Fixed accidentally building the board from player2 perspective.

Gameboard.ShogiUI.BoardState/Move.cs

@@ -1,7 +1,7 @@
 using System.Diagnostics;
 using System.Numerics;
 
-namespace Gameboard.ShogiUI.BoardState
+namespace Gameboard.ShogiUI.Rules
 {
   [DebuggerDisplay("{From} - {To}")]
   public class Move

Gameboard.ShogiUI.BoardState/Pieces/Bishop.cs

@@ -1,7 +1,7 @@
 using PathFinding;
 using System.Collections.Generic;
 
-namespace Gameboard.ShogiUI.BoardState.Pieces
+namespace Gameboard.ShogiUI.Rules.Pieces
 {
   public class Bishop : Piece
   {

Gameboard.ShogiUI.BoardState/Pieces/GoldGeneral.cs

@@ -1,7 +1,7 @@
 using PathFinding;
 using System.Collections.Generic;
 
-namespace Gameboard.ShogiUI.BoardState.Pieces
+namespace Gameboard.ShogiUI.Rules.Pieces
 {
   public class GoldenGeneral : Piece
   {

Gameboard.ShogiUI.BoardState/Pieces/King.cs

@@ -1,7 +1,7 @@
 using PathFinding;
 using System.Collections.Generic;
 
-namespace Gameboard.ShogiUI.BoardState.Pieces
+namespace Gameboard.ShogiUI.Rules.Pieces
 {
   public class King : Piece
   {

Gameboard.ShogiUI.BoardState/Pieces/Knight.cs

@@ -1,7 +1,7 @@
 using PathFinding;
 using System.Collections.Generic;
 
-namespace Gameboard.ShogiUI.BoardState.Pieces
+namespace Gameboard.ShogiUI.Rules.Pieces
 {
   public class Knight : Piece
   {

Gameboard.ShogiUI.BoardState/Pieces/Lance.cs

@@ -1,7 +1,7 @@
 using PathFinding;
 using System.Collections.Generic;
 
-namespace Gameboard.ShogiUI.BoardState.Pieces
+namespace Gameboard.ShogiUI.Rules.Pieces
 {
   public class Lance : Piece
   {

Gameboard.ShogiUI.BoardState/Pieces/Pawn.cs

@@ -1,7 +1,7 @@
 using PathFinding;
 using System.Collections.Generic;
 
-namespace Gameboard.ShogiUI.BoardState.Pieces
+namespace Gameboard.ShogiUI.Rules.Pieces
 {
   public class Pawn : Piece
   {

Gameboard.ShogiUI.BoardState/Pieces/Piece.cs

@@ -1,7 +1,7 @@
 using PathFinding;
 using System.Diagnostics;
 
-namespace Gameboard.ShogiUI.BoardState.Pieces
+namespace Gameboard.ShogiUI.Rules.Pieces
 {
   [DebuggerDisplay("{WhichPiece} {Owner}")]
   public abstract class Piece : IPlanarElement

Gameboard.ShogiUI.BoardState/Pieces/Rook.cs

@@ -1,7 +1,7 @@
 using PathFinding;
 using System.Collections.Generic;
 
-namespace Gameboard.ShogiUI.BoardState.Pieces
+namespace Gameboard.ShogiUI.Rules.Pieces
 {
   public class Rook : Piece
   {

Gameboard.ShogiUI.BoardState/Pieces/SilverGeneral.cs

@@ -1,7 +1,7 @@
 using PathFinding;
 using System.Collections.Generic;
 
-namespace Gameboard.ShogiUI.BoardState.Pieces
+namespace Gameboard.ShogiUI.Rules.Pieces
 {
   public class SilverGeneral : Piece
   {

Gameboard.ShogiUI.BoardState/PlanarCollection.cs

@@ -3,7 +3,7 @@ using System;
 using System.Collections;
 using System.Collections.Generic;
 
-namespace Gameboard.ShogiUI.BoardState
+namespace Gameboard.ShogiUI.Rules
 {
   public class PlanarCollection<T> : IPlanarCollection<T>, IEnumerable<T> where T : IPlanarElement
   {

