import { noop } from 'lodash'
import { RefObject, useCallback, useRef } from 'react'
import {
  FlatList,
  LayoutChangeEvent,
  NativeScrollEvent,
  NativeSyntheticEvent,
  Platform,
} from 'react-native'

const REST_OFFSET = 1

/**
 * iOS starts a sheet's interactive dismissal once the content scroll view sits at its
 * top content edge — for an inverted list, wherever the newest message rests. Resting
 * the list 1pt in from that edge keeps a drag at the bottom of a conversation scrolling
 * history instead of swiping the modal away.
 */
export const useRestAwayFromDismissEdge = ({
  listRef,
  enabled = Platform.OS === 'ios',
}: {
  listRef: RefObject<FlatList | null>
  enabled?: boolean
}) => {
  const layoutHeight = useRef(0)
  const contentHeight = useRef(0)
  const didSetInitialOffset = useRef(false)

  const canRestAwayFromEdge = useCallback(
    () => layoutHeight.current > 0 && contentHeight.current - layoutHeight.current >= REST_OFFSET,
    []
  )

  const restAwayFromDismissEdge = useCallback(() => {
    if (!canRestAwayFromEdge()) return
    listRef.current?.scrollToOffset({ animated: false, offset: REST_OFFSET })
  }, [canRestAwayFromEdge, listRef])

  const applyInitialOffsetOnceScrollable = useCallback(() => {
    if (didSetInitialOffset.current || !canRestAwayFromEdge()) return
    didSetInitialOffset.current = true
    restAwayFromDismissEdge()
  }, [canRestAwayFromEdge, restAwayFromDismissEdge])

  const handleLayout = useCallback(
    (event: LayoutChangeEvent) => {
      layoutHeight.current = event.nativeEvent.layout.height
      applyInitialOffsetOnceScrollable()
    },
    [applyInitialOffsetOnceScrollable]
  )

  const handleContentSizeChange = useCallback(
    (_width: number, height: number) => {
      contentHeight.current = height
      applyInitialOffsetOnceScrollable()
    },
    [applyInitialOffsetOnceScrollable]
  )

  // A negative offset means the bounce is still animating; let it settle first.
  const handleScrollSettled = useCallback(
    (event: NativeSyntheticEvent<NativeScrollEvent>) => {
      const offsetY = event.nativeEvent.contentOffset.y

      if (offsetY >= 0 && offsetY < REST_OFFSET) {
        restAwayFromDismissEdge()
      }
    },
    [restAwayFromDismissEdge]
  )

  if (!enabled) {
    return {
      restOffset: 0,
      onLayout: noop,
      onContentSizeChange: noop,
      onScrollEndDrag: noop,
      onMomentumScrollEnd: noop,
    }
  }

  return {
    restOffset: REST_OFFSET,
    onLayout: handleLayout,
    onContentSizeChange: handleContentSizeChange,
    onScrollEndDrag: handleScrollSettled,
    onMomentumScrollEnd: handleScrollSettled,
  }
}