import { InfiniteData } from '@tanstack/react-query'
import { ApiCollection, MessageResource } from '../../types'
import { RequestData } from '../client'

export type MessagesWindow = InfiniteData<
  ApiCollection<MessageResource>,
  Partial<RequestData> | undefined
>

export const livePageParam: Partial<RequestData> = {}

export const anchoredPageParam = (anchor: string): Partial<RequestData> => ({
  where: { id_around: anchor },
})

export function isBehindLiveEdge(data: MessagesWindow | undefined): boolean {
  return !!data?.pages[0]?.meta?.prev
}

export function newerPageParam(
  firstPage: ApiCollection<MessageResource>
): Partial<RequestData> | undefined {
  const newestId = firstPage.meta?.prev?.idGt
  if (!newestId) return undefined

  // Without asc the server hands back the newest page instead, leaving a gap.
  return { where: { id_gt: newestId }, order: 'asc' }
}

// The server returns newer pages oldest first, linking only to the next newer page.
// Storing them newest first with an older link lets a refetch replay the window
// forward from its top page like any other.
export function newestFirst<Page extends ApiCollection<MessageResource>>(
  page: Page,
  pageParam: Partial<RequestData> | undefined
): Page {
  if (pageParam?.order !== 'asc') return page

  const data = [...page.data].reverse()
  const oldest = data[data.length - 1]
  return {
    ...page,
    data,
    meta: { ...page.meta, prev: page.meta?.next, next: oldest && { idLt: oldest.id } },
  }
}

export function markLiveIfCaughtUp(data: MessagesWindow | undefined): MessagesWindow | undefined {
  if (!data) return data

  const topIsLive = !data.pageParams[0]?.where
  if (topIsLive || isBehindLiveEdge(data)) return data

  return { ...data, pageParams: [livePageParam, ...data.pageParams.slice(1)] }
}