mchess-server/chess/board.go

package chess

import (
	"local/m/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, HasMoved: false}

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

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

	pieceAtEndSquare := b.getPieceAt(move.EndSquare)
	if pieceAtEndSquare != nil {
		if pieceAtEndSquare.GetColor() == pieceAtStartSquare.GetColor() {
			return false, "same-coloured piece at end square"
		}
	}
	// 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.

	legal := lo.Contains(pieceAtStartSquare.GetAllLegalAndIllegalMoves(b, move.StartSquare), move.EndSquare)
	if !legal {
		return false, "not a legal square"
	}

	//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 := b.getSquareOfPiece(King{Color: movingColor})
	if ownKingCoordinate == nil {
		return false, string(movingColor) + " king not found"
	}

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

	//Check for checkmate
	//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
    delete(b, move.StartSquare)
    b[move.EndSquare] = pieceAtStartSquare

    pieceAtStartSquare.AfterMoveAction()
	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.GetAllLegalAndIllegalMoves(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
}