en passant rule

app/src/main/java/chess/controller/PlayerCommand.java

@@ -3,5 +3,12 @@ package chess.controller;
 import chess.model.Game;
 
 public abstract class PlayerCommand extends Command{
-	public abstract CommandResult undo(Game game, OutputSystem outputSystem);
+
+	public CommandResult undo(Game game, OutputSystem outputSystem) {
+		CommandResult result = undoImpl(game, outputSystem);
+		game.updateLastMove();
+		return result;
+	}
+
+	protected abstract CommandResult undoImpl(Game game, OutputSystem outputSystem);
 }

app/src/main/java/chess/controller/commands/CastlingCommand.java

@@ -16,7 +16,7 @@ public class CastlingCommand extends PlayerCommand {
 	}
 
 	@Override
-	public CommandResult undo(Game game, OutputSystem outputSystem) {
+	protected CommandResult undoImpl(Game game, OutputSystem outputSystem) {
 		// TODO Auto-generated method stub
 		throw new UnsupportedOperationException("Unimplemented method 'undo'");
 	}

app/src/main/java/chess/controller/commands/GrandCastlingCommand.java

@@ -16,7 +16,7 @@ public class GrandCastlingCommand extends PlayerCommand {
 	}
 
 	@Override
-	public CommandResult undo(Game game, OutputSystem outputSystem) {
+	protected CommandResult undoImpl(Game game, OutputSystem outputSystem) {
 		// TODO Auto-generated method stub
 		throw new UnsupportedOperationException("Unimplemented method 'undo'");
 	}

app/src/main/java/chess/controller/commands/MoveCommand.java

@@ -10,7 +10,7 @@ import chess.model.Piece;
 import chess.model.visitor.PiecePathChecker;
 
 public class MoveCommand extends PlayerCommand {
-	
+
 	private final Move move;
 	private Piece deadPiece;
 
@@ -42,7 +42,7 @@ public class MoveCommand extends PlayerCommand {
 		if (!valid)
 			return CommandResult.NotAllowed;
 
-		this.deadPiece = board.pieceAt(move.getFinish());
+		this.deadPiece = board.pieceAt(move.getDeadPieceCoords());
 		board.applyMove(move);
 
 		if (board.isKingInCheck(game.getPlayerTurn())) {
@@ -50,14 +50,15 @@ public class MoveCommand extends PlayerCommand {
 			return CommandResult.NotAllowed;
 		}
 
-		if (game.pawnShouldBePromoted()) 
+		if (game.pawnShouldBePromoted())
 			return CommandResult.ActionNeeded;
 
+		board.setLastMove(this.move);
 		return CommandResult.Moved;
 	}
 
 	@Override
-	public CommandResult undo(Game game, OutputSystem outputSystem) {
+	protected CommandResult undoImpl(Game game, OutputSystem outputSystem) {
 		final ChessBoard board = game.getBoard();
 
 		board.undoMove(move, deadPiece);

app/src/main/java/chess/controller/commands/PromoteCommand.java

@@ -75,7 +75,7 @@ public class PromoteCommand extends PlayerCommand {
 	}
 
 	@Override
-	public CommandResult undo(Game game, OutputSystem outputSystem) {
+	protected CommandResult undoImpl(Game game, OutputSystem outputSystem) {
 		final ChessBoard board = game.getBoard();
 
 		Piece promoted = board.pieceAt(this.pieceCoords);

app/src/main/java/chess/model/ChessBoard.java

@@ -25,6 +25,7 @@ public class ChessBoard {
 	}
 
 	private final Cell[][] cells;
+	private Move lastVirtualMove;
 	private Move lastMove;
 	private Piece lastEjectedPiece;
 
@@ -35,35 +36,38 @@ public class ChessBoard {
 				this.cells[i][j] = new Cell();
 			}
 		}
+		this.lastVirtualMove = null;
 		this.lastMove = null;
 		this.lastEjectedPiece = null;
 	}
 
 	public void applyMove(Move move) {
 		assert move.isValid() : "Invalid move !";
-		Piece deadPiece = pieceAt(move.getFinish());
+		Piece deadPiece = pieceAt(move.getDeadPieceCoords());
 		if (deadPiece != null) {
 			this.lastEjectedPiece = deadPiece;
 		} else {
 			this.lastEjectedPiece = null;
 		}
 		Piece movingPiece = pieceAt(move.getStart());
-		pieceComes(movingPiece, move.getFinish());
+		pieceLeaves(move.getDeadPieceCoords());
 		pieceLeaves(move.getStart());
+		pieceComes(movingPiece, move.getFinish());
 		movingPiece.move();
-		this.lastMove = move;
+		this.lastVirtualMove = move;
 	}
 
 	public void undoLastMove() {
-		assert this.lastMove != null: "Can't undo at the beginning!";
+		assert this.lastVirtualMove != null: "Can't undo at the beginning!";
 
-		undoMove(this.lastMove, this.lastEjectedPiece);
+		undoMove(this.lastVirtualMove, this.lastEjectedPiece);
 	}
 
 	public void undoMove(Move move, Piece deadPiece) {
 		Piece movingPiece = pieceAt(move.getFinish());
 		pieceComes(movingPiece, move.getStart());
-		pieceComes(deadPiece, move.getFinish());
+		pieceLeaves(move.getFinish());
+		pieceComes(deadPiece, move.getDeadPieceCoords());
 		movingPiece.unMove();
 	}
 
