prevent bot farming - closes #4839

modules/round/src/main/BotFarming.scala

@@ -0,0 +1,33 @@
+package lila.round
+
+import lila.common.LightUser.IsBotSync
+import lila.game.{ Game, GameRepo, CrosstableApi }
+
+private final class BotFarming(
+    crosstableApi: CrosstableApi,
+    isBotSync: IsBotSync
+) {
+
+  val SAME_PLIES = 20
+  val PREV_GAMES = 2
+
+  /* true if
+   * - at least one bot
+   * - rated
+   * - recent game in same matchup has same first SAME_PLIES and same winner
+   */
+  def apply(g: Game): Fu[Boolean] = g.userIds.distinct match {
+    case List(u1, u2) if g.finished && g.rated && g.userIds.exists(isBotSync) =>
+      crosstableApi(u1, u2) flatMap {
+        _ ?? { ct =>
+          GameRepo.gamesFromSecondary(ct.results.reverse.take(PREV_GAMES).map(_.gameId)) map {
+            _ exists { prev =>
+              g.winnerUserId == prev.winnerUserId &&
+                g.pgnMoves.take(SAME_PLIES) == prev.pgnMoves.take(SAME_PLIES)
+            }
+          }
+        }
+      }
+    case _ => fuccess(false)
+  }
+}

modules/round/src/main/Env.scala

@@ -152,7 +152,9 @@ final class Env(
     isRecentTv = recentTvGames get _
   )
 
-  lazy val perfsUpdater = new PerfsUpdater(historyApi, rankingApi)
+  private lazy val botFarming = new BotFarming(crosstableApi, isBotSync)
+
+  lazy val perfsUpdater = new PerfsUpdater(historyApi, rankingApi, botFarming)
 
   lazy val forecastApi: ForecastApi = new ForecastApi(
     coll = db(CollectionForecast),

modules/round/src/main/PerfsUpdater.scala

@@ -10,16 +10,18 @@ import lila.user.{ UserRepo, User, Perfs, RankingApi }
 
 final class PerfsUpdater(
     historyApi: HistoryApi,
-    rankingApi: RankingApi
+    rankingApi: RankingApi,
+    botFarming: BotFarming
 ) {
 
   private val VOLATILITY = Glicko.default.volatility
   private val TAU = 0.75d
   private val system = new RatingCalculator(VOLATILITY, TAU)
 
   // returns rating diffs
-  def save(game: Game, white: User, black: User): Fu[Option[RatingDiffs]] =
-    PerfPicker.main(game) ?? { mainPerf =>
+  def save(game: Game, white: User, black: User): Fu[Option[RatingDiffs]] = botFarming(game) flatMap {
+    case true => fuccess(none)
+    case _ => PerfPicker.main(game) ?? { mainPerf =>
       (game.rated && game.finished && game.accountable && !white.lame && !black.lame) ?? {
         val ratingsW = mkRatings(white.perfs)
         val ratingsB = mkRatings(black.perfs)
@@ -73,6 +75,7 @@ final class PerfsUpdater(
           rankingApi.save(black, game.perfType, perfsB) inject ratingDiffs.some
       }
     }
+  }
 
   private final case class Ratings(
       chess960: Rating,