Save trending hashtags as labels

src/cron.ts

@@ -5,6 +5,7 @@ import { getTrendingNotes } from '@/trends/trending-notes.ts';
 import { Time } from '@/utils/time.ts';
 import { AdminSigner } from '@/signers/AdminSigner.ts';
 import { handleEvent } from '@/pipeline.ts';
+import { getTrendingHashtags } from '@/trends/trending-hashtags.ts';
 
 const console = new Stickynotes('ditto:trends');
 
@@ -32,7 +33,32 @@ async function updateTrendingNotesCache() {
   console.info('Trending notes cache updated.');
 }
 
+async function updateTrendingHashtagsCache() {
+  console.info('Updating trending hashtags cache...');
+  const kysely = await DittoDB.getInstance();
+  const yesterday = Math.floor((Date.now() - Time.days(1)) / 1000);
+  const signal = AbortSignal.timeout(1000);
+
+  const hashtags = await getTrendingHashtags(kysely, { since: yesterday, limit: 20, threshold: 3 });
+  const signer = new AdminSigner();
+
+  const label = await signer.signEvent({
+    kind: 1985,
+    content: '',
+    tags: [
+      ['L', 'pub.ditto.trends'],
+      ['l', 'hashtags', 'pub.ditto.trends'],
+      ...hashtags.map(({ tag }) => ['t', tag]),
+    ],
+    created_at: Math.floor(Date.now() / 1000),
+  });
+
+  await handleEvent(label, signal);
+  console.info('Trending hashtags cache updated.');
+}
+
 /** Start cron jobs for the application. */
 export function cron() {
   Deno.cron('update trending notes cache', { minute: { every: 15 } }, updateTrendingNotesCache);
+  Deno.cron('update trending hashtags cache', { dayOfMonth: { every: 1 } }, updateTrendingHashtagsCache);
 }

src/trends/trending-hashtags.ts

@@ -0,0 +1,38 @@
+import { Kysely } from 'kysely';
+
+import { DittoTables } from '@/db/DittoTables.ts';
+
+interface GetTrendingHashtagsOpts {
+  /** Unix timestamp in _seconds_ for the starting point of this query. */
+  since: number;
+  /** Maximum number of trending hashtags to return. */
+  limit: number;
+  /** Minimum number of unique accounts that have used a hashtag to be considered trending. */
+  threshold: number;
+}
+
+/** Get the trending hashtags in the given time frame. */
+export async function getTrendingHashtags(
+  /** Kysely instance to execute queries on. */
+  kysely: Kysely<DittoTables>,
+  /** Options for this query. */
+  opts: GetTrendingHashtagsOpts,
+): Promise<{ tag: string; accounts: number; uses: number }[]> {
+  const { since, limit, threshold } = opts;
+
+  return await kysely
+    .selectFrom('nostr_tags')
+    .innerJoin('nostr_events', 'nostr_events.id', 'nostr_tags.event_id')
+    .select(({ fn }) => [
+      'nostr_tags.value as tag',
+      fn.agg<number>('count', ['nostr_events.pubkey']).distinct().as('accounts'),
+      fn.countAll<number>().as('uses'),
+    ])
+    .where('nostr_tags.name', '=', 't')
+    .where('nostr_events.created_at', '>', since)
+    .groupBy('nostr_tags.value')
+    .having((c) => c(c.fn.agg('count', ['nostr_events.pubkey']).distinct(), '>=', threshold))
+    .orderBy((c) => c.fn.agg('count', ['nostr_events.pubkey']).distinct(), 'desc')
+    .limit(limit)
+    .execute();
+}