mchess-server/chess/board.go

package chess

import (
	"mchess_server/types"

	"github.com/samber/lo"
)

type Board map[types.Coordinate]Piece

func (b Board) Init() {
	var coord types.Coordinate

	for i := 1; i <= 8; i++ {
		coord.Row = 2
		coord.Col = i
		b[coord] = Pawn{Color: types.White}

		coord.Row = 7
		coord.Col = i
		b[coord] = Pawn{Color: types.Black}
	}

	b[types.Coordinate{Row: 1, Col: 1}] = Rook{Color: types.White}
	b[types.Coordinate{Row: 1, Col: 2}] = Knight{Color: types.White}
	b[types.Coordinate{Row: 1, Col: 3}] = Bishop{Color: types.White}
	b[types.Coordinate{Row: 1, Col: 4}] = Queen{Color: types.White}
	b[types.Coordinate{Row: 1, Col: 5}] = King{Color: types.White}
	b[types.Coordinate{Row: 1, Col: 6}] = Bishop{Color: types.White}
	b[types.Coordinate{Row: 1, Col: 7}] = Knight{Color: types.White}
	b[types.Coordinate{Row: 1, Col: 8}] = Rook{Color: types.White}

	b[types.Coordinate{Row: 8, Col: 1}] = Rook{Color: types.Black}
	b[types.Coordinate{Row: 8, Col: 2}] = Knight{Color: types.Black}
	b[types.Coordinate{Row: 8, Col: 3}] = Bishop{Color: types.Black}
	b[types.Coordinate{Row: 8, Col: 4}] = Queen{Color: types.Black}
	b[types.Coordinate{Row: 8, Col: 5}] = King{Color: types.Black}
	b[types.Coordinate{Row: 8, Col: 6}] = Bishop{Color: types.Black}
	b[types.Coordinate{Row: 8, Col: 7}] = Knight{Color: types.Black}
	b[types.Coordinate{Row: 8, Col: 8}] = Rook{Color: types.Black}
}

func (b Board) CheckMove(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
	tempBoard := b.getCopyOfBoard()

	//Check start square of move
	pieceAtStartSquare := b.getPieceAt(move.StartSquare)
	if pieceAtStartSquare == nil {
		return false, "no piece at start square"
	}
	movingColor := pieceAtStartSquare.GetColor()

	//Check end square of move
	pieceAtEndSquare := b.getPieceAt(move.EndSquare)
	if pieceAtEndSquare != nil {
		if pieceAtEndSquare.GetColor() == pieceAtStartSquare.GetColor() {
			return false, "same-coloured piece at end square"
		}
	}
	var wasPromotionMove bool
	// var piece types.PieceShortName
	switch pieceAtStartSquare.(type) {
	case Pawn:
		wasPromotionMove, _ = tempBoard.handlePossiblePromotion(move, movingColor)
	}

	if !wasPromotionMove {
		// 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.
		allMovesExceptBlocked := pieceAtStartSquare.GetAllMovesButBlocked(tempBoard, move.StartSquare)
		legal := lo.Contains(allMovesExceptBlocked, move.EndSquare)
		if !legal {
			return false, "not a legal square"
		}

		//We play the move on the temporary board
		delete(tempBoard, move.StartSquare)
		tempBoard[move.EndSquare] = pieceAtStartSquare
	}

	//Check if king of moving color is in check -> move not allowed
	//Do that by checking if the king is in a square attacked by the other color.
	ownKingCoordinate := tempBoard.getSquareOfPiece(King{Color: movingColor})
	if ownKingCoordinate == nil {
		return false, string(movingColor) + " king not found"
	}

	kingIsAttacked := tempBoard.isSquareAttacked(*ownKingCoordinate, movingColor.Opposite())
	if kingIsAttacked {
		return false, "king is attacked after move"
	}

	//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 = tempBoard

	return true, ""
}

func (b Board) getSquareOfPiece(piece Piece) *types.Coordinate {
	for k, v := range b {
		if v == piece {
			return &k
		}
	}
	return nil
}

func (b Board) isSquareAttacked(square types.Coordinate, byColor types.ChessColor) bool {
	var attackedSquares []types.Coordinate

	for square, piece := range b {
		attackedSquares = append(attackedSquares, piece.GetAllMovesButBlocked(b, square)...)
	}

	return lo.Contains(attackedSquares, square)
}

func (b Board) getPieceAt(coord types.Coordinate) Piece {
	piece, found := b[coord]
	if !found {
		return nil
	}

	return piece
}

func (b Board) handlePossiblePromotion(move types.Move, color types.ChessColor) (bool, types.PieceShortName) {
	var isPromotionMove bool
	var promotionToPiece types.PieceShortName

	messageContainsPromotion := move.IsPromotionMove()

	if messageContainsPromotion {
		promotionToPiece = *move.PromotionToPiece
	}

	switch color {
	case types.White:
		if move.StartSquare.Row == types.RangeLastValid-1 &&
			move.EndSquare.Row == types.RangeLastValid {
			isPromotionMove = true
		}

	case types.Black:
		if move.StartSquare.Row == types.RangeFirstValid+1 &&
			move.EndSquare.Row == types.RangeFirstValid {
			isPromotionMove = true
		}
	}

	if isPromotionMove {
		delete(b, move.StartSquare)
		b[move.EndSquare] = GetPieceForShortName(promotionToPiece)
	}

	return isPromotionMove, promotionToPiece
}

func (b Board) getCopyOfBoard() Board {
	board := make(map[types.Coordinate]Piece)

	for coord, piece := range b {
		board[coord] = piece
	}

	return board
}