don't pass Situation when only Board is needed

src/main/scala/Situation.scala

@@ -52,6 +52,8 @@ case class Situation(board: Board, color: Color) {
   )
 
   def canCastle = board.history.canCastle _
+
+  def unary_! = copy(color = !color)
 }
 
 object Situation {

src/main/scala/variant/Antichess.scala

@@ -33,7 +33,7 @@ case object Antichess extends Variant(
 
   // In antichess, there is no checkmate condition therefore a player may only draw either by agreement
   // , blockade or stalemate - a player always has sufficient material to win otherwise
-  override def insufficientWinningMaterial(situation: Situation, color: Color) = false
+  override def insufficientWinningMaterial(board: Board, color: Color) = false
 
   // No player can win if the only remaining pieces are opposing bishops on different coloured
   // diagonals. There may be pawns that are incapable of moving and do not attack the right color

src/main/scala/variant/Atomic.scala

@@ -108,8 +108,8 @@ case object Atomic extends Variant(
    * a piece in the opponent's king's proximity. On the other hand, a king alone or a king with
    * immobile pawns is not sufficient material to win with.
    */
-  override def insufficientWinningMaterial(situation: Situation, color: Color) =
-    situation.board.rolesOf(color) == List(King)
+  override def insufficientWinningMaterial(board: Board, color: Color) =
+    board.rolesOf(color) == List(King)
 
   /** Atomic chess has a special end where a king has been killed by exploding with an adjacent captured piece */
   override def specialEnd(situation: Situation) = situation.board.kingPos.size != 2

src/main/scala/variant/Horde.scala

@@ -46,10 +46,10 @@ case object Horde extends Variant(
    * In horde chess, white cannot win on * V K or [BN]{2} v K or just one piece since they don't have a king
    * for support.
    */
-  override def insufficientWinningMaterial(situation: Situation, color: Color) = {
-    color == Color.white && situation.board.piecesOf(Color.white).size == 1 ||
-      situation.board.piecesOf(Color.white).size == 2 &&
-        situation.board.piecesOf(Color.white).forall(_._2.isMinor)
+  override def insufficientWinningMaterial(board: Board, color: Color) = {
+    color == Color.white && board.piecesOf(Color.white).size == 1 ||
+      board.piecesOf(Color.white).size == 2 &&
+        board.piecesOf(Color.white).forall(_._2.isMinor)
   }
 
   override def isUnmovedPawn(color: Color, pos: Pos) = {

src/main/scala/variant/KingOfTheHill.scala

@@ -17,7 +17,7 @@ case object KingOfTheHill extends Variant(
   /**
    * You only need a king to be able to win in this variant
    */
-  override def insufficientWinningMaterial(situation: Situation, color: Color) = false
+  override def insufficientWinningMaterial(board: Board, color: Color) = false
 
   override def insufficientWinningMaterial(board: Board) = false
 }

src/main/scala/variant/Threecheck.scala

@@ -21,8 +21,8 @@ case object ThreeCheck extends Variant(
   /**
    * It's not possible to check or checkmate the opponent with only a king
    */
-  override def insufficientWinningMaterial(situation: Situation, color: Color) =
-    situation.board.rolesOf(color) == List(King)
+  override def insufficientWinningMaterial(board: Board, color: Color) =
+    board.rolesOf(color) == List(King)
 
   // When there is insufficient mating material, there is still potential to win by checking the opponent 3 times
   // by the variant ending. However, no players can check if there are only kings remaining

src/main/scala/variant/Variant.scala

@@ -97,7 +97,7 @@ abstract class Variant(
    * This can be used to determine whether a player losing on time against a player
    * who doesn't have enough material to win should draw instead.
    */
-  def insufficientWinningMaterial(situation: Situation, color: Color) = InsufficientMatingMaterial(situation.board, color)
+  def insufficientWinningMaterial(board: Board, color: Color) = InsufficientMatingMaterial(board, color)
 
   // Some variants have an extra effect on the board on a move. For example, in Atomic, some
   // pieces surrounding a capture explode