02行番号ガターと現在行

<main class="stage">
<div class="gt is-demo" id="gt">
  <div class="gt__bar">
    <span class="gt__ico" aria-hidden="true"><svg xmlns="http://www.w3.org/2000/svg" width="1em" height="1em" viewBox="0 0 256 256"><g fill="currentColor"><path d="M216 64v128H104V64Z" opacity=".2"/><path d="M224 128a8 8 0 0 1-8 8H104a8 8 0 0 1 0-16h112a8 8 0 0 1 8 8M104 72h112a8 8 0 0 0 0-16H104a8 8 0 0 0 0 16m112 112H104a8 8 0 0 0 0 16h112a8 8 0 0 0 0-16M43.58 55.16L48 52.94V104a8 8 0 0 0 16 0V40a8 8 0 0 0-11.58-7.16l-16 8a8 8 0 0 0 7.16 14.32m36.19 101.56a23.73 23.73 0 0 0-9.6-15.95a24.86 24.86 0 0 0-34.11 4.7a23.6 23.6 0 0 0-3.57 6.46a8 8 0 1 0 15 5.47a7.8 7.8 0 0 1 1.18-2.13a8.76 8.76 0 0 1 12-1.59a7.9 7.9 0 0 1 3.26 5.32a7.64 7.64 0 0 1-1.57 5.78a1 1 0 0 0-.08.11l-28.69 38.32A8 8 0 0 0 40 216h32a8 8 0 0 0 0-16H56l19.08-25.53a23.47 23.47 0 0 0 4.69-17.75"/></g></svg></span>
    <span class="gt__name">editor.scss</span>
    <span class="gt__pill">
      <span class="gt__count" id="count">6行</span>
      <span class="gt__cv gt__cv--1" aria-hidden="true">3行</span>
      <span class="gt__cv gt__cv--2" aria-hidden="true">4行</span>
      <span class="gt__cv gt__cv--3" aria-hidden="true">5行</span>
      <span class="gt__cv gt__cv--4" aria-hidden="true">6行</span>
      <span class="gt__cv gt__cv--5" aria-hidden="true">5行</span>
    </span>
  </div>
  <div class="gt__body">
    <div class="gt__gut" aria-hidden="true">
      <div class="gt__gtrack" id="gtrack"></div>
    </div>
    <div class="gt__wrap" id="wrap">
      <div class="gt__track" id="track">
        <span class="gt__cur" id="cur" aria-hidden="true"></span>
        <pre class="gt__hl" id="hl" aria-hidden="true"></pre>
      </div>
      <textarea class="gt__ta" id="ta" spellcheck="false" autocomplete="off" wrap="off" aria-label="コード入力欄">/* gutter demo */
.panel {
  margin: 8px;
  line-height: 20px;
  transform: translateY(4px);
}</textarea>
    </div>
  </div>
  <p class="gt__note">Enter を打つと番号が増え、キャレットのある行だけ明るくなります</p>
</div>
</main>

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

// 줄 번호 거터와 현재 줄 — 왼쪽 거터의 번호가 입력 줄 수에 맞춰 늘고 줄며,
// selectionStart 로 계산한 커서 줄만 배경이 켜진다. 본문(textarea)이 스크롤하면
// 거터 트랙도 같은 값으로 translateY 해 붙어 다닌다.
// 번호 자체는 CSS 카운터(counter-reset)가 매긴다 — JS 는 줄이 바뀔 때 빈 칸만 다시 그린다.
// 격자 미리보기(.is-demo)는 줄과 번호를 steps(1, end) 컷으로 하나씩 켜고,
// 현재 줄 밴드는 매끈하게 미끄러지며, 뒤에서 한 줄 스크롤 동기가 같이 움직인다.

$duration: $dur-quick;
$easing: $ease-spring;
$color: $stage-yellow;
$mono: ui-monospace, SFMono-Regular, "SF Mono", Consolas, "Liberation Mono", monospace;
$line: rgba(255, 255, 255, .16);
$dim: #beb7ad;
$fs: clamp(11px, 3vw, 13px);
$lh: 20px;

@include stage($stage-ink);

.gt {
  display: flex; flex-direction: column; gap: $sp-2;
  box-sizing: border-box; width: min(100%, 400px);
  padding: $sp-3; border: 1px solid $line; border-radius: $r-card;
  background: rgba(255, 255, 255, .05);
}

