feat(api): add domain-routed fallback email provider (#3506)

fluxer_api/pkgs/email/src/DomainRoutedEmailProvider.test.ts

@@ -0,0 +1,54 @@
+// SPDX-License-Identifier: AGPL-3.0-or-later
+
+import {DomainRoutedEmailProvider} from '@pkgs/email/src/DomainRoutedEmailProvider';
+import type {EmailMessage} from '@pkgs/email/src/EmailProviderTypes';
+import {EmailService} from '@pkgs/email/src/EmailService';
+import {describe, expect, it, vi} from 'vitest';
+
+function message(to: string): EmailMessage {
+	return {to, from: {email: '[email protected]', name: 'Example'}, subject: 'Hello', text: 'Body'};
+}
+
+describe('DomainRoutedEmailProvider', () => {
+	it.each([
+		{to: '[email protected]', route: 'fallback'},
+		{to: '[email protected]', route: 'fallback'},
+		{to: '[email protected]', route: 'fallback'},
+		{to: '[email protected]', route: 'primary'},
+		{to: '[email protected]', route: 'primary'},
+		{to: '[email protected]', route: 'primary'},
+		{to: '"[email protected]"@example.com', route: 'primary'},
+	])('sends $to through the $route provider', async ({to, route}) => {
+		const primary = {sendEmail: vi.fn().mockResolvedValue(true)};
+		const fallback = {sendEmail: vi.fn().mockResolvedValue(false)};
+		const provider = new DomainRoutedEmailProvider(primary, fallback, ['gmail.com', 'googlemail.com']);
+		const sent = message(to);
+		const result = await provider.sendEmail(sent);
+		const [chosen, other] = route === 'fallback' ? [fallback, primary] : [primary, fallback];
+		expect(chosen.sendEmail).toHaveBeenCalledWith(sent);
+		expect(other.sendEmail).not.toHaveBeenCalled();
+		expect(result).toBe(route === 'primary');
+	});
+
+	it('never reaches either provider for a bounced address', async () => {
+		const primary = {sendEmail: vi.fn().mockResolvedValue(true)};
+		const fallback = {sendEmail: vi.fn().mockResolvedValue(true)};
+		const service = new EmailService(
+			{
+				enabled: true,
+				fromEmail: '[email protected]',
+				fromName: 'Example',
+				appBaseUrl: 'https://example.com',
+				appealsEmail: null,
+				safetyEmail: null,
+				supportEmail: null,
+				productName: 'Example',
+			},
+			new DomainRoutedEmailProvider(primary, fallback, ['gmail.com']),
+			{isEmailBounced: async () => true},
+		);
+		expect(await service.sendPasswordResetEmail('[email protected]', 'user', 'token')).toBe(false);
+		expect(primary.sendEmail).not.toHaveBeenCalled();
+		expect(fallback.sendEmail).not.toHaveBeenCalled();
+	});
+});

fluxer_api/pkgs/email/src/DomainRoutedEmailProvider.ts

@@ -0,0 +1,28 @@
+// SPDX-License-Identifier: AGPL-3.0-or-later
+
+import {createLogger} from '@fluxer/logger/src/Logger';
+import type {EmailMessage, IEmailProvider} from '@pkgs/email/src/EmailProviderTypes';
+
+const logger = createLogger('@pkgs/email/src/DomainRoutedEmailProvider');
+
+export class DomainRoutedEmailProvider implements IEmailProvider {
+	private readonly primary: IEmailProvider;
+	private readonly fallback: IEmailProvider;
+	private readonly fallbackDomains: ReadonlySet<string>;
+
+	constructor(primary: IEmailProvider, fallback: IEmailProvider, fallbackDomains: ReadonlyArray<string>) {
+		this.primary = primary;
+		this.fallback = fallback;
+		this.fallbackDomains = new Set(fallbackDomains);
+	}
+
+	async sendEmail(message: EmailMessage): Promise<boolean> {
+		const domain = message.to
+			.slice(message.to.lastIndexOf('@') + 1)
+			.trim()
+			.toLowerCase();
+		const useFallback = this.fallbackDomains.has(domain);
+		logger.debug({domain, provider: useFallback ? 'fallback' : 'primary'}, 'Routing email');
+		return (useFallback ? this.fallback : this.primary).sendEmail(message);
+	}
+}