import { Semaphore } from '@lambdalisue/async';
import { NKinds, NostrEvent, NStore } from '@nostrify/nostrify';
import Debug from '@soapbox/stickynotes/debug';
import { InsertQueryBuilder, Kysely } from 'kysely';
import { LRUCache } from 'lru-cache';
import { SetRequired } from 'type-fest';

import { DittoDB } from '@/db/DittoDB.ts';
import { DittoTables } from '@/db/DittoTables.ts';
import { Storages } from '@/storages.ts';
import { findReplyTag, getTagSet } from '@/utils/tags.ts';

type AuthorStat = keyof Omit<DittoTables['author_stats'], 'pubkey'>;
type EventStat = keyof Omit<DittoTables['event_stats'], 'event_id'>;

type AuthorStatDiff = ['author_stats', pubkey: string, stat: AuthorStat, diff: number];
type EventStatDiff = ['event_stats', eventId: string, stat: EventStat, diff: number];
type StatDiff = AuthorStatDiff | EventStatDiff;

const debug = Debug('ditto:stats');

/** Store stats for the event. */
async function updateStats(event: NostrEvent) {
  let prev: NostrEvent | undefined;
  const queries: InsertQueryBuilder<DittoTables, any, unknown>[] = [];

  // Kind 3 is a special case - replace the count with the new list.
  if (event.kind === 3) {
    prev = await getPrevEvent(event);
    if (!prev || event.created_at >= prev.created_at) {
      queries.push(await updateFollowingCountQuery(event));
    }
  }

  const statDiffs = await getStatsDiff(event, prev);
  const pubkeyDiffs = statDiffs.filter(([table]) => table === 'author_stats') as AuthorStatDiff[];
  const eventDiffs = statDiffs.filter(([table]) => table === 'event_stats') as EventStatDiff[];

  if (statDiffs.length) {
    debug(JSON.stringify({ id: event.id, pubkey: event.pubkey, kind: event.kind, tags: event.tags, statDiffs }));
  }

  pubkeyDiffs.forEach(([_, pubkey]) => refreshAuthorStatsDebounced(pubkey));

  const kysely = await DittoDB.getInstance();

  if (pubkeyDiffs.length) queries.push(authorStatsQuery(kysely, pubkeyDiffs));
  if (eventDiffs.length) queries.push(eventStatsQuery(kysely, eventDiffs));

  if (queries.length) {
    await Promise.all(queries.map((query) => query.execute()));
  }
}

/** Calculate stats changes ahead of time so we can build an efficient query. */
async function getStatsDiff(event: NostrEvent, prev: NostrEvent | undefined): Promise<StatDiff[]> {
  const store = await Storages.db();
  const statDiffs: StatDiff[] = [];

  const firstTaggedId = event.tags.find(([name]) => name === 'e')?.[1];
  const inReplyToId = findReplyTag(event.tags)?.[1];

  switch (event.kind) {
    case 1:
      statDiffs.push(['author_stats', event.pubkey, 'notes_count', 1]);
      if (inReplyToId) {
        statDiffs.push(['event_stats', inReplyToId, 'replies_count', 1]);
      }
      break;
    case 3:
      statDiffs.push(...getFollowDiff(event, prev));
      break;
    case 5: {
      if (!firstTaggedId) break;

      const [repostedEvent] = await store.query(
        [{ kinds: [6], ids: [firstTaggedId], authors: [event.pubkey] }],
        { limit: 1 },
      );
      // Check if the event being deleted is of kind 6,
      // if it is then proceed, else just break
      if (!repostedEvent) break;

      const eventBeingRepostedId = repostedEvent.tags.find(([name]) => name === 'e')?.[1];
      const eventBeingRepostedPubkey = repostedEvent.tags.find(([name]) => name === 'p')?.[1];
      if (!eventBeingRepostedId || !eventBeingRepostedPubkey) break;

      const [eventBeingReposted] = await store.query(
        [{ kinds: [1], ids: [eventBeingRepostedId], authors: [eventBeingRepostedPubkey] }],
        { limit: 1 },
      );
      if (!eventBeingReposted) break;

      statDiffs.push(['event_stats', eventBeingRepostedId, 'reposts_count', -1]);
      break;
    }
    case 6:
      if (firstTaggedId) {
        statDiffs.push(['event_stats', firstTaggedId, 'reposts_count', 1]);
      }
      break;
    case 7:
      if (firstTaggedId) {
        statDiffs.push(['event_stats', firstTaggedId, 'reactions_count', 1]);
      }
  }

  return statDiffs;
}

/** Create an author stats query from the list of diffs. */
function authorStatsQuery(kysely: Kysely<DittoTables>, diffs: AuthorStatDiff[]) {
  const values: DittoTables['author_stats'][] = diffs.map(([_, pubkey, stat, diff]) => {
    const row: DittoTables['author_stats'] = {
      pubkey,
      followers_count: 0,
      following_count: 0,
      notes_count: 0,
    };
    row[stat] = diff;
    return row;
  });

  return kysely.insertInto('author_stats')
    .values(values)
    .onConflict((oc) =>
      oc
        .column('pubkey')
        .doUpdateSet((eb) => ({
          followers_count: eb('author_stats.followers_count', '+', eb.ref('excluded.followers_count')),
          following_count: eb('author_stats.following_count', '+', eb.ref('excluded.following_count')),
          notes_count: eb('author_stats.notes_count', '+', eb.ref('excluded.notes_count')),
        }))
    );
}

