halve human rating diff in a match against a bot

modules/rating/src/main/Glicko.scala

@@ -38,6 +38,12 @@ case class Glicko(
     volatility = volatility atMost Glicko.maxVolatility
   )
 
+  def average(other: Glicko) = Glicko(
+    rating = (rating + other.rating) / 2,
+    deviation = (deviation + other.deviation) / 2,
+    volatility = (volatility + other.volatility) / 2
+  )
+
   override def toString = s"$intRating $intDeviation"
 }
 

modules/rating/src/main/Perf.scala

@@ -38,6 +38,10 @@ case class Perf(
     add(Glicko.default, date)
   }
 
+  def averageGlicko(other: Perf) = copy(
+    glicko = glicko average other.glicko
+  )
+
   def refund(points: Int): Perf = {
     val newGlicko = glicko refund points
     copy(

modules/round/src/main/PerfsUpdater.scala

@@ -57,8 +57,8 @@ final class PerfsUpdater(
           }
           case _ =>
         }
-        val perfsW = mkPerfs(ratingsW, white.perfs, game)
-        val perfsB = mkPerfs(ratingsB, black.perfs, game)
+        val perfsW = mkPerfs(ratingsW, white -> black, game)
+        val perfsB = mkPerfs(ratingsB, black -> white, game)
         def intRatingLens(perfs: Perfs) = mainPerf(perfs).glicko.intRating
         val ratingDiffs = Color.Map(
           intRatingLens(perfsW) - intRatingLens(white.perfs),
@@ -124,16 +124,24 @@ final class PerfsUpdater(
     }
     try {
       system.updateRatings(results)
-    } catch {
+    }
+    catch {
       case e: Exception => logger.error("update ratings", e)
     }
   }
 
-  private def mkPerfs(ratings: Ratings, perfs: Perfs, game: Game): Perfs = {
+  private def mkPerfs(ratings: Ratings, users: (User, User), game: Game): Perfs = users match {
+    case (player, opponent) =>
+      val perfs = player.perfs
       val speed = game.speed
       val isStd = game.ratingVariant.standard
+      val isHumanVsMachine = player.noBot && opponent.isBot
       def addRatingIf(cond: Boolean, perf: Perf, rating: Rating) =
-      if (cond) perf.addOrReset(_.round.error.glicko, s"game ${game.id}")(rating, game.movedAt)
+        if (cond) {
+          val p = perf.addOrReset(_.round.error.glicko, s"game ${game.id}")(rating, game.movedAt)
+          if (isHumanVsMachine) perf averageGlicko p // halve rating diffs for human
+          else p
+        }
         else perf
       val perfs1 = perfs.copy(
         chess960 = addRatingIf(game.ratingVariant.chess960, perfs.chess960, ratings.chess960),