import { useRef } from 'react'
import type { GestureResponderEvent, ScrollView as RNScrollView } from 'react-native'
import type { ScrollBridge } from './types'

interface ResponderState {
  lastPageY: number
  dragAt: number
  dys: number[]
  isScrolling: boolean
  isDraggingScrollArea: boolean
  scrollEngaged: boolean
  prevScrollY: number
  handoffOccurred: boolean
  handoffDragOffset: number
}

interface UseSheetScrollViewGesturesProps {
  scrollRef: React.RefObject<RNScrollView | null>
  scrollBridge: ScrollBridge
  hasScrollableContent: boolean
  scrollEnabled: boolean
  setScrollEnabled: (enabled: boolean, lockTo?: number) => void
}

/**
 * Native gesture handling for Sheet ScrollView.
 * Returns responder props for the ScrollView component.
 */
export function useSheetScrollViewGestures({
  scrollBridge,
  hasScrollableContent,
  scrollEnabled,
  setScrollEnabled,
}: UseSheetScrollViewGesturesProps) {
  const state = useRef<ResponderState>({
    lastPageY: 0,
    dragAt: 0,
    dys: [],
    isScrolling: false,
    isDraggingScrollArea: false,
    scrollEngaged: false,
    prevScrollY: 0,
    handoffOccurred: false,
    handoffDragOffset: 0,
  })

  const release = () => {
    const s = state.current
    if (!s.isDraggingScrollArea) return

    s.isDraggingScrollArea = false
    scrollBridge.scrollStartY = -1
    scrollBridge.scrollLock = false
    s.isScrolling = false
    s.scrollEngaged = false
    s.prevScrollY = 0
    s.handoffOccurred = false
    s.handoffDragOffset = 0
    setScrollEnabled(true)

    let vy = 0
    if (s.dys.length) {
      const recentDys = s.dys.slice(-10)
      const dist = recentDys.reduce((a, b) => a + b, 0)
      vy = (dist / recentDys.length) * 0.04
    }
    s.dys = []

    scrollBridge.release({ dragAt: s.dragAt, vy })
  }

  const onStartShouldSetResponder = () => {
    const s = state.current
    scrollBridge.scrollStartY = -1
    s.isDraggingScrollArea = true
    s.scrollEngaged = scrollBridge.y > 0
    s.prevScrollY = scrollBridge.y
    s.handoffOccurred = false
    s.handoffDragOffset = 0
    return false
  }

  const onMoveShouldSetResponder = (e: GestureResponderEvent) => {
    if (!scrollEnabled) return false
    const s = state.current
    const { pageY } = e.nativeEvent
    if (s.lastPageY === 0) {
      s.lastPageY = pageY
      return false
    }
    return Math.abs(pageY - s.lastPageY) > 10
  }

  const onResponderMove = (e: GestureResponderEvent) => {
    const s = state.current
    const { pageY } = e.nativeEvent

    if (!s.isScrolling && scrollBridge.scrollStartY === -1) {
      scrollBridge.scrollStartY = pageY
      s.lastPageY = pageY
    }

    const dragAt = pageY - scrollBridge.scrollStartY
    const dy = pageY - s.lastPageY
    s.lastPageY = pageY
    const isDraggingDown = dy > 0
    const isPaneAtTop = scrollBridge.paneY <= scrollBridge.paneMinY + 5
    const currentScrollY = scrollBridge.y

    if (currentScrollY > 0) s.scrollEngaged = true

    const wasScrolledNowAtZero =
      s.scrollEngaged && s.prevScrollY > 0 && currentScrollY <= 0

    if (wasScrolledNowAtZero && !s.handoffOccurred) {
      s.handoffOccurred = true
      s.handoffDragOffset = 0
    }

    s.prevScrollY = currentScrollY

    let panHandles = false
    if (!isPaneAtTop) {
      panHandles = isDraggingDown ? currentScrollY <= 0 || !hasScrollableContent : true
    } else if (isDraggingDown) {
      if (currentScrollY > 0 && hasScrollableContent && !s.handoffOccurred) {
        panHandles = false
      } else {
        panHandles = s.handoffOccurred || wasScrolledNowAtZero || currentScrollY <= 0
      }
    } else {
      panHandles = !hasScrollableContent
      if (!panHandles) {
        s.isScrolling = true
        scrollBridge.scrollLock = true
        setScrollEnabled(true)
        return
      }
    }

    if (panHandles) {
      setScrollEnabled(false)
      let effectiveDragAt = dragAt
      if (s.handoffOccurred) {
        s.handoffDragOffset += dy
        effectiveDragAt = s.handoffDragOffset
      }
      scrollBridge.drag(effectiveDragAt)
      s.dragAt = effectiveDragAt
      s.dys.push(dy)
      if (s.dys.length > 100) s.dys = s.dys.slice(-10)
    } else {
      setScrollEnabled(true)
    }
  }

  return {
    onResponderRelease: release,
    onStartShouldSetResponder,
    onMoveShouldSetResponder,
    onResponderMove,
  }
}