- Fix it with AI ... (somehow)

Author: guhilling

2026-02-05-Retro_Copilot/src/main/java/de/hilling/chess/ChessException.java

@@ -10,6 +10,7 @@
 public class ChessGame {
     private ChessPiece[][] board = new ChessPiece[8][8];
     private List<String> moves = new LinkedList<>();
+    private MoveValidator validator = new MoveValidator(this.board);
 
     public ChessGame() {
         for(int x=0; x<8; x++) {
@@ -68,6 +69,7 @@ public void move(String move) {
         Position to = Position.of(move.substring(2, 4));
         ChessPiece fromPiece = board[from.x][from.y];
         if(fromPiece != null) {
+            validator.validateMove(from, to, fromPiece);
             board[to.x][to.y] = fromPiece;
             board[from.x][from.y] = null;
             moves.add(move);

2026-02-05-Retro_Copilot/src/main/java/de/hilling/chess/ChessGame.java

@@ -0,0 +1,48 @@
+package de.hilling.chess;
+
+public class MoveValidator {
+    private final ChessPiece[][] board;
+
+    public MoveValidator(ChessPiece[][] board) {
+        this.board = board;
+    }
+
+    public void validateMove(Position from, Position to, ChessPiece piece) {
+        if (piece.type == PieceType.PAWN) {
+            validatePawnMove(from, to, piece);
+        }
+    }
+
+    private void validatePawnMove(Position from, Position to, ChessPiece piece) {
+        int direction = piece.color == Color.WHITE ? 1 : -1;
+        int startRow = piece.color == Color.WHITE ? 1 : 6;
+
+        // Must move in same column (no capture implemented yet)
+        if (from.x != to.x) {
+            throw new IllegalArgumentException("Pawn must move straight forward");
+        }
+
+        // Check if target square is empty
+        if (board[to.x][to.y] != null) {
+            throw new IllegalArgumentException("Target square is occupied");
+        }
+
+        int yDiff = to.y - from.y;
+
+        // Move one square forward
+        if (yDiff == direction) {
+            return;
+        }
+
+        // Move two squares forward from starting position
+        if (from.y == startRow && yDiff == 2 * direction) {
+            // Check if path is clear
+            if (board[from.x][from.y + direction] == null) {
+                return;
+            }
+            throw new IllegalArgumentException("Path is blocked");
+        }
+
+        throw new IllegalArgumentException("Invalid pawn move");
+    }
+}

2026-02-05-Retro_Copilot/src/main/java/de/hilling/chess/MoveValidator.java

@@ -48,7 +48,6 @@ void setUp() {
         chessGame = new ChessGame();
     }
 
-    // TODO: test more pieces, refactoring
     @Test
     void testSetup() {
         ChessPiece whitePawn = chessGame.get(Position.of(1, 1));
@@ -84,6 +83,16 @@ void illegalMoveCharacters() {
         }
     }
 
+    @Test
+    void illegalMoveMoveNotPossibleForPawn() {
+        try {
+            chessGame.move("a2a5");
+            fail("Illegal move exception");
+        } catch (IllegalArgumentException iae) {
+            assertEquals("Invalid pawn move", iae.getMessage());
+        }
+    }
+
     @Test
     void movePawn() {
         chessGame.move("e2e4");