<template>
  <view class="swiper-list">
    <scroll-view ref="tabScroll" class="swiper-tabs" direction="horizontal" :show-scrollbar="false">
      <view class="flex-row">
        <text ref="swipertab" space="nbsp" class="swiper-tabs-item"
          :class="swiperIndex==index ? 'swiper-tabs-item-active' : ''" v-for="(item, index) in swiperList" :key="index"
          @click="onTabClick(index)">
          {{item.title}}
        </text>
      </view>
      <view ref="indicator" class="swiper-tabs-indicator"></view>
    </scroll-view>
    <swiper ref="swiper" class="swiper-view" :current="swiperIndex" @transition="onSwiperTransition"
      @animationfinish="onSwiperAnimationfinish">
      <swiper-item class="swiper-item" v-for="(_, index) in swiperList" :key="index">
        <text class="swiper-item-text">{{index}}</text>
        <!-- 可以将上述text组件替换为list组件，实现可左右滑动的长列表 -->
      </swiper-item>
    </swiper>
  </view>
</template>

<script setup lang="ts">
type SwiperTabsItem = {
  x : number,
  w : number
}

type SwiperViewItem = {
  title : string,
}

/**
 * 根据权重在两个值之间执行线性插值.
 * @constructor
 * @param {number} value1 - 第一个值，该值应为下限.
 * @param {number} value2 - 第二个值，该值应为上限.
 * @param {number} amount - 应介于 0 和 1 之间，指示内插的权重.
 * @returns {number} 内插值
 */
function lerpNumber(value1 : number, value2 : number, amount : number) : number {
  return (value1 + (value2 - value1) * amount)
}

const swiperList = ref<SwiperViewItem[]>([])
const swiperIndex = ref(0)
const tabScroll = ref<UniScrollViewElement | null>(null)
const indicator = ref<UniElement | null>(null)
const swiper = ref<UniSwiperElement | null>(null)
const swipertab = ref<UniTextElement[] | null>(null)
const animationFinishIndex = ref(0)
const swiperWidth = ref(0)
const swiperTabsRect = ref<SwiperTabsItem[]>([])

function updateTabIndicator(current_index : number, move_to_index : number, percentage : number) {
  const current_size = swiperTabsRect.value[current_index]
  const move_to_size = swiperTabsRect.value[move_to_index]
  const indicator_line_x = lerpNumber(current_size.x, move_to_size.x, percentage)
  const indicator_line_w = lerpNumber(current_size.w, move_to_size.w, percentage)
  // #ifdef APP
  const x = indicator_line_x + indicator_line_w / 2
  indicator.value?.style?.setProperty('transform', `translateX(${x}px) scaleX(${indicator_line_w})`)
  // #endif
  // #ifdef WEB || MP
  // TODO chrome windows系统 transform scaleX渲染bug
  const x = indicator_line_x
  indicator.value?.style?.setProperty('width', `${indicator_line_w}px`)
  indicator.value?.style?.setProperty('transform', `translateX(${x}px)`)
  // #endif
  const scroll_x = x - swiperWidth.value / 2
  // app 平台后续支持 scrollTo()
  // #ifndef MP-WEIXIN
  tabScroll.value!.scrollLeft = scroll_x
  // #endif
  // #ifdef MP-WEIXIN
  tabScroll.value!.scrollTo({
    left: scroll_x
  })
  // #endif
}

function setSwiperIndex(index : number, updateIndicator : boolean) {
  if (swiperIndex.value === index) {
    return
  }
  swiperIndex.value = index
  if (updateIndicator) {
    updateTabIndicator(index, index, 1)
  }
}

function onTabClick(index : number) {
  setSwiperIndex(index, false)
}

function onSwiperTransition(e : SwiperTransitionEvent) {
  const offset_x = e.detail.dx
  const current_offset_x = offset_x % swiperWidth.value
  const current_offset_i = offset_x / swiperWidth.value
  const current_index = animationFinishIndex.value + parseInt(current_offset_i + '')
  let move_to_index = current_index
  if (current_offset_x > 0 && move_to_index < swiperList.value.length - 1) {
    move_to_index += 1
  } else if (current_offset_x < 0 && move_to_index > 0) {
    move_to_index -= 1
  }
  const percentage = Math.abs(current_offset_x) / swiperWidth.value
  if (current_index != move_to_index) {
    updateTabIndicator(current_index, move_to_index, percentage)
  }
}

function onSwiperAnimationfinish(e : SwiperAnimationFinishEvent) {
  setSwiperIndex(e.detail.current, true)
  animationFinishIndex.value = e.detail.current
}

async function cacheTabItemsSize() {
  swiperTabsRect.value.length = 0;
  const tabs = swipertab.value as UniElement[]
  for (let i = 0; i < tabs.length; i++) {
    const element = tabs[i];
    // #ifdef MP
    const rect = await element.getBoundingClientRectAsync()!
    const x = rect.left
    const w = rect.width
    // #endif
    // #ifndef MP
    const x = element.offsetLeft
    const w = element.offsetWidth
    // #endif
    swiperTabsRect.value.push({
      x,
      w
    } as SwiperTabsItem)
  }
}

onLoad(() => {
  for (let i = 0; i < 8; i++) {
    const space = " ".repeat(i)
    swiperList.value.push({
      title: "Tab " + space + i
    } as SwiperViewItem)
  }
})

onReady(() => {
  (swiper.value as UniSwiperElement).getBoundingClientRectAsync()!.then((res : DOMRect) : Promise<void> => {
    swiperWidth.value = res.width
    return cacheTabItemsSize()
  }).then(() => {
    updateTabIndicator(swiperIndex.value, swiperIndex.value, 1)
  });
})

</script>

<style>
  .flex-row {
    flex-direction: row;
    align-self: flex-start;
  }

  .swiper-list {
    flex: 1;
  }

  .swiper-tabs {
    background-color: #ffffff;
  }

  .swiper-tabs-item {
    color: #555;
    font-size: 16px;
    padding: 12px 25px;
    white-space: nowrap;
  }

  .swiper-tabs-item-active {
    color: #007AFF;
  }

  .swiper-tabs-indicator {
    width: 1px;
    height: 2px;
    background-color: #007AFF;
  }

  .swiper-view {
    flex: 1;
  }

  .swiper-item {
    flex: 1;
    align-items: center;
    justify-content: center;
  }

  .swiper-item-text {
    font-size: 72px;
    font-weight: bold;
  }
</style>