03Scroll that follows the cursor

<main class="stage">
  <div class="pal is-demo" role="dialog" aria-modal="true" aria-label="Command palette">
    <div class="pal__bar">
      <span class="pal__mag" aria-hidden="true"><svg viewBox="0 0 256 256" width="13" height="13"><g fill="currentColor"><path d="M192 112a80 80 0 1 1-80-80a80 80 0 0 1 80 80" opacity=".2"/><path d="m229.66 218.34l-50.06-50.06a88.21 88.21 0 1 0-11.32 11.31l50.06 50.07a8 8 0 0 0 11.32-11.32M40 112a72 72 0 1 1 72 72a72.08 72.08 0 0 1-72-72"/></g></svg></span>
      <input class="pal__input" id="q" type="text" role="combobox" aria-expanded="true" aria-controls="list" aria-label="Search commands" placeholder="Search commands" autocomplete="off">
      <kbd class="pal__kbd">↓</kbd>
    </div>
    <div class="pal__box" id="box">
      <span class="pal__cursor" aria-hidden="true"></span>
      <div class="pal__track" id="list" role="listbox" aria-label="Command palette">
        <div class="pal__opt" id="o1" role="option" aria-selected="false" tabindex="-1">Create document</div>
        <div class="pal__opt" id="o2" role="option" aria-selected="false" tabindex="-1">Create folder</div>
        <div class="pal__opt" id="o3" role="option" aria-selected="false" tabindex="-1">Invite member</div>
        <div class="pal__opt" id="o4" role="option" aria-selected="false" tabindex="-1">Mute notifications</div>
        <div class="pal__opt" id="o5" role="option" aria-selected="false" tabindex="-1">Change theme</div>
        <div class="pal__opt" id="o6" role="option" aria-selected="false" tabindex="-1">Export</div>
        <div class="pal__opt" id="o7" role="option" aria-selected="false" tabindex="-1">Sign out</div>
      </div>
    </div>
  </div>
</main>

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

$duration: $dur-quick;
$easing: $ease-out;
$color: $subject-blue;

@include stage($stage-orange);

.pal {
  box-sizing: border-box;
  width: min(264px, 88vw);
  padding: $sp-2;
  background: #fff;
  border-radius: $r-card;
  box-shadow: $shadow-raised;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  color: $subject-ink;
}

.pal__bar {
  box-sizing: border-box;
  height: 30px;
  display: flex; align-items: center; gap: $sp-2;
  padding: 0 $sp-2;
  border-radius: $r-sm;
  background: rgba(23, 20, 26, .05);
}
.pal__mag { display: inline-flex; color: rgba(23, 20, 26, .42); }
.pal__input {
  flex: 1 1 auto;
  min-width: 0;
  border: 0; background: transparent;
  font-family: inherit;
  font-size: 12px; font-weight: 600;
  color: $subject-ink;
}
.pal__input:focus-visible { outline: 2px solid $color; outline-offset: 2px; border-radius: $r-xs; }
.pal__kbd {
  flex: 0 0 auto;
  height: 14px;
  display: inline-flex; align-items: center;
  padding: 0 $sp-2;
  border-radius: $r-xs;
  background: #fff;
  box-shadow: 0 1px 0 rgba(23, 20, 26, .22);
  font-family: inherit;
  font-size: 9px; font-weight: 800;
  color: rgba(23, 20, 26, .5);
}

.pal__box {
  position: relative;
  box-sizing: border-box;
  height: 96px;
  margin: $sp-2 0 0;
  overflow-y: auto;
  overscroll-behavior: contain;
  scrollbar-width: none;
}
.pal__box::-webkit-scrollbar { width: 0; }
.pal__cursor {
  position: absolute;
  left: 0; top: 0;
  z-index: 0;
  width: 100%; height: 24px;
  border-radius: $r-sm;
  background: rgba(47, 109, 246, .14);
  opacity: 0;
}
.pal__track { position: relative; z-index: 1; }
.pal__opt {
  box-sizing: border-box;
  height: 24px;
  display: flex; align-items: center;
  padding: 0 $sp-2;
  border-radius: $r-sm;
  font-size: 12px; font-weight: 600;
  color: $subject-ink;   // 목록이 흰 상자 밖(주황 무대)으로 밀려 나온 줄까지 읽히게 — 알파 없이
  cursor: pointer;
}
.pal__opt.is-at { background: rgba(47, 109, 246, .14); color: $color; }