Gameboard.ShogiUI.BoardState/ShogiBoard.cs

@@ -1,10 +1,10 @@
-using Gameboard.ShogiUI.BoardState.Pieces;
+using Gameboard.ShogiUI.Rules.Pieces;
 using PathFinding;
 using System;
 using System.Collections.Generic;
 using System.Numerics;
 
-namespace Gameboard.ShogiUI.BoardState
+namespace Gameboard.ShogiUI.Rules
 {
   /// <summary>
   /// Facilitates Shogi board state transitions, cognisant of Shogi rules.
@@ -14,16 +14,20 @@ namespace Gameboard.ShogiUI.BoardState
   public class ShogiBoard
   {
     private delegate void MoveSetCallback(Piece piece, Vector2 position);
+    private readonly bool isValidationBoard;
     private readonly PathFinder2D<Piece> pathFinder;
     private ShogiBoard validationBoard;
     private Vector2 player1King;
     private Vector2 player2King;
     public IReadOnlyDictionary<WhichPlayer, List<Piece>> Hands { get; }
-    public PlanarCollection<Piece> Board { get; }
+    public PlanarCollection<Piece> Board { get; } //TODO: Hide this being a getter method
     public List<Move> MoveHistory { get; }
     public WhichPlayer WhoseTurn => MoveHistory.Count % 2 == 0 ? WhichPlayer.Player1 : WhichPlayer.Player2;
     public WhichPlayer? InCheck { get; private set; }
     public bool IsCheckmate { get; private set; }
+    
+
+    public string Error { get; private set; }
 
     public ShogiBoard()
     {
@@ -35,8 +39,8 @@ namespace Gameboard.ShogiUI.BoardState
       };
       pathFinder = new PathFinder2D<Piece>(Board);
       InitializeBoardState();
-      player1King = new Vector2(4, 0);
-      player2King = new Vector2(4, 8);
+      player1King = new Vector2(4, 8);
+      player2King = new Vector2(4, 0);
     }
 
     public ShogiBoard(IList<Move> moves) : this()
@@ -46,13 +50,14 @@ namespace Gameboard.ShogiUI.BoardState
         if (!Move(moves[i]))
         {
           // Todo: Add some smarts to know why a move was invalid. In check? Piece not found? etc.
-          throw new InvalidOperationException($"Unable to construct ShogiBoard with the given move at index {i}.");
+          throw new InvalidOperationException($"Unable to construct ShogiBoard with the given move at index {i}. {Error}");
         }
       }
     }
 
     private ShogiBoard(ShogiBoard toCopy)
     {
+      isValidationBoard = true;
       Board = new PlanarCollection<Piece>(9, 9);
       for (var x = 0; x < 9; x++)
         for (var y = 0; y < 9; y++)
@@ -143,8 +148,8 @@ namespace Gameboard.ShogiUI.BoardState
           minimumY = WhoseTurn == WhichPlayer.Player1 ? 7 : 1;
           break;
       }
-      if (WhoseTurn == WhichPlayer.Player1 && move.To.Y > minimumY) return false;
-      if (WhoseTurn == WhichPlayer.Player2 && move.To.Y < minimumY) return false;
+      if (WhoseTurn == WhichPlayer.Player1 && move.To.Y < minimumY) return false;
+      if (WhoseTurn == WhichPlayer.Player2 && move.To.Y > minimumY) return false;
 
