const stackStyle = (stackIndex: number) => {
  if (stackIndex >= 3) return { display: 'none' }

  const scaleMap = [1, 0.95, 0.90]      // 越靠后越小
  const yOffsetMap = [0, 12, 24]         // 越靠后越向下
  const zIndexMap = [30, 29, 28]         // 越靠前越高

  return {
    zIndex: zIndexMap[stackIndex],
    transform: `scale(${scaleMap[stackIndex]}) translateY(${yOffsetMap[stackIndex]}px)`,
    transition: stackIndex === 0 && isDragging.value
      ? 'none'                           // 拖拽中不要過渡
      : 'transform 0.35s ease'
  }
}

const SWIPE_THRESHOLD = 72  // px，超過此值觸發(fā)飛出
const isDragging = ref(false)
const dragX = ref(0)

const onPointerDown = (e: PointerEvent) => {
  isDragging.value = true
  startX.value = e.clientX
  ;(e.target as HTMLElement).setPointerCapture(e.pointerId)
}

const onPointerMove = (e: PointerEvent) => {
  if (!isDragging.value) return
  dragX.value = e.clientX - startX.value
}

const onPointerUp = () => {
  if (!isDragging.value) return
  isDragging.value = false

  if (Math.abs(dragX.value) > SWIPE_THRESHOLD) {
    // 觸發(fā)飛出
    const direction = dragX.value > 0 ? 'right' : 'left'
    flyAway(direction)
  } else {
    // 復(fù)位
    dragX.value = 0
  }
}

const feedbackColor = computed(() => {
  const ratio = Math.min(Math.abs(dragX.value) / SWIPE_THRESHOLD, 1)
  if (dragX.value > 0) {
    return `rgba(34, 197, 94, ${ratio * 0.3})`  // 綠色 = 認(rèn)識(shí)
  } else if (dragX.value < 0) {
    return `rgba(239, 68, 68, ${ratio * 0.3})`  // 紅色 = 不認(rèn)識(shí)
  }
  return 'transparent'
})

const checkIconOpacity = computed(() =>
  dragX.value > 0 ? Math.min(dragX.value / SWIPE_THRESHOLD, 1) : 0
)

const crossIconOpacity = computed(() =>
  dragX.value < 0 ? Math.min(-dragX.value / SWIPE_THRESHOLD, 1) : 0
)

const flyAway = (direction: 'left' | 'right') => {
  const targetX = direction === 'right' ? window.innerWidth * 1.5 : -window.innerWidth * 1.5
  flyX.value = targetX
  flyRotation.value = direction === 'right' ? 20 : -20

  // 記錄結(jié)果
  const result = direction === 'right' ? 'known' : 'forgotten'
  submitReview(currentWord.value.id, result)

  // 動(dòng)畫結(jié)束后移除當(dāng)前詞，推進(jìn)隊(duì)列
  setTimeout(() => {
    words.value.shift()
    flyX.value = 0
    flyRotation.value = 0
    dragX.value = 0
    // 隊(duì)列快用完時(shí)預(yù)加載
    if (words.value.length < 5) fetchMoreWords()
  }, 350)
}

type QueueMode = 'high' | 'outline' | 'mixed' | 'wrong'

const switchQueue = async (mode: QueueMode) => {
  currentMode.value = mode
  words.value = []
  await fetchWords(mode)
}