the-algorithm/timelineranker/server/src/main/scala/com/twitter/timelineranker/core/FollowGraphDataFuture.scala

package com.twitter.timelineranker.core

import com.twitter.timelines.model.UserId
import com.twitter.util.Future

/**
 * Similar to FollowGraphData but makes available its fields as separate futures.
 */
case class FollowGraphDataFuture(
  userId: UserId,
  followedUserIdsFuture: Future[Seq[UserId]],
  mutuallyFollowingUserIdsFuture: Future[Set[UserId]],
  mutedUserIdsFuture: Future[Set[UserId]],
  retweetsMutedUserIdsFuture: Future[Set[UserId]]) {

  def inNetworkUserIdsFuture: Future[Seq[UserId]] = followedUserIdsFuture.map(_ :+ userId)

  def get(): Future[FollowGraphData] = {
    Future
      .join(
        followedUserIdsFuture,
        mutuallyFollowingUserIdsFuture,
        mutedUserIdsFuture,
        retweetsMutedUserIdsFuture
      )
      .map {
        case (followedUserIds, mutuallyFollowingUserIds, mutedUserIds, retweetsMutedUserIds) =>
          FollowGraphData(
            userId,
            followedUserIds,
            mutuallyFollowingUserIds,
            mutedUserIds,
            retweetsMutedUserIds
          )
      }
  }
}

object FollowGraphDataFuture {
  private def mkEmptyFuture(field: String) = {
    Future.exception(
      new IllegalStateException(s"FollowGraphDataFuture field $field accessed without being set")
    )
  }

  val EmptyFollowGraphDataFuture: FollowGraphDataFuture = FollowGraphDataFuture(
    userId = 0L,
    followedUserIdsFuture = mkEmptyFuture("followedUserIdsFuture"),
    mutuallyFollowingUserIdsFuture = mkEmptyFuture("mutuallyFollowingUserIdsFuture"),
    mutedUserIdsFuture = mkEmptyFuture("mutedUserIdsFuture"),
    retweetsMutedUserIdsFuture = mkEmptyFuture("retweetsMutedUserIdsFuture")
  )
}