       // Mutate the board.
       Board[move.To.X, move.To.Y] = Hands[WhoseTurn][index];
@@ -156,9 +161,21 @@ namespace Gameboard.ShogiUI.BoardState
     private bool PlaceFromBoard(Move move)
     {
       var fromPiece = Board[move.From.X, move.From.Y];
-      if (fromPiece == null) return false; // Invalid move
-      if (fromPiece.Owner != WhoseTurn) return false; // Invalid move; cannot move other players pieces.
-      if (IsPathable(move.From, move.To) == false) return false; // Invalid move; move not part of move-set.
+      if (fromPiece == null)
+      {
+        Error = $"No piece exists at {nameof(move)}.{nameof(move.From)}.";
+        return false; // Invalid move
+      }
+      if (fromPiece.Owner != WhoseTurn)
+      {
+        Error = "Not allowed to move the opponents piece";
+        return false; // Invalid move; cannot move other players pieces.
+      }
+      if (IsPathable(move.From, move.To) == false)
+      {
+        Error = $"Illegal move for {fromPiece.WhichPiece}. {nameof(move)}.{nameof(move.To)} is not part of the move-set.";
+        return false; // Invalid move; move not part of move-set.
+      }
 
       var captured = Board[move.To.X, move.To.Y];
       if (captured != null)
@@ -171,11 +188,11 @@ namespace Gameboard.ShogiUI.BoardState
       //Mutate the board.
       if (move.IsPromotion)
       {
-        if (WhoseTurn == WhichPlayer.Player1 && (move.To.Y > 5 || move.From.Y > 5))
+        if (WhoseTurn == WhichPlayer.Player1 && (move.To.Y < 3 || move.From.Y < 3))
         {
           fromPiece.Promote();
         }
-        else if (WhoseTurn == WhichPlayer.Player2 && (move.To.Y < 3 || move.From.Y < 3))
+        else if (WhoseTurn == WhichPlayer.Player2 && (move.To.Y > 5 || move.From.Y > 5))
         {
           fromPiece.Promote();
         }
@@ -313,12 +330,12 @@ namespace Gameboard.ShogiUI.BoardState
     }
     private void ResetFrontRow(WhichPlayer player)
     {
-      int y = player == WhichPlayer.Player1 ? 2 : 6;
+      int y = player == WhichPlayer.Player1 ? 6 : 2;
       for (int x = 0; x < 9; x++) Board[x, y] = new Pawn(player);
     }
     private void ResetMiddleRow(WhichPlayer player)
     {
-      int y = player == WhichPlayer.Player1 ? 1 : 7;
+      int y = player == WhichPlayer.Player1 ? 7 : 1;
 
       Board[0, y] = null;
       for (int x = 2; x < 7; x++) Board[x, y] = null;
@@ -336,7 +353,7 @@ namespace Gameboard.ShogiUI.BoardState
     }
     private void ResetRearRow(WhichPlayer player)
     {
-      int y = player == WhichPlayer.Player1 ? 0 : 8;
+      int y = player == WhichPlayer.Player1 ? 8 : 0;
 
       Board[0, y] = new Lance(player);
       Board[1, y] = new Knight(player);
@@ -350,13 +367,13 @@ namespace Gameboard.ShogiUI.BoardState
     }
     private void InitializeBoardState()
     {
-      ResetRearRow(WhichPlayer.Player1);
-      ResetMiddleRow(WhichPlayer.Player1);
-      ResetFrontRow(WhichPlayer.Player1);
-      ResetEmptyRows();
-      ResetFrontRow(WhichPlayer.Player2);
-      ResetMiddleRow(WhichPlayer.Player2);
       ResetRearRow(WhichPlayer.Player2);
+      ResetMiddleRow(WhichPlayer.Player2);
+      ResetFrontRow(WhichPlayer.Player2);
+      ResetEmptyRows();
+      ResetFrontRow(WhichPlayer.Player1);
+      ResetMiddleRow(WhichPlayer.Player1);
+      ResetRearRow(WhichPlayer.Player1);
     }
     #endregion
   }

Gameboard.ShogiUI.BoardState/WhichPiece.cs

@@ -1,4 +1,4 @@
-namespace Gameboard.ShogiUI.BoardState
+namespace Gameboard.ShogiUI.Rules
 {
   public enum WhichPiece
   {

Gameboard.ShogiUI.BoardState/WhichPlayer.cs

@@ -1,4 +1,4 @@
-namespace Gameboard.ShogiUI.BoardState
+namespace Gameboard.ShogiUI.Rules
 {
   public enum WhichPlayer
   {