core/io.github.lunalobos.chess4kt.js/Position

Position

Class to represent a position on the chessboard. It is immutable.

This class provides all the necessary information to perform conventional logical operations based on a position, primarily through bitboard representations. This class cannot be instantiated directly but must be accessed via the factory function positionOf, which ensures the provided FEN string (if any) is well-formed and valid.

This is a facade created to enable exporting the code to JS, though it can also be used directly within the JS modules of any KMP project.

Properties

bitboards

val bitboards: JsReadonlyArray<Bitboard>

Array of Bitboards. The index in the array is equal to the ordinal value minus one of the corresponding piece (e.g., Black Knight distribution is at index BN.ordinal - 1).

blackCastleKingside

val blackCastleKingside: Boolean

True if Black can castle kingside (short castling). False otherwise.

blackCastleQueenside

val blackCastleQueenside: Boolean

True if Black can castle queenside (long castling). False otherwise.

check

val check: Boolean

True if the current side to move is in check. False otherwise.

checkmate

val checkmate: Boolean

True if the position is a checkmate (the current side is in check and has no legal moves). False otherwise.

children

val children: JsReadonlyArray<Tuple>

A list of tuples, where each tuple represents a legal move from this position and the resulting new position (Tuple). This list effectively defines the legal branches of the game tree from the current position.

draw

val draw: Boolean

True if the position is a forced draw. This is true if the position results in a stalemate or lackOfMaterial. False otherwise.

enPassant

val enPassant: Int

The square index (0-63) where a pawn can be captured en passant. Returns -1 if no en passant capture is possible.

enPassantSquare

val enPassantSquare: Square?

The square exposed to an en passant capture, if one exists. Returns null if no en passant capture is possible in the current position.

fen

val fen: String

The FEN (Forsyth-Edwards Notation) string representation of the position.

fiftyMoves

val fiftyMoves: Boolean

True if the position has reached or exceeded 50 half-moves without a pawn move or capture.

gameOver

val gameOver: Boolean

True if the game state is concluded (terminal position), either due to a forced draw or checkmate. False otherwise.

halfMovesCounter

val halfMovesCounter: Int

The number of half-moves since the last pawn move or capture. This is used for the 50-move rule.

lackOfMaterial

val lackOfMaterial: Boolean

True if the position is a draw due to insufficient mating material (e.g., King vs. King). False otherwise.

movesCounter

val movesCounter: Int

The full move number in the game (starts at 1 and is incremented after Black's move).

sideToMove

val sideToMove: Side

The side (WHITE or BLACK) whose turn it is to move.

squares

val squares: IntArray

A 64-element array where the index corresponds to the square order defined in Square (A1=0, H8=63). The value of each element is the ordinal of the Piece occupying that square (0 for EMPTY, 1 for WP, and so on).

stalemate

val stalemate: Boolean

True if the position is a stalemate (the current side is not in check but has no legal moves). False otherwise.

whiteCastleKingside

val whiteCastleKingside: Boolean

True if White can castle kingside (short castling). False otherwise.

whiteCastleQueenside

val whiteCastleQueenside: Boolean

True if White can castle queenside (long castling). False otherwise.

whiteMove

val whiteMove: Boolean

True if it is White's turn to move. False if it is Black's turn.

zobrist

val zobrist: Bitboard

The Zobrist hash key of the position. This is used for efficient position lookup and repetition detection.

Functions

blackLacksOfMaterial

fun blackLacksOfMaterial(): Boolean

Determines if Black has insufficient material to win the game. Returns true if the current pieces for Black cannot potentially lead to a checkmate.

equals

open operator override fun equals(other: Any?): Boolean

hashCode

open override fun hashCode(): Int

isLegal

fun isLegal(move: Move): Boolean

Returns true if the evaluated Move is legal in the current position, and false otherwise.

move

fun move(move: Move): Position

Retrieves the new Position that results from executing the provided legal Move. Throws a MoveException if the provided move is not legal in the current position.

moveFromString

fun moveFromString(move: String, notation: Notation = UCI): Position

Retrieves the new Position that results from executing the move specified in the given notation. Throws a MoveException if the move is not legal. If no notation is provided, UCI notation is assumed.

pieceAt

fun pieceAt(square: Square): Piece

Retrieves the piece object that occupies the given square.

toString

open override fun toString(): String

whiteLacksOfMaterial

fun whiteLacksOfMaterial(): Boolean

Determines if White has insufficient material to win the game. Returns true if the current pieces for White cannot potentially lead to a checkmate.