Allow copying to FastSimpleGame from GameState, and add getSubject to…

… GameState

src/main/java/net/royalur/rules/simple/fast/FastSimpleGame.java

@@ -2,6 +2,8 @@
 
 import net.royalur.Game;
 import net.royalur.model.*;
+import net.royalur.rules.state.GameState;
+import net.royalur.rules.state.WaitingForMoveGameState;
 
 import javax.annotation.Nullable;
 import java.util.List;
@@ -68,13 +70,17 @@ public void copyFrom(FastSimpleGame other) {
         this.isFinished = other.isFinished;
     }
 
+    public void copyFrom(GameState state) {
+        board.copyFrom(state.getBoard());
+        light.copyFrom(state.getLightPlayer());
+        dark.copyFrom(state.getDarkPlayer());
+        this.isLightTurn = (state.getSubject() == PlayerType.LIGHT);
+        this.rollValue = (state instanceof WaitingForMoveGameState wfm ? wfm.getRoll().value() : -1);
+        this.isFinished = state.isFinished();
+    }
+
     public void copyFrom(Game game) {
-        board.copyFrom(game.getBoard());
-        light.copyFrom(game.getLightPlayer());
-        dark.copyFrom(game.getDarkPlayer());
-        this.isLightTurn = (game.getTurn() == PlayerType.LIGHT);
-        this.rollValue = (game.isWaitingForMove() ? game.getRoll().value() : -1);
-        this.isFinished = game.isFinished();
+        copyFrom(game.getState());
     }
 
     /**

src/main/java/net/royalur/rules/state/ControlGameState.java

@@ -47,6 +47,11 @@ public ControlGameState(
         this(board, lightPlayer, darkPlayer, null);
     }
 
+    @Override
+    public @Nullable PlayerType getSubject() {
+        return player;
+    }
+
     @Override
     public boolean isPlayable() {
         return false;

src/main/java/net/royalur/rules/state/EndGameState.java

@@ -95,6 +95,11 @@ public PlayerState getLosingPlayer() {
         return getPlayerState(getLoser());
     }
 
+    @Override
+    public @Nullable PlayerType getSubject() {
+        return winner;
+    }
+
     @Override
     public String describe() {
         if (winner == null)

src/main/java/net/royalur/rules/state/GameState.java

@@ -2,6 +2,8 @@
 
 import net.royalur.model.*;
 
+import javax.annotation.Nullable;
+
 /**
  * A game state represents a single point within a game.
  */
@@ -79,6 +81,12 @@ public PlayerState getPlayerState(PlayerType player) {
         };
     }
 
+    /**
+     * Get the subject player of the game state. e.g., player
+     * to roll/move, player that rolled/moved, player that won.
+     */
+    public abstract @Nullable PlayerType getSubject();
+
     /**
      * Returns whether this state is a valid state to be played from.
      * @return Whether this state is a valid state to be played from.

src/main/java/net/royalur/rules/state/OngoingGameState.java

@@ -72,6 +72,11 @@ public PlayerState getWaitingPlayer() {
         return getPlayerState(getWaiting());
     }
 
+    @Override
+    public PlayerType getSubject() {
+        return turn;
+    }
+
     @Override
     public boolean equals(Object obj) {
         if (this == obj)