06Direction enter & exit

<main class="stage">
  <section class="dt is-demo" id="dt" aria-label="Direction enter and exit demo">
    <header class="dt__head">
      <p class="dt__title">Direction enter and exit</p>
      <p class="dt__attr"><code>scrollTop</code></p>
    </header>
    <div class="dt__view" id="dt-view" tabindex="0" role="region" aria-label="Card list — the look changes with scroll direction">
      <div class="dt__track">
        <p class="dt__hint">Scroll down</p>
        <article class="dt__card" id="dt-card">
          <b>Work 07</b>
          <span>Tilts away as it passes downward</span>
        </article>
        <p class="dt__filler" aria-hidden="true">Next section</p>
      </div>
    </div>
    <footer class="dt__foot">
      <span class="dt__dirBox" aria-hidden="true">
        <span class="dt__dir dt__dir--down">
          <svg class="dt__ico" xmlns="http://www.w3.org/2000/svg" viewBox="0 0 256 256" aria-hidden="true"><g fill="currentColor"><path d="m200 144l-72 72l-72-72Z" opacity=".2"/><path d="M207.39 140.94A8 8 0 0 0 200 136h-64V40a8 8 0 0 0-16 0v96H56a8 8 0 0 0-5.66 13.66l72 72a8 8 0 0 0 11.32 0l72-72a8 8 0 0 0 1.73-8.72M128 204.69L75.31 152h105.38Z"/></g></svg>
          <span>Moving down</span>
        </span>
        <span class="dt__dir dt__dir--up">
          <svg class="dt__ico" xmlns="http://www.w3.org/2000/svg" viewBox="0 0 256 256" aria-hidden="true"><g fill="currentColor"><path d="M200 112H56l72-72Z" opacity=".2"/><path d="m205.66 106.34l-72-72a8 8 0 0 0-11.32 0l-72 72A8 8 0 0 0 56 120h64v96a8 8 0 0 0 16 0v-96h64a8 8 0 0 0 5.66-13.66M75.31 104L128 51.31L180.69 104Z"/></g></svg>
          <span>Moving up</span>
        </span>
      </span>
      <span class="dt__phase">
        <span class="dt__phaseWait">Waiting for scroll</span>
        <span class="dt__phaseIn">Entering</span>
        <span class="dt__phaseOut">Exit detected</span>
      </span>
    </footer>
  </section>
</main>

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

// 방향 감지 진입·퇴장 — 진입(is-visible) 은 아래에서 떠오르고 퇴장(is-exit) 은 기울며 스치고 나간다
// 방향 값은 isIntersecting 이 바뀌는 순간마다 갱신된다(data-dir). 미리보기(.is-demo)는 아래 방향 한 주기를 재생한다
$duration: $dur-loop;
$easing: $ease-spring;
$color: $subject-blue-light;

@include stage($stage-ink);

.dt {
  position: relative;
  box-sizing: border-box;
  width: min(312px, 92vw);
  border-radius: $r-card;
  background: $tick-panel;
  border: 1px solid rgba($subject-cream, .16);
  color: $subject-cream;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  overflow: hidden;
  box-shadow: $shadow-raised;
}

.dt__head {
  display: flex;
  align-items: baseline;
  justify-content: space-between;
  gap: $sp-2;
  padding: $sp-2 $sp-3;
}
.dt__title {
  margin: 0;
  font-size: 13px;
  font-weight: 800;
  line-height: 1.3;
}
.dt__attr {
  margin: 0;
  font-size: 10px;
  font-weight: 400;
  line-height: 1.3;
  color: rgba($subject-cream, .75);
  code { font-family: "Consolas", "Menlo", monospace; }
}

.dt__view {
  height: 168px;
  overflow-y: auto;
  padding: 0 $sp-3;
  outline: none;
}
.dt__track {
  display: grid;
  gap: $sp-3;
  padding-top: $sp-2;
  padding-bottom: 120px;
}

.dt__hint {
  margin: 0;
  box-sizing: border-box;
  font-size: 10px;
  font-weight: 700;
  line-height: 1.3;
  color: rgba($subject-cream, .75);
  border: 1px dashed rgba($subject-cream, .32);
  border-radius: $r-control;
  padding: $sp-3 0;
  text-align: center;
}

