the-algorithm/tweetypie/server/src/main/scala/com/twitter/tweetypie/handler/GetTweetCountsHandler.scala

package com.twitter.tweetypie
package handler

import com.twitter.servo.util.FutureArrow
import com.twitter.stitch.Stitch
import com.twitter.tweetypie.repository._
import com.twitter.tweetypie.thriftscala._

/**
 * Handler for the `getTweetCounts` endpoint.
 */
object GetTweetCountsHandler {
  type Type = FutureArrow[GetTweetCountsRequest, Seq[GetTweetCountsResult]]

  def apply(repo: TweetCountsRepository.Type): Type = {

    def idToResult(id: TweetId, req: GetTweetCountsRequest): Stitch[GetTweetCountsResult] =
      Stitch
        .join(
          // .liftToOption() converts any failures to None result
          if (req.includeRetweetCount) repo(RetweetsKey(id)).liftToOption() else Stitch.None,
          if (req.includeReplyCount) repo(RepliesKey(id)).liftToOption() else Stitch.None,
          if (req.includeFavoriteCount) repo(FavsKey(id)).liftToOption() else Stitch.None,
          if (req.includeQuoteCount) repo(QuotesKey(id)).liftToOption() else Stitch.None,
          if (req.includeBookmarkCount) repo(BookmarksKey(id)).liftToOption() else Stitch.None
        ).map {
          case (retweetCount, replyCount, favoriteCount, quoteCount, bookmarkCount) =>
            GetTweetCountsResult(
              tweetId = id,
              retweetCount = retweetCount,
              replyCount = replyCount,
              favoriteCount = favoriteCount,
              quoteCount = quoteCount,
              bookmarkCount = bookmarkCount
            )
        }

    FutureArrow[GetTweetCountsRequest, Seq[GetTweetCountsResult]] { request =>
      Stitch.run(
        Stitch.traverse(request.tweetIds)(idToResult(_, request))
      )
    }
  }
}