Hiding excess fields from other layers.kt

object Presenter { // presentation layer
    fun loadDataForList() {
        val dataToShow: List<UiDataShort> = DataStore.retrieveDataList()
    }

    fun loadDataForDetailedView(clickedData: UiDataShort) {
        val dataToShow: UIDataDetailed = DataStore.getDetails(clickedData)
    }
}

interface UiDataShort { // some list items
    val title: String
    val authorName: String
    val authorIconUrl: String
}

interface UIDataDetailed { // data for some full page
    val title: String
    val headerImage: String
    val authorName: String
    val authorIconUrl: String
    val content: String
}

object DataStore { // data payer
    private val someData = List(10) { // data layer has access to full data
        DataEntity(-1, "title", "header img url", "author", "author ic url", "content", false)
    }

    fun retrieveDataList(): List<UiDataShort> {
        return someData.map { it.ProxyShort() }
    }

    fun getDetails(short: UiDataShort): UIDataDetailed {
        require(short is DataEntity.Inner) // otherwise, this data was not created in the data layer
        return short.entity.ProxyDetailed()
    }
}

class DataEntity(
    val id: Int,
    val title: String,
    val headerImage: String,
    val authorName: String,
    val authorIconUrl: String,
    val content: String,
    val isLast: Boolean
) {

    abstract class Inner(val entity: DataEntity)

    inner class ProxyShort : Inner(this@DataEntity), UiDataShort {
        override val title: String get() = this@DataEntity.title
        override val authorName: String get() = this@DataEntity.authorName
        override val authorIconUrl: String get() = this@DataEntity.authorIconUrl
    }

    inner class ProxyDetailed : Inner(this@DataEntity), UIDataDetailed {
        override val title: String get() = this@DataEntity.title
        override val headerImage: String get() = this@DataEntity.headerImage
        override val authorName: String get() = this@DataEntity.authorName
        override val authorIconUrl: String get() = this@DataEntity.authorIconUrl
        override val content: String get() = this@DataEntity.content
    }
}