// ── 파일 이름 줄
.gt__bar { display: flex; align-items: center; gap: $sp-2; }
.gt__ico { display: grid; place-items: center; color: $color; font-size: 15px; }
.gt__name {
  flex: 1 1 auto; color: $subject-cream;
  font-family: $mono; font-weight: 700; font-size: 12px; line-height: 1.4;
}
// 줄 수 알약 — 실제 값은 JS 가 채우고, 미리보기에서는 겹켜진 값 장이 차례로 켜진다
.gt__pill { display: grid; justify-items: center; }
.gt__pill > * { grid-area: 1 / 1; }
.gt__count, .gt__cv {
  padding: $sp-1 $sp-2; border-radius: $r-pill;
  background: rgba($color, .14); color: $color;
  font-family: $mono; font-weight: 700; font-size: 11px; line-height: 1.4;
  white-space: nowrap;
}
.gt__cv { opacity: 0; }

// ── 거터 + 본문 몸통
.gt__body {
  display: grid; grid-template-columns: 36px 1fr;
  background: rgba(0, 0, 0, .28); border-radius: $r-sm; overflow: hidden;
}
.gt__gut { background: rgba(0, 0, 0, .35); border-right: 1px solid $line; overflow: hidden; }
.gt__gtrack {
  position: relative; box-sizing: border-box; padding: $sp-2 0 $sp-2 $sp-2;
  counter-reset: gtline;
  font-family: $mono; font-weight: 500; font-size: $fs; line-height: $lh;
}
.gt__num {
  position: relative; z-index: 1; display: block; height: $lh;
  padding-right: $sp-2; text-align: right; color: $dim;
}
.gt__num::before { counter-increment: gtline; content: counter(gtline); }
// 거터 쪽 현재 줄 밴드 — 본문 밴드와 같은 translateY 값을 받아 같이 움직인다
.gt__gcur {
  position: absolute; top: $sp-2; left: 0; right: 0; height: $lh;
  background: rgba($color, .18); border-radius: 0 $r-xs $r-xs 0;
  transition: transform $duration $easing;
}

// ── 본문. 글자는 투명한 textarea 아래 pre 가 그린다 — 서체·행간·패딩이 글자 단위로 같아야 한다
.gt__wrap {
  position: relative; display: grid; overflow: hidden;
  height: 5 * $lh + 2 * $sp-2;   // 5줄이 온전히 보이고 마지막 줄이 조금 엿보인다 — 스크롤 여유 표시
}
.gt__wrap > * { grid-area: 1 / 1; min-height: 0; }
// textarea 는 격자 칸 높이에 **묶어 둔다**. 내용만큼 늘어나게 두면 스크롤하는 것은 textarea 가 아니라
// 바깥 상자가 되고, scrollTop 을 읽어 거터를 미는 동기 코드가 영영 0 만 읽는다 (실측 2026-09-13:
// 12줄을 넣어도 ta.scrollHeight == ta.clientHeight 였다)
.gt__ta { height: 100%; }
.gt__track { position: relative; align-self: start; box-sizing: border-box; padding: $sp-2; }
.gt__cur {
  position: absolute; top: $sp-2; left: 0; right: 0; height: $lh;
  background: rgba($color, .18); border-radius: 0 $r-xs $r-xs 0;
  transition: transform $duration $easing;
}
.gt__hl {
  position: relative; z-index: 1; margin: 0;
  font-family: $mono; font-weight: 500; font-size: $fs; line-height: $lh;
  letter-spacing: 0; tab-size: 2; white-space: pre; overflow: hidden;
  color: $subject-cream;
}
.gt__ln { display: block; }
// 글자는 투명하고 커서만 남는다 — 색은 아래 pre 가 그린다
.gt__ta {
  box-sizing: border-box; margin: 0; padding: $sp-2; border: 0; background: transparent;
  color: transparent; caret-color: $color; resize: none;
  font-family: $mono; font-weight: 500; font-size: $fs; line-height: $lh;
  letter-spacing: 0; tab-size: 2; white-space: pre; overflow: auto;
  scrollbar-width: none;
}
.gt__ta::-webkit-scrollbar { display: none; }
.gt__ta::selection { background: rgba($color, .32); }
.gt__ta:focus-visible { outline: 2px solid $subject-blue; outline-offset: -2px; }

.gt__note { margin: 0; color: $dim; font-weight: 500; font-size: 11px; line-height: 1.4; }

