/**
 * 滚动入场动画 composable
 * 元素进入视口时触发淡入上滑动画
 * 自动尊重 prefers-reduced-motion
 */
export default function useScrollReveal() {
  onMounted(() => {
    // 尊重用户减少动效偏好
    if (window.matchMedia('(prefers-reduced-motion: reduce)').matches) return

    const observer = new IntersectionObserver(
      (entries) => {
        entries.forEach((entry) => {
          if (entry.isIntersecting) {
            entry.target.classList.add('is-visible')
            observer.unobserve(entry.target)
          }
        })
      },
      { threshold: 0.1, rootMargin: '0px 0px -40px 0px' }
    )

    document.querySelectorAll('.reveal').forEach((el) => {
      observer.observe(el)
    })

    onUnmounted(() => observer.disconnect())
  })
}