// 카드는 첫 화면 밖에 있다가 방향값을 달고 들어온다 — margin 으로 접힌 아래까지 민다
.dt__card {
  box-sizing: border-box;
  margin-top: 116px;
  display: grid;
  gap: $sp-1;
  padding: $sp-3;
  border-radius: $r-control;
  background: $subject-cream;
  color: $subject-ink;
  opacity: 0;
  transform: translateY(28px);
  transition-property: opacity, transform;
  transition-duration: $dur-quick, $dur-enter;
  transition-timing-function: ease-out, $easing;
  b { font-size: 15px; font-weight: 800; line-height: 1.2; color: $subject-blue-deep; }
  span { font-size: 11px; font-weight: 700; line-height: 1.3; }
}
// 위로 스크롤해 들어오면 반대편(위)에서 내려온다 — 진입 방향이 모습을 바꾼다
.dt__card[data-dir="up"] { transform: translateY(-28px); }
.dt__card.is-visible {
  opacity: 1;
  transform: none;
}
// 퇴장 — 나가는 쪽으로 기울며 스친다. 아래로 스크롤 중 벗어나면 위 변으로, 위로 스크롤 중 벗어나면 아래 변으로
.dt__card.is-exit[data-dir="down"] {
  opacity: 0;
  transform: translateY(-30px) rotate(-5deg) scale(.94);
}
.dt__card.is-exit[data-dir="up"] {
  opacity: 0;
  transform: translateY(34px) rotate(5deg) scale(.94);
}

.dt__filler {
  margin: 0;
  font-size: 10px;
  font-weight: 700;
  line-height: 1.3;
  color: rgba($subject-cream, .75);
  border-radius: $r-control;
  background: rgba($subject-cream, .08);
  padding: $sp-6 0;
  text-align: center;
}

.dt__foot {
  display: flex;
  align-items: center;
  gap: $sp-2;
  padding: $sp-2 $sp-3;
  border-top: 1px solid rgba($subject-cream, .16);
  font-size: 10px;
  font-weight: 700;
  line-height: 1.3;
}
// 방향·단계 표시는 같은 자리에 겹쳐 두고 하나만 보인다 — 세 개를 나란히 두면 폭이 넘쳐 줄이 접힌다
.dt__dirBox {
  position: relative;
  height: 20px;
  flex: 0 0 auto;
}
.dt__dir {
  position: absolute;
  inset: 0;
  display: inline-flex;
  align-items: center;
  gap: $sp-1;
  white-space: nowrap;
  opacity: 0;
  font-size: 10px;
  font-weight: 700;
  line-height: 1.3;
  color: $subject-blue-light;
}
[data-dir="down"] .dt__dir--down { opacity: 1; }
[data-dir="up"] .dt__dir--up { opacity: 1; }
.dt__ico {
  width: 12px;
  height: 12px;
}

.dt__phase {
  position: relative;
  height: 20px;
  margin-left: auto;
}
.dt__phaseWait,
.dt__phaseIn,
.dt__phaseOut {
  position: absolute;
  right: 0;
  top: 0;
  display: inline-block;
  padding: $sp-1 $sp-2;
  border-radius: $r-pill;
  font-size: 9px;
  font-weight: 800;
  line-height: 1.3;
  white-space: nowrap;
  opacity: 0;
}
.dt__phaseWait {
  background: rgba($subject-cream, .16);
  color: $subject-cream;
  opacity: 1;
}
.dt__phaseIn {
  background: $subject-blue-light;
  color: $subject-ink;
}
.dt__phaseOut {
  background: $subject-cream;
  color: $subject-ink;
}
.dt.is-enter .dt__phaseWait { opacity: 0; }
.dt.is-enter .dt__phaseIn { opacity: 1; }
.dt.is-leave .dt__phaseWait { opacity: 0; }
.dt.is-leave .dt__phaseOut { opacity: 1; }