/** Create an event stats query from the list of diffs. */
function eventStatsQuery(kysely: Kysely<DittoTables>, diffs: EventStatDiff[]) {
  const values: DittoTables['event_stats'][] = diffs.map(([_, event_id, stat, diff]) => {
    const row: DittoTables['event_stats'] = {
      event_id,
      replies_count: 0,
      reposts_count: 0,
      reactions_count: 0,
    };
    row[stat] = diff;
    return row;
  });

  return kysely.insertInto('event_stats')
    .values(values)
    .onConflict((oc) =>
      oc
        .column('event_id')
        .doUpdateSet((eb) => ({
          replies_count: eb('event_stats.replies_count', '+', eb.ref('excluded.replies_count')),
          reposts_count: eb('event_stats.reposts_count', '+', eb.ref('excluded.reposts_count')),
          reactions_count: eb('event_stats.reactions_count', '+', eb.ref('excluded.reactions_count')),
        }))
    );
}

/** Get the last version of the event, if any. */
async function getPrevEvent(event: NostrEvent): Promise<NostrEvent | undefined> {
  if (NKinds.replaceable(event.kind) || NKinds.parameterizedReplaceable(event.kind)) {
    const store = await Storages.db();

    const [prev] = await store.query([
      { kinds: [event.kind], authors: [event.pubkey], limit: 1 },
    ]);

    return prev;
  }
}

/** Set the following count to the total number of unique "p" tags in the follow list. */
async function updateFollowingCountQuery({ pubkey, tags }: NostrEvent) {
  const following_count = new Set(
    tags
      .filter(([name]) => name === 'p')
      .map(([_, value]) => value),
  ).size;

  const kysely = await DittoDB.getInstance();
  return kysely.insertInto('author_stats')
    .values({
      pubkey,
      following_count,
      followers_count: 0,
      notes_count: 0,
    })
    .onConflict((oc) =>
      oc
        .column('pubkey')
        .doUpdateSet({ following_count })
    );
}

/** Compare the old and new follow events (if any), and return a diff array. */
function getFollowDiff(event: NostrEvent, prev?: NostrEvent): AuthorStatDiff[] {
  const prevTags = prev?.tags ?? [];

  const prevPubkeys = new Set(
    prevTags
      .filter(([name]) => name === 'p')
      .map(([_, value]) => value),
  );

  const pubkeys = new Set(
    event.tags
      .filter(([name]) => name === 'p')
      .map(([_, value]) => value),
  );

  const added = [...pubkeys].filter((pubkey) => !prevPubkeys.has(pubkey));
  const removed = [...prevPubkeys].filter((pubkey) => !pubkeys.has(pubkey));

  return [
    ...added.map((pubkey): AuthorStatDiff => ['author_stats', pubkey, 'followers_count', 1]),
    ...removed.map((pubkey): AuthorStatDiff => ['author_stats', pubkey, 'followers_count', -1]),
  ];
}

/** Refresh the author's stats in the database. */
async function refreshAuthorStats(pubkey: string): Promise<DittoTables['author_stats']> {
  const store = await Storages.db();
  const stats = await countAuthorStats(store, pubkey);

  const kysely = await DittoDB.getInstance();
  await kysely.insertInto('author_stats')
    .values(stats)
    .onConflict((oc) => oc.column('pubkey').doUpdateSet(stats))
    .execute();

  return stats;
}

/** Calculate author stats from the database. */
async function countAuthorStats(
  store: SetRequired<NStore, 'count'>,
  pubkey: string,
): Promise<DittoTables['author_stats']> {
  const [{ count: followers_count }, { count: notes_count }, [followList]] = await Promise.all([
    store.count([{ kinds: [3], '#p': [pubkey] }]),
    store.count([{ kinds: [1], authors: [pubkey] }]),
    store.query([{ kinds: [3], authors: [pubkey], limit: 1 }]),
  ]);

  return {
    pubkey,
    followers_count,
    following_count: getTagSet(followList?.tags ?? [], 'p').size,
    notes_count,
  };
}

const authorStatsSemaphore = new Semaphore(10);
const refreshedAuthors = new LRUCache<string, true>({ max: 1000 });

/** Calls `refreshAuthorStats` only once per author. */
function refreshAuthorStatsDebounced(pubkey: string): void {
  if (refreshedAuthors.get(pubkey)) {
    return;
  }

  refreshedAuthors.set(pubkey, true);
  debug('refreshing author stats:', pubkey);

  authorStatsSemaphore
    .lock(() => refreshAuthorStats(pubkey).catch(() => {}));
}

export { refreshAuthorStats, refreshAuthorStatsDebounced, updateStats };