feat: introduce retention-rate aggregation

packages/backend/src/server/api/endpoints/retention.ts

@@ -0,0 +1,47 @@
+import { IsNull } from 'typeorm';
+import { Inject, Injectable } from '@nestjs/common';
+import type { RetentionAggregationsRepository } from '@/models/index.js';
+import { Endpoint } from '@/server/api/endpoint-base.js';
+import { DI } from '@/di-symbols.js';
+
+export const meta = {
+	tags: ['users'],
+
+	requireCredential: false,
+
+	res: {
+	},
+
+	allowGet: true,
+	cacheSec: 60 * 60,
+} as const;
+
+export const paramDef = {
+	type: 'object',
+	properties: {},
+	required: [],
+} as const;
+
+// eslint-disable-next-line import/no-default-export
+@Injectable()
+export default class extends Endpoint<typeof meta, typeof paramDef> {
+	constructor(
+		@Inject(DI.retentionAggregationsRepository)
+		private retentionAggregationsRepository: RetentionAggregationsRepository,
+	) {
+		super(meta, paramDef, async (ps, me) => {
+			const records = await this.retentionAggregationsRepository.find({
+				order: {
+					id: 'DESC',
+				},
+				take: 30,
+			});
+
+			return records.map(record => ({
+				createdAt: record.createdAt.toISOString(),
+				users: record.usersCount,
+				data: record.data,
+			}));
+		});
+	}
+}