// 미리보기 — 아래로 스크롤하는 한 주기: 떠오르는 진입, 머무름, 기울며 퇴장
// 나타남·사라짐은 steps 컷(dt-cut), 이동·기울임은 이징(dt-move) — 페이드 중간 프레임이 유령으로 찍히지 않는다
// 안내 문구는 카드가 들어오는 컷과 같은 순간에 사라진다 — 등록 순간의 변화가 퇴장보다 커야 poster 가 주인공 있는 장면이 된다
.dt.is-demo {
  .dt__track {
    animation-name: dt-flow;
    animation-duration: $duration;
    animation-timing-function: $easing;
    animation-iteration-count: infinite;
    animation-fill-mode: backwards;
  }
  .dt__card {
    animation-name: dt-cut, dt-move;
    animation-duration: $duration, $duration;
    animation-timing-function: steps(1, end), $easing;
    animation-iteration-count: infinite, infinite;
    animation-fill-mode: backwards, backwards;
  }
  .dt__hint {
    animation-name: dt-hint;
    animation-duration: $duration;
    animation-timing-function: steps(1, end);
    animation-iteration-count: infinite;
  }
  .dt__phaseWait {
    animation-name: dt-p-wait;
    animation-duration: $duration;
    animation-timing-function: steps(1, end);
    animation-iteration-count: infinite;
  }
  .dt__phaseIn {
    animation-name: dt-p-in;
    animation-duration: $duration;
    animation-timing-function: steps(1, end);
    animation-iteration-count: infinite;
  }
  .dt__phaseOut {
    animation-name: dt-p-out;
    animation-duration: $duration;
    animation-timing-function: steps(1, end);
    animation-iteration-count: infinite;
  }
}

@keyframes dt-flow {
  0%, 8% { transform: translateY(0); }
  // 퇴장 구간(56% 부터)은 linear 로 길게 — 이징이 한 프레임에 몰리면 그 장이 poster 로 뽑힌다
  26%, 56% { transform: translateY(-144px); animation-timing-function: linear; }
  80%, 100% { transform: translateY(-264px); }
}
@keyframes dt-cut {
  0% { opacity: 0; }
  // 카드는 80% 이전에 화면 밖으로 나갔으므로 이 컷은 빈 화면을 바꾼다 (변화 0)
  10%, 78% { opacity: 1; }
  80%, 100% { opacity: 0; }
}
@keyframes dt-move {
  0% { transform: translateY(28px); }
  26%, 56% { transform: none; animation-timing-function: linear; }
  80%, 100% { transform: translateY(-30px) rotate(-5deg) scale(.94); }
}
@keyframes dt-hint {
  0%, 10% { opacity: 1; }
  12%, 100% { opacity: 0; }
}
@keyframes dt-p-wait {
  0%, 12% { opacity: 1; }
  14%, 100% { opacity: 0; }
}
@keyframes dt-p-in {
  0%, 12% { opacity: 0; }
  14%, 58% { opacity: 1; }
  60%, 100% { opacity: 0; }
}
@keyframes dt-p-out {
  0%, 60% { opacity: 0; }
  62%, 100% { opacity: 1; }
}

@media (max-width: 340px) {
  .dt { width: 100%; }
  .dt__head { padding: $sp-1 $sp-2; }
  .dt__view { height: 108px; }
  .dt__hint { padding: $sp-2 0; }
  .dt__card { margin-top: 96px; }
  .dt__filler { padding: $sp-4 0; }
  .dt__foot { padding: $sp-1 $sp-2; }
}

@media (prefers-reduced-motion: reduce) {
  .dt__card { transition: none !important; }
  .dt.is-demo .dt__track,
  .dt.is-demo .dt__card,
  .dt.is-demo .dt__hint,
  .dt.is-demo .dt__phaseWait,
  .dt.is-demo .dt__phaseIn,
  .dt.is-demo .dt__phaseOut { animation: none !important; }
  // 정지 상태 — 카드가 화면 안에 그대로 보인다
  .dt.is-demo .dt__card { opacity: 1 !important; transform: none !important; }
  .dt.is-demo .dt__track { transform: translateY(-144px) !important; }
  .dt.is-demo .dt__hint { opacity: 0 !important; }
  .dt.is-demo .dt__phaseIn { opacity: 1 !important; }
  .dt.is-demo .dt__phaseWait,
  .dt.is-demo .dt__phaseOut { opacity: 0 !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);
}

.dt {
  position: relative;
  box-sizing: border-box;
  width: min(312px, 92vw);
  border-radius: 16px;
  background: #231f28;
  border: 1px solid rgba(255, 247, 230, 0.16);
  color: #fff7e6;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  overflow: hidden;
  box-shadow: 0 14px 24px rgba(23, 20, 26, 0.32);
}

.dt__head {
  display: flex;
  align-items: baseline;
  justify-content: space-between;
  gap: 8px;
  padding: 8px 12px;
}