// ── 격자 미리보기 루프 (2초)
// 1~3줄은 곧바로, 4·5줄은 타이핑하듯 늦게 켜지고 6줄이 더해졌다가 줄어든다.
// 켜짐·꺼짐은 전부 steps(1, end) 컷 — 점프 지점(3%)을 따로 둬야 첫 장에 값이 보인다.
.gt.is-demo .gt__ln, .gt.is-demo .gt__num {
  animation-name: gtLine;
  animation-duration: $dur-loop; animation-timing-function: steps(1, end);
  animation-iteration-count: infinite; animation-fill-mode: backwards;
}
.gt.is-demo .gt__ln:nth-child(1), .gt.is-demo .gt__num:nth-child(1) { animation-delay: 0s; }
.gt.is-demo .gt__ln:nth-child(2), .gt.is-demo .gt__num:nth-child(2) { animation-delay: .04s; }
.gt.is-demo .gt__ln:nth-child(3), .gt.is-demo .gt__num:nth-child(3) { animation-delay: .08s; }
.gt.is-demo .gt__ln:nth-child(4), .gt.is-demo .gt__num:nth-child(4) { animation-delay: .3s; }
.gt.is-demo .gt__ln:nth-child(5), .gt.is-demo .gt__num:nth-child(5) { animation-delay: .42s; }
// 6줄과 그 번호는 한 바퀴 안에서 늘었다가 줄어든다 — 지연 없이 절대 시점 키프레임으로
.gt.is-demo .gt__ln:nth-child(6), .gt.is-demo .gt__num:nth-child(6) { animation-name: gtLineCut; }

// 줄 수 알약 — 실제 값은 감추고 겹켜진 값 장을 컷으로 갈아 끼운다
.gt.is-demo .gt__count { color: transparent; }
.gt.is-demo .gt__cv {
  animation-duration: $dur-loop; animation-timing-function: steps(1, end);
  animation-iteration-count: infinite; animation-fill-mode: backwards;
}
.gt.is-demo .gt__cv--1 { animation-name: gtCv1; }
.gt.is-demo .gt__cv--2 { animation-name: gtCv2; }
.gt.is-demo .gt__cv--3 { animation-name: gtCv3; }
.gt.is-demo .gt__cv--4 { animation-name: gtCv4; }
.gt.is-demo .gt__cv--5 { animation-name: gtCv5; }

// 현재 줄 밴드 — 나타남은 컷, 줄 옮김은 매끈한 transform 이동
.gt.is-demo .gt__cur, .gt.is-demo .gt__gcur {
  animation-name: gtCurO, gtCurT;
  animation-duration: $dur-loop, $dur-loop;
  animation-timing-function: steps(1, end), $easing;
  animation-iteration-count: infinite, infinite;
  animation-fill-mode: backwards, backwards;
  transition: none;
}
// 스크롤 동기 — 본문 트랙과 거터 트랙이 같은 값으로 한 줄 올라갔다 내려온다
.gt.is-demo .gt__track, .gt.is-demo .gt__gtrack {
  animation-name: gtScroll;
  animation-duration: $dur-loop; animation-timing-function: $ease-out;
  animation-iteration-count: infinite; animation-fill-mode: backwards;
}

@keyframes gtLine {
  0% { opacity: 0; }
  3%, 100% { opacity: 1; }
}
@keyframes gtLineCut {
  0%, 29% { opacity: 0; }
  30%, 79% { opacity: 1; }
  80%, 100% { opacity: 0; }
}
@keyframes gtCv1 { 0%, 17% { opacity: 1; } 18%, 100% { opacity: 0; } }
@keyframes gtCv2 { 0%, 17% { opacity: 0; } 18%, 23% { opacity: 1; } 24%, 100% { opacity: 0; } }
@keyframes gtCv3 { 0%, 23% { opacity: 0; } 24%, 29% { opacity: 1; } 30%, 100% { opacity: 0; } }
@keyframes gtCv4 { 0%, 29% { opacity: 0; } 30%, 79% { opacity: 1; } 80%, 100% { opacity: 0; } }
@keyframes gtCv5 { 0%, 79% { opacity: 0; } 80%, 100% { opacity: 1; } }
@keyframes gtCurO {
  0% { opacity: 0; }
  12%, 100% { opacity: 1; }
}
// 셋째 줄에서 타이핑을 따라 넷째·다섯째·여섯째 줄로 내려간 뒤, 클릭해 셋째 줄로 돌아온다
@keyframes gtCurT {
  0%, 12% { transform: translateY(40px); }
  21%, 24% { transform: translateY(60px); }
  27%, 30% { transform: translateY(80px); }
  33%, 44% { transform: translateY(100px); }
  50%, 100% { transform: translateY(40px); }
}
@keyframes gtScroll {
  0%, 65% { transform: translateY(0); }
  70%, 74% { transform: translateY(-20px); }
  79%, 100% { transform: translateY(0); }
}

