import { ref, computed } from 'vue'

// RAF 封装
const rafFn = (cb) => uni.requestAnimationFrame ? uni.requestAnimationFrame(cb) : setTimeout(cb, 16)
const cafFn = (id) => uni.cancelAnimationFrame ? uni.cancelAnimationFrame(id) : clearTimeout(id)

export function useSwipe() {
  const bgOffsetX = ref(0)
  const screenWidth = ref(375)
  const tileWidth = ref(375)
  
  let rawOffsetX = 0
  let touchStartX = 0
  let lastMoveX = 0
  let lastMoveTime = 0
  let velocity = 0
  let inertiaRaf = null
  let isInertiaPhase = false
  let touchInBanner = false
  
  let onTileChange = null

  const cabinLayerStyle = computed(() => ({
    transform: `translateX(${-tileWidth.value + bgOffsetX.value}px)`
  }))

  const backgroundStripStyle = computed(() => ({
    width: `${tileWidth.value * 3}px`,
    transform: `translateX(${-tileWidth.value + bgOffsetX.value}px)`
  }))

  const clampOffset = (offset) => {
    const w = tileWidth.value
    return (((offset % w) + w) % w) - w
  }

  const normalizeOffset = (offset) => {
    const w = tileWidth.value
    const normalized = clampOffset(offset)
    const prevTileN = Math.floor(-rawOffsetX / w)
    rawOffsetX += offset - bgOffsetX.value
    const nextTileN = Math.floor(-rawOffsetX / w)
    const delta = nextTileN - prevTileN
    
    if (delta !== 0 && onTileChange) {
      onTileChange(delta, isInertiaPhase)
    }
    
    return normalized
  }

  const stopInertia = () => {
    if (inertiaRaf) {
      cafFn(inertiaRaf)
      inertiaRaf = null
    }
    isInertiaPhase = false
  }

  const scrollPage = (direction) => {
    stopInertia()
    
    if (onTileChange) {
      onTileChange(direction, false)
    }
    
    const DURATION = 300
    const FRAME = 16
    const totalFrames = Math.round(DURATION / FRAME)
    const totalDelta = tileWidth.value * direction * -1
    let frame = 0

    const step = () => {
      frame++
      const progress = frame / totalFrames
      const eased = 1 - Math.pow(1 - progress, 3)
      const prevEased = frame === 1 ? 0 : 1 - Math.pow(1 - (frame - 1) / totalFrames, 3)
      const delta = totalDelta * (eased - prevEased)
      
      bgOffsetX.value = clampOffset(bgOffsetX.value + delta)
      rawOffsetX += delta
      
      if (frame < totalFrames) {
        inertiaRaf = rafFn(step)
      }
    }

    inertiaRaf = rafFn(step)
  }

  const getBannerBottom = () => (screenWidth.value / 750) * 496

  const onBgTouchStart = (e) => {
    const touchY = e.touches[0].clientY
    touchInBanner = touchY < getBannerBottom()
    if (touchInBanner) return
    
    stopInertia()
    touchStartX = e.touches[0].clientX
    lastMoveX = touchStartX
    lastMoveTime = Date.now()
    velocity = 0
  }

  const onBgTouchMove = (e) => {
    if (touchInBanner) return
    e.preventDefault()

    const currentX = e.touches[0].clientX
    const now = Date.now()
    const dt = now - lastMoveTime || 1
    velocity = (currentX - lastMoveX) / dt
    lastMoveX = currentX
    lastMoveTime = now
    
    bgOffsetX.value = normalizeOffset(bgOffsetX.value + (currentX - touchStartX))
    touchStartX = currentX
  }

  const onBgTouchEnd = () => {
    if (touchInBanner) {
      touchInBanner = false
      return
    }
    touchInBanner = false
    isInertiaPhase = true
    
    const FRICTION = 0.8
    const MIN_VELOCITY = 0.2

    const step = () => {
      velocity *= FRICTION
      if (Math.abs(velocity) < MIN_VELOCITY) {
        isInertiaPhase = false
        return
      }
      bgOffsetX.value = normalizeOffset(bgOffsetX.value + velocity * 16)
      inertiaRaf = rafFn(step)
    }

    inertiaRaf = rafFn(step)
  }

  const onBgTouchCancel = () => {
    touchInBanner = false
    stopInertia()
    velocity = 0
  }

  const initSwipe = ({ screenW, tileW, onTileChangeCallback }) => {
    screenWidth.value = screenW
    tileWidth.value = tileW
    onTileChange = onTileChangeCallback
    bgOffsetX.value = 0
    rawOffsetX = 0
    velocity = 0
  }

  const reset = () => {
    stopInertia()
    bgOffsetX.value = 0
    rawOffsetX = 0
    velocity = 0
  }

  return {
    bgOffsetX,
    rawOffsetX,
    velocity,
    cabinLayerStyle,
    backgroundStripStyle,
    scrollPage,
    stopInertia,
    initSwipe,
    reset,
    onBgTouchStart,
    onBgTouchMove,
    onBgTouchEnd,
    onBgTouchCancel,
  }
}