ZIO learning - structured services - vertical composition / published by https://github.com/dacr/code-examples-manager #73bc55eb-d065-4fcc-81c0-db0ead534f96/67c613e406230c38bdc8739a1dd58fd9a3456c42

zio-learning-26-structured-services-3-vertical-composition.sc

// summary : ZIO learning - structured services - vertical composition
// keywords : scala, zio, learning, services, pure-functional, @testable
// publish : gist
// authors : Rock the JVM
// license : Apache License Version 2.0 (https://www.apache.org/licenses/LICENSE-2.0.txt)
// id : 73bc55eb-d065-4fcc-81c0-db0ead534f96
// created-on : 2021-05-03T18:43:49+02:00
// managed-by : https://github.com/dacr/code-examples-manager
// run-with : scala-cli $file

// Highly inspired from Structuring Services in Scala with ZIO and ZLayer : https://www.youtube.com/watch?v=PaogLRrYo64
// And lately updated or Scala3 & ZIO2

// ---------------------
//> using scala "3.4.2"
//> using dep "dev.zio::zio:2.0.13"
// ---------------------

import zio.*

// ----------------------------------------------------------------------------------------
case class User(name: String, email: String)

// ----------------------------------------------------------------------------------------
// This is the classical service pattern used within ZIO, with the standard naming scheme

// Service definition
trait UserEmailer:
  def notify(user: User, message: String): Task[Unit]

object UserEmailer:

  class UserEmailerImpl() extends UserEmailer:
    override def notify(user: User, message: String): Task[Unit] =
      ZIO.attempt(println(s"[User emailer] Sending '$message' to ${user.email}'"))

  val live: URLayer[Any, UserEmailer] = ZLayer.succeed(UserEmailerImpl())

  // Front-facing API - helper function
  def notify(user: User, message: String): RIO[UserEmailer, Unit] =
    ZIO.serviceWithZIO(_.notify(user, message))

// ----------------------------------------------------------------------------------------
trait UserDb:
  def insert(user: User): Task[Unit]

object UserDb:
  class UserDbImpl extends UserDb:
    override def insert(user: User) = ZIO.attempt(
      println(s"[Database] insert into public.user value ('${user.email}')")
    )

  val live = ZLayer.succeed(UserDbImpl())

  def insert(user: User): RIO[UserDb, Unit] =
    ZIO.serviceWithZIO(_.insert(user))

// ----------------------------------------------------------------------------------------

class UserSubscription(notifier: UserEmailer, userDb: UserDb):
  def subscribe(user: User): Task[User] =
    for
      _ <- userDb.insert(user)
      _ <- notifier.notify(user, s"Welcome to this site, ${user.email}")
    yield user

object UserSubscription:

  val live: URLayer[UserEmailer & UserDb, UserSubscription] = ZLayer(
    for
      userEmailer <- ZIO.service[UserEmailer]
      userDb      <- ZIO.service[UserDb]
    yield UserSubscription(userEmailer, userDb)
  )

  // front-facing API
  def subscribe(user: User): RIO[UserSubscription, User] =
    ZIO.serviceWithZIO(_.subscribe(user))

// ----------------------------------------------------------------------------------------

object Encapsulated extends ZIOAppDefault:

  val david = User("david", "[email protected]")

  val layers = ZLayer.make[UserDb & UserEmailer & UserSubscription](
    UserDb.live,
    UserEmailer.live,
    UserSubscription.live
  )

  val logic =
    UserSubscription
      .subscribe(david)
      .provideLayer(layers)

  override def run = logic

Encapsulated.main(Array.empty)