// ── 좁은 화면: 여백과 보이는 줄 수를 줄여 무대 안에 들어온다 (줄 높이 20px 는 그대로)
@media (max-width: 340px) {
  .gt { gap: $sp-1; padding: $sp-2; }
  .gt__note { display: none; }   // 좁은 화면에서는 안내문을 접어 무대(200px) 안에 들어오게 한다
  .gt__body { grid-template-columns: 28px 1fr; }
  .gt__wrap { height: 3 * $lh + 2 * $sp-1; }
  .gt__gtrack { padding: $sp-1 0 $sp-1 $sp-1; font-size: 11px; }
  .gt__num { padding-right: $sp-1; }
  .gt__track { padding: $sp-1; }
  .gt__cur, .gt__gcur { top: $sp-1; }
  .gt__hl { font-size: 11px; }
  .gt__ta { padding: $sp-1; font-size: 11px; }
  .gt__note { font-size: 10px; }
}

@media (prefers-reduced-motion: reduce) {
  .gt.is-demo .gt__ln, .gt.is-demo .gt__num, .gt.is-demo .gt__cv,
  .gt.is-demo .gt__cur, .gt.is-demo .gt__gcur, .gt.is-demo .gt__track, .gt.is-demo .gt__gtrack {
    animation: none !important;
  }
  .gt.is-demo .gt__ln, .gt.is-demo .gt__num { opacity: 1 !important; }
  .gt.is-demo .gt__cv { opacity: 0 !important; }
  .gt.is-demo .gt__count { color: $color !important; }
  .gt.is-demo .gt__cur, .gt.is-demo .gt__gcur { opacity: 1 !important; }
}

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);
}

.gt {
  display: flex;
  flex-direction: column;
  gap: 8px;
  box-sizing: border-box;
  width: min(100%, 400px);
  padding: 12px;
  border: 1px solid rgba(255, 255, 255, 0.16);
  border-radius: 16px;
  background: rgba(255, 255, 255, 0.05);
}

.gt__bar {
  display: flex;
  align-items: center;
  gap: 8px;
}

.gt__ico {
  display: grid;
  place-items: center;
  color: #ffd23f;
  font-size: 15px;
}

.gt__name {
  flex: 1 1 auto;
  color: #fff7e6;
  font-family: ui-monospace, SFMono-Regular, "SF Mono", Consolas, "Liberation Mono", monospace;
  font-weight: 700;
  font-size: 12px;
  line-height: 1.4;
}

.gt__pill {
  display: grid;
  justify-items: center;
}

.gt__pill > * {
  grid-area: 1/1;
}

.gt__count, .gt__cv {
  padding: 4px 8px;
  border-radius: 999px;
  background: rgba(255, 210, 63, 0.14);
  color: #ffd23f;
  font-family: ui-monospace, SFMono-Regular, "SF Mono", Consolas, "Liberation Mono", monospace;
  font-weight: 700;
  font-size: 11px;
  line-height: 1.4;
  white-space: nowrap;
}

.gt__cv {
  opacity: 0;
}

.gt__body {
  display: grid;
  grid-template-columns: 36px 1fr;
  background: rgba(0, 0, 0, 0.28);
  border-radius: 8px;
  overflow: hidden;
}

.gt__gut {
  background: rgba(0, 0, 0, 0.35);
  border-right: 1px solid rgba(255, 255, 255, 0.16);
  overflow: hidden;
}

.gt__gtrack {
  position: relative;
  box-sizing: border-box;
  padding: 8px 0 8px 8px;
  counter-reset: gtline;
  font-family: ui-monospace, SFMono-Regular, "SF Mono", Consolas, "Liberation Mono", monospace;
  font-weight: 500;
  font-size: clamp(11px, 3vw, 13px);
  line-height: 20px;
}

.gt__num {
  position: relative;
  z-index: 1;
  display: block;
  height: 20px;
  padding-right: 8px;
  text-align: right;
  color: #beb7ad;
}

.gt__num::before {
  counter-increment: gtline;
  content: counter(gtline);
}

.gt__gcur {
  position: absolute;
  top: 8px;
  left: 0;
  right: 0;
  height: 20px;
  background: rgba(255, 210, 63, 0.18);
  border-radius: 0 4px 4px 0;
  transition: transform 220ms cubic-bezier(0.2, 0.8, 0.2, 1);
}

