reducer.kt

val reducer = BiFunction { previousState: CountryListViewState, result: CountryListResult ->
    when (result) {
        is LoadCountriesResult ->
            when (result) {
                is LoadCountriesResult.Success -> {
                    previousState.copy(
                        isLoading = false,
                        isRefreshing = false,
                        countries = result.countries
                    )
                }
                is LoadCountriesResult.Failure -> {
                    previousState.copy(
                        isLoading = false,
                        error = result.error
                    )
                }
                is LoadCountriesResult.InProgress -> {
                    if (result.isRefreshing) {
                        previousState.copy(
                            isLoading = false,
                            isRefreshing = true
                        )
                    } else previousState.copy(
                        isLoading = true,
                        isRefreshing = false
                    ) 
                }
            }
    } 
}