import { useQuery, useQueryClient, type QueryClient } from '@tanstack/react-query'
import { useShallow } from 'zustand/react/shallow'
import { useFilterStore, filtersToParams } from '../store/filterStore'
import { usePhotosBackgroundLoadingStore } from '../store/photosBackgroundLoadingStore'
import api from '../services/api'
import type { Photo } from '../types/photo'

export function usePhotosLoadingMore(): boolean {
  return usePhotosBackgroundLoadingStore((s) => s.inFlight > 0)
}

/**
 * Optimistically strip the supplied photo ids from every cached
 * timeline list. Used by discard / delete flows so the photos vanish
 * from the grid the instant the user acts, without waiting for the
 * mutation round-trip + invalidation refetch. The subsequent invalidate
 * still runs and reconciles the cache with server truth.
 */
export function stripPhotosFromCache(queryClient: QueryClient, ids: string[]) {
  if (ids.length === 0) return
  const removed = new Set(ids)
  queryClient.setQueriesData<Photo[]>({ queryKey: ['photos'] }, (prev) => {
    if (!prev) return prev
    return prev.filter((p) => !removed.has(p.id))
  })
}

interface CursorPage {
  photos: Photo[]
  next_cursor: string | null
}

async function fetchCursorPage(
  params: Record<string, unknown>,
  signal?: AbortSignal,
): Promise<CursorPage> {
  const resp = await api.get<CursorPage>('/photos', { params, signal })
  return resp.data
}

/**
 * Single source of truth for the timeline photos query. Both Timeline and
 * PreviewView call this so they share one cache entry — previously
 * PreviewView looked the cache up by key directly, which broke the moment
 * Timeline's key gained the filter params.
 */
export function usePhotosQuery() {
  // Single shallow-compared selector that returns just the filter
  // surface area. Previously this hook ran 14 individual selectors,
  // each a fresh subscription that could trigger a re-render and a
  // useMemo recompute on any unrelated filter-store update. useShallow
  // collapses them into one subscription that only fires when the
  // shape's values actually change.
  const filterParams = useFilterStore(
    useShallow((s) =>
      filtersToParams({
        dateFrom: s.dateFrom,
        dateTo: s.dateTo,
        mediaTypes: s.mediaTypes,
        ratingMin: s.ratingMin,
        ratingMax: s.ratingMax,
        colorLabel: s.colorLabel,
        flag: s.flag,
        heapId: s.heapId,
        folderId: s.folderId,
        tagIds: s.tagIds,
        duplicates: s.duplicates,
        groupBy: s.groupBy,
        sortBy: s.sortBy,
        sortOrder: s.sortOrder,
      }),
    ),
  )

  const queryClient = useQueryClient()

  return useQuery({
    queryKey: ['photos', filterParams],
    queryFn: async ({ signal }) => {
      // Two-phase fetch using cursor-based (keyset) pagination.
      // Phase 1 returns the first page (resolves the useQuery promise
      // so consumers exit loading state). Phase 2 chains a bounded
      // background loop — each response includes a `next_cursor` that
      // seeks directly to the next slice via an indexed range scan,
      // O(1) regardless of depth (no OFFSET skipping).
      //
      // First page is small (~one viewport) so the grid paints fast;
      // background pages are larger so we still cover ~10k photos in
      // a few round-trips without burning through a 100k library on
      // cold load. If a user scrolls past that horizon we'll add an
      // infinite-query trigger; for now the cap keeps cold-load
      // memory / network pressure sane.
      const PER_PAGE_INITIAL = 100
      const PER_PAGE_BACKGROUND = 500
      const MAX_PAGES = 20
      const INTER_PAGE_DELAY_MS = 50

      const first = await fetchCursorPage(
        { per_page: PER_PAGE_INITIAL, ...filterParams },
        signal,
      )
      const firstBatch = first.photos || []
      let nextCursor: string | null = first.next_cursor

      if (nextCursor) {
        // Fire-and-forget background loop using cursor chaining.
        // start/stop balanced in try/finally so an aborted or erroring
        // loop can't leak the in-flight counter that drives the
        // bottom-of-grid spinner.
        usePhotosBackgroundLoadingStore.getState().start()
        void (async () => {
          try {
            for (let i = 0; i < MAX_PAGES && nextCursor; i++) {
              if (signal?.aborted) return
              try {
                const page = await fetchCursorPage(
                  { per_page: PER_PAGE_BACKGROUND, cursor: nextCursor, ...filterParams },
                  signal,
                )
                if (signal?.aborted) return
                const more = page.photos || []
                nextCursor = page.next_cursor
                queryClient.setQueryData<Photo[]>(
                  ['photos', filterParams],
                  (prev) => (prev ? [...prev, ...more] : more)
                )
                if (!nextCursor || more.length < PER_PAGE_BACKGROUND) return
                // Yield a beat between pages so the main thread stays
                // responsive (thumbnail decode, scroll handling) while
                // we're back-filling in the background.
                await new Promise((r) => setTimeout(r, INTER_PAGE_DELAY_MS))
              } catch {
                return
              }
            }
          } finally {
            usePhotosBackgroundLoadingStore.getState().stop()
          }
        })()
      }

      return firstBatch
    },
    staleTime: 30_000,
  })
}