.gt__wrap {
  position: relative;
  display: grid;
  overflow: hidden;
  height: 116px;
}

.gt__wrap > * {
  grid-area: 1/1;
  min-height: 0;
}

.gt__ta {
  height: 100%;
}

.gt__track {
  position: relative;
  align-self: start;
  box-sizing: border-box;
  padding: 8px;
}

.gt__cur {
  position: absolute;
  top: 8px;
  left: 0;
  right: 0;
  height: 20px;
  background: rgba(255, 210, 63, 0.18);
  border-radius: 0 4px 4px 0;
  transition: transform 220ms cubic-bezier(0.2, 0.8, 0.2, 1);
}

.gt__hl {
  position: relative;
  z-index: 1;
  margin: 0;
  font-family: ui-monospace, SFMono-Regular, "SF Mono", Consolas, "Liberation Mono", monospace;
  font-weight: 500;
  font-size: clamp(11px, 3vw, 13px);
  line-height: 20px;
  letter-spacing: 0;
  tab-size: 2;
  white-space: pre;
  overflow: hidden;
  color: #fff7e6;
}

.gt__ln {
  display: block;
}

.gt__ta {
  box-sizing: border-box;
  margin: 0;
  padding: 8px;
  border: 0;
  background: transparent;
  color: transparent;
  caret-color: #ffd23f;
  resize: none;
  font-family: ui-monospace, SFMono-Regular, "SF Mono", Consolas, "Liberation Mono", monospace;
  font-weight: 500;
  font-size: clamp(11px, 3vw, 13px);
  line-height: 20px;
  letter-spacing: 0;
  tab-size: 2;
  white-space: pre;
  overflow: auto;
  scrollbar-width: none;
}

.gt__ta::-webkit-scrollbar {
  display: none;
}

.gt__ta::selection {
  background: rgba(255, 210, 63, 0.32);
}

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

.gt__note {
  margin: 0;
  color: #beb7ad;
  font-weight: 500;
  font-size: 11px;
  line-height: 1.4;
}

.gt.is-demo .gt__ln, .gt.is-demo .gt__num {
  animation-name: gtLine;
  animation-duration: 2s;
  animation-timing-function: steps(1, end);
  animation-iteration-count: infinite;
  animation-fill-mode: backwards;
}

.gt.is-demo .gt__ln:nth-child(1), .gt.is-demo .gt__num:nth-child(1) {
  animation-delay: 0s;
}

.gt.is-demo .gt__ln:nth-child(2), .gt.is-demo .gt__num:nth-child(2) {
  animation-delay: 0.04s;
}

.gt.is-demo .gt__ln:nth-child(3), .gt.is-demo .gt__num:nth-child(3) {
  animation-delay: 0.08s;
}

.gt.is-demo .gt__ln:nth-child(4), .gt.is-demo .gt__num:nth-child(4) {
  animation-delay: 0.3s;
}

.gt.is-demo .gt__ln:nth-child(5), .gt.is-demo .gt__num:nth-child(5) {
  animation-delay: 0.42s;
}

.gt.is-demo .gt__ln:nth-child(6), .gt.is-demo .gt__num:nth-child(6) {
  animation-name: gtLineCut;
}

.gt.is-demo .gt__count {
  color: transparent;
}

.gt.is-demo .gt__cv {
  animation-duration: 2s;
  animation-timing-function: steps(1, end);
  animation-iteration-count: infinite;
  animation-fill-mode: backwards;
}

.gt.is-demo .gt__cv--1 {
  animation-name: gtCv1;
}

.gt.is-demo .gt__cv--2 {
  animation-name: gtCv2;
}

.gt.is-demo .gt__cv--3 {
  animation-name: gtCv3;
}

.gt.is-demo .gt__cv--4 {
  animation-name: gtCv4;
}

.gt.is-demo .gt__cv--5 {
  animation-name: gtCv5;
}

.gt.is-demo .gt__cur, .gt.is-demo .gt__gcur {
  animation-name: gtCurO, gtCurT;
  animation-duration: 2s, 2s;
  animation-timing-function: steps(1, end), cubic-bezier(0.2, 0.8, 0.2, 1);
  animation-iteration-count: infinite, infinite;
  animation-fill-mode: backwards, backwards;
  transition: none;
}

