/**
 * 智能滚动 Composable
 * 参考 @agentscope-ai/chat 的 StickToBottom 实现，提供智能的自动滚动体验
 */
import { ref, computed, onMounted, onUnmounted } from 'vue'

export interface StickToBottomOptions {
  /** 是否启用 */
  enabled?: boolean
  /** 触发滚动的偏移阈值（像素） */
  offset?: number
  /** 是否使用平滑滚动 */
  smooth?: boolean
  /** 滚动持续时间（毫秒） */
  duration?: number
}

export interface StickToBottomReturn {
  /** 是否在底部 */
  isAtBottom: import('vue').Ref<boolean>
  /** 是否在底部附近 */
  isNearBottom: import('vue').ComputedRef<boolean>
  /** 是否被用户滚动中断 */
  escapedFromLock: import('vue').Ref<boolean>
  /** 滚动元素引用 */
  scrollRef: import('vue').Ref<HTMLElement | null>
  /** 内容元素引用 */
  contentRef: import('vue').Ref<HTMLElement | null>
  /** 滚动到底部 */
  scrollToBottom: (options?: { force?: boolean; smooth?: boolean }) => Promise<void>
  /** 停止自动滚动 */
  stopScroll: () => void
  /** 检查是否在底部 */
  checkIsAtBottom: () => boolean
}

// 默认配置
const DEFAULT_OPTIONS: Required<StickToBottomOptions> = {
  enabled: true,
  offset: 70,
  smooth: true,
  duration: 350,
}

export function useStickToBottom(
  options: StickToBottomOptions = {}
): StickToBottomReturn {
  const opts = { ...DEFAULT_OPTIONS, ...options }
  
  const scrollRef = ref<HTMLElement | null>(null)
  const contentRef = ref<HTMLElement | null>(null)
  
  const isAtBottom = ref(true)
  const escapedFromLock = ref(false)
  let isScrolling = false
  let lastScrollTop = 0
  let isSelecting = false

  // 是否在底部附近
  const isNearBottom = computed(() => {
    if (!scrollRef.value) return false
    const { scrollHeight, scrollTop, clientHeight } = scrollRef.value
    return scrollHeight - scrollTop - clientHeight <= opts.offset
  })

  // 检查是否在底部
  const checkIsAtBottom = () => {
    if (!scrollRef.value) return false
    const { scrollHeight, scrollTop, clientHeight } = scrollRef.value
    return scrollHeight - scrollTop - clientHeight <= opts.offset
  }

  // 滚动到底部
  const scrollToBottom = async (scrollOptions?: { force?: boolean; smooth?: boolean }) => {
    const { force = false, smooth = opts.smooth } = scrollOptions || {}
    
    if (!scrollRef.value) return
    
    // 如果用户已经向上滚动，且不强制滚动，则跳过
    if (!force && escapedFromLock.value) return
    
    // 如果正在选择文本，不滚动
    if (isSelecting) return

    const element = scrollRef.value
    const targetScrollTop = element.scrollHeight - element.clientHeight

    // 已经在底部，无需滚动
    if (element.scrollTop >= targetScrollTop - 1) return

    isScrolling = true

    if (smooth && 'scrollBehavior' in document.documentElement.style) {
      // 使用原生平滑滚动
      element.scrollTo({ top: targetScrollTop, behavior: 'smooth' })
      
      // 等待滚动完成
      await new Promise<void>((resolve) => {
        const startedAt = performance.now()
        const checkScrollEnd = () => {
          if (!isScrolling || Math.abs(element.scrollTop - targetScrollTop) < 1
              || performance.now() - startedAt > opts.duration * 2) {
            isScrolling = false
            lastScrollTop = element.scrollTop
            resolve()
          } else {
            requestAnimationFrame(checkScrollEnd)
          }
        }
        setTimeout(checkScrollEnd, opts.duration)
      })
    } else {
      // 直接滚动
      element.scrollTop = targetScrollTop
      isScrolling = false
      lastScrollTop = element.scrollTop
    }

    isAtBottom.value = true
  }

  // 停止自动滚动
  const stopScroll = () => {
    escapedFromLock.value = true
    isAtBottom.value = false
  }

  // 处理滚动事件
  const handleScroll = () => {
    if (!scrollRef.value) return
    if (isScrolling) {
      lastScrollTop = scrollRef.value.scrollTop
      return
    }

    const element = scrollRef.value
    const currentScrollTop = element.scrollTop
    
    // 检测滚动方向
    const isScrollingUp = currentScrollTop < lastScrollTop
    const isScrollingDown = currentScrollTop > lastScrollTop
    
    lastScrollTop = currentScrollTop

    // 向上滚动，用户想要查看历史内容，中断自动滚动
    if (isScrollingUp) {
      escapedFromLock.value = true
      isAtBottom.value = false
    }

    // 向下滚动到底部，恢复自动滚动
    if ((isScrollingDown || checkIsAtBottom()) && isNearBottom.value) {
      escapedFromLock.value = false
      isAtBottom.value = true
    }
  }

  // 处理鼠标滚轮
  const handleWheel = (e: WheelEvent) => {
    if (!scrollRef.value) return
    
    // 如果用户向上滚动，确保我们记录这个行为
    if (e.deltaY < 0) {
      isScrolling = false
      escapedFromLock.value = true
      isAtBottom.value = false
    }
  }

  // 处理鼠标/触摸开始（选择文本）
  const handlePointerDown = () => {
    isSelecting = true
  }

  const handlePointerUp = () => {
    isSelecting = false
    // 选择结束后检查是否在底部
    setTimeout(() => {
      if (checkIsAtBottom()) {
        escapedFromLock.value = false
        isAtBottom.value = true
      }
    }, 100)
  }

  // ResizeObserver 监听内容变化
  let resizeObserver: ResizeObserver | null = null

  onMounted(() => {
    if (!scrollRef.value) return

    const element = scrollRef.value

    // 添加事件监听
    element.addEventListener('scroll', handleScroll, { passive: true })
    element.addEventListener('wheel', handleWheel, { passive: true })
    element.addEventListener('mousedown', handlePointerDown)
    element.addEventListener('touchstart', handlePointerDown)
    document.addEventListener('mouseup', handlePointerUp)
    document.addEventListener('touchend', handlePointerUp)

    // 监听内容变化
    if (contentRef.value && window.ResizeObserver) {
      resizeObserver = new ResizeObserver(() => {
        // 内容变化时，如果在底部则保持滚动到底部
        if (opts.enabled && isAtBottom.value && !escapedFromLock.value) {
          scrollToBottom({ smooth: false })
        }
      })
      resizeObserver.observe(contentRef.value)
    }

    // 初始化滚动位置
    if (opts.enabled) {
      scrollToBottom({ smooth: false })
    }
  })

  onUnmounted(() => {
    if (!scrollRef.value) return

    const element = scrollRef.value

    // 移除事件监听
    element.removeEventListener('scroll', handleScroll)
    element.removeEventListener('wheel', handleWheel)
    element.removeEventListener('mousedown', handlePointerDown)
    element.removeEventListener('touchstart', handlePointerDown)
    document.removeEventListener('mouseup', handlePointerUp)
    document.removeEventListener('touchend', handlePointerUp)

    // 断开 ResizeObserver
    if (resizeObserver) {
      resizeObserver.disconnect()
      resizeObserver = null
    }
  })

  return {
    isAtBottom,
    isNearBottom,
    escapedFromLock,
    scrollRef,
    contentRef,
    scrollToBottom,
    stopScroll,
    checkIsAtBottom,
  }
}

export default useStickToBottom