import 'intersection-observer'
import * as React from 'react'
import useLayoutEffect from '@react-hook/passive-layout-effect'

function useIntersectionObserver<T extends HTMLElement = HTMLElement>(
  target: React.RefObject<T> | T | null,
  options: IntersectionObserverOptions = {}
): MockIntersectionObserverEntry | IntersectionObserverEntry {
  const {
    root = null,
    pollInterval = null,
    useMutationObserver = false,
    rootMargin = '0px 0px 0px 0px',
    threshold = 0,
    initialIsIntersecting = false,
  } = options
  const [entry, setEntry] = React.useState<
    IntersectionObserverEntry | MockIntersectionObserverEntry
  >(() => ({
    boundingClientRect: null,
    intersectionRatio: 0,
    intersectionRect: null,
    isIntersecting: initialIsIntersecting,
    rootBounds: null,
    target: null,
    time: 0,
  }))
  const [observer, setObserver] = React.useState(() =>
    getIntersectionObserver({
      root,
      pollInterval,
      useMutationObserver,
      rootMargin,
      threshold,
    })
  )

  React.useEffect(() => {
    const observer = getIntersectionObserver({
      root,
      pollInterval,
      useMutationObserver,
      rootMargin,
      threshold,
    })
    setObserver(observer)
    // eslint-disable-next-line react-hooks/exhaustive-deps
  }, [
    root,
    rootMargin,
    pollInterval,
    useMutationObserver,
    JSON.stringify(threshold),
  ])

  useLayoutEffect(() => {
    const targetEl = target && 'current' in target ? target.current : target
    if (!observer || !targetEl) return
    let didUnsubscribe = false
    observer.observer.observe(targetEl)

    const callback = (entries: IntersectionObserverEntry[]) => {
      if (didUnsubscribe) return

      for (let i = 0; i < entries.length; i++) {
        const entry = entries[i]
        if (entry.target === targetEl) {
          setEntry(entry)
        }
      }
    }

    observer.subscribe(callback)

    return () => {
      didUnsubscribe = true
      observer.observer.unobserve(targetEl)
      observer.unsubscribe(callback)
    }
  }, [target, observer])

  return entry
}

function createIntersectionObserver({
  root = null,
  pollInterval = null,
  useMutationObserver = false,
  rootMargin = '0px 0px 0px 0px',
  threshold = 0,
}: IntersectionObserverOptions) {
  const callbacks: Set<IntersectionObserverCallback> = new Set()
  if (typeof IntersectionObserver === 'undefined') return null
  const observer = new IntersectionObserver(
    (entries) => {
      for (const callback of callbacks) callback(entries, observer)
    },
    {root, rootMargin, threshold}
  )
  // @ts-ignore
  observer.POLL_INTERVAL = pollInterval
  // @ts-ignore
  observer.USE_MUTATION_OBSERVER = useMutationObserver

  return {
    observer,
    getListeners() {
      return callbacks
    },
    subscribe: (callback: IntersectionObserverCallback) =>
      callbacks.add(callback),
    unsubscribe: (callback: IntersectionObserverCallback) =>
      callbacks.delete(callback),
  }
}

const _intersectionObserver: Map<
  HTMLElement | null | undefined,
  Record<string, ReturnType<typeof createIntersectionObserver>>
> = new Map()

function getIntersectionObserver(options: IntersectionObserverOptions) {
  const {root, ...keys} = options
  const key = JSON.stringify(keys)
  let base = _intersectionObserver.get(root)
  if (!base) {
    base = {}
    _intersectionObserver.set(root, base)
  }
  return !base[key]
    ? (base[key] = createIntersectionObserver(options))
    : base[key]
}

export type UseIntersectionObserverCallback = (
  entry: IntersectionObserverEntry,
  observer: IntersectionObserver
) => any

export interface IntersectionObserverOptions {
  root?: HTMLElement | null
  pollInterval?: number | null
  useMutationObserver?: boolean
  rootMargin?: string
  threshold?: number | number[]
  initialIsIntersecting?: boolean
}

export interface IntersectionObserverBounds {
  readonly height: number
  readonly width: number
  readonly top: number
  readonly left: number
  readonly right: number
  readonly bottom: number
}

export interface MockIntersectionObserverEntry {
  readonly time: number | null
  readonly rootBounds: IntersectionObserverBounds | null
  readonly boundingClientRect: IntersectionObserverBounds | null
  readonly intersectionRect: IntersectionObserverBounds | null
  readonly intersectionRatio: number | null
  readonly target: HTMLElement | null
  readonly isIntersecting: boolean
}

export default useIntersectionObserver