Add notifications module with application service and domain event subscriber

Author: aliondev

src/Contexts/Mooc/Notifications/application/SendWelcomeUserEmail/SendWelcomeUserEmail.ts

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+import { EmailSender } from '../../domain/EmailSender';
+import { EmailAddress } from '../../domain/EmailAddress';
+import { WelcomeUserEmail } from '../../domain/WelcomeUserEmail';
+import { WelcomeUserEmailError } from '../../domain/WelcomeUserEmailError';
+
+export default class SendWelcomeUserEmail {
+  constructor(private emailSender: EmailSender) {}
+
+  async run(userEmailAddress: EmailAddress): Promise<void> {
+    const welcomeUserEmail = new WelcomeUserEmail(userEmailAddress);
+    try {
+      await this.emailSender.send(welcomeUserEmail);
+    } catch (error) {
+      throw new WelcomeUserEmailError(userEmailAddress);
+    }
+  }
+}

src/Contexts/Mooc/Notifications/application/SendWelcomeUserEmail/SendWelcomeUserEmailOnUserRegistered.ts

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+import { DomainEventSubscriber } from '../../../../Shared/domain/DomainEventSubscriber';
+import { UserRegisteredDomainEvent } from '../../domain/UserRegisteredDomainEvent';
+import { DomainEventClass } from '../../../../Shared/domain/DomainEvent';
+import SendWelcomeUserEmail from './SendWelcomeUserEmail';
+import { EmailAddress } from '../../domain/EmailAddress';
+
+export default class SendWelcomeUserEmailOnUserRegistered implements DomainEventSubscriber<UserRegisteredDomainEvent> {
+  constructor(private sendWelcomeUserEmail: SendWelcomeUserEmail) {}
+
+  subscribedTo(): DomainEventClass[] {
+    return [UserRegisteredDomainEvent];
+  }
+
+  async on(domainEvent: UserRegisteredDomainEvent): Promise<void> {
+    const userEmailAddress = new EmailAddress(domainEvent.userEmailAddress);
+    await this.sendWelcomeUserEmail.run(userEmailAddress);
+  }
+}

src/Contexts/Mooc/Notifications/domain/Email.ts

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+import { EmailAddress } from './EmailAddress';
+import { EmailId } from './EmailId';
+import { Uuid } from '../../../Shared/domain/value-object/Uuid';
+
+type ConstructorParams = {
+  id?: EmailId;
+  from: EmailAddress;
+  to: EmailAddress;
+  subject: string;
+  body: string;
+};
+
+export class Email {
+  readonly id: EmailId;
+  readonly from: EmailAddress;
+  readonly to: EmailAddress;
+  readonly subject: string;
+  readonly body: string;
+
+  constructor(params: ConstructorParams) {
+    this.id = params.id || new EmailId(Uuid.random().value);
+    this.from = params.from;
+    this.to = params.to;
+    this.subject = params.subject;
+    this.body = params.body;
+  }
+
+  equals(otherEmail: Email): boolean {
+    return (
+      this.id.value === otherEmail.id.value &&
+      this.from.value === otherEmail.from.value &&
+      this.to.value === otherEmail.to.value &&
+      this.subject === otherEmail.subject &&
+      this.body === otherEmail.body
+    );
+  }
+}

src/Contexts/Mooc/Notifications/domain/EmailAddress.ts

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+import { StringValueObject } from '../../../Shared/domain/value-object/StringValueObject';
+
+export class EmailAddress extends StringValueObject {}

src/Contexts/Mooc/Notifications/domain/EmailId.ts

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+import { Uuid } from '../../../Shared/domain/value-object/Uuid';
+
+export class EmailId extends Uuid {}

src/Contexts/Mooc/Notifications/domain/EmailSender.ts

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+import { Email } from './Email';
+
+export interface EmailSender {
+  send(email: Email): Promise<void>;
+}

src/Contexts/Mooc/Notifications/domain/UserRegisteredDomainEvent.ts

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+import { DomainEvent } from '../../../Shared/domain/DomainEvent';
+
+type UserRegisteredDomainEventBody = { userEmailAddress: string };
+
+export class UserRegisteredDomainEvent extends DomainEvent {
+  static readonly EVENT_NAME = 'user.registered';
+  readonly userEmailAddress: string;
+
+  constructor(data: {
+    id: string;
+    userEmailAddress: string;
+    eventId?: string;
+    occurredOn?: Date;
+  }) {
+    const { id, eventId, occurredOn, userEmailAddress } = data;
+    super(UserRegisteredDomainEvent.EVENT_NAME, id, eventId, occurredOn);
+    this.userEmailAddress = userEmailAddress;
+  }
+
+  toPrimitive(): Object {
+    return { userEmailAddress: this.userEmailAddress };
+  }
+
+  static fromPrimitives(
+    aggregateId: string,
+    body: UserRegisteredDomainEventBody,
+    eventId: string,
+    occurredOn: Date
+  ): DomainEvent {
+    return new UserRegisteredDomainEvent({
+      id: aggregateId,
+      userEmailAddress: body.userEmailAddress,
+      eventId,
+      occurredOn
+    });
+  }
+}

src/Contexts/Mooc/Notifications/domain/WelcomeUserEmail.ts

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+import { Email } from './Email';
+import { EmailAddress } from './EmailAddress';
+
+export class WelcomeUserEmail extends Email {
+  constructor(to: EmailAddress) {
+    super({
+      from: new EmailAddress('welcome@foo.com'),
+      to,
+      subject: 'Welcome',
+      body: 'Welcome to our platform'
+    });
+  }
+}

src/Contexts/Mooc/Notifications/domain/WelcomeUserEmailError.ts

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+import { EmailAddress } from './EmailAddress';
+
+export class WelcomeUserEmailError extends Error {
+  constructor(userEmailAddress: EmailAddress) {
+    super(`Error sending WelcomeUser email to ${userEmailAddress.value}`);
+  }
+}

tests/Contexts/Mooc/Notifications/__mocks__/EmailSenderMock.ts

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+import { EmailSender } from '../../../../../src/Contexts/Mooc/Notifications/domain/EmailSender';
+import { Email } from '../../../../../src/Contexts/Mooc/Notifications/domain/Email';
+
+export class EmailSenderMock implements EmailSender {
+  private sendSpy = jest.fn();
+
+  async send(email: Email): Promise<void> {
+    this.sendSpy(email);
+  }
+
+  assertSentTimes(times: number): void {
+    expect(this.sendSpy.mock.calls.length).toBe(times);
+  }
+
+  lastEmailSent(): Email {
+    const sendCalls = this.sendSpy.mock.calls;
+    const lastSendCall = sendCalls[sendCalls.length - 1] || [];
+    const lastEmailSent = lastSendCall[0] as Email;
+
+    return lastEmailSent;
+  }
+}