From 65aa6014833eda1d43e9881d6b1d6bd66f9634ac Mon Sep 17 00:00:00 2001
From: Tolly <ptolemyhill@sky.com>
Date: Thu, 2 Mar 2023 13:52:11 +0000
Subject: [PATCH] Implement move undo

---
 ChessGame.cs       | 13 ++++++++-----
 CustomGame.xaml.cs |  2 +-
 MainWindow.xaml    |  2 ++
 MainWindow.xaml.cs | 16 ++++++++++++++++
 4 files changed, 27 insertions(+), 6 deletions(-)

diff --git a/ChessGame.cs b/ChessGame.cs
index 9d61562..205f558 100644
--- a/ChessGame.cs
+++ b/ChessGame.cs
@@ -51,6 +51,7 @@ public class ChessGame
         /// </summary>
         public List<(Point, Point)> Moves { get; }
         public List<string> MoveText { get; }
+        public ChessGame? PreviousGameState { get; private set; }
         public List<Pieces.Piece> CapturedPieces { get; }
 
         public Point? EnPassantSquare { get; private set; }
@@ -110,7 +111,7 @@ public ChessGame()
         public ChessGame(Pieces.Piece?[,] board, bool currentTurnWhite, bool gameOver, List<(Point, Point)> moves, List<string> moveText,
             List<Pieces.Piece> capturedPieces, Point? enPassantSquare, bool whiteMayCastleKingside, bool whiteMayCastleQueenside,
             bool blackMayCastleKingside, bool blackMayCastleQueenside, int staleMoveCounter, Dictionary<string, int> boardCounts,
-            string? initialState)
+            string? initialState, ChessGame? previousGameState)
         {
             if (board.GetLength(0) != 8 || board.GetLength(1) != 8)
             {
@@ -148,6 +149,7 @@ public ChessGame(Pieces.Piece?[,] board, bool currentTurnWhite, bool gameOver, L
             BoardCounts = boardCounts;
 
             InitialState = initialState ?? ToString();
+            PreviousGameState = previousGameState;
         }
 
         /// <summary>
@@ -167,7 +169,7 @@ public ChessGame Clone()
             return new ChessGame(boardClone, CurrentTurnWhite, GameOver, new(Moves), new(MoveText),
                 CapturedPieces.Select(c => c.Clone()).ToList(), EnPassantSquare, WhiteMayCastleKingside,
                 WhiteMayCastleQueenside, BlackMayCastleKingside, BlackMayCastleQueenside, StaleMoveCounter,
-                new(BoardCounts), InitialState);
+                new(BoardCounts), InitialState, PreviousGameState?.Clone());
         }
 
         /// <summary>
@@ -245,7 +247,7 @@ public bool IsCastlePossible(bool kingside)
         /// If a pawn is promoted, what <see cref="Pieces.Piece"/> should it be promoted to. <see langword="null"/> means the user should be prompted for the type.
         /// </param>
         /// <param name="updateMoveText">
-        /// Whether the move should update the game move text. This should usually be <see langword="true"/>,
+        /// Whether the move should update the game move text and update <see cref="PreviousGameState"/>. This should usually be <see langword="true"/>,
         /// but may be set to <see langword="false"/> for performance optimisations in clone games for analysis.
         /// </param>
         /// <returns><see langword="true"/> if the move was valid and executed, <see langword="false"/> otherwise</returns>
@@ -267,11 +269,12 @@ public bool MovePiece(Point source, Point destination, bool forceMove = false, T
                 return false;
             }
 
-            // Used for generating new move text
+            // Used for generating new move text and move undoing
             ChessGame? oldGame = null;
             if (updateMoveText)
             {
                 oldGame = Clone();
+                PreviousGameState = oldGame;
             }
 
             bool pieceMoved;
@@ -750,7 +753,7 @@ public static ChessGame FromForsythEdwards(string forsythEdwards)
             // For the PGN standard, if black moves first then a single move "..." is added to the start of the move text list
             return new ChessGame(board, currentTurnWhite, EndingStates.Contains(BoardAnalysis.DetermineGameState(board, currentTurnWhite)),
                 new(), currentTurnWhite ? new() : new() { "..." }, new(), enPassant, whiteKingside, whiteQueenside, blackKingside, blackQueenside,
-                staleMoves, new(), null);
+                staleMoves, new(), null, null);
         }
     }
 }
diff --git a/CustomGame.xaml.cs b/CustomGame.xaml.cs
index 1905f55..24a7793 100644
--- a/CustomGame.xaml.cs
+++ b/CustomGame.xaml.cs
@@ -145,7 +145,7 @@ private void startButton_Click(object sender, RoutedEventArgs e)
                 ChessGame.EndingStates.Contains(BoardAnalysis.DetermineGameState(Board, currentTurnWhite)),
                 new(), currentTurnWhite ? new() : new() { "..." }, new(), EnPassantSquare, castleWhiteKingside.IsChecked ?? false,
                 castleWhiteQueenside.IsChecked ?? false, castleBlackKingside.IsChecked ?? false,
-                castleBlackQueenside.IsChecked ?? false, 0, new(), null);
+                castleBlackQueenside.IsChecked ?? false, 0, new(), null, null);
             Close();
         }
 
diff --git a/MainWindow.xaml b/MainWindow.xaml
index 8e963c5..b5ee4f1 100644
--- a/MainWindow.xaml
+++ b/MainWindow.xaml
@@ -23,6 +23,8 @@
                 <MenuItem Header="New Game (1 Player - _Black)" Click="NewGameCpuBlack_Click"/>
                 <MenuItem Header="New Game (0 Player - _Computer Only)" Click="NewGameCpuOnly_Click"/>
                 <Separator/>
+                <MenuItem Header="_Undo Move" Click="UndoMove_Click"/>
+                <Separator/>
                 <MenuItem Header="Custom _Game..." Click="CustomGame_Click"/>
                 <Separator/>
                 <MenuItem Header="Export to _PGN" Click="PGNExport_Click"/>
diff --git a/MainWindow.xaml.cs b/MainWindow.xaml.cs
index dd0564d..8dad05b 100644
--- a/MainWindow.xaml.cs
+++ b/MainWindow.xaml.cs
@@ -899,6 +899,22 @@ private void CustomiseItem_Click(object sender, RoutedEventArgs e)
             UpdateGameDisplay();
         }
 
+        private async void UndoMove_Click(object sender, RoutedEventArgs e)
+        {
+            if (game.PreviousGameState is not null
+                && ((game.CurrentTurnWhite && !whiteIsComputer) || (!game.CurrentTurnWhite && !blackIsComputer)))
+            {
+                game = game.PreviousGameState;
+                if (whiteIsComputer ||  blackIsComputer)
+                {
+                    // Reverse two moves if the opponent is computer controlled
+                    game = game.PreviousGameState!;
+                }
+                UpdateGameDisplay();
+                await CheckComputerMove();
+            }
+        }
+
         private void whiteDepthBackingSlider_ValueChanged(object sender, RoutedPropertyChangedEventArgs<double> e)
         {
             if (!updateDepthSliders)