task-stream/libs/api/tracker/application/src/lib/notifications/notifier.ts

import { Injectable, Logger } from '@nestjs/common';
import {
  NotificationKind,
  NotificationReadModel,
  SYSTEM_ACTOR_ID,
  SYSTEM_ACTOR_NAME,
  TrackerEvent,
} from '@task-stream/api/tracker/domain';
import { ChangeFeed } from '../ports/change-feed';
import { NotificationMailer } from '../ports/notification-mailer';
import { NotificationsRepository } from '../ports/notifications.repository';
import { UserDirectory } from '../ports/user-directory';
import { versionOf } from '../event-handlers/read-model-notifier';

export interface NotificationDraft {
  userId: string;
  kind: NotificationKind;
  summary: string;
}

export interface NotificationContext {
  projectId: string;
  projectKey: string;
  issueId: string | null;
  issueKey: string | null;
}

/**
 * Delivers notifications: stored for the recipient, pushed live, and copied
 * by e-mail to whoever asked for it. Nobody is told about what they did
 * themselves, and each person is told once per event — the first reason wins.
 */
@Injectable()
export class Notifier {
  private readonly logger = new Logger(Notifier.name);

  constructor(
    private readonly notifications: NotificationsRepository,
    private readonly changeFeed: ChangeFeed,
    private readonly mailer: NotificationMailer,
    private readonly users: UserDirectory,
  ) {}

  async deliver(
    event: TrackerEvent,
    context: NotificationContext,
    drafts: NotificationDraft[],
  ): Promise<void> {
    const seen = new Set<string>([event.actorId]);
    const wanted = drafts.filter((draft) => {
      if (seen.has(draft.userId)) return false;
      seen.add(draft.userId);
      return true;
    });
    if (!wanted.length) return;

    const refs = await this.users.refs([event.actorId]);
    const actor =
      event.actorId === SYSTEM_ACTOR_ID
        ? { id: SYSTEM_ACTOR_ID, name: SYSTEM_ACTOR_NAME }
        : refs.of(event.actorId);

    await this.send(
      wanted.map((draft) => ({
        id: `${event.aggregateId}:${versionOf(event)}:${draft.userId}`,
        userId: draft.userId,
        kind: draft.kind,
        ...context,
        actor,
        summary: draft.summary,
        readAt: null,
        createdAt: event.occurredAt,
      })),
    );
  }

  /**
   * Stores, pushes and e-mails ready-made notifications. Their id makes them
   * idempotent: one that is already there is not sent again.
   */
  async send(notifications: NotificationReadModel[]): Promise<void> {
    const delivered: NotificationReadModel[] = [];
    for (const notification of notifications) {
      // Delivered again (at-least-once): already told, nothing to repeat.
      if (!(await this.notifications.insert(notification))) continue;
      await this.changeFeed.publishNotification(notification);
      delivered.push(notification);
    }
    if (this.mailer.enabled && delivered.length) {
      await this.email(delivered);
    }
  }

  /** A failed e-mail never blocks the event stream: it is logged and skipped. */
  private async email(notifications: NotificationReadModel[]): Promise<void> {
    const contacts = new Map(
      (await this.users.contacts(notifications.map((n) => n.userId))).map(
        (c) => [c.id, c],
      ),
    );
    for (const notification of notifications) {
      const contact = contacts.get(notification.userId);
      if (!contact?.email) continue;
      if (!(await this.notifications.settings(notification.userId)).email)
        continue;
      try {
        await this.mailer.send(
          { name: contact.name, email: contact.email },
          notification,
        );
      } catch (error) {
        this.logger.warn(
          `E-mail to ${notification.userId} failed: ${(error as Error).message}`,
        );
      }
    }
  }
}