Fallbacks When AI Is Unavailable

sealed interface AiOutcome<out T> {
    data class Ok<T>(val value: T, val source: String) : AiOutcome<T>
    data class Unavailable(val reason: Reason) : AiOutcome<Nothing>
    enum class Reason { OFFLINE, LIMITED, BLOCKED, FAILED }
}

class ResilientSummarizer(
    private val primary: Summarizer,      // e.g. cloud Flash
    private val secondary: Summarizer?,   // e.g. on-device, or a lighter model
    private val cache: SummaryCache,
    private val flags: AiFlags,           // remote config kill switch, model names
) {
    suspend fun summarize(key: String, text: String): AiOutcome<String> {
        if (!flags.summariesEnabled) return AiOutcome.Unavailable(AiOutcome.Reason.FAILED)
        cache.get(key)?.let { return AiOutcome.Ok(it, "cache") }

        val first = attempt(primary, text, retries = 1)
        if (first is AttemptResult.Success) return first.save(key, "primary")
        if (first is AttemptResult.Blocked) return AiOutcome.Unavailable(AiOutcome.Reason.BLOCKED)

        secondary?.let { s ->
            val second = attempt(s, text, retries = 0)
            if (second is AttemptResult.Success) return second.save(key, "secondary")
        }
        return AiOutcome.Unavailable(if (first is AttemptResult.Offline) AiOutcome.Reason.OFFLINE else AiOutcome.Reason.LIMITED)
    }

    private suspend fun attempt(s: Summarizer, text: String, retries: Int): AttemptResult {
        repeat(retries + 1) { i ->
            val r = try {
                withTimeout(15_000) { AttemptResult.Success(s.summarize(text)) }
            } catch (e: TimeoutCancellationException) { AttemptResult.Failed
            } catch (e: IOException) { AttemptResult.Offline
            } catch (e: BlockedException) { return AttemptResult.Blocked
            } catch (e: RateLimitedException) { AttemptResult.Failed }
            if (r is AttemptResult.Success) return r
            if (i < retries) delay(1_000L * (i + 1) + Random.nextLong(250))     // backoff with jitter
        }
        return AttemptResult.Failed
    }

    private suspend fun AttemptResult.Success.save(key: String, source: String): AiOutcome<String> {
        cache.put(key, value); return AiOutcome.Ok(value, source)
    }
}
// AttemptResult (Success/Failed/Offline/Blocked) and the exceptions map from your SDK's errors.