Restructure special move handling.

chess/board.go

@@ -57,20 +57,18 @@ func (b *Board) Init() {
 	b.position[types.Coordinate{Row: 8, Col: 8}] = Rook{Color: types.Black}
 }
 
-func (b *Board) CheckAndPlay(move types.Move) (bool, string) {
-	// We make a copy of the original board to play moves on it,
-	// We can play the move on it and then check if it is invalid
+func (b *Board) CheckAndPlay(move types.Move) (bool, Violation) {
 	tempBoard := b.getCopyOfBoard()
 
 	//Check start square of move
 	pieceAtStartSquare := tempBoard.getPieceAt(move.StartSquare)
 	if pieceAtStartSquare == nil {
-		return false, "no piece at start square"
+		return false, NoPieceAtStartSquare
 	}
 
 	move.ColorMoved = pieceAtStartSquare.GetColor()
 	if move.ColorMoved != tempBoard.colorToMove {
-		return false, "wrong color moved"
+		return false, WrongColorMoved
 	}
 	move.PieceMoved = GetShortNameForPiece(pieceAtStartSquare)
 
@@ -78,19 +76,17 @@ func (b *Board) CheckAndPlay(move types.Move) (bool, string) {
 	pieceAtEndSquare := tempBoard.getPieceAt(move.EndSquare)
 	if pieceAtEndSquare != nil {
 		if pieceAtEndSquare.GetColor() == pieceAtStartSquare.GetColor() {
-			return false, "same-coloured piece at end square"
+			return false, TargetSquareIsOccupied
 		}
 	}
 
-	wasSpecialMove := tempBoard.handleSpecialMove(move)
-
-	if !wasSpecialMove {
-		// At the moment, we do not need to check if the correct color is moving,
-		//since we are only reading moves from the player whose turn it is.
+	wasSpecialMove, err := tempBoard.handleSpecialMove(move)
+	
+    if !wasSpecialMove {
 		allMovesExceptBlocked := pieceAtStartSquare.GetAllNonBlockedMoves(tempBoard, move.StartSquare)
 		legal := lo.Contains(allMovesExceptBlocked, move.EndSquare)
 		if !legal {
-			return false, "not a legal square"
+			return false, InvalidMove
 		}
 
 		//We play the move on the temporary board
@@ -100,25 +96,12 @@ func (b *Board) CheckAndPlay(move types.Move) (bool, string) {
 
 	kingAttacked, err := tempBoard.isKingOfMovingColorInCheck(move.ColorMoved)
 	if err != nil {
-		return false, "something went wrong"
+		return false, SomethingWentWrong
 	}
 	if kingAttacked {
-		return false, "king would be in check after move"
+		return false, KingInCheck
 	}
 
-	//Check for checkmat&e
-	//Is every square that the king can move to attacked? And can no other
-	//piece block? -> checkmate
-
-	//only check if paths of attacking pieces can be blocked
-
-	//Maybe for checking checkmate, we have to check the 'path' in which the
-	//checkmate is given
-
-	// |K| | | | |Q|
-	// in this scenaria the path are all the squares between queen and king.
-	// If a piece can be moved into the path, it is no checkmate
-
 	//We play the move on the real board
 	b.position = tempBoard.position
 	b.history = tempBoard.history
@@ -202,18 +185,19 @@ func (p Position) getCopyOfPosition() Position {
 	return position
 }
 
-func (b *Board) handleSpecialMove(move types.Move) bool {
+func (b *Board) handleSpecialMove(move types.Move) (bool, error) {
 	var was bool
+    var err error
 	var pieceAtStartSquare = b.getPieceAt(move.StartSquare)
 
 	switch piece := pieceAtStartSquare.(type) {
 	case Pawn:
-		was = piece.HandlePossiblePromotion(b, move)
+		was, err = piece.HandlePossiblePromotion(b, move)
 		if !was {
-			was = piece.HandleEnPassant(b, move, b.getLastMove())
+			was, err = piece.HandleEnPassant(b, move, b.getLastMove())
 		}
 	case King:
-		was = piece.HandleCastling(b, move)
+		was, err = piece.HandleCastling(b, move)
 	}
-	return was
+	return was, err 
 }

