feat: notifications in the app and, optionally, by e-mail

Derived from events and kept per person: whoever a ticket is assigned to,
whoever reports or works on it when it moves, fails QA or gets a comment,
and whoever joins a project. Never about what you did yourself, once per
event. They arrive live through a subscription to a bell in the header,
and are copied by e-mail to whoever turns it on when SMTP_URL is set.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

libs/api/tracker/application/src/lib/notifications/index.ts

@@ -0,0 +1,3 @@
+export * from './notifier';
+export * from './notifications.queries';
+export * from './notifications.commands';

libs/api/tracker/application/src/lib/notifications/notifications.commands.ts

@@ -0,0 +1,51 @@
+import { Command, CommandHandler, ICommandHandler } from '@nestjs/cqrs';
+import { NotificationsRepository } from '../ports/notifications.repository';
+
+/*
+ * Per-person state, outside the event store: whether a notification was read
+ * and whether to copy them by e-mail concern nobody else and need no history.
+ */
+
+export class MarkNotificationsReadCommand extends Command<void> {
+  constructor(
+    public readonly userId: string,
+    /** Null: all of them. */
+    public readonly ids: string[] | null,
+  ) {
+    super();
+  }
+}
+
+export class UpdateNotificationSettingsCommand extends Command<void> {
+  constructor(
+    public readonly userId: string,
+    public readonly email: boolean,
+  ) {
+    super();
+  }
+}
+
+@CommandHandler(MarkNotificationsReadCommand)
+export class MarkNotificationsReadCommandHandler
+  implements ICommandHandler<MarkNotificationsReadCommand>
+{
+  constructor(private readonly notifications: NotificationsRepository) {}
+
+  async execute(command: MarkNotificationsReadCommand): Promise<void> {
+    await this.notifications.markRead(command.userId, command.ids);
+  }
+}
+
+@CommandHandler(UpdateNotificationSettingsCommand)
+export class UpdateNotificationSettingsCommandHandler
+  implements ICommandHandler<UpdateNotificationSettingsCommand>
+{
+  constructor(private readonly notifications: NotificationsRepository) {}
+
+  async execute(command: UpdateNotificationSettingsCommand): Promise<void> {
+    await this.notifications.saveSettings({
+      userId: command.userId,
+      email: command.email,
+    });
+  }
+}

libs/api/tracker/application/src/lib/notifications/notifications.event-handler.ts

