Resource.kt

sealed class Resource<out T> {
    
    data class Success<out T>(val data: T) : Resource<T>()
    data class Loading<out T>(val partialData: T? = null) : Resource<T>()
    data class Failure<out T>(val throwable: Throwable? = null) : Resource<T>()

    val extractData: T? get() = when (this) {
        is Success -> data
        is Loading -> partialData
        is Failure -> null
    }
    
    inline fun <Y> mapResource(crossinline transform: (T) -> Y): Resource<Y> = try {
        when (this) {
            is Success<T> -> Success<Y>(transform(data))
            is Loading<T> -> Loading<Y>(partialData?.let { transform(it) })
            is Failure<T> -> Failure<Y>(throwable)
        }
    } catch (e: Throwable) {
        Resource.Failure<Y>(e)
    }

    fun onSuccess(onSuccess: (data: T) -> Unit): Resource<T> {
        if (this is Success)
            onSuccess(data)

        return this
    }

    fun onLoading(onLoading: (partialData: T?) -> Unit): Resource<T> {
        if (this is Loading)
            onLoading(partialData)

        return this
    }

    fun onFailure(onFailure: (throwable: Throwable?) -> Unit): Resource<T> {
        if (this is Failure)
            onFailure(throwable)

        return this
    }

}