.dt__title {
  margin: 0;
  font-size: 13px;
  font-weight: 800;
  line-height: 1.3;
}

.dt__attr {
  margin: 0;
  font-size: 10px;
  font-weight: 400;
  line-height: 1.3;
  color: rgba(255, 247, 230, 0.75);
}
.dt__attr code {
  font-family: "Consolas", "Menlo", monospace;
}

.dt__view {
  height: 168px;
  overflow-y: auto;
  padding: 0 12px;
  outline: none;
}

.dt__track {
  display: grid;
  gap: 12px;
  padding-top: 8px;
  padding-bottom: 120px;
}

.dt__hint {
  margin: 0;
  box-sizing: border-box;
  font-size: 10px;
  font-weight: 700;
  line-height: 1.3;
  color: rgba(255, 247, 230, 0.75);
  border: 1px dashed rgba(255, 247, 230, 0.32);
  border-radius: 12px;
  padding: 12px 0;
  text-align: center;
}

.dt__card {
  box-sizing: border-box;
  margin-top: 116px;
  display: grid;
  gap: 4px;
  padding: 12px;
  border-radius: 12px;
  background: #fff7e6;
  color: #17141a;
  opacity: 0;
  transform: translateY(28px);
  transition-property: opacity, transform;
  transition-duration: 220ms, 600ms;
  transition-timing-function: ease-out, cubic-bezier(0.2, 0.8, 0.2, 1);
}
.dt__card b {
  font-size: 15px;
  font-weight: 800;
  line-height: 1.2;
  color: #0a4fe8;
}
.dt__card span {
  font-size: 11px;
  font-weight: 700;
  line-height: 1.3;
}

.dt__card[data-dir=up] {
  transform: translateY(-28px);
}

.dt__card.is-visible {
  opacity: 1;
  transform: none;
}

.dt__card.is-exit[data-dir=down] {
  opacity: 0;
  transform: translateY(-30px) rotate(-5deg) scale(0.94);
}

.dt__card.is-exit[data-dir=up] {
  opacity: 0;
  transform: translateY(34px) rotate(5deg) scale(0.94);
}

.dt__filler {
  margin: 0;
  font-size: 10px;
  font-weight: 700;
  line-height: 1.3;
  color: rgba(255, 247, 230, 0.75);
  border-radius: 12px;
  background: rgba(255, 247, 230, 0.08);
  padding: 24px 0;
  text-align: center;
}

.dt__foot {
  display: flex;
  align-items: center;
  gap: 8px;
  padding: 8px 12px;
  border-top: 1px solid rgba(255, 247, 230, 0.16);
  font-size: 10px;
  font-weight: 700;
  line-height: 1.3;
}

.dt__dirBox {
  position: relative;
  height: 20px;
  flex: 0 0 auto;
}

.dt__dir {
  position: absolute;
  inset: 0;
  display: inline-flex;
  align-items: center;
  gap: 4px;
  white-space: nowrap;
  opacity: 0;
  font-size: 10px;
  font-weight: 700;
  line-height: 1.3;
  color: #5b8cf8;
}

[data-dir=down] .dt__dir--down {
  opacity: 1;
}

[data-dir=up] .dt__dir--up {
  opacity: 1;
}

.dt__ico {
  width: 12px;
  height: 12px;
}

.dt__phase {
  position: relative;
  height: 20px;
  margin-left: auto;
}

.dt__phaseWait,
.dt__phaseIn,
.dt__phaseOut {
  position: absolute;
  right: 0;
  top: 0;
  display: inline-block;
  padding: 4px 8px;
  border-radius: 999px;
  font-size: 9px;
  font-weight: 800;
  line-height: 1.3;
  white-space: nowrap;
  opacity: 0;
}

.dt__phaseWait {
  background: rgba(255, 247, 230, 0.16);
  color: #fff7e6;
  opacity: 1;
}

