it fricken works!

Gameboard.ShogiUI.BoardState/ShogiBoard.cs

@@ -15,10 +15,10 @@ namespace Gameboard.ShogiUI.BoardState
   public class ShogiBoard
   {
     private delegate void MoveSetCallback(Piece piece, Vector2 position);
-    private ShogiBoard validationBoard;
+    private readonly PathFinder2D<Piece> pathFinder;
+    public ShogiBoard validationBoard;
     private Vector2 player1King;
     private Vector2 player2King;
-    private PathFinder2D<Piece> pathFinder;
     public IReadOnlyDictionary<WhichPlayer, List<Piece>> Hands { get; }
     public Array2D<Piece> Board { get; }
     public List<Move> MoveHistory { get; }
@@ -44,15 +44,11 @@ namespace Gameboard.ShogiUI.BoardState
     {
       for (var i = 0; i < moves.Count; i++)
       {
-        if (!TryMove(moves[i]))
+        if (!Move(moves[i]))
         {
           throw new InvalidOperationException($"Unable to construct ShogiBoard with the given move at index {i}.");
         }
       }
-      if (EvaluateCheckAfterMove(WhoseTurn))
-      {
-        InCheck = WhoseTurn;
-      }
     }
 
     private ShogiBoard(ShogiBoard toCopy)
@@ -75,7 +71,7 @@ namespace Gameboard.ShogiUI.BoardState
 
     public bool Move(Move move)
     {
-
+      var otherPlayer = WhoseTurn == WhichPlayer.Player1 ? WhichPlayer.Player2 : WhichPlayer.Player1;
       var moveSuccess = TryMove(move);
 
       if (!moveSuccess)
@@ -84,13 +80,10 @@ namespace Gameboard.ShogiUI.BoardState
       }
 
       // Evaluate check
-      if (EvaluateCheckAfterMove(WhoseTurn))
+      if (EvaluateCheckAfterMove(move, otherPlayer))
       {
-        InCheck = WhoseTurn;
-        if (InCheck.HasValue)
-        {
-          //IsCheckmate = EvaluateCheckmate();
-        }
+        InCheck = otherPlayer;
+        IsCheckmate = EvaluateCheckmate();
       }
       return true;
     }
@@ -114,11 +107,14 @@ namespace Gameboard.ShogiUI.BoardState
         validationBoard = null;
         return false;
       }
-      // Assert that this move does not put the moving player in check.
-      if (validationBoard.EvaluateCheckAfterMove(WhoseTurn))
+      // If already in check, assert the move that resulted in check no longer results in check.
+      if (InCheck == WhoseTurn)
       {
-        // Sneakily using this.WhoseTurn instead of validationBoard.WhoseTurn;
-        return false;
+        if (validationBoard.EvaluateCheckAfterMove(MoveHistory[^1], WhoseTurn))
+        {
+          // Sneakily using this.WhoseTurn instead of validationBoard.WhoseTurn;
+          return false;
+        }
       }
 
       // The move is valid and legal; update board state.
@@ -251,13 +247,11 @@ namespace Gameboard.ShogiUI.BoardState
       Console.WriteLine(builder.ToString());
     }
     #region Rules Validation
-    private bool EvaluateCheckAfterMove(WhichPlayer whichPlayer)
+    private bool EvaluateCheckAfterMove(Move move, WhichPlayer whichPlayer)
     {
       var isCheck = false;
       var kingPosition = whichPlayer == WhichPlayer.Player1 ? player1King : player2King;
 
-      // Get last move.
-      var move = MoveHistory[^1];
       // Check if the move put the king in check.
       if (pathFinder.PathTo(move.To, kingPosition)) return true;
 
@@ -327,10 +321,15 @@ namespace Gameboard.ShogiUI.BoardState
           pathFinder.PathEvery(from, (other, position) =>
         {
           if (validationBoard == null) validationBoard = new ShogiBoard(this);
-          var moveSuccess = validationBoard.TryMove(new Move { From = from, To = position });
+          var moveToTry = new Move { From = from, To = position };
+          var moveSuccess = validationBoard.TryMove(moveToTry);
           if (moveSuccess)
           {
-            isCheckmate = false;
+            validationBoard = null;
+            if (!EvaluateCheckAfterMove(moveToTry, InCheck.Value))
+            {
+              isCheckmate = false;
+            }
           }
         });
         }