before deleting Rules

Gameboard.ShogiUI.Sockets/Models/BoardState.cs

@@ -1,5 +1,6 @@
 using Gameboard.ShogiUI.Rules;
 using System.Collections.Generic;
+using System.Collections.ObjectModel;
 using System.Linq;
 using ServiceTypes = Gameboard.ShogiUI.Sockets.ServiceModels.Socket.Types;
 
@@ -7,28 +8,53 @@ namespace Gameboard.ShogiUI.Sockets.Models
 {
   public class BoardState
   {
-    public Piece[,] Board { get; set; }
-    public IReadOnlyCollection<Piece> Player1Hand { get; set; }
-    public IReadOnlyCollection<Piece> Player2Hand { get; set; }
+    // TODO: Create a custom 2D array implementation which removes the (x,y) or (y,x) ambiguity.
+    public Piece?[,] Board { get; }
+    public IReadOnlyCollection<Piece> Player1Hand { get; }
+    public IReadOnlyCollection<Piece> Player2Hand { get; }
+    /// <summary>
+    /// Move is null in the first BoardState of a Session, before any moves have been made.
+    /// </summary>
+    public Move? Move { get; }
+
+    public BoardState() : this(new ShogiBoard()) { }
+
+    public BoardState(Piece?[,] board, IList<Piece> player1Hand, ICollection<Piece> player2Hand, Move move)
+    {
+      Board = board;
+      Player1Hand = new ReadOnlyCollection<Piece>(player1Hand);
+    }
 
     public BoardState(ShogiBoard shogi)
     {
       Board = new Piece[9, 9];
       for (var x = 0; x < 9; x++)
         for (var y = 0; y < 9; y++)
-          Board[x, y] = new Piece(shogi.Board[x, y]);
+        {
+          var piece = shogi.Board[x, y];
+          if (piece != null)
+          {
+            Board[x, y] = new Piece(piece);
+          }
+        }
 
       Player1Hand = shogi.Hands[WhichPlayer.Player1].Select(_ => new Piece(_)).ToList();
       Player2Hand = shogi.Hands[WhichPlayer.Player2].Select(_ => new Piece(_)).ToList();
+      Move = new Move(shogi.MoveHistory[^1]);
     }
 
     public ServiceTypes.BoardState ToServiceModel()
     {
       var board = new ServiceTypes.Piece[9, 9];
-      Board = new Piece[9, 9];
       for (var x = 0; x < 9; x++)
         for (var y = 0; y < 9; y++)
-          board[x, y] = Board[x, y].ToServiceModel();
+        {
+          var piece = Board[x, y];
+          if (piece != null)
+          {
+            board[x, y] = piece.ToServiceModel();
+          }
+        }
       return new ServiceTypes.BoardState
       {
         Board = board,