.dt__phaseIn {
  background: #5b8cf8;
  color: #17141a;
}

.dt__phaseOut {
  background: #fff7e6;
  color: #17141a;
}

.dt.is-enter .dt__phaseWait {
  opacity: 0;
}

.dt.is-enter .dt__phaseIn {
  opacity: 1;
}

.dt.is-leave .dt__phaseWait {
  opacity: 0;
}

.dt.is-leave .dt__phaseOut {
  opacity: 1;
}

.dt.is-demo .dt__track {
  animation-name: dt-flow;
  animation-duration: 2s;
  animation-timing-function: cubic-bezier(0.2, 0.8, 0.2, 1);
  animation-iteration-count: infinite;
  animation-fill-mode: backwards;
}
.dt.is-demo .dt__card {
  animation-name: dt-cut, dt-move;
  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;
}
.dt.is-demo .dt__hint {
  animation-name: dt-hint;
  animation-duration: 2s;
  animation-timing-function: steps(1, end);
  animation-iteration-count: infinite;
}
.dt.is-demo .dt__phaseWait {
  animation-name: dt-p-wait;
  animation-duration: 2s;
  animation-timing-function: steps(1, end);
  animation-iteration-count: infinite;
}
.dt.is-demo .dt__phaseIn {
  animation-name: dt-p-in;
  animation-duration: 2s;
  animation-timing-function: steps(1, end);
  animation-iteration-count: infinite;
}
.dt.is-demo .dt__phaseOut {
  animation-name: dt-p-out;
  animation-duration: 2s;
  animation-timing-function: steps(1, end);
  animation-iteration-count: infinite;
}

@keyframes dt-flow {
  0%, 8% {
    transform: translateY(0);
  }
  26%, 56% {
    transform: translateY(-144px);
    animation-timing-function: linear;
  }
  80%, 100% {
    transform: translateY(-264px);
  }
}
@keyframes dt-cut {
  0% {
    opacity: 0;
  }
  10%, 78% {
    opacity: 1;
  }
  80%, 100% {
    opacity: 0;
  }
}
@keyframes dt-move {
  0% {
    transform: translateY(28px);
  }
  26%, 56% {
    transform: none;
    animation-timing-function: linear;
  }
  80%, 100% {
    transform: translateY(-30px) rotate(-5deg) scale(0.94);
  }
}
@keyframes dt-hint {
  0%, 10% {
    opacity: 1;
  }
  12%, 100% {
    opacity: 0;
  }
}
@keyframes dt-p-wait {
  0%, 12% {
    opacity: 1;
  }
  14%, 100% {
    opacity: 0;
  }
}
@keyframes dt-p-in {
  0%, 12% {
    opacity: 0;
  }
  14%, 58% {
    opacity: 1;
  }
  60%, 100% {
    opacity: 0;
  }
}
@keyframes dt-p-out {
  0%, 60% {
    opacity: 0;
  }
  62%, 100% {
    opacity: 1;
  }
}
@media (max-width: 340px) {
  .dt {
    width: 100%;
  }
  .dt__head {
    padding: 4px 8px;
  }
  .dt__view {
    height: 108px;
  }
  .dt__hint {
    padding: 8px 0;
  }
  .dt__card {
    margin-top: 96px;
  }
  .dt__filler {
    padding: 16px 0;
  }
  .dt__foot {
    padding: 4px 8px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .dt__card {
    transition: none !important;
  }
  .dt.is-demo .dt__track,
  .dt.is-demo .dt__card,
  .dt.is-demo .dt__hint,
  .dt.is-demo .dt__phaseWait,
  .dt.is-demo .dt__phaseIn,
  .dt.is-demo .dt__phaseOut {
    animation: none !important;
  }
  .dt.is-demo .dt__card {
    opacity: 1 !important;
    transform: none !important;
  }
  .dt.is-demo .dt__track {
    transform: translateY(-144px) !important;
  }
  .dt.is-demo .dt__hint {
    opacity: 0 !important;
  }
  .dt.is-demo .dt__phaseIn {
    opacity: 1 !important;
  }
  .dt.is-demo .dt__phaseWait,
  .dt.is-demo .dt__phaseOut {
    opacity: 0 !important;
  }
}