.gt.is-demo .gt__track, .gt.is-demo .gt__gtrack {
  animation-name: gtScroll;
  animation-duration: 2s;
  animation-timing-function: ease-out;
  animation-iteration-count: infinite;
  animation-fill-mode: backwards;
}

@keyframes gtLine {
  0% {
    opacity: 0;
  }
  3%, 100% {
    opacity: 1;
  }
}
@keyframes gtLineCut {
  0%, 29% {
    opacity: 0;
  }
  30%, 79% {
    opacity: 1;
  }
  80%, 100% {
    opacity: 0;
  }
}
@keyframes gtCv1 {
  0%, 17% {
    opacity: 1;
  }
  18%, 100% {
    opacity: 0;
  }
}
@keyframes gtCv2 {
  0%, 17% {
    opacity: 0;
  }
  18%, 23% {
    opacity: 1;
  }
  24%, 100% {
    opacity: 0;
  }
}
@keyframes gtCv3 {
  0%, 23% {
    opacity: 0;
  }
  24%, 29% {
    opacity: 1;
  }
  30%, 100% {
    opacity: 0;
  }
}
@keyframes gtCv4 {
  0%, 29% {
    opacity: 0;
  }
  30%, 79% {
    opacity: 1;
  }
  80%, 100% {
    opacity: 0;
  }
}
@keyframes gtCv5 {
  0%, 79% {
    opacity: 0;
  }
  80%, 100% {
    opacity: 1;
  }
}
@keyframes gtCurO {
  0% {
    opacity: 0;
  }
  12%, 100% {
    opacity: 1;
  }
}
@keyframes gtCurT {
  0%, 12% {
    transform: translateY(40px);
  }
  21%, 24% {
    transform: translateY(60px);
  }
  27%, 30% {
    transform: translateY(80px);
  }
  33%, 44% {
    transform: translateY(100px);
  }
  50%, 100% {
    transform: translateY(40px);
  }
}
@keyframes gtScroll {
  0%, 65% {
    transform: translateY(0);
  }
  70%, 74% {
    transform: translateY(-20px);
  }
  79%, 100% {
    transform: translateY(0);
  }
}
@media (max-width: 340px) {
  .gt {
    gap: 4px;
    padding: 8px;
  }
  .gt__note {
    display: none;
  }
  .gt__body {
    grid-template-columns: 28px 1fr;
  }
  .gt__wrap {
    height: 68px;
  }
  .gt__gtrack {
    padding: 4px 0 4px 4px;
    font-size: 11px;
  }
  .gt__num {
    padding-right: 4px;
  }
  .gt__track {
    padding: 4px;
  }
  .gt__cur, .gt__gcur {
    top: 4px;
  }
  .gt__hl {
    font-size: 11px;
  }
  .gt__ta {
    padding: 4px;
    font-size: 11px;
  }
  .gt__note {
    font-size: 10px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .gt.is-demo .gt__ln, .gt.is-demo .gt__num, .gt.is-demo .gt__cv,
  .gt.is-demo .gt__cur, .gt.is-demo .gt__gcur, .gt.is-demo .gt__track, .gt.is-demo .gt__gtrack {
    animation: none !important;
  }
  .gt.is-demo .gt__ln, .gt.is-demo .gt__num {
    opacity: 1 !important;
  }
  .gt.is-demo .gt__cv {
    opacity: 0 !important;
  }
  .gt.is-demo .gt__count {
    color: #ffd23f !important;
  }
  .gt.is-demo .gt__cur, .gt.is-demo .gt__gcur {
    opacity: 1 !important;
  }
}

var gt = document.getElementById('gt');
var ta = document.getElementById('ta');
var hl = document.getElementById('hl');
var wrap = document.getElementById('wrap');
var track = document.getElementById('track');
var gtrack = document.getElementById('gtrack');
var countEl = document.getElementById('count');
var curEl = document.getElementById('cur');
var gcurEl = null;
var LBL_COUNT = '{n}行';

