import { useMemo } from 'react';
import { useMutation, useQuery, useQueryClient } from '@tanstack/react-query';
import { useCurrentUser } from '@/hooks/useCurrentUser';
import { useNostrPublish } from '@/hooks/useNostrPublish';
import { useSkateRelays } from '@/hooks/useSkateRelays';
import {
  CALENDAR_EVENT_KIND,
  CALENDAR_RSVP_KIND,
  parseEventRsvp,
  type EventRsvp,
  type RsvpStatus,
  type SkateEvent,
} from '@/lib/types';

/**
 * NIP-52 RSVP layer for skate calendar events (calendar event kind 31923, RSVP kind 31925).
 * ─────────────────────────────────────────────────────────────────────────────
 * Given a calendar event coordinate ("31923:pubkey:d") we fetch every RSVP that
 * references it, keep the newest per person, and expose:
 *   • counts by status (going / interested / declined)
 *   • the ordered lists of pubkeys (for avatar stacks)
 *   • the logged-in user's own current status
 *
 * Publishing a new RSVP reuses the person's existing `d` identifier so it
 * REPLACES their prior RSVP (addressable), letting them freely switch between
 * Going / Interested / Can't make it.
 */

export interface EventRsvpSummary {
  going: string[];
  tentative: string[];
  declined: string[];
  goingCount: number;
  tentativeCount: number;
  /** All RSVPs, newest per person. */
  rsvps: EventRsvp[];
  /** The logged-in user's current RSVP, if any. */
  myRsvp: EventRsvp | null;
  myStatus: RsvpStatus | null;
  isLoading: boolean;
}

/** Build the addressable coordinate for a calendar event. */
export function eventCoord(event: Pick<SkateEvent, 'pubkey' | 'identifier'>): string {
  return `${CALENDAR_EVENT_KIND}:${event.pubkey}:${event.identifier}`;
}

export function useEventRsvps(coord: string | undefined): EventRsvpSummary {
  const { querySkateContent, getQueryKeySuffix } = useSkateRelays();
  const { user } = useCurrentUser();

  const query = useQuery({
    queryKey: ['event-rsvps', coord, getQueryKeySuffix()],
    enabled: !!coord,
    staleTime: 30_000,
    queryFn: async (c) => {
      const signal = AbortSignal.any([c.signal, AbortSignal.timeout(6000)]);
      const events = await querySkateContent(
        [{ kinds: [CALENDAR_RSVP_KIND], '#a': [coord!], limit: 500 }],
        { signal },
      );

      // Keep the newest RSVP per pubkey (an addressable replace can arrive as
      // multiple copies across relays / revisions).
      const byPubkey = new Map<string, EventRsvp>();
      for (const ev of events) {
        const rsvp = parseEventRsvp(ev);
        if (!rsvp || rsvp.eventCoord !== coord) continue;
        const existing = byPubkey.get(rsvp.pubkey);
        if (!existing || rsvp.createdAt > existing.createdAt) {
          byPubkey.set(rsvp.pubkey, rsvp);
        }
      }
      return Array.from(byPubkey.values());
    },
  });

  return useMemo(() => {
    const rsvps = query.data ?? [];
    const going: string[] = [];
    const tentative: string[] = [];
    const declined: string[] = [];

    // Newest first so avatar stacks show the most recent RSVPs.
    const sorted = [...rsvps].sort((a, b) => b.createdAt - a.createdAt);
    for (const r of sorted) {
      if (r.status === 'accepted') going.push(r.pubkey);
      else if (r.status === 'tentative') tentative.push(r.pubkey);
      else if (r.status === 'declined') declined.push(r.pubkey);
    }

    const myRsvp = user ? rsvps.find((r) => r.pubkey === user.pubkey) ?? null : null;

    return {
      going,
      tentative,
      declined,
      goingCount: going.length,
      tentativeCount: tentative.length,
      rsvps: sorted,
      myRsvp,
      myStatus: myRsvp?.status ?? null,
      isLoading: query.isLoading,
    };
  }, [query.data, query.isLoading, user]);
}

