なんかもうめっちゃ変えた

packages/backend/src/core/UtilityService.ts

@@ -0,0 +1,37 @@
+import { URL } from 'node:url';
+import { toASCII } from 'punycode';
+import { Inject, Injectable } from '@nestjs/common';
+import { DI } from '@/di-symbols.js';
+import { Config } from '@/config.js';
+
+@Injectable()
+export class UtilityService {
+	constructor(
+		@Inject(DI.config)
+		private config: Config,
+	) {
+	}
+
+	public getFullApAccount(username: string, host: string | null): string {
+		return host ? `${username}@${this.toPuny(host)}` : `${username}@${this.toPuny(this.config.host)}`;
+	}
+
+	public isSelfHost(host: string | null): boolean {
+		if (host == null) return true;
+		return this.toPuny(this.config.host) === this.toPuny(host);
+	}
+
+	public extractDbHost(uri: string): string {
+		const url = new URL(uri);
+		return this.toPuny(url.hostname);
+	}
+
+	public toPuny(host: string): string {
+		return toASCII(host.toLowerCase());
+	}
+
+	public toPunyNullable(host: string | null | undefined): string | null {
+		if (host == null) return null;
+		return toASCII(host.toLowerCase());
+	}
+}