package com.twitter.timelines.prediction.common.aggregates.real_time

import com.twitter.conversions.DurationOps._
import com.twitter.finagle.stats.StatsReceiver
import com.twitter.storehaus.ReplicatedReadableStore
import com.twitter.storehaus.Store
import com.twitter.timelines.clients.memcache_common._
import com.twitter.timelines.util.FailOpenHandler
import com.twitter.util.Future

object ServedFeaturesMemcacheConfigBuilder {
  def getTwCacheDestination(cluster: String, isProd: Boolean = false): String =
    if (!isProd) {
      s"/srv#/test/$cluster/cache//twemcache_timelines_served_features_cache"
    } else {
      s"/srv#/prod/$cluster/cache/timelines_served_features"
    }

  /**
   * @cluster The DC of the cache that this client will send requests to. This
   *   can be different to the DC where the summingbird job is running in.
   * @isProd  Define if this client is part of a production summingbird job as
   *   different accesspoints will need to be chosen.
   */
  def build(cluster: String, isProd: Boolean = false): StorehausMemcacheConfig =
    StorehausMemcacheConfig(
      destName = getTwCacheDestination(cluster, isProd),
      keyPrefix = "",
      requestTimeout = 200.milliseconds,
      numTries = 2,
      globalTimeout = 400.milliseconds,
      tcpConnectTimeout = 200.milliseconds,
      connectionAcquisitionTimeout = 200.milliseconds,
      numPendingRequests = 1000,
      isReadOnly = false
    )
}

/**
 * If lookup key does not exist locally, make a call to the replicated store(s).
 * If value exists remotely, write the first returned value to the local store
 * and return it. Map any exceptions to None so that the subsequent operations
 * may proceed.
 */
class LocallyReplicatedStore[-K, V](
  localStore: Store[K, V],
  remoteStore: ReplicatedReadableStore[K, V],
  scopedStatsReceiver: StatsReceiver)
    extends Store[K, V] {
  private[this] val failOpenHandler = new FailOpenHandler(scopedStatsReceiver.scope("failOpen"))
  private[this] val localFailsCounter = scopedStatsReceiver.counter("localFails")
  private[this] val localWritesCounter = scopedStatsReceiver.counter("localWrites")
  private[this] val remoteFailsCounter = scopedStatsReceiver.counter("remoteFails")

  override def get(k: K): Future[Option[V]] =
    failOpenHandler {
      localStore
        .get(k)
        .flatMap {
          case Some(v) => Future.value(Some(v))
          case _ => {
            localFailsCounter.incr()
            val replicatedOptFu = remoteStore.get(k)
            // async write if result is not empty
            replicatedOptFu.onSuccess {
              case Some(v) => {
                localWritesCounter.incr()
                localStore.put((k, Some(v)))
              }
              case _ => {
                remoteFailsCounter.incr()
                Unit
              }
            }
            replicatedOptFu
          }
        }
    } { _: Throwable => Future.None }
}