CustomerRepo.kt

interface CustomerRepo {
    fun fetchCustomerDetail(): Single<CustomerDetail>
}

class CustomerRepoImpl(
           private val customerEndPoint: CustomerEndPoint): CustomerRepo
 {
    override fun fetchCustomerDetail(): Single<CustomerDetail> {
        return customerEndPoint
                .getCustomerData()               
                .flatMap { response ->
                    response.body()?.let { 
                    Single.just(it.data) 
                 }
              ?: Single.error(HttpException(response))
        }
                .subscribeOn(Schedulers.io())
    }
}