// 방향 감지 — 직전 scrollTop 과 비교해 위로 가는지 아래로 가는지를 정하고
// 들어올 때(is-visible) 와 벗어날 때(is-exit) 모습을 다르게 쓴다
var root = document.getElementById('dt');
var view = document.getElementById('dt-view');
var card = document.getElementById('dt-card');
var lastY = view.scrollTop;
var curDir = 'down';
function readDir() {
  // 직전 스크롤 위치와 비교해 진행 방향을 정한다 — 아래로 가면 down, 위로 가면 up
  var y = view.scrollTop;
  if (y > lastY) curDir = 'down';
  else if (y < lastY) curDir = 'up';
  root.setAttribute('data-dir', curDir);
  lastY = y;
}
var met = false;
var io = new IntersectionObserver(function (entries) {
  entries.forEach(function (entry) {
    // isIntersecting 이 바뀌는 순간마다 방향 값을 갱신한다 — 직전 비교값(curDir) 을 카드에 찍는다
    root.setAttribute('data-dir', curDir);
    card.setAttribute('data-dir', curDir);
    if (entry.isIntersecting) {
      met = true;
      card.classList.add('is-visible');
      card.classList.remove('is-exit');
      root.classList.add('is-enter');
      root.classList.remove('is-leave');
    } else if (met) {
      // 한 번이라도 들어온 뒤에만 퇴장으로 친다 — 첫 적재의 화면 밖 상태는 대기다
      card.classList.remove('is-visible');
      card.classList.add('is-exit');
      root.classList.add('is-leave');
      root.classList.remove('is-enter');
    }
  });
}, { root: view, threshold: 0.2 });
io.observe(card);
view.addEventListener('scroll', function () {
  root.classList.remove('is-demo');
  readDir();
}, { passive: true });
view.addEventListener('pointerdown', function () { root.classList.remove('is-demo'); });
view.addEventListener('keydown', function (e) {
  if (e.key === 'ArrowDown' || e.key === 'ArrowUp') root.classList.remove('is-demo');
});

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

export type DirectionEnterExitProps = {
  title?: string;
  attr?: string;
  hint?: string;
  cardNo?: string;
  cardText?: string;
  filler?: string;
  dirDown?: string;
  dirUp?: string;
  phaseWait?: string;
  phaseIn?: string;
  phaseOut?: string;
  groupLabel?: string;
  listLabel?: string;
  /** 격자 미리보기용 2초 자동 루프. 사람이 손대면 꺼진다 */
  demo?: boolean;
  duration?: number;
  easing?: string;
  color?: string;
};

type Vars = CSSProperties & { "--duration"?: string; "--easing"?: string; "--color"?: string };
// ambient 가 얇아 DOM 요소 타입을 못 쓴다 — 필요한 꼴만 로컬 타입으로 선언
type Box<T> = { current: T };
type KeyEvt = { key: string };

const ICON_DOWN =
  'M207.39 140.94A8 8 0 0 0 200 136h-64V40a8 8 0 0 0-16 0v96H56a8 8 0 0 0-5.66 13.66l72 72a8 8 0 0 0 11.32 0l72-72a8 8 0 0 0 1.73-8.72M128 204.69L75.31 152h105.38Z';
const ICON_DOWN_SOFT = 'm200 144l-72 72l-72-72Z';
const ICON_UP =
  'm205.66 106.34l-72-72a8 8 0 0 0-11.32 0l-72 72A8 8 0 0 0 56 120h64v96a8 8 0 0 0 16 0v-96h64a8 8 0 0 0 5.66-13.66M75.31 104L128 51.31L180.69 104Z';
const ICON_UP_SOFT = 'M200 112H56l72-72Z';

export default function DirectionEnterExit({
  title = "방향 감지 진입·퇴장",
  attr = "scrollTop",
  hint = "아래로 스크롤",
  cardNo = "작품 07",
  cardText = "아래로 지나가면 기울며 퇴장",
  filler = "다음 섹션",
  dirDown = "아래로 이동",
  dirUp = "위로 이동",
  phaseWait = "스크롤 대기",
  phaseIn = "진입 중",
  phaseOut = "퇴장 감지",
  groupLabel = "방향 감지 진입·퇴장 데모",
  listLabel = "카드 목록 — 스크롤 방향에 따라 모습이 달라집니다",
  demo = true,
  duration = 2000,
  easing = "cubic-bezier(.2, .8, .2, 1)",
  color = "#5b8cf8",
}: DirectionEnterExitProps) {
  const [live, setLive] = useState(demo);
  const [dir, setDir] = useState<"down" | "up">("down");
  const [phase, setPhase] = useState<"wait" | "enter" | "leave">("wait");
  const viewRef = useRef<HTMLDivElement>(null) as unknown as Box<HTMLDivElement | null>;
  const cardRef = useRef<HTMLElement | null>(null) as unknown as Box<HTMLElement | null>;
  const lastY = useRef(0) as unknown as Box<number>;
  const met = useRef(false) as unknown as Box<boolean>;
  const curDir = useRef<"down" | "up">("down") as unknown as Box<"down" | "up">;

