/**
 * Composable for home page hero scroll behavior
 * Linear: hero shrinks 1:1 with scroll, from full screen to fixed header
 */
export const useHeroScroll = () => {
  const scrollY = ref(0)

  // Hero height = viewport height minus some space
  const heroBaseHeight = ref(0)
  const collapsedHeight = 100 // Fixed header height when collapsed

  // Calculate hero height based on viewport
  const updateHeroHeight = () => {
    if (import.meta.client) {
      heroBaseHeight.value = window.innerHeight - 80
    }
  }

  // Linear: height = base - scroll, clamped to min
  const heroHeight = computed(() => {
    return Math.max(collapsedHeight, heroBaseHeight.value - scrollY.value)
  })

  // Linear progress 0..1
  const collapseProgress = computed(() => {
    const maxScroll = heroBaseHeight.value - collapsedHeight
    if (maxScroll <= 0) return 1
    return Math.min(1, Math.max(0, scrollY.value / maxScroll))
  })

  // Is fully collapsed?
  const isCollapsed = computed(() => heroHeight.value <= collapsedHeight)

  const onScroll = () => {
    if (import.meta.client) {
      scrollY.value = window.scrollY
    }
  }

  const onResize = () => {
    updateHeroHeight()
  }

  onMounted(() => {
    if (import.meta.client) {
      updateHeroHeight()
      window.addEventListener('scroll', onScroll, { passive: true })
      window.addEventListener('resize', onResize, { passive: true })
      onScroll()
    }
  })

  onUnmounted(() => {
    if (import.meta.client) {
      window.removeEventListener('scroll', onScroll)
      window.removeEventListener('resize', onResize)
    }
  })

  return {
    scrollY: readonly(scrollY),
    heroBaseHeight: readonly(heroBaseHeight),
    heroHeight,
    collapseProgress,
    isCollapsed,
    collapsedHeight
  }
}