/**
 * Batch RSVP counts for a whole list of events in ONE relay query.
 *
 * Rendering a grid of EventCards used to fire one RSVP query PER card (an N+1
 * storm on a 100-event page). This queries every event coordinate at once with
 * a single `#a` filter, dedupes to the newest RSVP per person per event, and
 * returns a Map of coordinate → { goingCount, tentativeCount }.
 */
export function useBatchEventRsvps(
  coords: string[],
): Map<string, { goingCount: number; tentativeCount: number }> {
  const { querySkateContent, getQueryKeySuffix } = useSkateRelays();

  // Stable key regardless of order so we don't refetch on re-render churn.
  const sortedKey = useMemo(() => [...coords].sort().join(','), [coords]);

  const query = useQuery({
    queryKey: ['batch-event-rsvps', sortedKey, getQueryKeySuffix()],
    enabled: coords.length > 0,
    staleTime: 30_000,
    queryFn: async (c) => {
      const signal = AbortSignal.any([c.signal, AbortSignal.timeout(6000)]);
      const events = await querySkateContent(
        [{ kinds: [CALENDAR_RSVP_KIND], '#a': coords, limit: 2000 }],
        { signal },
      );

      // newest RSVP per (coord, pubkey)
      const latest = new Map<string, EventRsvp>();
      for (const ev of events) {
        const rsvp = parseEventRsvp(ev);
        if (!rsvp || !coords.includes(rsvp.eventCoord)) continue;
        const key = `${rsvp.eventCoord}|${rsvp.pubkey}`;
        const existing = latest.get(key);
        if (!existing || rsvp.createdAt > existing.createdAt) latest.set(key, rsvp);
      }

      const counts = new Map<string, { goingCount: number; tentativeCount: number }>();
      for (const rsvp of latest.values()) {
        const entry = counts.get(rsvp.eventCoord) ?? { goingCount: 0, tentativeCount: 0 };
        if (rsvp.status === 'accepted') entry.goingCount += 1;
        else if (rsvp.status === 'tentative') entry.tentativeCount += 1;
        counts.set(rsvp.eventCoord, entry);
      }
      return counts;
    },
  });

  return query.data ?? new Map();
}

/**
 * Publish (or replace) the logged-in user's RSVP to a calendar event.
 * Reuses an existing RSVP `d` so switching status replaces the prior one.
 */
export function useRsvp() {
  const { mutateAsync: publish, isPending } = useNostrPublish();
  const { user } = useCurrentUser();
  const queryClient = useQueryClient();

  const mutation = useMutation({
    mutationFn: async (opts: {
      event: SkateEvent;
      status: RsvpStatus;
      /** Reuse the existing RSVP identifier when the user already RSVP'd. */
      existingIdentifier?: string;
      note?: string;
    }) => {
      if (!user) throw new Error('You must be logged in to RSVP.');

      const coord = eventCoord(opts.event);
      const d = opts.existingIdentifier || crypto.randomUUID();

      const tags: string[][] = [
        ['d', d],
        ['a', coord],
        ['e', opts.event.id],
        ['status', opts.status],
        // Let the host easily query RSVPs addressed to them.
        ['p', opts.event.pubkey],
        // Free/busy hint (omit for declined per NIP-52).
        ...(opts.status !== 'declined' ? [['fb', 'busy']] : []),
        ['alt', `RSVP (${opts.status}) to a skate event`],
      ];

      return publish({
        kind: CALENDAR_RSVP_KIND,
        content: opts.note ?? '',
        tags,
      });
    },
    onSuccess: (_data, variables) => {
      const coord = eventCoord(variables.event);
      queryClient.invalidateQueries({ queryKey: ['event-rsvps', coord] });
    },
  });

  return { ...mutation, isPending: isPending || mutation.isPending };
}