// ── 자동 루프: 커서가 넷째 줄까지 내려간 뒤로는 커서가 서고 목록이 대신 밀려 올라간다 ──
// 커서와 목록이 각각 transform 으로만 움직인다 (실제 scrollLeft·scrollTop 은 WAAPI 로 못 잰다)
.pal.is-demo .pal__cursor { opacity: 1; animation: cur-run $dur-loop $easing infinite; }
.pal.is-demo .pal__track { animation: track-follow $dur-loop $easing infinite; }
@keyframes cur-run {
  0%        { transform: translateY(0); }
  28%, 66%  { transform: translateY(72px); }
  90%, 100% { transform: translateY(0); }
}
@keyframes track-follow {
  0%, 28%   { transform: translateY(0); }
  52%, 66%  { transform: translateY(-72px); }
  90%, 100% { transform: translateY(0); }
}

@media (prefers-reduced-motion: reduce) {
  .pal.is-demo .pal__cursor,
  .pal.is-demo .pal__track { animation: none !important; }
  .pal.is-demo .pal__cursor { opacity: 1; }
}

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);
}

.pal {
  box-sizing: border-box;
  width: min(264px, 88vw);
  padding: 8px;
  background: #fff;
  border-radius: 16px;
  box-shadow: 0 14px 24px rgba(23, 20, 26, 0.32);
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  color: #17141a;
}

.pal__bar {
  box-sizing: border-box;
  height: 30px;
  display: flex;
  align-items: center;
  gap: 8px;
  padding: 0 8px;
  border-radius: 8px;
  background: rgba(23, 20, 26, 0.05);
}

.pal__mag {
  display: inline-flex;
  color: rgba(23, 20, 26, 0.42);
}

.pal__input {
  flex: 1 1 auto;
  min-width: 0;
  border: 0;
  background: transparent;
  font-family: inherit;
  font-size: 12px;
  font-weight: 600;
  color: #17141a;
}

.pal__input:focus-visible {
  outline: 2px solid #2f6df6;
  outline-offset: 2px;
  border-radius: 4px;
}

.pal__kbd {
  flex: 0 0 auto;
  height: 14px;
  display: inline-flex;
  align-items: center;
  padding: 0 8px;
  border-radius: 4px;
  background: #fff;
  box-shadow: 0 1px 0 rgba(23, 20, 26, 0.22);
  font-family: inherit;
  font-size: 9px;
  font-weight: 800;
  color: rgba(23, 20, 26, 0.5);
}

.pal__box {
  position: relative;
  box-sizing: border-box;
  height: 96px;
  margin: 8px 0 0;
  overflow-y: auto;
  overscroll-behavior: contain;
  scrollbar-width: none;
}

.pal__box::-webkit-scrollbar {
  width: 0;
}

.pal__cursor {
  position: absolute;
  left: 0;
  top: 0;
  z-index: 0;
  width: 100%;
  height: 24px;
  border-radius: 8px;
  background: rgba(47, 109, 246, 0.14);
  opacity: 0;
}

.pal__track {
  position: relative;
  z-index: 1;
}

.pal__opt {
  box-sizing: border-box;
  height: 24px;
  display: flex;
  align-items: center;
  padding: 0 8px;
  border-radius: 8px;
  font-size: 12px;
  font-weight: 600;
  color: #17141a;
  cursor: pointer;
}

.pal__opt.is-at {
  background: rgba(47, 109, 246, 0.14);
  color: #2f6df6;
}

.pal.is-demo .pal__cursor {
  opacity: 1;
  animation: cur-run 2s ease-out infinite;
}

.pal.is-demo .pal__track {
  animation: track-follow 2s ease-out infinite;
}

@keyframes cur-run {
  0% {
    transform: translateY(0);
  }
  28%, 66% {
    transform: translateY(72px);
  }
  90%, 100% {
    transform: translateY(0);
  }
}
@keyframes track-follow {
  0%, 28% {
    transform: translateY(0);
  }
  52%, 66% {
    transform: translateY(-72px);
  }
  90%, 100% {
    transform: translateY(0);
  }
}
@media (prefers-reduced-motion: reduce) {
  .pal.is-demo .pal__cursor,
  .pal.is-demo .pal__track {
    animation: none !important;
  }
  .pal.is-demo .pal__cursor {
    opacity: 1;
  }
}

