backoff.kt

fun <T> backoff(times: Int = Int.MAX_VALUE, predicate: (Throwable, Int) -> Boolean = { _, _ -> true }): ObservableTransformer<T, T> {
    return ObservableTransformer {
        it.retryWhen { attempts ->
            val counter = AtomicInteger()
            attempts.takeWhile { e -> counter.getAndIncrement() < times && predicate(e, counter.get()) }
                    .flatMap { Observable.timer(counter.get().toLong(), TimeUnit.SECONDS) }
        }
    }
}