Check and Checkmate of King

src/backend/Board.java

@@ -19,6 +19,28 @@ public class Board {
 		this.pieces = new ArrayList<>();
 		//TODO
 	}
+	
+	public Board(Board other) {
+	    this.width = other.width;
+	    this.height = other.height;
+	    this.turnNumber = other.turnNumber;
+	    this.turnWhite = other.turnWhite;
+	    this.selected = other.selected != null ? new int[]{other.selected[0], other.selected[1]} : null;
+
+	    this.pieces = new ArrayList<>();
+	    for (Piece p : other.pieces) {
+	        this.pieces.add(new Piece(p)); // uses Piece copy constructor (next step)
+	    }
+
+	    this.highlighted = new ArrayList<>();
+	    for (int[] pos : other.highlighted) {
+	        this.highlighted.add(new int[]{pos[0], pos[1]});
+	    }
+
+	    this.moveHistory = new ArrayList<>(other.moveHistory);
+	}
+
+
 
 	public int getWidth() {
 		//TODO
@@ -112,10 +134,57 @@ public class Board {
 
 	    return sb.toString();
 	}
-	
+
+
 	public ArrayList<Piece> getPieces() {
 		return pieces;
 	}
+	
+	public Piece getKing(boolean isWhite) {
+	    for (Piece p : pieces) {
+	        if (p.isWhite() == isWhite && p.getType() == PieceType.King) {
+	            return p;
+	        }
+	    }
+	    return null;
+	}
+	
+	public boolean isInCheck(boolean whitePlayer) {
+	    Piece king = getKing(whitePlayer);
+	    if (king == null) return false;
+
+	    int kingX = king.getX();
+	    int kingY = king.getY();
+
+	    for (Piece piece : pieces) {
+	        if (piece.isWhite() != whitePlayer) {
+	            ArrayList<int[]> enemyMoves = getLegalMoves(piece, false); // disable check validation
+	            for (int[] move : enemyMoves) {
+	                if (move[0] == kingX && move[1] == kingY) {
+	                    return true;
+	                }
+	            }
+	        }
+	    }
+	    return false;
+	}
+
+	
+	public boolean isCheckmate(boolean whitePlayer) {
+	    if (!isInCheck(whitePlayer)) return false;
+
+	    for (Piece p : pieces) {
+	        if (p.isWhite() == whitePlayer) {
+	            ArrayList<int[]> legalMoves = getLegalMoves(p);
+	            if (!legalMoves.isEmpty()) return false;
+	        }
+	    }
+
+	    return true;
+	}
+
+
+
 
 	public void userTouch(int x, int y) {
 	    Piece clickedPiece = getPieceAt(x, y);
@@ -149,34 +218,34 @@ public class Board {
 
 	
 	public ArrayList<int[]> getLegalMoves(Piece piece) {
+	    return getLegalMoves(piece, true); // default: check for king safety
+	}
+
+	public ArrayList<int[]> getLegalMoves(Piece piece, boolean validateCheck) {
 	    ArrayList<int[]> moves = new ArrayList<>();
 	    int x = piece.getX(), y = piece.getY();
 	    int dir = piece.isWhite() ? 1 : -1;
 
 	    switch (piece.getType()) {
 	        case Pawn:
-	        	int forwardY = y + dir;
+	            int forwardY = y + dir;
 
-	            // Move one square forward if it's empty
 	            if (isInBounds(x, forwardY) && getPieceAt(x, forwardY) == null) {
-	                moves.add(new int[] {x, forwardY});
-
-	                // Move two squares forward if at starting position and both squares are empty
+	                moves.add(new int[]{x, forwardY});
 	                int twoForwardY = y + 2 * dir;
 	                boolean atStartingRank = (piece.isWhite() && y == 1) || (!piece.isWhite() && y == 6);
 	                if (atStartingRank && isInBounds(x, twoForwardY) && getPieceAt(x, twoForwardY) == null) {
-	                    moves.add(new int[] {x, twoForwardY});
+	                    moves.add(new int[]{x, twoForwardY});
 	                }
 	            }
 
-	            // Capture diagonally
 	            Piece diagLeft = getPieceAt(x - 1, forwardY);
 	            if (diagLeft != null && diagLeft.isWhite() != piece.isWhite())
-	                moves.add(new int[] {x - 1, forwardY});
+	                moves.add(new int[]{x - 1, forwardY});
 
 	            Piece diagRight = getPieceAt(x + 1, forwardY);
 	            if (diagRight != null && diagRight.isWhite() != piece.isWhite())
-	                moves.add(new int[] {x + 1, forwardY});
+	                moves.add(new int[]{x + 1, forwardY});
 	            break;
 
 	        case Rook:
@@ -229,8 +298,25 @@ public class Board {
 	            }
 	            break;
 	    }
-	    return moves;
+
+	    if (!validateCheck) return moves;
+
+	    // Filter out moves that put own king in check
+	    ArrayList<int[]> legalMoves = new ArrayList<>();
+	    for (int[] move : moves) {
+	        Board copy = new Board(this);
+	        Piece p = copy.getPieceAt(x, y);
+	        Piece captured = copy.getPieceAt(move[0], move[1]);
+	        Move testMove = new Move(p, x, y, move[0], move[1], captured);
+	        copy.playMove(testMove);
+
+	        if (!copy.isInCheck(piece.isWhite())) {
+	            legalMoves.add(move);
+	        }
+	    }
+	    return legalMoves;
 	}
+
 	
 	private void addLinearMoves(ArrayList<int[]> moves, Piece piece, int dx, int dy) {
 	    int x = piece.getX(), y = piece.getY();
@@ -314,22 +400,6 @@ public void undoLastMove() {
 	    selected = null;
 	    highlighted.clear();
 	}
-
-	public Board(Board board) {
-		if (moveHistory.isEmpty()) return;
-
-	    Move lastMove = moveHistory.remove(moveHistory.size() - 1);
-	    Piece movedPiece = lastMove.getPieceMoved();
-	    movedPiece.setPosition(lastMove.getFromX(), lastMove.getFromY());
-
-	    if (lastMove.getPieceCaptured() != null) {
-	        pieces.add(lastMove.getPieceCaptured());
-	    }
-
-	    turnWhite = !turnWhite;
-	    turnNumber--;
-
-	}
 	
 	public void playMove(Move move) {
 		 Piece piece = move.getPieceMoved();

src/backend/Game.java

@@ -109,5 +109,7 @@ public class Game extends Thread {
 	public void toggleAI(boolean isWhite) {
 		this.activationAIFlags[isWhite?1:0] = !this.activationAIFlags[isWhite?1:0];
 	}
+	
+	
 
 }

src/backend/Piece.java

@@ -36,6 +36,13 @@ public class Piece {
 	public void setPosition(int x , int y) {
 		this.x=x;
 		this.y=y;	
-	}	
+	}
+	public Piece(Piece other) {
+	    this.isWhite = other.isWhite;
+	    this.type = other.type;
+	    this.x = other.x;
+	    this.y = other.y;
+	}
+
 	
 }