04Notch tab — a groove is cut into the selected tab's corner by a notch-depth value

<main class="stage">
<div class="wrap is-demo" id="wrap">
  <div class="tabs" id="tabs" role="tablist" aria-label="Switch notch tab">
    <button class="tab" id="tab0" role="tab" aria-selected="true" tabindex="0" type="button">One</button>
    <button class="tab" id="tab1" role="tab" aria-selected="false" tabindex="-1" type="button">Two</button>
    <button class="tab" id="tab2" role="tab" aria-selected="false" tabindex="-1" type="button">Three</button>
  </div>
  <p class="readout" id="readout" aria-live="polite">Notch depth 0.0</p>
</div>
</main>

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

// 계산 겹은 index.html 에 있다 — 탭이 바뀔 때 노치 깊이가 감쇠 진동(스프링 오버슛)으로 안정된다.
@include stage($stage-paper);

.wrap {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: $sp-4;
}

.tabs {
  display: flex;
  gap: $sp-2;
  background: $subject-cream;
  padding: $sp-2;
  border-radius: $r-control;
}

.tab {
  appearance: none;
  border: none;
  padding: $sp-2 $sp-6;
  font-size: 14px;
  font-weight: 700;
  color: $subject-ink;
  background: $subject-lilac;
  corner-shape: notch;
  border-radius: $r-xs;
  cursor: pointer;

  &[aria-selected="true"] { background: $subject-sky; }
  &:focus-visible { outline: 2px solid $subject-ink; outline-offset: 2px; }
}

@supports not (corner-shape: notch) {
  .tab { border: 1px solid rgba($subject-ink, .2); }
}

.readout {
  margin: 0;
  color: $subject-ink;
  font-size: 13px;
  font-weight: 600;
  font-variant-numeric: tabular-nums;
}

@media (max-width: 340px) {
  .tab { padding: $sp-1 $sp-4; font-size: 13px; }
}

@media (prefers-reduced-motion: reduce) {
  .tab { transition: none; }
}

html, body {
  margin: 0;
  overflow: hidden;
}

.stage {
  box-sizing: border-box;
  min-height: 100vh;
  display: grid;
  place-items: center;
  margin: 0;
  background: #ffffff;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  padding: clamp(8px, 4vw, 24px);
}

.wrap {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 16px;
}

.tabs {
  display: flex;
  gap: 8px;
  background: #fff7e6;
  padding: 8px;
  border-radius: 12px;
}

.tab {
  appearance: none;
  border: none;
  padding: 8px 24px;
  font-size: 14px;
  font-weight: 700;
  color: #17141a;
  background: #b9a0ff;
  corner-shape: notch;
  border-radius: 4px;
  cursor: pointer;
}
.tab[aria-selected=true] {
  background: #6ec8ff;
}
.tab:focus-visible {
  outline: 2px solid #17141a;
  outline-offset: 2px;
}

@supports not (corner-shape: notch) {
  .tab {
    border: 1px solid rgba(23, 20, 26, 0.2);
  }
}
.readout {
  margin: 0;
  color: #17141a;
  font-size: 13px;
  font-weight: 600;
  font-variant-numeric: tabular-nums;
}

@media (max-width: 340px) {
  .tab {
    padding: 4px 16px;
    font-size: 13px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .tab {
    transition: none;
  }
}

(function () {
  var NOTCH_MAX = 14; // 활성 탭이 도달하는 Notch depth 상한(px)
  var SPRING_MS = 560; // 탭이 바뀐 뒤 스프링이 안정되기까지 걸리는 시간
  var AUTO_MS = 1700; // 자동 루프에서 탭이 한 칸 넘어가는 간격
  var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;
  var SUPPORTS = CSS.supports('corner-shape', 'notch');

  var wrap = document.getElementById('wrap');
  var tabs = [document.getElementById('tab0'), document.getElementById('tab1'), document.getElementById('tab2')];
  var readout = document.getElementById('readout');
  var isDemo = true;
  var active = 0;
  var phaseStart = 0;