// 실제 동작: ↑↓ 로 커서를 옮기고, 커서가 상자 밖으로 나가려는 순간 scrollIntoView 가 목록만 밀어 올린다.
var pal = document.querySelector('.pal');
var input = document.getElementById('q');
var opts = [].slice.call(document.querySelectorAll('.pal__opt'));
var at = -1;

function move(i) {
  pal.classList.remove('is-demo');
  at = Math.max(0, Math.min(i, opts.length - 1));
  opts.forEach(function (o, k) { o.classList.toggle('is-at', k === at); });
  input.setAttribute('aria-activedescendant', opts[at].id);
  // block: 'nearest' 라서 이미 보이는 줄이면 스크롤이 아예 일어나지 않는다
  opts[at].scrollIntoView({ block: 'nearest' });
}
document.addEventListener('keydown', function (e) {
  if (e.key === 'ArrowDown' || e.key === 'ArrowUp') {
    move(at + (e.key === 'ArrowDown' ? 1 : -1)); e.preventDefault();
  } else if (e.key === 'Home' || e.key === 'End') {
    move(e.key === 'Home' ? 0 : opts.length - 1); e.preventDefault();
  } else if (e.key === 'Enter' && opts[at]) {
    opts.forEach(function (o) { o.setAttribute('aria-selected', String(o === opts[at])); });
    e.preventDefault();
  } else if (e.key === 'Escape') {
    opts.forEach(function (o) { o.classList.remove('is-at'); });
    at = -1; input.focus({ preventScroll: true });
  }
});
opts.forEach(function (o, i) { o.addEventListener('mousemove', function () { move(i); }); });

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

export type ScrollFollowPaletteProps = {
  placeholder?: string;
  options?: string[];
  rows?: number;
  duration?: number;
  easing?: string;
  color?: string;
};

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

const DEFAULT_OPTIONS = [
  "Create document", "Create folder", "Invite member", "Mute notifications",
  "Change theme", "Export", "Sign out",
];

export default function ScrollFollowPalette({
  placeholder = "Search commands",
  options = DEFAULT_OPTIONS,
  rows = 4,
  duration = 220,
  easing = "ease-out",
  color = "#2f6df6",
}: ScrollFollowPaletteProps) {
  const [at, setAt] = useState(-1);
  const [picked, setPicked] = useState<string | null>(null);
  const inputRef = useRef<HTMLInputElement>(null);
  const rowRefs = useRef<(HTMLDivElement | null)[]>([]) as { current: (HTMLDivElement | null)[] };
  const vars: Vars = { "--duration": `${duration}ms`, "--easing": easing, "--color": color, height: `${rows * 24}px` };

  // block: "nearest" 라서 이미 보이는 줄이면 스크롤이 아예 일어나지 않는다 — 커서가 끝에 닿을 때만 목록이 움직인다
  function move(next: number) {
    const i = Math.max(0, Math.min(next, options.length - 1));
    setAt(i);
    rowRefs.current[i]?.scrollIntoView({ block: "nearest" });
  }

  return (
    <div className={styles.pal} role="dialog" aria-modal="true" aria-label="Command palette">
      <div className={styles.bar}>
        <span className={styles.mag} aria-hidden="true">
          <svg viewBox="0 0 256 256" width="13" height="13">
            <g fill="currentColor">
              <path d="M192 112a80 80 0 1 1-80-80a80 80 0 0 1 80 80" opacity=".2" />
              <path d="m229.66 218.34l-50.06-50.06a88.21 88.21 0 1 0-11.32 11.31l50.06 50.07a8 8 0 0 0 11.32-11.32M40 112a72 72 0 1 1 72 72a72.08 72.08 0 0 1-72-72" />
            </g>
          </svg>
        </span>
        <input
          ref={inputRef}
          className={styles.input}
          type="text"
          role="combobox"
          aria-expanded="true"
          aria-controls="sf-list"
          aria-activedescendant={at >= 0 ? `sf-o${at}` : undefined}
          aria-label={placeholder}
          placeholder={placeholder}
          autoComplete="off"
          onKeyDown={(e: KeyEvt) => {
            if (e.key === "ArrowDown" || e.key === "ArrowUp") {
              e.preventDefault();
              move(at + (e.key === "ArrowDown" ? 1 : -1));
            } else if (e.key === "Home" || e.key === "End") {
              e.preventDefault();
              move(e.key === "Home" ? 0 : options.length - 1);
            } else if (e.key === "Enter" && at >= 0) {
              e.preventDefault();
              setPicked(options[at]);
            } else if (e.key === "Escape") {
              setAt(-1);
              inputRef.current?.focus({ preventScroll: true });
            }
          }}
        />
        <kbd className={styles.kbd}>↓</kbd>
      </div>
      <div className={styles.box} style={vars}>
        <div className={styles.track} id="sf-list" role="listbox" aria-label="Command palette">
          {options.map((label, i) => (
            <div
              key={label}
              id={`sf-o${i}`}
              ref={(el: HTMLDivElement | null) => { rowRefs.current[i] = el; }}
              className={`${styles.opt} ${i === at ? styles.isAt : ""}`}
              role="option"
              aria-selected={label === picked}
              tabIndex={-1}
              onMouseMove={() => move(i)}
              onClick={() => setPicked(label)}
            >
              {label}
            </div>
          ))}
        </div>
      </div>
    </div>
  );
}