@@ -0,0 +1,143 @@
+import { EventsHandler, IEventHandler } from '@nestjs/cqrs';
+import {
+  CommentAddedEvent,
+  IssueAssignedEvent,
+  IssueCreatedEvent,
+  IssueStatusChangedEvent,
+  NotificationKind,
+  ProjectMemberAddedEvent,
+  StatusCategory,
+  TrackerEvent,
+} from '@task-stream/api/tracker/domain';
+import { FindIssuesRepository } from '../ports/find-issues.repository';
+import { FindProjectsRepository } from '../ports/find-projects.repository';
+import { UserDirectory } from '../ports/user-directory';
+import { NotificationDraft, Notifier } from './notifier';
+
+/* Read by people, like the activity feed: Spanish. */
+
+const excerpt = (text: string, max = 120) => {
+  const flat = text.replace(/\s+/g, ' ').trim();
+  return flat.length > max ? `${flat.slice(0, max - 1)}…` : flat;
+};
+
+/**
+ * Who is told what, for the events that concern someone in particular:
+ * whoever a ticket is assigned to, whoever reported or works on it when it
+ * moves or gets a comment, whoever joins a project.
+ */
+@EventsHandler(
+  IssueCreatedEvent,
+  IssueAssignedEvent,
+  IssueStatusChangedEvent,
+  CommentAddedEvent,
+  ProjectMemberAddedEvent,
+)
+export class NotificationsEventHandler implements IEventHandler<TrackerEvent> {
+  constructor(
+    private readonly notifier: Notifier,
+    private readonly findIssues: FindIssuesRepository,
+    private readonly findProjects: FindProjectsRepository,
+    private readonly users: UserDirectory,
+  ) {}
+
+  async handle(event: TrackerEvent): Promise<void> {
+    const project = await this.findProjects.findById(event.projectId);
+    if (!project) return;
+    const actor = (await this.users.refs([event.actorId])).of(
+      event.actorId,
+    ).name;
+
+    if (event instanceof ProjectMemberAddedEvent) {
+      return this.notifier.deliver(
+        event,
+        {
+          projectId: project.id,
+          projectKey: project.key,
+          issueId: null,
+          issueKey: null,
+        },
+        [
+          {
+            userId: event.userId,
+            kind: NotificationKind.ADDED_TO_PROJECT,
+            summary: `${actor} te añadió al proyecto ${project.name} (${project.key})`,
+          },
+        ],
+      );
+    }
+
+    const issueId =
+      event instanceof CommentAddedEvent
+        ? event.comment.issueId
+        : event.aggregateId;
+    const issue =
+      event instanceof IssueCreatedEvent
+        ? event.issue
+        : await this.findIssues.findById(issueId);
+    if (!issue) return;
+    const reporterId =
+      'reporterId' in issue ? issue.reporterId : issue.reporter.id;
+    const assigneeId =
+      'assigneeId' in issue ? issue.assigneeId : (issue.assignee?.id ?? null);
+    const ticket = `${issue.key}: ${issue.title}`;
+
+    const drafts: NotificationDraft[] = [];
+    if (event instanceof IssueCreatedEvent && assigneeId) {
+      drafts.push({
+        userId: assigneeId,
+        kind: NotificationKind.ASSIGNED,
+        summary: `${actor} te asignó ${ticket}`,
+      });
+    }
+    if (event instanceof IssueAssignedEvent && event.assigneeId) {
+      drafts.push({
+        userId: event.assigneeId,
+        kind: NotificationKind.ASSIGNED,
+        summary: `${actor} te asignó ${ticket}`,
+      });
+    }
+    if (event instanceof IssueStatusChangedEvent) {
+      const to = event.meta?.toName ?? event.to;
+      // Back from QA without passing: the one move whoever did the work must hear about.
+      const failedQa =
+        event.meta?.fromCategory === StatusCategory.QA &&
+        event.meta?.toCategory !== StatusCategory.QA &&
+        event.meta?.toCategory !== StatusCategory.DONE;
+      const reason = event.reason ? `: ${excerpt(event.reason)}` : '';
+      for (const userId of [assigneeId, reporterId]) {
+        if (!userId) continue;
+        drafts.push({
+          userId,
+          kind: failedQa
+            ? NotificationKind.QA_FAILED
+            : NotificationKind.STATUS_CHANGED,
+          summary: failedQa
+            ? `${actor} devolvió ${ticket} desde QA${reason}`
+            : `${actor} movió ${ticket} a ${to}${reason}`,
+        });
+      }
+    }
+    if (event instanceof CommentAddedEvent) {
+      for (const userId of [assigneeId, reporterId]) {
+        if (!userId) continue;
+        drafts.push({
+          userId,
+          kind: NotificationKind.COMMENTED,
+          summary: `${actor} comentó en ${issue.key}: «${excerpt(event.comment.body)}»`,
+        });
+      }
+    }
+
+    await this.notifier.deliver(
+      event,
+      {
+        projectId: project.id,
+        projectKey: project.key,
+        issueId: issue.id,
+        issueKey: issue.key,
+      },
+      drafts,
+    );
+  }
+}