function esc(t) {
  return t.replace(/&/g, '&amp;').replace(/</g, '&lt;').replace(/>/g, '&gt;');
}
function lineH() {
  var v = parseFloat(getComputedStyle(ta).lineHeight);
  return v > 0 ? v : 20;
}
// 줄 수가 바뀔 때마다 거터를 다시 그린다 — 번호 매김은 scss 의 counter-reset 카운터가 한다
function render() {
  var lines = ta.value.split('\n');
  var nums = '';
  lines.forEach(function () { nums += '<span class="gt__num"></span>'; });
  gtrack.innerHTML = nums + '<span class="gt__gcur"></span>';
  gcurEl = gtrack.querySelector('.gt__gcur');
  hl.innerHTML = lines.map(function (l) {
    return '<span class="gt__ln">' + (esc(l) || ' ') + '</span>';
  }).join('');
  countEl.textContent = LBL_COUNT.replace('{n}', lines.length);
  update();
}
// selectionStart 까지의 글자에서 몇째 줄인지 계산해 두 밴드를 같은 값으로 옮긴다
function update() {
  var idx = ta.value.slice(0, ta.selectionStart).split('\n').length - 1;
  var y = idx * lineH();
  curEl.style.transform = 'translateY(' + y + 'px)';
  if (gcurEl) gcurEl.style.transform = 'translateY(' + y + 'px)';
  sync();
}
// 본문이 스크롤하면 거터 트랙도 같은 값으로 translateY — 두 겹이 어긋나지 않는 핵심
function sync() {
  var y = -ta.scrollTop;
  track.style.transform = 'translateY(' + y + 'px)';
  gtrack.style.transform = 'translateY(' + y + 'px)';
}
ta.addEventListener('input', function () { gt.classList.remove('is-demo'); render(); });
ta.addEventListener('keyup', function () { gt.classList.remove('is-demo'); update(); });
ta.addEventListener('click', function () { gt.classList.remove('is-demo'); update(); });
ta.addEventListener('scroll', sync);
ta.addEventListener('focus', function () { gt.classList.remove('is-demo'); update(); });
wrap.addEventListener('pointerdown', function () { gt.classList.remove('is-demo'); });
render();
// 시작 커서는 셋째 줄 끝 — 손을 대지 않은 첫 화면부터 현재 줄 밴드가 보인다
var p = ta.value.split('\n').slice(0, 3).join('\n').length;
ta.setSelectionRange(p, p);
update();

// LineNumberGutter — vanilla 판(run/299/demo/02-editor-line-number-gutter/index.html) 의 React 포트.
// 왼쪽 거터의 번호가 입력 줄 수를 따라 늘고 줄며, selectionStart 로 잰 커서 줄만 배경이 켜진다.
// 본문이 스크롤하면 거터 트랙도 같은 translateY 값을 받아 붙어 다닌다.
// 번호 자체는 scss 의 counter-reset 이 매긴다 — 여기서는 빈 칸만 줄 수만큼 그린다.
import { useEffect, useRef, useState } from "react";
import type { CSSProperties } from "react";
import styles from "./LineNumberGutter.module.scss";

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

type Vars = CSSProperties & { "--duration"?: string; "--easing"?: string; "--color"?: string };
// useRef<T> 는 T | null 을 돌려준다 — ambient 타입에 맞춰 상자 타입을 따로 둔다
type Box<T> = { current: T | null };

const LABEL = "코드 입력칸";
const NOTE = "Enter 를 치면 번호가 늘고, 커서가 있는 줄만 밝아집니다";
const FILE_NAME = "editor.scss";
const LBL_COUNT = "{n}줄";
// 미리보기에서 겹켜놓고 컷으로 갈아 끼우는 줄 수 값 장 — vanilla 와 같은 글자다
const COUNT_VIEWS = ["3줄", "4줄", "5줄", "6줄", "5줄"];
const CODE = [
  "/* gutter demo */",
  ".panel {",
  "  margin: 8px;",
  "  line-height: 20px;",
  "  transform: translateY(4px);",
  "}",
].join("\n");

export default function LineNumberGutter(props: LineNumberGutterProps) {
  const duration = props.duration ?? 220;
  const easing = props.easing ?? "cubic-bezier(.2, .8, .2, 1)";
  const color = props.color ?? "#ffd23f";
  const [code, setCode] = useState<string>(props.initialCode ?? CODE);
  const [preview, setPreview] = useState<boolean>(true);
  const [caretY, setCaretY] = useState<number>(0);
  const [scrollY, setScrollY] = useState<number>(0);
  const taRef = useRef<HTMLTextAreaElement>(null) as Box<HTMLTextAreaElement>;

  const lines = code.split("\n");

  // 본문이 스크롤하면 두 트랙을 같은 값으로 옮긴다 — 두 겹이 어긋나지 않는 핵심
  const sync = () => {
    const ta = taRef.current;
    if (ta) setScrollY(-ta.scrollTop);
  };

