'ArrowRight') return;
  e.preventDefault();
  root.classList.remove('is-demo');
  setW(panel.getBoundingClientRect().width + (e.key === 'ArrowRight' ? 16 : -16));
});

import { useEffect, useRef, useState } from "react";
import type { CSSProperties, ReactNode } from "react";
import styles from "./AutoTruncate.module.scss";

export type AutoTruncateProps = {
  path?: string[];
  duration?: number;
  easing?: string;
  color?: string;
};

type KeyEvt = { key: string; preventDefault(): void };
type PtrEvt = { clientX: number; pointerId: number; preventDefault(): void };
type Vars = CSSProperties & { "--duration"?: string; "--easing"?: string; "--color"?: string };

const CaretRight = () => (
  <span className={styles.sep} aria-hidden="true"><svg viewBox="0 0 256 256" width="12" height="12" aria-hidden="true"><g fill="currentColor"><path d="m176 128l-80 80V48Z" opacity=".2"/><path d="m181.66 122.34l-80-80A8 8 0 0 0 88 48v160a8 8 0 0 0 13.66 5.66l80-80a8 8 0 0 0 0-11.32M104 188.69V67.31L164.69 128Z"/></g></svg></span>
);
const DotsThree = () => (
  <svg viewBox="0 0 256 256" width="16" height="16" aria-hidden="true"><g fill="currentColor"><path d="M240 96v64a16 16 0 0 1-16 16H32a16 16 0 0 1-16-16V96a16 16 0 0 1 16-16h192a16 16 0 0 1 16 16" opacity=".2"/><path d="M140 128a12 12 0 1 1-12-12a12 12 0 0 1 12 12m56-12a12 12 0 1 0 12 12a12 12 0 0 0-12-12m-136 0a12 12 0 1 0 12 12a12 12 0 0 0-12-12"/></g></svg>
);

export default function AutoTruncate({
  path = ["Home", "Electronics", "Computers", "Laptops", "13-inch gaming"],
  duration = 300,
  easing = "cubic-bezier(.2,.8,.2,1)",
  color = "#2f6df6",
}: AutoTruncateProps) {
  // 앞쪽(홈 다음)부터 몇 칸을 hidden 으로 숨겼는지
  const [cut, setCut] = useState(0);
  const frameRef = useRef<HTMLDivElement>(null);
  const panelRef = useRef<HTMLDivElement>(null);
  const navRef = useRef<HTMLElement>(null);
  const listRef = useRef<HTMLOListElement>(null);
  const dragging = useRef(false);
  const vars: Vars = { "--duration": `${duration}ms`, "--easing": easing, "--color": color };

  useEffect(() => {
    const panel = panelRef.current;
    const nav = navRef.current;
    const list = listRef.current;
    if (!panel || !nav || !list) return;
    // scrollWidth 가 clientWidth 를 넘으면 앞 단계부터 hidden — 재는 동안만 리스트를 자연 폭으로 편다
    const fit = (): void => {
      const middles = Array.prototype.filter.call(
        list.children, (el: HTMLElement) => el.dataset.hide === "1") as HTMLElement[];
      const dots = Array.prototype.find.call(
        list.children, (el: HTMLElement) => el.dataset.dots === "1") as HTMLElement | undefined;
      if (!middles.length || !dots) return;
      list.style.maxWidth = "none";
      middles.forEach((el: HTMLElement): void => { el.hidden = false; });
      dots.hidden = true;
      let n = 0;
      while (n < middles.length && list.scrollWidth > nav.clientWidth) {
        dots.hidden = false;
        middles[n].hidden = true;
        n++;
      }
      list.style.maxWidth = "";
      setCut(n);
    };
    const ro = new ResizeObserver(fit);
    ro.observe(panel);
    return () => ro.disconnect();
  }, []);

  function setW(px: number): void {
    const frame = frameRef.current;
    const panel = panelRef.current;
    if (!frame || !panel) return;
    const fw = frame.clientWidth;
    const w = Math.max(104, Math.min(px, fw));
    panel.style.width = `${(w / fw) * 100}%`;
  }
  function onDown(e: PtrEvt): void {
    dragging.current = true;
    e.preventDefault();
  }
  function onMove(e: PtrEvt): void {
    const frame = frameRef.current;
    if (!dragging.current || !frame) return;
    setW(e.clientX - frame.getBoundingClientRect().left + 8);
  }
  function onUp(): void { dragging.current = false; }
  function onKey(e: KeyEvt): void {
    if (e.key !== "ArrowLeft" && e.key !== "ArrowRight") return;
    e.preventDefault();
    const panel = panelRef.current;
    if (!panel) return;
    setW(panel.getBoundingClientRect().width + (e.key === "ArrowRight" ? 16 : -16));
  }

  const last = path.length - 1;
  const rows: ReactNode[] = [];
  path.forEach((name: string, i: number) => {
    if (i === last) {
      rows.push(
        <li className={styles.item} key={name}>
          <span className={`${styles.crumb} ${styles.now}`} aria-current="page">{name}</span>
        </li>
      );
      return;
    }
    rows.push(
      <li className={styles.item} key={name} data-hide={i > 0 ? "1" : undefined} hidden={i > 0 && i <= cut}>
        <a className={styles.crumb} href="#">{name}</a>
        <CaretRight />
      </li>
    );
    if (i === 0) {
      rows.push(
        <li className={styles.item} key={name + "-dots"} data-dots="1" hidden={cut === 0}>
          <span className={`${styles.crumb} ${styles.dots}`} aria-label="Hidden steps"><DotsThree /></span>
          <CaretRight />
        </li>
      );
    }
  });

  return (
    <div className={styles.at} style={vars}>
      <div className={styles.frame} ref={frameRef}>
        <div className={styles.panel} ref={panelRef}>
          <nav className={styles.nav} ref={navRef} aria-label="Breadcrumb">
            <ol className={styles.list} ref={listRef}>{rows}</ol>
          </nav>
          <span
            className={styles.handle}
            role="separator"
            aria-orientation="vertical"
            aria-label="Resize width"
            tabIndex={0}
            onPointerDown={onDown}
            onPointerMove={onMove}
            onPointerUp={onUp}
            onPointerCancel={onUp}
            onKeyDown={onKey}
          />
        </div>
      </div>
      <p className={styles.cap}>Drag the handle — front steps hide first</p>
    </div>
  );
}