package com.twitter.tweetypie.storage

import com.twitter.finagle.stats.StatsReceiver
import com.twitter.stitch.Stitch
import com.twitter.tweetypie.storage.TweetStorageClient.Undelete
import com.twitter.tweetypie.storage.TweetUtils._
import com.twitter.util.Time

object UndeleteHandler {
  def apply(
    read: ManhattanOperations.Read,
    localInsert: ManhattanOperations.Insert,
    remoteInsert: ManhattanOperations.Insert,
    delete: ManhattanOperations.Delete,
    undeleteWindowHours: Int,
    stats: StatsReceiver
  ): Undelete = {
    def withinUndeleteWindow(timestampMs: Long) =
      (Time.now - Time.fromMilliseconds(timestampMs)).inHours < undeleteWindowHours

    def prepareUndelete(
      tweetId: TweetId,
      records: Seq[TweetManhattanRecord]
    ): (Undelete.Response, Option[TweetManhattanRecord]) = {
      val undeleteRecord =
        Some(TweetStateRecord.Undeleted(tweetId, Time.now.inMillis).toTweetMhRecord)

      TweetStateRecord.mostRecent(records) match {
        // check if we need to undo a soft deletion
        case Some(TweetStateRecord.SoftDeleted(_, createdAt)) =>
          if (createdAt > 0) {
            if (withinUndeleteWindow(createdAt)) {
              (
                mkSuccessfulUndeleteResponse(tweetId, records, Some(createdAt)),
                undeleteRecord
              )
            } else {
              (Undelete.Response(Undelete.UndeleteResponseCode.BackupNotFound), None)
            }
          } else {
            throw InternalError(s"Timestamp unavailable for $tweetId")
          }

        // BounceDeleted tweets may not be undeleted. see go/bouncedtweet
        case Some(_: TweetStateRecord.HardDeleted | _: TweetStateRecord.BounceDeleted) =>
          (Undelete.Response(Undelete.UndeleteResponseCode.BackupNotFound), None)

        case Some(_: TweetStateRecord.Undeleted) =>
          // We still want to write the undelete record, because at this point, we only know that the local DC's
          // winning record is not a soft/hard deletion record, while its possible that the remote DC's winning
          // record might still be a soft deletion record. Having said that, we don't want to set it to true
          // if the winning record is forceAdd, as the forceAdd call should have ensured that both DCs had the
          // forceAdd record.
          (mkSuccessfulUndeleteResponse(tweetId, records), undeleteRecord)

        case Some(_: TweetStateRecord.ForceAdded) =>
          (mkSuccessfulUndeleteResponse(tweetId, records), None)

        // lets write the undeletion record just in case there is a softdeletion record in flight
        case None => (mkSuccessfulUndeleteResponse(tweetId, records), undeleteRecord)
      }
    }

    // Write the undelete record both locally and remotely to protect
    // against races with hard delete replication. We only need this
    // protection for the insertion of the undelete record.
    def multiInsert(record: TweetManhattanRecord): Stitch[Unit] =
      Stitch
        .collect(
          Seq(
            localInsert(record).liftToTry,
            remoteInsert(record).liftToTry
          )
        )
        .map(collectWithRateLimitCheck)
        .lowerFromTry

    def deleteSoftDeleteRecord(tweetId: TweetId): Stitch[Unit] = {
      val mhKey = TweetKey.softDeletionStateKey(tweetId)
      delete(mhKey, None)
    }

    tweetId =>
      for {
        records <- read(tweetId)
        (response, undeleteRecord) = prepareUndelete(tweetId, records)
        _ <- Stitch.collect(undeleteRecord.map(multiInsert)).unit
        _ <- deleteSoftDeleteRecord(tweetId)
      } yield {
        response
      }
  }

  private[storage] def mkSuccessfulUndeleteResponse(
    tweetId: TweetId,
    records: Seq[TweetManhattanRecord],
    timestampOpt: Option[Long] = None
  ) =
    Undelete.Response(
      Undelete.UndeleteResponseCode.Success,
      Some(
        StorageConversions.fromStoredTweet(buildStoredTweet(tweetId, records))
      ),
      archivedAtMillis = timestampOpt
    )
}