<script lang="ts" setup>
import { ref, computed, nextTick, reactive, watchEffect, onUnmounted } from 'vue'

const props = defineProps<{
  listData: Array<any>
}>()

// 列表HTMLElementDom
const ulRef = ref<any>(null)

// 屏幕高度
const screenH = document.documentElement.clientHeight

const data = reactive<any>({
  // 列表第一項(xiàng)的高度（起始高度）
  initH: 0,

  // 一行的高度
  unitH: 0,

  // 屏幕范圍內(nèi)能顯示個數(shù)
  displayCount: 1,

  // 列表起始值
  startIdx: 0
})

const listData = computed(() => {
  let endIdx = data.startIdx + data.displayCount
  if (endIdx >= props.listData.length) endIdx = props.listData.length

  return props.listData.slice(data.startIdx, endIdx).map((v, k) => {
    v.idx = data.startIdx + k + 1
    return v
  })
})

function scrollHandler() {
  // 當(dāng)前滾動高度
  const curScrollTop = document.documentElement.scrollTop
  if (curScrollTop > data.initH) {
    const addCount = Math.floor((curScrollTop - data.initH) / data.unitH)
    ulRef.value.style.setProperty('padding-top', `${addCount * data.unitH}px`)
    data.startIdx = addCount
  } else {
    ulRef.value.style.setProperty('padding-top', '0px')
    data.startIdx = 0
  }
}

watchEffect(() => {
  if (props.listData.length > 0) {
    nextTick(() => {
      // 列表距離頂部距離
      data.initH = ulRef.value.getBoundingClientRect().top + document.documentElement.scrollTop
      // 計(jì)算每行高度
      data.unitH = ulRef.value.children[0].offsetHeight
      // 計(jì)算屏幕內(nèi)能顯示的行數(shù)
      data.displayCount = Math.ceil(screenH / data.unitH)
      // 設(shè)置列表總高度 = 一行高度 * 行數(shù)
      const listH = data.unitH * props.listData.length
      ulRef.value.style.setProperty('height', `${listH}px`)

      window.removeEventListener('scroll', scrollHandler)
      window.addEventListener('scroll', scrollHandler)
    })
  }
})

onUnmounted(() => {
  window.removeEventListener('scroll', scrollHandler)
})
</script>

<template>
  <ul ref="ulRef">
    <li v-for="(listItem, listIndex) in listData" :key="`list-${listIndex}`" :data-idx="listItem.idx">
      <slot :listItem="listItem"></slot>
    </li>
  </ul>
</template>

<script lang="ts" setup>
import InfiniteList from './InfiniteList.vue'

const songs = [] // 列表數(shù)據(jù)
</script>

<template>
  <infinite-list :listData="songs">
    <template #default="{ listItem }">
      <div>{{ listItem.title }}</div>
      <!-- ... -->
    </template>
  </infinite-list>
</template>