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

  // 계산 겹: 탭이 바뀔 때 노치 깊이가 목표값을 살짝 넘겼다가 가라앉는 감쇠 진동(스프링 오버슛)으로 움직인다
  function springOvershoot(t) {
    if (t <= 0) return 0;
    if (t >= 1) return 1;
    var c4 = (2 * Math.PI) / 3;
    return Math.pow(2, -10 * t) * Math.sin((t * 10 - 0.75) * c4) + 1;
  }

  function applyDepth(tab, depth) {
    if (SUPPORTS) {
      tab.style.cornerShape = 'notch';
      tab.style.borderRadius = Math.max(0, depth).toFixed(2) + 'px';
    } else {
      // 근사 폴백: 파인 노치 대신 같은 크기의 둥근 모서리로 흉내(파임/둥긂만 다르다)
      tab.style.borderRadius = Math.max(0, depth).toFixed(2) + 'px';
    }
  }

  function setActive(i, ts) {
    if (active === i) return;
    tabs[active].setAttribute('aria-selected', 'false');
    tabs[active].tabIndex = -1;
    applyDepth(tabs[active], 0);
    active = i;
    tabs[active].setAttribute('aria-selected', 'true');
    tabs[active].tabIndex = 0;
    phaseStart = ts || performance.now();
  }

  tabs.forEach(function (tab, i) {
    tab.addEventListener('click', function () { human(); setActive(i, performance.now()); tab.focus({ preventScroll: true }); });
  });
  document.getElementById('tabs').addEventListener('keydown', function (e) {
    if (e.key !== 'ArrowRight' && e.key !== 'ArrowLeft') return;
    e.preventDefault();
    human();
    var next = e.key === 'ArrowRight' ? (active + 1) % tabs.length : (active + tabs.length - 1) % tabs.length;
    setActive(next, performance.now());
    tabs[next].focus({ preventScroll: true });
  });

  var start = 0;
  function loop(ts) {
    if (!start) { start = ts; phaseStart = ts; }
    if (isDemo && !reduce) {
      var cyclePos = Math.floor((ts - start) / AUTO_MS) % tabs.length;
      if (cyclePos !== active) setActive(cyclePos, ts);
    }
    var elapsed = reduce ? 1 : Math.min(1, (ts - phaseStart) / SPRING_MS);
    var depth = NOTCH_MAX * (reduce ? 1 : springOvershoot(elapsed));
    applyDepth(tabs[active], depth);
    readout.textContent = 'Notch depth ' + Math.max(0, depth).toFixed(1);
    requestAnimationFrame(loop);
  }
  requestAnimationFrame(loop);
})();

// NotchTab — vanilla 판(run/372/demo/04-corner-shape-notch-tab/index.html) 의 React 포트.
// 탭이 바뀔 때 노치 깊이가 목표값을 살짝 넘겼다가 가라앉는 감쇠 진동(스프링 오버슛)으로 움직인다.
import { useEffect, useRef } from "react";
import styles from "./NotchTab.module.scss";

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

const NOTCH_MAX = 14; // 활성 탭이 도달하는 노치 깊이 상한(px)
const SPRING_MS = 560; // 탭이 바뀐 뒤 스프링이 안정되기까지 걸리는 시간
const AUTO_MS = 1700; // 자동 루프에서 탭이 한 칸 넘어가는 간격
const LABELS = ["하나", "둘", "셋"];

export default function NotchTab() {
  const rootRef = useRef(null) as unknown as Box<HTMLDivElement>;
  const tabsRef = useRef(null) as unknown as Box<HTMLDivElement>;
  const tabRefs = useRef([]) as unknown as Box<HTMLButtonElement[]>;
  const readoutRef = useRef(null) as unknown as Box<HTMLParagraphElement>;
  const rafRef = useRef(0) as unknown as Box<number>;

  useEffect(() => {
    const reduce = window.matchMedia("(prefers-reduced-motion: reduce)").matches;
    const SUPPORTS = CSS.supports("corner-shape", "notch");

    const root = rootRef.current;
    const tabsEl = tabsRef.current;
    const tabs = tabRefs.current;
    const readout = readoutRef.current;
    if (!root || !tabsEl || tabs.length === 0 || !readout) return;

    let isDemo = true;
    let active = 0;
    let phaseStart = 0;

    function human() { if (isDemo) { root!.classList.remove(styles.isDemo); isDemo = false; } }