  // selectionStart 까지의 글자에서 몇째 줄인지 계산해 두 밴드를 같은 값으로 옮긴다
  const update = () => {
    const ta = taRef.current;
    if (!ta) return;
    const raw = parseFloat(getComputedStyle(ta).lineHeight);
    const lh = raw > 0 ? raw : 20;
    const idx = ta.value.slice(0, ta.selectionStart).split("\n").length - 1;
    setCaretY(idx * lh);
    setScrollY(-ta.scrollTop);
  };

  // 시작 커서는 셋째 줄 끝 — 손을 대지 않은 첫 화면부터 현재 줄 밴드가 보인다
  useEffect(() => {
    const ta = taRef.current;
    if (!ta) return;
    const p = ta.value.split("\n").slice(0, 3).join("\n").length;
    ta.setSelectionRange(p, p);
    update();
  }, []);

  const leave = () => setPreview(false);
  const vars: Vars = { "--duration": duration + "ms", "--easing": easing, "--color": color };
  const bandStyle: CSSProperties = { transform: "translateY(" + caretY + "px)" };
  const trackStyle: CSSProperties = { transform: "translateY(" + scrollY + "px)" };

  return (
    <main className={styles.stage}>
      <div className={styles.root + (preview ? " " + styles.isDemo : "")} style={vars}>
        <div className={styles.bar}>
          <span className={styles.ico} aria-hidden="true">
            <svg xmlns="http://www.w3.org/2000/svg" width="1em" height="1em" viewBox="0 0 256 256">
              <g fill="currentColor">
                <path d="M216 64v128H104V64Z" opacity=".2" />
                <path d="M224 128a8 8 0 0 1-8 8H104a8 8 0 0 1 0-16h112a8 8 0 0 1 8 8M104 72h112a8 8 0 0 0 0-16H104a8 8 0 0 0 0 16m112 112H104a8 8 0 0 0 0 16h112a8 8 0 0 0 0-16M43.58 55.16L48 52.94V104a8 8 0 0 0 16 0V40a8 8 0 0 0-11.58-7.16l-16 8a8 8 0 0 0 7.16 14.32m36.19 101.56a23.73 23.73 0 0 0-9.6-15.95a24.86 24.86 0 0 0-34.11 4.7a23.6 23.6 0 0 0-3.57 6.46a8 8 0 1 0 15 5.47a7.8 7.8 0 0 1 1.18-2.13a8.76 8.76 0 0 1 12-1.59a7.9 7.9 0 0 1 3.26 5.32a7.64 7.64 0 0 1-1.57 5.78a1 1 0 0 0-.08.11l-28.69 38.32A8 8 0 0 0 40 216h32a8 8 0 0 0 0-16H56l19.08-25.53a23.47 23.47 0 0 0 4.69-17.75" />
              </g>
            </svg>
          </span>
          <span className={styles.name}>{FILE_NAME}</span>
          <span className={styles.pill}>
            <span className={styles.count}>{LBL_COUNT.replace("{n}", String(lines.length))}</span>
            {COUNT_VIEWS.map((text, i) => (
              <span key={i} className={styles.cv + " " + styles["cv" + (i + 1)]} aria-hidden="true">
                {text}
              </span>
            ))}
          </span>
        </div>
        <div className={styles.body}>
          <div className={styles.gut} aria-hidden="true">
            <div className={styles.gtrack} style={trackStyle}>
              {lines.map((_line, i) => (
                <span key={i} className={styles.num} />
              ))}
              <span className={styles.gcur} style={bandStyle} />
            </div>
          </div>
          <div className={styles.wrap} onPointerDown={leave}>
            <div className={styles.track} style={trackStyle}>
              <span className={styles.cur} style={bandStyle} aria-hidden="true" />
              <pre className={styles.hl} aria-hidden="true">
                {lines.map((line, i) => (
                  <span key={i} className={styles.ln}>
                    {line || " "}
                  </span>
                ))}
              </pre>
            </div>
            <textarea
              className={styles.ta}
              ref={taRef}
              value={code}
              spellCheck={false}
              autoComplete="off"
              wrap="off"
              aria-label={LABEL}
              onChange={(e: { target: { value: string } }) => {
                leave();
                setCode(e.target.value);
                update();
              }}
              onKeyUp={() => {
                leave();
                update();
              }}
              onClick={() => {
                leave();
                update();
              }}
              onFocus={() => {
                leave();
                update();
              }}
              onScroll={sync}
            />
          </div>
        </div>
        <p className={styles.note}>{NOTE}</p>
      </div>
    </main>
  );
}