EmailService.ts

import { make } from "@effect/platform/Template";
import { SqlClient } from "@effect/sql";
import { Array, Context, Effect, Layer, pipe, Stream } from "effect";

interface EmailMessage {
  contents: string;
  recipients: string | string[];
}

const makeLiveEmailService = Effect.gen(function* () {
  const sql = yield* SqlClient.SqlClient;

  const getContactsForBroadcast = (recipients: string[]) =>
    sql<{ email: string }>`SELECT * FROM contacts WHERE email ${sql.in(
      recipients,
    )}`.stream.pipe(Stream.map((row) => row.email));

  const sendEmail = (recipient: string, email: EmailMessage) =>
    Effect.gen(function* () {
      // Send the email
    });

  return {
    processAndSendEmails: (email: EmailMessage) =>
      pipe(
        email.recipients,
        Array.ensure,
        getContactsForBroadcast,
        Stream.mapEffect((contact) => sendEmail(contact, email), {
          concurrency: 4,
        }),
        Stream.runDrain,
        sql.withTransaction,
      ),
  };
});

const makeNoopEmailService = Effect.gen(function* () {
  return {
    processAndSendEmails: (email: EmailMessage) =>
      Effect.logInfo("Sent email", email),
  };
});

export class EmailService extends Context.Tag("EmailService")<
  EmailService,
  Effect.Effect.Success<typeof makeLiveEmailService>
>() {
  static readonly live = Layer.effect(this, makeLiveEmailService);
  static readonly noop = Layer.effect(this, makeNoopEmailService);
}

// Elsewhere...

const mainProgram = Effect.gen(function* () {
  const emailService = yield* EmailService;

  yield* emailService.processAndSendEmails({
    contents: "Hello, world!",
    recipients: ["[email protected]"],
  });
});

// Example of dependency injection for prod vs test/dev

const runLiveProgram = mainProgram.pipe(Effect.provide(EmailService.live));
const runTestProgram = mainProgram.pipe(Effect.provide(EmailService.noop));