    // 계산 겹: 탭이 바뀔 때 노치 깊이가 목표값을 살짝 넘겼다가 가라앉는 감쇠 진동(스프링 오버슛)으로 움직인다
    function springOvershoot(t: number) {
      if (t <= 0) return 0;
      if (t >= 1) return 1;
      const c4 = (2 * Math.PI) / 3;
      return Math.pow(2, -10 * t) * Math.sin((t * 10 - 0.75) * c4) + 1;
    }

    function applyDepth(tab: HTMLButtonElement, depth: number) {
      if (SUPPORTS) (tab.style as any).cornerShape = "notch";
      tab.style.borderRadius = Math.max(0, depth).toFixed(2) + "px";
    }

    function setActive(i: number, ts: number) {
      if (active === i) return;
      tabs[active].setAttribute("aria-selected", "false");
      tabs[active].tabIndex = -1;
      applyDepth(tabs[active], 0);
      active = i;
      tabs[active].setAttribute("aria-selected", "true");
      tabs[active].tabIndex = 0;
      phaseStart = ts;
    }

    const onTabClick = (i: number) => () => { human(); setActive(i, performance.now()); tabs[i].focus({ preventScroll: true }); };
    const clickHandlers = tabs.map((_, i) => onTabClick(i));
    tabs.forEach((tab, i) => tab.addEventListener("click", clickHandlers[i]));

    function onKeyDown(e: KeyboardEvent) {
      if (e.key !== "ArrowRight" && e.key !== "ArrowLeft") return;
      e.preventDefault();
      human();
      const next = e.key === "ArrowRight" ? (active + 1) % tabs.length : (active + tabs.length - 1) % tabs.length;
      setActive(next, performance.now());
      tabs[next].focus({ preventScroll: true });
    }
    tabsEl.addEventListener("keydown", onKeyDown);

    let start = 0;
    function loop(ts: number) {
      if (!start) { start = ts; phaseStart = ts; }
      if (isDemo && !reduce) {
        const cyclePos = Math.floor((ts - start) / AUTO_MS) % tabs.length;
        if (cyclePos !== active) setActive(cyclePos, ts);
      }
      const elapsed = reduce ? 1 : Math.min(1, (ts - phaseStart) / SPRING_MS);
      const depth = NOTCH_MAX * (reduce ? 1 : springOvershoot(elapsed));
      applyDepth(tabs[active], depth);
      readout!.textContent = "노치 깊이 " + Math.max(0, depth).toFixed(1);
      rafRef.current = requestAnimationFrame(loop);
    }
    rafRef.current = requestAnimationFrame(loop);

    return () => {
      tabs.forEach((tab, i) => tab.removeEventListener("click", clickHandlers[i]));
      tabsEl.removeEventListener("keydown", onKeyDown);
      cancelAnimationFrame(rafRef.current);
    };
  }, []);

  return (
    <main className={styles.stage}>
      <div className={styles.wrap + " " + styles.isDemo} ref={rootRef}>
        <div className={styles.tabs} ref={tabsRef} role="tablist" aria-label="노치 탭 전환">
          {LABELS.map((label, i) => (
            <button
              key={label}
              className={styles.tab}
              ref={(el: HTMLButtonElement | null) => { if (el) tabRefs.current[i] = el; }}
              role="tab"
              aria-selected={i === 0}
              tabIndex={i === 0 ? 0 : -1}
              type="button"
            >{label}</button>
          ))}
        </div>
        <p className={styles.readout} ref={readoutRef} aria-live="polite">노치 깊이 0.0</p>
      </div>
    </main>
  );
}