chess/game.go

@@ -75,13 +75,13 @@ func (game *Game) Handle() {
 			gameState = CheckMove
 
 		case CheckMove:
-			valid, reason := game.board.CheckAndPlay(receivedMove)
+			valid, ruleViolation := game.board.CheckAndPlay(receivedMove)
 
 			if valid {
 				gameState = CheckPlayerChange
 			} else {
-				log.Println("invalid move because " + reason)
-				invalidMoveMessage, err := api.GetInvalidMoveMessage(receivedMove, reason)
+				log.Println(err)
+				invalidMoveMessage, err := api.GetInvalidMoveMessage(receivedMove, ruleViolation.String())
 				if err != nil {
 					log.Println("Error marshalling 'colorDetermined' message for player 1", err)
 					return

chess/king.go

@@ -29,14 +29,14 @@ func (k King) AfterMoveAction(board *Board, fromSquare types.Coordinate) {
 	}
 }
 
-func (k King) HandleCastling(board *Board, move types.Move) bool {
+func (k King) HandleCastling(board *Board, move types.Move) (bool,error) {
 	if k.hadMovedBefore(board) {
-		return false
+		return false, nil
 	}
 
 	valid, dir := k.movedOnValidCastlingSquare(board, move)
 	if !valid {
-		return false
+		return false, nil
 	}
 
 	switch k.Color {
@@ -47,7 +47,7 @@ func (k King) HandleCastling(board *Board, move types.Move) bool {
 	}
 
 	k.playCastlingOnBoard(board, move, dir)
-	return true
+	return true, nil
 }
 
 func (k King) hadMovedBefore(b *Board) bool {

chess/pawn.go

@@ -32,7 +32,7 @@ func (p Pawn) GetColor() types.ChessColor {
 	return p.Color
 }
 
-func (p *Pawn) HandlePossiblePromotion(b *Board, move types.Move) bool {
+func (p *Pawn) HandlePossiblePromotion(b *Board, move types.Move) (bool,error) {
 	var isPromotionMove bool
 	var promotionToPiece types.PieceShortName
 
@@ -62,14 +62,14 @@ func (p *Pawn) HandlePossiblePromotion(b *Board, move types.Move) bool {
 		b.position[move.EndSquare] = GetPieceForShortName(promotionToPiece, move.ColorMoved)
 	}
 
-	return isPromotionMove
+	return isPromotionMove, nil
 }
 
-func (p *Pawn) HandleEnPassant(b *Board, move, lastMove types.Move) bool {
+func (p *Pawn) HandleEnPassant(b *Board, move, lastMove types.Move) (bool, error){
 	var wasEnPassant bool
 
 	if lastMove.PieceMoved != types.PawnShortName {
-		return false
+		return false, nil
 	}
 
 	switch move.ColorMoved {
@@ -126,7 +126,7 @@ func (p *Pawn) HandleEnPassant(b *Board, move, lastMove types.Move) bool {
 		b.position[move.EndSquare] = GetPieceForShortName(move.PieceMoved, move.ColorMoved)
 	}
 
-	return wasEnPassant
+	return wasEnPassant, nil
 }
 func (p Pawn) getAllMoves(fromSquare types.Coordinate) []types.Coordinate {
 	theoreticalMoves := make([]types.Coordinate, 0, 4)

chess/violation.go

@@ -0,0 +1,16 @@
+package chess
+
+type Violation string
+
+var (
+	InvalidMove  Violation = "invalid move"
+    NoPieceAtStartSquare Violation = "no piece at start square"
+    WrongColorMoved Violation =  "wrong color moved"
+    TargetSquareIsOccupied Violation =  "target square is occupied"
+    KingInCheck Violation =  "king would be in check after move"
+    SomethingWentWrong Violation =  "something went wrong"
+)
+
+func (v Violation) String() string {
+    return string(v)
+}