service3.scala

import zio.{Task, ZIO, ZLayer, ZManaged}

object DB {
  // 1. service
  trait Service {
    def execute(sql: String): Task[Unit]
  }

  // 2. layer
  val liveRelationalDB: ZLayer[HasConnectionPool, Throwable, DB] = ZLayer.fromService 
    { cp => new Service {
      override def execute(sql: String): Task[Unit] =
        Task(println(s"Running: $sql, on: $cp"))
    } }
  }

// 1. procedural, low-level interface
class ConnectionPool(url: String) {
  def close(): Unit = ()
  override def toString: String = s"ConnectionPool($url)"
}

// 2. integration with ZIO
object ConnectionPoolIntegration {
  def createConnectionPool(cfg: DBConfig): ZIO[Any, Throwable, ConnectionPool] =
    ZIO.effect(new ConnectionPool(cfg.url))
  val closeConnectionPool: ConnectionPool => ZIO[Any, Nothing, Unit] = 
    (cp: ConnectionPool) => ZIO.effect(cp.close()).catchAll(_ => ZIO.unit)
  def managedConnectionPool(cfg: DBConfig): ZManaged[Any, Throwable, ConnectionPool] =
    ZManaged.make(createConnectionPool(cfg))(closeConnectionPool)

  val live: ZLayer[HasDBConfig, Throwable, HasConnectionPool] =
    ZLayer.fromServiceManaged(managedConnectionPool)
}

// ---

// 4. type aliases in package.scala
type HasDBConfig = Has[DBConfig]
type HasConnectionPool = Has[ConnectionPool]
type DB = Has[DB.Service]