/**
 * NOTE
 * The ./unread.ts API:
 *
 * - Provides a `checkUnread()` function to sync with the server,
 * - Periodically calls `checkUnread()`, and
 * - Caches the first page of notifications.
 *
 * IMPORTANT: This query uses ./unread.ts's cache as its first page,
 * IMPORTANT: which means the cache-freshness of this query is driven by the unread API.
 *
 * Follow these rules:
 *
 * 1. Call `checkUnread()` if you want to fetch latest in the background.
 * 2. Call `checkUnread({invalidate: true})` if you want latest to sync into this query's results immediately.
 * 3. Don't call this query's `refetch()` if you're trying to sync latest; call `checkUnread()` instead.
 */

import {useEffect, useRef} from 'react'
import {AppBskyFeedDefs} from '@atproto/api'
import {
  useInfiniteQuery,
  InfiniteData,
  QueryKey,
  useQueryClient,
  QueryClient,
} from '@tanstack/react-query'
import {useModerationOpts} from '../preferences'
import {useUnreadNotificationsApi} from './unread'
import {fetchPage} from './util'
import {FeedPage} from './types'
import {useMutedThreads} from '#/state/muted-threads'
import {STALE} from '..'
import {embedViewRecordToPostView, getEmbeddedPost} from '../util'

export type {NotificationType, FeedNotification, FeedPage} from './types'

const PAGE_SIZE = 30

type RQPageParam = string | undefined

export function RQKEY() {
  return ['notification-feed']
}

export function useNotificationFeedQuery(opts?: {enabled?: boolean}) {
  const queryClient = useQueryClient()
  const moderationOpts = useModerationOpts()
  const threadMutes = useMutedThreads()
  const unreads = useUnreadNotificationsApi()
  const enabled = opts?.enabled !== false
  // state tracked across page fetches
  const pageState = useRef({pageNum: 0, hasMarkedRead: false})

  const query = useInfiniteQuery<
    FeedPage,
    Error,
    InfiniteData<FeedPage>,
    QueryKey,
    RQPageParam
  >({
    staleTime: STALE.INFINITY,
    queryKey: RQKEY(),
    async queryFn({pageParam}: {pageParam: RQPageParam}) {
      let page
      if (!pageParam) {
        // for the first page, we check the cached page held by the unread-checker first
        page = unreads.getCachedUnreadPage()
        // reset the page state
        pageState.current = {pageNum: 0, hasMarkedRead: false}
      }
      if (!page) {
        page = await fetchPage({
          limit: PAGE_SIZE,
          cursor: pageParam,
          queryClient,
          moderationOpts,
          threadMutes,
        })
      }

      // NOTE
      // this section checks to see if we need to mark notifs read
      // we want to wait until we've seen a read notification because
      // of a timing challenge; marking read on the first page would
      // cause subsequent pages of unread notifs to incorrectly come
      // back as "read". we use page 6 as an abort condition, which means
      // after ~180 notifs we give up on tracking unread state correctly
      // -prf
      if (!pageState.current.hasMarkedRead) {
        let hasMarkedRead = false
        if (
          pageState.current.pageNum > 5 ||
          page.items.some(item => item.notification.isRead)
        ) {
          unreads.markAllRead()
          hasMarkedRead = true
        }
        pageState.current = {
          pageNum: pageState.current.pageNum + 1,
          hasMarkedRead,
        }
      }

      return page
    },
    initialPageParam: undefined,
    getNextPageParam: lastPage => lastPage.cursor,
    enabled,
  })

  useEffect(() => {
    const {isFetching, hasNextPage, data} = query

    let count = 0
    let numEmpties = 0
    for (const page of data?.pages || []) {
      if (!page.items.length) {
        numEmpties++
      }
      count += page.items.length
    }

    if (!isFetching && hasNextPage && count < PAGE_SIZE && numEmpties < 3) {
      query.fetchNextPage()
    }
  }, [query])

  return query
}

/**
 * This helper is used by the post-thread placeholder function to
 * find a post in the query-data cache
 */
export function findPostInQueryData(
  queryClient: QueryClient,
  uri: string,
): AppBskyFeedDefs.PostView | undefined {
  const generator = findAllPostsInQueryData(queryClient, uri)
  const result = generator.next()
  if (result.done) {
    return undefined
  } else {
    return result.value
  }
}

export function* findAllPostsInQueryData(
  queryClient: QueryClient,
  uri: string,
): Generator<AppBskyFeedDefs.PostView, void> {
  const queryDatas = queryClient.getQueriesData<InfiniteData<FeedPage>>({
    queryKey: ['notification-feed'],
  })
  for (const [_queryKey, queryData] of queryDatas) {
    if (!queryData?.pages) {
      continue
    }
    for (const page of queryData?.pages) {
      for (const item of page.items) {
        if (item.subject?.uri === uri) {
          yield item.subject
        }
        const quotedPost = getEmbeddedPost(item.subject?.embed)
        if (quotedPost?.uri === uri) {
          yield embedViewRecordToPostView(quotedPost)
        }
      }
    }
  }
}