Add a stats module (draft)

src/stats.ts

@@ -0,0 +1,32 @@
+import { open as lmdb } from 'npm:lmdb';
+import { Event } from '@/deps.ts';
+
+const db = lmdb({ path: 'data/ditto.lmdb' });
+
+/** Store stats for the event in LMDB. */
+async function saveStats(event: Event): Promise<void> {
+  switch (event.kind) {
+    case 6:
+      return await incrementMentionedEvent(event, 'reposts');
+    case 7:
+      return await incrementMentionedEvent(event, 'reactions');
+  }
+}
+
+/** Increment the subkey for the first mentioned event. */
+async function incrementMentionedEvent(event: Event, subkey: string): Promise<void> {
+  const eventId = event.tags.find(([name]) => name === 'e')?.[1];
+  if (eventId) {
+    return await incrementKey([eventId, subkey]);
+  }
+}
+
+/** Increase the counter by 1, or set the key if it doesn't exist. */
+function incrementKey(key: string[]): Promise<void> {
+  return db.transaction(() => {
+    const value = db.get(key) || 0;
+    db.put(key, value + 1);
+  });
+}
+
+export { saveStats };