  // 직전 스크롤 위치와 비교해 진행 방향을 정한다 — 아래로 가면 down, 위로 가면 up
  const readDir = () => {
    const el = viewRef.current;
    if (!el) return;
    const y = el.scrollTop;
    if (y > lastY.current) curDir.current = "down";
    else if (y < lastY.current) curDir.current = "up";
    setDir(curDir.current);
    lastY.current = y;
  };

  useEffect(() => {
    if (live) return;
    const root = viewRef.current;
    const card = cardRef.current;
    if (!root || !card) return;
    // isIntersecting 이 바뀌는 순간마다 방향 값을 갱신한다 — 직전 비교값(curDir) 을 화면에 반영한다
    const io = new IntersectionObserver(
      (entries) => {
        entries.forEach((entry) => {
          setDir(curDir.current);
          if (entry.isIntersecting) {
            met.current = true;
            setPhase("enter");
          } else if (met.current) {
            // 한 번이라도 들어온 뒤에만 퇴장으로 친다 — 첫 적재의 화면 밖 상태는 대기다
            setPhase("leave");
          }
        });
      },
      { root, threshold: 0.2 }
    );
    io.observe(card);
    return () => io.disconnect();
  }, [live]);

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

  return (
    <section
      className={`${styles.dt} ${live ? styles.isDemo : ""}`}
      style={vars}
      aria-label={groupLabel}
    >
      <header className={styles.head}>
        <p className={styles.title}>{title}</p>
        <p className={styles.attr}><code>{attr}</code></p>
      </header>
      <div
        className={styles.view}
        ref={viewRef as unknown as Box<HTMLDivElement>}
        onScroll={() => {
          setLive(false);
          readDir();
        }}
        onPointerDown={() => setLive(false)}
        onKeyDown={(e: KeyEvt) => {
          if (e.key === "ArrowDown" || e.key === "ArrowUp") setLive(false);
        }}
        tabIndex={0}
        role="region"
        aria-label={listLabel}
      >
        <div className={styles.track}>
          <p className={styles.hint}>{hint}</p>
          <article
            ref={(el: HTMLElement | null) => {
              cardRef.current = el;
            }}
            className={`${styles.card} ${styles["dir" + (dir === "down" ? "Down" : "Up")]} ${
              phase === "enter" ? styles.isVisible : ""
            } ${phase === "leave" ? styles.isExit : ""}`}
          >
            <b>{cardNo}</b>
            <span>{cardText}</span>
          </article>
          <p className={styles.filler} aria-hidden="true">{filler}</p>
        </div>
      </div>
      <footer className={styles.foot}>
        <span className={styles.dirBox} aria-hidden="true">
          <span className={`${styles.dir} ${dir === "down" ? styles.on : ""}`}>
            <svg className={styles.ico} xmlns="http://www.w3.org/2000/svg" viewBox="0 0 256 256" aria-hidden="true">
              <g fill="currentColor"><path d={ICON_DOWN_SOFT} opacity=".2" /><path d={ICON_DOWN} /></g>
            </svg>
            <span>{dirDown}</span>
          </span>
          <span className={`${styles.dir} ${dir === "up" ? styles.on : ""}`}>
            <svg className={styles.ico} xmlns="http://www.w3.org/2000/svg" viewBox="0 0 256 256" aria-hidden="true">
              <g fill="currentColor"><path d={ICON_UP_SOFT} opacity=".2" /><path d={ICON_UP} /></g>
            </svg>
            <span>{dirUp}</span>
          </span>
        </span>
        <span className={styles.phase}>
          <span className={`${styles.phaseChip} ${styles.phaseWait} ${phase === "wait" ? styles.on : ""}`}>{phaseWait}</span>
          <span className={`${styles.phaseChip} ${styles.phaseIn} ${phase === "enter" ? styles.on : ""}`}>{phaseIn}</span>
          <span className={`${styles.phaseChip} ${styles.phaseOut} ${phase === "leave" ? styles.on : ""}`}>{phaseOut}</span>
        </span>
      </footer>
    </section>
  );
}