arrowInjekt.kt

package com.example.sample

import arrow.core.Either
import arrow.core.NonEmptyList
import arrow.core.computations.either
import arrow.core.flatMap
import arrow.core.nonEmptyListOf
import arrow.core.right
import arrow.core.traverseEither
import arrow.core.zip
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: Db, public val db: Nw)

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

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

public class NewsRepositoryImpl(private val newsDataSource: NewsDataSource) : NewsRepository {
    override suspend fun headlines(): Either<Failure, NonEmptyList<NewsItem>> =
            newsDataSource.fetchNwHeadlines().zip(newsDataSource.fetchDbHeadlines()) { nw, db -> nw + db }
}

public interface HttpNewsDataSource {
    public suspend fun fetchNwHeadlines(): Either<Failure, NonEmptyList<NewsItem>>
}

public interface DbNewsDataSource {
    public suspend fun fetchDbHeadlines(): Either<Failure, NonEmptyList<NewsItem>>
}

public interface NewsDataSource : HttpNewsDataSource, DbNewsDataSource
public class NewsDataSourceImpl(
        private val retroFit: Db,
        private val db: Nw
) : NewsDataSource {
    override suspend fun fetchNwHeadlines(): Either<Failure, NonEmptyList<NewsItem>> =
            nonEmptyListOf(
                    NewsItem("1"),
                    NewsItem("2"),
                    NewsItem("3"),
            ).right()

    override suspend fun fetchDbHeadlines(): Either<Failure, NonEmptyList<NewsItem>> =
            nonEmptyListOf(
                    NewsItem("4"),
                    NewsItem("5"),
                    NewsItem("6"),
            ).right()
}

public interface ListModule {
    public val newsRepository: NewsRepository
}

public suspend fun ListModule.headlines(): Either<Failure, NonEmptyList<NewsItem>> = newsRepository.headlines()

public fun newsListModule(appModule: AppModule): ListModule =
        object : ListModule {
            override val newsRepository: NewsRepository
                get() = NewsRepositoryImpl(NewsDataSourceImpl(appModule.retrofit, appModule.db))
        }
//</editor-fold>

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

public class DetailRepositoryImpl(private val detailDataSource: DetailDataSource) : DetailRepository {
    override suspend fun detail(newsItem: NewsItem): Either<Failure, Detail> =
            either {
                raceN(
                        { detailDataSource.fetchNwDetail(newsItem).bind() },
                        { detailDataSource.fetchDbDetail(newsItem).bind() }
                ).mapLeft { Failure }.bind()
            }
}

public interface HttpDetailDataSource {
    public suspend fun fetchNwDetail(newsItem: NewsItem): Either<Failure, Detail>
}

public interface DbDetailDataSource {
    public suspend fun fetchDbDetail(newsItem: NewsItem): Either<Failure, Detail>
}

public interface DetailDataSource : HttpDetailDataSource, DbDetailDataSource
public class DetailDataSourceImpl(private val retrofit: Db, private val db: Nw) : DetailDataSource {
    override suspend fun fetchNwDetail(newsItem: NewsItem): Either<Failure, Detail> =
            Detail(newsItem.id, "Nw: Content of $newsItem").right()

    override suspend fun fetchDbDetail(newsItem: NewsItem): Either<Failure, Detail> =
            Detail(newsItem.id, "Db: Content of $newsItem").right()
}

public interface DetailModule {
    public val detailRepository: DetailRepository
}

public suspend fun DetailModule.detail(newsItem: NewsItem): Either<Failure, Detail> = detailRepository.detail(newsItem)

public fun detailModule(appModule: AppModule): DetailModule =
        object : DetailModule {
            override val detailRepository: DetailRepository =
                    DetailRepositoryImpl(DetailDataSourceImpl(appModule.retrofit, appModule.db))
        }
//</editor-fold>

public suspend fun main() {
    val newsList = newsListModule(appModule)
    val detailModule = detailModule(appModule)
    val detailPages =
            newsList.headlines()
                    .flatMap {
                        it.traverseEither { newsItem -> detailModule.detail(newsItem) }
                    }
    println(detailPages)
}