Receiver Context Dependency Injection

arrowInjekt.kt

package com.example.sample

import arrow.core.*
import arrow.core.computations.either
import arrow.fx.coroutines.raceN

public data class NewsItem(val id: String)
public data class Detail(val id: String, val content: String)

public object Failure

public class Db
public class Nw

//<editor-fold desc="Singleton">
public class AppModule(public val retrofit: Nw, public val db: Db)

public val appModule: AppModule = AppModule(Nw(), Db())
//</editor-fold>

//<editor-fold desc="News List">
public interface NewsRepository {
  public suspend fun headlines(): Either<Failure, NonEmptyList<NewsItem>>

  fun zip(other: NewsRepository): NewsRepository =
    object : NewsRepository {
      override suspend fun headlines(): Either<Failure, NonEmptyList<NewsItem>> =
        [email protected]().zip(other.headlines()) { nw, db -> nw + db }
    }
}

class NewsDatabaseImpl(private val database: Db) : NewsRepository {
  override suspend fun headlines(): Either<Failure, NonEmptyList<NewsItem>> =
    nonEmptyListOf(
      NewsItem("4"),
      NewsItem("5"),
      NewsItem("6"),
    ).right()
}

class NewsNetworkImpl(private val network: Nw) : NewsRepository {
  override suspend fun headlines(): Either<Failure, NonEmptyList<NewsItem>> =
    nonEmptyListOf(
      NewsItem("1"),
      NewsItem("2"),
      NewsItem("3"),
    ).right()
}

//</editor-fold>

//<editor-fold desc="Detail">
public interface DetailRepository {
  public suspend fun detail(newsItem: NewsItem): Either<Failure, Detail>
}

public class DetailRepositoryImpl(
  private val network: DetailRepository,
  private val database: DetailRepository
  ) : DetailRepository {
  override suspend fun detail(newsItem: NewsItem): Either<Failure, Detail> =
    either {
      raceN(
        { network.detail(newsItem).bind() },
        { database.detail(newsItem).bind() }
      ).merge()
    }
}


class NetworkDetailDataSource(private val retrofit: Nw): DetailRepository {
  override suspend fun detail(newsItem: NewsItem): Either<Failure, Detail> =
    Detail(newsItem.id, "Nw: Content of $newsItem").right()
}
class DatabaseDetailDataSource(private val db: Db): DetailRepository {
  override suspend fun detail(newsItem: NewsItem): Either<Failure, Detail> =
    Detail(newsItem.id, "Db: Content of $newsItem").right()
}

//</editor-fold>

interface Module: NewsRepository, DetailRepository

fun module(newsRepository: NewsRepository, detailRepository: DetailRepository): Module =
  object : Module, NewsRepository by newsRepository, DetailRepository by detailRepository { }

suspend fun Module.program(): Either<Failure, NonEmptyList<Detail>> =
  headlines().flatMap { 
    it.traverseEither { detail(it) }
  }
    
    
public suspend fun main() {
  val news: NewsRepository =
    NewsNetworkImpl(appModule.retrofit).zip(NewsDatabaseImpl(appModule.db))
  
  val detail: DetailRepository =
    DetailRepositoryImpl(
      NetworkDetailDataSource(appModule.retrofit),
      DatabaseDetailDataSource(appModule.db)
    )
  
  val module = module(news, detail)
  
  val detailPages = module.program()
  
  println(detailPages)
}