07Hide on scroll

<main class="stage is-demo">
  <div class="layout">
    <nav class="rail" aria-label="Contents">
      <a class="rail__link" href="#">Overview</a>
      <a class="rail__link" href="#">Install</a>
      <a class="rail__link" href="#">Usage</a>
      <a class="rail__link" href="#">Troubleshooting</a>
    </nav>
    <div class="content" id="content">
      <p>Scroll this area down and the left rail steps aside.</p>
      <p>Scroll back up and the rail returns instantly.</p>
      <p>Keeps a table of contents from hogging screen space in long documents.</p>
      <p>The rail watches this content area's scroll, not the whole window.</p>
    </div>
  </div>
</main>

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

// ── 변수 3개 ──────────────────────────────────────────
$duration: $dur-quick;      // 220ms — 실제 스크롤 시 숨는 속도
$easing: $ease-out;
$color: $subject-cream;     // 레일 링크 강조색

// ── 데모 무대 ───────────────────────────────────────────
@include stage($stage-orange);

.layout {
  display: flex;
  width: min(90vw, 340px);
  height: min(50vw, 150px);
  border-radius: $r-card;
  overflow: hidden;
  background: $stage-paper;
  box-shadow: $shadow-raised;
}

.rail {
  flex: none;
  width: 96px;
  box-sizing: border-box;
  display: flex; flex-direction: column; gap: $sp-1;
  padding: $sp-3 $sp-2;
  background: $stage-ink;
  transform: translateX(0);
  transition: transform $duration $easing;
}
.rail__link {
  padding: $sp-1 $sp-2;
  border-radius: $r-xs;
  color: $stage-paper; text-decoration: none; font-weight: 500; font-size: 11px; line-height: 1.2; font-family: inherit;
  &:hover, &:focus-visible { color: $color; background: rgba($stage-paper, .12); }
}
.rail.is-hidden { transform: translateX(-100%); }

.content {
  flex: 1;
  overflow-y: auto;
  box-sizing: border-box;
  padding: $sp-3;
  display: flex; flex-direction: column; gap: $sp-4;
  color: $stage-ink;

  p { margin: 0; font-size: clamp(10px, 3vmin, 12px); line-height: 1.5; opacity: .8; }
}

// 데모 루프: 레일이 나갔다 들어왔다를 2초에 한 바퀴(실제 스크롤 여부와 무관)
.stage.is-demo .rail { animation: rail-loop $dur-loop ease-in-out infinite; }

@keyframes rail-loop {
  0%, 100% { transform: translateX(0); }
  40%, 70% { transform: translateX(-100%); }
}

@media (prefers-reduced-motion: reduce) {
  .stage.is-demo .rail { animation: none; }
  .rail { transition-duration: 1ms; }
}

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

.stage {
  box-sizing: border-box;
  min-height: 100vh;
  display: grid;
  place-items: center;
  margin: 0;
  background: #ff4d1f;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  padding: clamp(8px, 4vw, 24px);
}

.layout {
  display: flex;
  width: min(90vw, 340px);
  height: min(50vw, 150px);
  border-radius: 16px;
  overflow: hidden;
  background: #ffffff;
  box-shadow: 0 14px 24px rgba(23, 20, 26, 0.32);
}

.rail {
  flex: none;
  width: 96px;
  box-sizing: border-box;
  display: flex;
  flex-direction: column;
  gap: 4px;
  padding: 12px 8px;
  background: #17141a;
  transform: translateX(0);
  transition: transform 220ms ease-out;
}

.rail__link {
  padding: 4px 8px;
  border-radius: 4px;
  color: #ffffff;
  text-decoration: none;
  font-weight: 500;
  font-size: 11px;
  line-height: 1.2;
  font-family: inherit;
}
.rail__link:hover, .rail__link:focus-visible {
  color: #fff7e6;
  background: rgba(255, 255, 255, 0.12);
}

.rail.is-hidden {
  transform: translateX(-100%);
}

.content {
  flex: 1;
  overflow-y: auto;
  box-sizing: border-box;
  padding: 12px;
  display: flex;
  flex-direction: column;
  gap: 16px;
  color: #17141a;
}
.content p {
  margin: 0;
  font-size: clamp(10px, 3vmin, 12px);
  line-height: 1.5;
  opacity: 0.8;
}

.stage.is-demo .rail {
  animation: rail-loop 2s ease-in-out infinite;
}

@keyframes rail-loop {
  0%, 100% {
    transform: translateX(0);
  }
  40%, 70% {
    transform: translateX(-100%);
  }
}
@media (prefers-reduced-motion: reduce) {
  .stage.is-demo .rail {
    animation: none;
  }
  .rail {
    transition-duration: 1ms;
  }
}

// 콘텐츠 스크롤 방향을 비교해 레일을 translateX 로 숨기고 보인다. 실제 스크롤이 오면 데모 루프를 넘긴다.
(function () {
  var stage = document.querySelector('.stage');
  var rail = document.querySelector('.rail');
  var content = document.getElementById('content');
  var last = 0;
  content.addEventListener('scroll', function () {
    stage.classList.remove('is-demo');
    var y = content.scrollTop;
    if (y > last + 4) rail.classList.add('is-hidden');
    else if (y < last - 4) rail.classList.remove('is-hidden');
    last = y;
  });
})();

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

type ScrollEv = { currentTarget: HTMLDivElement };

export type ScrollHideRailProps = {
  duration?: number;
  easing?: string;
  color?: string;
};

const LINKS = ["개요", "설치", "사용법", "문제 해결"];

export default function ScrollHideRail({
  duration = 220,
  easing = "ease-out",
  color = "#fff7e6",
}: ScrollHideRailProps) {
  const [hidden, setHidden] = useState(false);
  const lastY = useRef(0);

  function onScroll(e: ScrollEv) {
    const y = e.currentTarget.scrollTop;
    const last = lastY.current ?? 0;
    if (y > last + 4) setHidden(true);
    else if (y < last - 4) setHidden(false);
    lastY.current = y;
  }

  const vars: CSSProperties = { "--duration": `${duration}ms`, "--easing": easing, "--color": color };

  return (
    <div className={styles.stage} style={vars}>
      <div className={styles.layout}>
        <nav className={styles.rail} data-hidden={hidden} aria-label="목차">
          {LINKS.map((label) => (
            <a key={label} className={styles.link} href="#">{label}</a>
          ))}
        </nav>
        <div className={styles.content} onScroll={onScroll}>
          <p>이 영역을 아래로 스크롤하면 왼쪽 레일이 비켜난다.</p>
          <p>다시 위로 스크롤하면 레일이 즉시 돌아온다.</p>
          <p>본문이 긴 문서에서 목차가 화면을 계속 차지하지 않게 한다.</p>
          <p>레일은 창 전체가 아니라 이 콘텐츠 영역의 스크롤만 본다.</p>
        </div>
      </div>
    </div>
  );
}