mchess-server/chess/king.go

package chess

import (
	"mchess_server/types"
)

type King struct {
	Color types.ChessColor
}

func (k King) GetAllAttackedSquares(board Board, fromSquare types.Coordinate) []types.Coordinate {
	return k.GetAllNonBlockedSquares(board, fromSquare)
}

func (k King) GetColor() types.ChessColor {
	return k.Color
}

func (k King) GetAllNonBlockedSquares(board Board, fromSquare types.Coordinate) []types.Coordinate {
	return board.GetNonBlockedKingMoves(fromSquare)
}

func (k King) AfterMoveAction(board *Board, fromSquare types.Coordinate) {
	switch k.Color {
	case types.Black:
		board.state.BlackKingMoved = true
	case types.White:
		board.state.WhiteKingMoved = true
	}
}

func (k King) HandleCastling(board *Board, move types.Move) (bool, Violation) {
	if !k.isMoveCastlingMove(board, move) {
		return false, ""
	}

	if k.hadMovedBefore(board) {
		return false, ""
	}

	if board.isSquareAttacked(move.StartSquare, k.Color.Opposite()) {
		return false, CastlingWhileKingInCheck
	}

	valid, dir := k.isCastlingAllowed(board, move)
	if !valid {
		return false, ""
	}

	k.playCastlingOnBoard(board, move, dir)
	return true, ""
}

func (k King) hadMovedBefore(b *Board) bool {
	var hasMoved bool
	switch k.Color {
	case types.White:
		hasMoved = b.state.WhiteKingMoved
	case types.Black:
		hasMoved = b.state.BlackKingMoved
	}
	return hasMoved
}

type CastlingDirection string

const (
	NoDirection   CastlingDirection = ""
	CastlingRight CastlingDirection = "right"
	CastlingLeft  CastlingDirection = "left"
)

func (k King) isMoveCastlingMove(b *Board, move types.Move) bool {
	var destinationSquareForKingRight types.Coordinate
	var destinationSquareForKingLeft types.Coordinate

	switch k.Color {
	case types.White:
		destinationSquareForKingRight = types.Coordinate{Col: 7, Row: 1}
		destinationSquareForKingLeft = types.Coordinate{Col: 3, Row: 1}

	case types.Black:
		destinationSquareForKingRight = types.Coordinate{Col: 7, Row: 8}
		destinationSquareForKingLeft = types.Coordinate{Col: 3, Row: 8}
	}

	if move.EndSquare == destinationSquareForKingRight ||
		move.EndSquare == destinationSquareForKingLeft {
		return true
	}

	return false
}

func (k King) isCastlingAllowed(b *Board, move types.Move) (bool, CastlingDirection) {
	var valid = false

	switch k.Color {
	case types.White:
		destinationSquareForKingRight := types.Coordinate{Col: 7, Row: 1}
		destinationSquareForKingLeft := types.Coordinate{Col: 3, Row: 1}

		if move.EndSquare == destinationSquareForKingRight &&
			b.getPieceAt(destinationSquareForKingRight) == nil &&
			b.getPieceAt(*destinationSquareForKingRight.Left(1)) == nil &&
			!b.isSquareAttacked(destinationSquareForKingRight, types.Black) &&
			!b.isSquareAttacked(*destinationSquareForKingRight.Left(1), types.Black) &&
			!b.state.WhiteHRookMoved {
			_, ok := b.getPieceAt(types.Coordinate{Col: 8, Row: 1}).(Rook)
			if ok {
				return true, CastlingRight
			}
		}

		if move.EndSquare == destinationSquareForKingLeft &&
			b.getPieceAt(destinationSquareForKingLeft) == nil &&
			b.getPieceAt(*destinationSquareForKingLeft.Right(1)) == nil &&
			b.getPieceAt(*destinationSquareForKingLeft.Left(1)) == nil &&
			!b.isSquareAttacked(destinationSquareForKingLeft, types.Black) &&
			!b.isSquareAttacked(*destinationSquareForKingLeft.Right(1), types.Black) &&
			!b.state.WhiteARookMoved {
			_, ok := b.getPieceAt(types.Coordinate{Col: 1, Row: 1}).(Rook)
			if ok {
				return true, CastlingLeft
			}
		}
	case types.Black:
		destinationSquareForKingRight := types.Coordinate{Col: 7, Row: 8}
		destinationSquareForKingLeft := types.Coordinate{Col: 3, Row: 8}

		if move.EndSquare == destinationSquareForKingRight &&
			b.getPieceAt(destinationSquareForKingRight) == nil &&
			b.getPieceAt(*destinationSquareForKingRight.Left(1)) == nil &&
			!b.isSquareAttacked(destinationSquareForKingRight, types.White) &&
			!b.isSquareAttacked(*destinationSquareForKingRight.Left(1), types.White) &&
			!b.state.BlackHRookMoved {
			_, ok := b.getPieceAt(types.Coordinate{Col: 8, Row: 8}).(Rook)
			if ok {
				return true, CastlingRight
			}
		}

		if move.EndSquare == destinationSquareForKingLeft &&
			b.getPieceAt(destinationSquareForKingLeft) == nil &&
			b.getPieceAt(*destinationSquareForKingLeft.Right(1)) == nil &&
			b.getPieceAt(*destinationSquareForKingLeft.Left(1)) == nil &&
			!b.isSquareAttacked(destinationSquareForKingLeft, types.White) &&
			!b.isSquareAttacked(*destinationSquareForKingLeft.Right(1), types.White) &&
			!b.state.BlackARookMoved {
			_, ok := b.getPieceAt(types.Coordinate{Col: 1, Row: 8}).(Rook)
			if ok {
				return true, CastlingLeft
			}
		}
	}
	return valid, NoDirection
}

func (k King) playCastlingOnBoard(board *Board, move types.Move, dir CastlingDirection) {
	onRow := move.StartSquare.Row

	switch dir {
	case CastlingRight:
		delete(board.position, types.Coordinate{Col: 8, Row: onRow})
		delete(board.position, types.Coordinate{Col: 5, Row: onRow})
		board.position[types.Coordinate{Col: 7, Row: onRow}] = King{Color: k.Color}
		board.position[types.Coordinate{Col: 6, Row: onRow}] = Rook(k)
	case CastlingLeft:
		delete(board.position, types.Coordinate{Col: 1, Row: onRow})
		delete(board.position, types.Coordinate{Col: 5, Row: onRow})
		board.position[types.Coordinate{Col: 3, Row: onRow}] = King{Color: k.Color}
		board.position[types.Coordinate{Col: 4, Row: onRow}] = Rook(k)
	}
}