なんかもうめっちゃ変えた

packages/backend/src/core/InstanceActorService.ts

@@ -0,0 +1,42 @@
+import { Inject, Injectable } from '@nestjs/common';
+import { IsNull } from 'typeorm';
+import type { ILocalUser } from '@/models/entities/User.js';
+import { UsersRepository } from '@/models/index.js';
+import { Cache } from '@/misc/cache.js';
+import { DI } from '@/di-symbols.js';
+import { CreateSystemUserService } from './CreateSystemUserService.js';
+
+const ACTOR_USERNAME = 'instance.actor' as const;
+
+@Injectable()
+export class InstanceActorService {
+	#cache: Cache<ILocalUser>;
+
+	constructor(
+		@Inject(DI.usersRepository)
+		private usersRepository: UsersRepository,
+
+		private createSystemUserService: CreateSystemUserService,
+	) {
+		this.#cache = new Cache<ILocalUser>(Infinity);
+	}
+
+	public async getInstanceActor(): Promise<ILocalUser> {
+		const cached = this.#cache.get(null);
+		if (cached) return cached;
+	
+		const user = await this.usersRepository.findOneBy({
+			host: IsNull(),
+			username: ACTOR_USERNAME,
+		}) as ILocalUser | undefined;
+	
+		if (user) {
+			this.#cache.set(null, user);
+			return user;
+		} else {
+			const created = await this.createSystemUserService.createSystemUser(ACTOR_USERNAME) as ILocalUser;
+			this.#cache.set(null, created);
+			return created;
+		}
+	}
+}