import { useEffect, useMemo } from 'react';
import { useQuery, useQueryClient } from '@tanstack/react-query';

import { useNostr } from '@nostrify/react';
import type { NostrEvent } from '@nostrify/nostrify';
import { useCurrentUser } from './useCurrentUser';
import { onlyVerified } from '@/lib/verifyEvents';
import {
  HOUSE_TRUST_PROVIDER,
  NIP85_PROVIDER_LIST_KIND,
  NIP85_USER_ASSERTION_KIND,
  parseProviderDesignation,
  parseUserTrustAssertions,
  resolveProvider,
  type TrustProvider,
  type UserTrustAssertion,
} from '@/lib/nip85';

/**
 * Read kind-30382 Trusted Assertions (NIP-85) for a set of subjects, from the
 * provider the viewer designates via their own kind-10040 — falling back to the
 * configured house provider. Signatures are verified and the event author must
 * equal the resolved provider before a score is used.
 *
 * BATCHING
 * --------
 * TrustBadge is rendered once per card, so a naive hook would fire one relay
 * query per author. Instead every consumer registers its targets into a shared
 * per-viewer union, and ONE query fetches the whole union; each caller then
 * reads only its own subjects out of the result. New targets arriving later
 * (an infinite list) trigger a single debounced refetch.
 *
 * A missing assertion yields no entry: that means "nothing published", which is
 * NOT the same as distrust. Callers must treat absence as `unknown`.
 */

const MAX_UNION = 600;
const BATCH_WINDOW_MS = 100;

interface PendingBatch {
  targets: Set<string>;
  timer: ReturnType<typeof setTimeout> | null;
}

const batches = new Map<string, PendingBatch>();

function batchFor(viewer: string): PendingBatch {
  let batch = batches.get(viewer);
  if (!batch) {
    batch = { targets: new Set(), timer: null };
    batches.set(viewer, batch);
  }
  return batch;
}

/**
 * Register the targets one consumer needs. Returns true when the union grew, so
 * the caller can schedule a refetch. Idempotent, and deliberately called during
 * render so a whole grid registers before the shared query's first pass.
 */
function registerTargets(viewer: string, targets: string[]): boolean {
  const batch = batchFor(viewer);
  let grew = false;
  for (const target of targets) {
    if (!batch.targets.has(target)) {
      batch.targets.add(target);
      grew = true;
    }
  }
  // Cap the union (insertion order) so a long session cannot grow forever.
  while (batch.targets.size > MAX_UNION) {
    const oldest = batch.targets.values().next().value;
    if (oldest === undefined) break;
    batch.targets.delete(oldest);
  }
  return grew;
}

export function useTrustAssertions(pubkeys: string[]) {
  const { nostr } = useNostr();
  const { user } = useCurrentUser();
  const queryClient = useQueryClient();

  const viewer = user?.pubkey ?? '';
  const key = useMemo(() => [...new Set(pubkeys)].sort().join(','), [pubkeys]);
  const targets = useMemo(() => (key ? key.split(',') : []), [key]);

  const grew = registerTargets(viewer, targets);

  const queryKey = useMemo(() => ['trust-assertions-batch', viewer], [viewer]);

  useEffect(() => {
    if (!grew) return;
    // The first fetch already sees the targets registered before it ran; only a
    // later addition to an established batch needs a refetch.
    if (queryClient.getQueryState(queryKey)?.data === undefined) return;
    const batch = batchFor(viewer);
    if (batch.timer) clearTimeout(batch.timer);
    batch.timer = setTimeout(() => {
      batch.timer = null;
      queryClient.invalidateQueries({ queryKey });
    }, BATCH_WINDOW_MS);
  }, [grew, viewer, queryKey, queryClient]);

  const query = useQuery({
    queryKey,
    queryFn: async (c): Promise<Map<string, UserTrustAssertion>> => {
      const out = new Map<string, UserTrustAssertion>();
      const all = [...batchFor(viewer).targets];
      if (all.length === 0) return out;

      const signal = AbortSignal.any([c.signal, AbortSignal.timeout(8000)]);

      // 1. Resolve the provider: the viewer's own designation, else the house.
      let provider: TrustProvider = HOUSE_TRUST_PROVIDER;
      try {
        if (viewer) {
          const designationEvents = onlyVerified(await nostr.query(
            [{ kinds: [NIP85_PROVIDER_LIST_KIND], authors: [viewer], limit: 1 }],
            { signal },
          ));
          const designation = parseProviderDesignation(designationEvents[0]);
          provider = resolveProvider(
            designation,
            NIP85_USER_ASSERTION_KIND,
            'rank',
            HOUSE_TRUST_PROVIDER,
          );
        }
      } catch {
        // Designation lookup failed — the house provider is the fallback.
      }

      // 2. Fetch the assertions for the whole batch from the resolved provider.
      const filter = {
        kinds: [NIP85_USER_ASSERTION_KIND],
        authors: [provider.pubkey],
        '#d': all,
        limit: all.length,
      };

      try {
        let events: NostrEvent[];
        if (provider.relay) {
          try {
            events = await nostr.relay(provider.relay).query([filter], { signal });
          } catch {
            events = await nostr.query([filter], { signal });
          }
        } else {
          events = await nostr.query([filter], { signal });
        }
        return parseUserTrustAssertions(onlyVerified(events), provider.pubkey);
      } catch {
        // Provider unreachable — absence, not distrust.
        return out;
      }
    },
    enabled: targets.length > 0,
    staleTime: 60 * 60 * 1000, // 1h
    gcTime: 24 * 60 * 60 * 1000,
    retry: 1,
  });

  // Hand each caller only its own subjects out of the shared batch result.
  const data = useMemo(() => {
    const full = query.data;
    if (!full) return undefined;
    const out = new Map<string, UserTrustAssertion>();
    for (const target of targets) {
      const assertion = full.get(target);
      if (assertion) out.set(target, assertion);
    }
    return out;
  }, [query.data, targets]);

  return { data, isLoading: query.isLoading, isFetching: query.isFetching };
}