@@ -177,4 +181,12 @@ public class ChessBoard {
 		return result;
 	}
 
+	public Move getLastMove() {
+		return this.lastMove;
+	}
+
+	public void setLastMove(Move lastMove) {
+		this.lastMove = lastMove;
+	}
+
 }

app/src/main/java/chess/model/Game.java

@@ -4,6 +4,7 @@ import java.util.EmptyStackException;
 import java.util.Stack;
 
 import chess.controller.PlayerCommand;
+import chess.controller.commands.MoveCommand;
 import chess.model.visitor.PawnIdentifier;
 
 public class Game {
@@ -99,4 +100,14 @@ public class Game {
 		}
 	}
 
+	public void updateLastMove() {
+		if (this.movesHistory.isEmpty())
+			return;
+
+		PlayerCommand last = this.movesHistory.getLast();
+		if (last instanceof MoveCommand move) {
+			this.board.setLastMove(move.getMove());
+		}
+	}
+
 }

app/src/main/java/chess/model/Move.java

@@ -3,10 +3,12 @@ package chess.model;
 public class Move {
 	private final Coordinate start;
 	private final Coordinate finish;
+	private Coordinate deadPieceCoords;
 
 	public Move(Coordinate start, Coordinate finish) {
 		this.start = start;
 		this.finish = finish;
+		this.deadPieceCoords = finish;
 	}
 
 	public boolean isValid() {
@@ -39,4 +41,16 @@ public class Move {
 		return 0;
 	}
 
+	public Coordinate getMiddle() {
+		return Coordinate.fromIndex((getStart().toIndex() + getFinish().toIndex()) / 2);
+	}
+
+	public void setDeadPieceCoords(Coordinate deadCoords) {
+		this.deadPieceCoords = deadCoords;
+	}
+
+	public Coordinate getDeadPieceCoords() {
+		return deadPieceCoords;
+	}
+
 }

app/src/main/java/chess/model/visitor/PiecePathChecker.java

@@ -35,31 +35,27 @@ public class PiecePathChecker implements PieceVisitor<Boolean> {
 
 	@Override
 	public Boolean visitPiece(Bishop bishop) {
-		if (!new PermissiveRuleChecker(this.move).isValidFor(bishop))
-			return false;
-		return testPath(bishop.getColor());
+		return basicCheck(bishop);
 	}
 
 	@Override
 	public Boolean visitPiece(King king) {
-		if (!new PermissiveRuleChecker(this.move).isValidFor(king))
-			return false;
-
-		Piece destPiece = board.pieceAt(this.move.getFinish());
-		if (destPiece == null)
-			return true;
-		return destPiece.getColor() != king.getColor();
+		return destCheck(king);
 	}
 
 	@Override
 	public Boolean visitPiece(Knight knight) {
-		if (!new PermissiveRuleChecker(this.move).isValidFor(knight))
-			return false;
+		return destCheck(knight);
+	}
 
-		Piece destPiece = board.pieceAt(this.move.getFinish());
-		if (destPiece == null)
-			return true;
-		return destPiece.getColor() != knight.getColor();
+	@Override
+	public Boolean visitPiece(Queen queen) {
+		return basicCheck(queen);
+	}
+
+	@Override
+	public Boolean visitPiece(Rook rook) {
+		return basicCheck(rook);
 	}
 
 	@Override
@@ -74,6 +70,9 @@ public class PiecePathChecker implements PieceVisitor<Boolean> {
 
 		assert moveDirection == Direction.FrontLeft || moveDirection == Direction.FrontRight;
 
+		if (checkEnPassant())
+			return true;
+
 		Piece destPiece = this.board.pieceAt(this.move.getFinish());
 		if (destPiece == null)
 			return false;
@@ -81,18 +80,44 @@ public class PiecePathChecker implements PieceVisitor<Boolean> {
 		return destPiece.getColor() != pawn.getColor();
 	}
 
-	@Override
-	public Boolean visitPiece(Queen queen) {
-		if (!new PermissiveRuleChecker(this.move).isValidFor(queen))
+	private boolean checkEnPassant() {
+		Move lastMove = this.board.getLastMove();
+
+		if (lastMove == null)
 			return false;
-		return testPath(queen.getColor());
+
+		Piece pieceToEat = this.board.pieceAt(lastMove.getFinish());
+
+		if (pieceToEat == null)
+			return false;
+
+		Piece pawn = this.board.pieceAt(this.move.getStart());
+
+		if (pieceToEat.getColor() == pawn.getColor())
+			return false;
+
+		if (lastMove.getMiddle().equals(this.move.getFinish())
+				&& new PawnIdentifier(pieceToEat.getColor()).isPawn(pieceToEat)) {
+			this.move.setDeadPieceCoords(lastMove.getFinish());
+			return true;
+		}
+		return false;
 	}
 
-	@Override
-	public Boolean visitPiece(Rook rook) {
-		if (!new PermissiveRuleChecker(this.move).isValidFor(rook))
+	private boolean destCheck(Piece piece) {
+		if (!new PermissiveRuleChecker(this.move).isValidFor(piece))
 			return false;
-		return testPath(rook.getColor());
+
+		Piece destPiece = board.pieceAt(this.move.getFinish());
+		if (destPiece == null)
+			return true;
+		return destPiece.getColor() != piece.getColor();
+	}
+
+	private boolean basicCheck(Piece piece) {
+		if (!new PermissiveRuleChecker(this.move).isValidFor(piece))
+			return false;
+		return testPath(piece.getColor());
 	}
 
 	private boolean testPath(Color color) {