libs/api/tracker/application/src/lib/notifications/notifications.queries.ts

@@ -0,0 +1,71 @@
+import { IQueryHandler, Query, QueryHandler } from '@nestjs/cqrs';
+import { NotificationReadModel } from '@task-stream/api/tracker/domain';
+import { NotificationMailer } from '../ports/notification-mailer';
+import { NotificationsRepository } from '../ports/notifications.repository';
+
+export interface MyNotifications {
+  items: NotificationReadModel[];
+  unread: number;
+}
+
+export interface MyNotificationSettings {
+  /** Copies by e-mail (the user's choice). */
+  email: boolean;
+  /** Whether this installation can send e-mail at all. */
+  emailAvailable: boolean;
+}
+
+export class GetMyNotificationsQuery extends Query<MyNotifications> {
+  constructor(
+    public readonly userId: string,
+    public readonly unreadOnly: boolean,
+    public readonly limit: number,
+  ) {
+    super();
+  }
+}
+
+export class GetMyNotificationSettingsQuery extends Query<MyNotificationSettings> {
+  constructor(public readonly userId: string) {
+    super();
+  }
+}
+
+@QueryHandler(GetMyNotificationsQuery)
+export class GetMyNotificationsQueryHandler
+  implements IQueryHandler<GetMyNotificationsQuery, MyNotifications>
+{
+  constructor(private readonly notifications: NotificationsRepository) {}
+
+  async execute(query: GetMyNotificationsQuery): Promise<MyNotifications> {
+    const [items, unread] = await Promise.all([
+      this.notifications.findForUser(query.userId, {
+        unreadOnly: query.unreadOnly,
+        limit: Math.min(Math.max(query.limit, 1), 100),
+      }),
+      this.notifications.countUnread(query.userId),
+    ]);
+    return { items, unread };
+  }
+}
+
+@QueryHandler(GetMyNotificationSettingsQuery)
+export class GetMyNotificationSettingsQueryHandler
+  implements
+    IQueryHandler<GetMyNotificationSettingsQuery, MyNotificationSettings>
+{
+  constructor(
+    private readonly notifications: NotificationsRepository,
+    private readonly mailer: NotificationMailer,
+  ) {}
+
+  async execute(
+    query: GetMyNotificationSettingsQuery,
+  ): Promise<MyNotificationSettings> {
+    const settings = await this.notifications.settings(query.userId);
+    return {
+      email: this.mailer.enabled && settings.email,
+      emailAvailable: this.mailer.enabled,
+    };
+  }
+}

libs/api/tracker/application/src/lib/notifications/notifications.spec.ts

@@ -0,0 +1,176 @@
+import {
+  CommentAddedEvent,
+  IssueAssignedEvent,
+  IssueStatusChangedEvent,
+  NotificationKind,
+  NotificationReadModel,
+  NotificationSettingsReadModel,
+  ProjectMemberAddedEvent,
+  ProjectRole,
+  StatusCategory,
+  TrackerEvent,
+} from '@task-stream/api/tracker/domain';
+import { FakeUserDirectory } from '../../testing/in-memory';
+import { ChangeFeed } from '../ports/change-feed';
+import { FindIssuesRepository } from '../ports/find-issues.repository';
+import { FindProjectsRepository } from '../ports/find-projects.repository';
+import { NotificationMailer } from '../ports/notification-mailer';
+import { NotificationsRepository } from '../ports/notifications.repository';
+import { NotificationsEventHandler } from './notifications.event-handler';
+import { Notifier } from './notifier';
+
+class InMemoryNotifications extends NotificationsRepository {
+  readonly all: NotificationReadModel[] = [];
+  readonly emailOn = new Set<string>();
+  async insert(n: NotificationReadModel) {
+    if (this.all.some((x) => x.id === n.id)) return false;
+    this.all.push(n);
+    return true;
+  }
+  async findForUser(userId: string) {
+    return this.all.filter((n) => n.userId === userId);
+  }
+  async countUnread(userId: string) {
+    return this.all.filter((n) => n.userId === userId && !n.readAt).length;
+  }
+  async markRead() {
+    return;
+  }
+  async settings(userId: string): Promise<NotificationSettingsReadModel> {
+    return { userId, email: this.emailOn.has(userId) };
+  }
+  async saveSettings() {
+    return;
+  }
+}
+
+const at = <T extends TrackerEvent>(event: T, version = 2): T =>
+  Object.assign(event, {
+    aggregateVersion: version,
+    occurredAt: '2026-10-08T10:00:00.000Z',
+  });
+
+function setup(mailEnabled = false) {
+  const repo = new InMemoryNotifications();
+  const published: NotificationReadModel[] = [];
+  const mailed: string[] = [];
+  const users = new FakeUserDirectory().add('ana').add('bob').add('qa');
+  const issue = {
+    id: 'i-1',
+    key: 'WEB-1',
+    title: 'Login roto',
+    reporter: { id: 'qa', name: 'QA' },
+    assignee: { id: 'bob', name: 'Bob' },
+  };
+  const notifier = new Notifier(
+    repo,
+    {
+      publishNotification: async (n: NotificationReadModel) => {
+        published.push(n);
+      },
+    } as unknown as ChangeFeed,
+    {
+      enabled: mailEnabled,
+      send: async (to: { email: string }) => {
+        mailed.push(to.email);
+      },
+    } as unknown as NotificationMailer,
+    users,
+  );
+  const handler = new NotificationsEventHandler(
+    notifier,
+    { findById: async () => issue } as unknown as FindIssuesRepository,
+    {
+      findById: async () => ({ id: 'p-1', key: 'WEB', name: 'Web' }),
+    } as unknown as FindProjectsRepository,
+    users,
+  );
+  return { repo, published, mailed, handler };
+}
+
+describe('notifications', () => {
+  it('tells whoever a ticket is assigned to, not whoever assigned it', async () => {
+    const { handler, repo, published } = setup();
+    await handler.handle(
+      at(new IssueAssignedEvent('ana', 'i-1', 'p-1', 'bob', null)),
+    );
+    await handler.handle(
+      at(new IssueAssignedEvent('ana', 'i-1', 'p-1', 'ana', null), 3),
+    );
+
+    expect(repo.all.map((n) => [n.userId, n.kind])).toEqual([
+      ['bob', NotificationKind.ASSIGNED],
+    ]);
+    expect(published).toHaveLength(1);
+    expect(repo.all[0].summary).toContain('WEB-1');
+  });
+
+  it('marks a ticket sent back from QA as such, for whoever works on it and reported it', async () => {
+    const { handler, repo } = setup();
+    await handler.handle(
+      at(
+        new IssueStatusChangedEvent(
+          'ana',
+          'i-1',
+          'p-1',
+          'IN_QA',
+          'QA_FAILED',
+          'Falla en Safari',
+          {
+            fromName: 'En QA',
+            toName: 'QA fallido',
+            fromCategory: StatusCategory.QA,
+            toCategory: StatusCategory.IN_PROGRESS,
+          },
+        ),
+      ),
+    );
+
+    expect(repo.all.map((n) => [n.userId, n.kind])).toEqual([
+      ['bob', NotificationKind.QA_FAILED],
+      ['qa', NotificationKind.QA_FAILED],
+    ]);
+    expect(repo.all[0].summary).toContain('Falla en Safari');
+  });
+
+  it('tells about a comment everyone but its author, once even when redelivered', async () => {
+    const { handler, repo } = setup();
+    const comment = at(
+      new CommentAddedEvent('bob', {
+        id: 'c-1',
+        issueId: 'i-1',
+        projectId: 'p-1',
+        authorId: 'bob',
+        body: 'Ya está arreglado',
+        deleted: false,
+        createdAt: '2026-10-08T10:00:00.000Z',
+        editedAt: null,
+      }),
+      1,
+    );
+    await handler.handle(comment);
+    await handler.handle(comment);
+
+    expect(repo.all.map((n) => n.userId)).toEqual(['qa']);
+  });
+
+  it('copies by e-mail only to whoever asked for it, when mail is configured', async () => {
+    const { handler, repo, mailed } = setup(true);
+    repo.emailOn.add('bob');
+    await handler.handle(
+      at(new ProjectMemberAddedEvent('ana', 'p-1', 'bob', ProjectRole.MEMBER)),
+    );
+    await handler.handle(
+      at(
+        new ProjectMemberAddedEvent('ana', 'p-1', 'qa', ProjectRole.MEMBER),
+        3,
+      ),
+    );
+
+    expect(mailed).toEqual(['bob@example.org']);
+    expect(repo.all.map((n) => n.kind)).toEqual([
+      NotificationKind.ADDED_TO_PROJECT,
+      NotificationKind.ADDED_TO_PROJECT,
+    ]);
+  });
+});

libs/api/tracker/application/src/lib/notifications/notifier.ts

@@ -0,0 +1,110 @@
+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);
+
+    const delivered: NotificationReadModel[] = [];
+    for (const draft of wanted) {
+      const notification: NotificationReadModel = {
+        id: `${event.aggregateId}:${versionOf(event)}:${draft.userId}`,
+        userId: draft.userId,
+        kind: draft.kind,
+        ...context,
+        actor,
+        summary: draft.summary,
+        readAt: null,
+        createdAt: event.occurredAt,
+      };
+      // 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}`,
+        );
+      }
+    }
+  }
+}