feat: generate legal moves for a square
This commit is contained in:
Cozma Rares
+247
-82
@@ -36,6 +36,8 @@ export type Piece = {
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color: Color;
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};
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export type Board = (Piece | null)[];
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// prettier-ignore
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export const SQUARES = Object.freeze([
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'a8', 'b8', 'c8', 'd8', 'e8', 'f8', 'g8', 'h8',
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@@ -99,95 +101,36 @@ export const COLOR_MASKS: Record<keyof typeof COLOR, number> = Object.freeze({
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BLACK: 0b10,
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} as const);
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const PAWN_PROMOTION_RANK = Object.freeze({
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w: 8,
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b: 1,
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});
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const PAWN_OFFSETS = Object.freeze({
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w: 8,
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b: -8,
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});
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const PIECE_OFFSETS = Object.freeze({
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n: [-10, -17, -15, -6, 10, 17, 15, 6],
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b: [-9, -7, 9, 7],
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r: [-8, 1, 8, -1],
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q: [-9, -7, 9, 7, -8, 1, 8, -1],
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k: [-9, -7, 9, 7, -8, 1, 8, -1],
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});
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export type Board = (Piece | null)[];
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function generatePawnMoves(
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board: Readonly<Board>,
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position: number,
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color: Color
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) {
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const moves: Move[] = [];
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const generatePromotionMoves = (from: number, to: number) => {
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const fromAlgebraic = algebraic(from);
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const toAlgebraic = algebraic(to);
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PIECE_PROMOTION.forEach(piece =>
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moves.push({
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from: fromAlgebraic,
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to: toAlgebraic,
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promotion: piece,
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flag: MOVE_FLAGS.PROMOTION,
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})
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);
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};
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const offset = PAWN_OFFSETS[color];
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const nextPosition = position + offset;
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if (board[nextPosition] == null) {
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if (rank(nextPosition) == PAWN_PROMOTION_RANK[color])
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generatePromotionMoves(position, nextPosition);
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else {
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moves.push({
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from: algebraic(position),
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to: algebraic(nextPosition),
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flag: MOVE_FLAGS.NORMAL,
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});
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const jumpPosition = nextPosition + offset;
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if (board[jumpPosition] == null)
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moves.push({
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from: algebraic(position),
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to: algebraic(jumpPosition),
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flag: MOVE_FLAGS.PAWN_JUMP,
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});
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}
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}
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[1, -1].forEach(value => {
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const attackPosition = nextPosition + value;
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if (board[attackPosition] != null)
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moves.push({
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from: algebraic(position),
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to: algebraic(attackPosition),
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flag: MOVE_FLAGS.CAPTURE,
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});
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});
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return moves;
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}
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function generatePieceMoves(board: Readonly<Board>) {}
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export function rank(squareIdx: number): number {
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return squareIdx >> 3;
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}
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export const RANK = Object.freeze({
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FIRST: 0,
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SECOND: 1,
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THIRD: 2,
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FORTH: 3,
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FIFTH: 4,
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SIXTH: 5,
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SEVENTH: 6,
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EIGHTH: 7,
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} as const);
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export function file(squareIdx: number): number {
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return squareIdx & 0b111;
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}
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export const FILE: Record<string, number> = Object.freeze({
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A: 0,
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B: 1,
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C: 2,
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D: 3,
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E: 4,
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F: 5,
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G: 6,
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H: 7,
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});
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export function isDigit(c: string): boolean {
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return /^\d$/.test(c);
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}
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@@ -314,6 +257,222 @@ export function validateFEN(fen: string): void {
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validatePosition(fields[0]);
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}
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const PAWN_MOVE_INFO = Object.freeze({
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w: { offset: 8, promotion: RANK.EIGHTH },
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b: { offset: -8, promotion: RANK.FIRST },
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});
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const PAWN_ATTACKS = Object.freeze([
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{ offset: 1, excludedFile: FILE.H },
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{ offset: -1, excludedFile: FILE.A },
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]);
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const PIECE_MOVE_INFO = Object.freeze({
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n: {
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generateMultiple: false,
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moves: [
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{ offset: -10, excludedFiles: [FILE.A, FILE.B] },
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{ offset: -17, excludedFiles: [FILE.H] },
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{ offset: -15, excludedFiles: [FILE.A] },
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{ offset: -6, excludedFiles: [FILE.G, FILE.H] },
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{ offset: 10, excludedFiles: [FILE.G, FILE.H] },
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{ offset: 17, excludedFiles: [FILE.G] },
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{ offset: 15, excludedFiles: [FILE.A] },
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{ offset: 6, excludedFiles: [FILE.A, FILE.B] },
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],
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},
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b: {
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generateMultiple: true,
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moves: [
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{ offset: -9, excludedFiles: [FILE.H] },
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{ offset: -7, excludedFiles: [FILE.A] },
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{ offset: 9, excludedFiles: [FILE.H] },
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{ offset: 7, excludedFiles: [FILE.A] },
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],
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},
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r: {
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generateMultiple: true,
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moves: [
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{ offset: -8, excludedFiles: [] },
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{ offset: 1, excludedFiles: [FILE.H] },
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{ offset: 8, excludedFiles: [] },
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{ offset: -1, excludedFiles: [FILE.A] },
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],
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},
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q: {
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generateMultiple: true,
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moves: [
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{ offset: -9, excludedFiles: [FILE.H] },
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{ offset: -7, excludedFiles: [FILE.A] },
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{ offset: 9, excludedFiles: [FILE.H] },
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{ offset: 7, excludedFiles: [FILE.A] },
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{ offset: -8, excludedFiles: [] },
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{ offset: 1, excludedFiles: [FILE.H] },
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{ offset: 8, excludedFiles: [] },
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{ offset: -1, excludedFiles: [FILE.A] },
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],
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},
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k: {
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generateMultiple: false,
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moves: [
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{ offset: -9, excludedFiles: [FILE.H] },
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{ offset: -7, excludedFiles: [FILE.A] },
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{ offset: 9, excludedFiles: [FILE.H] },
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{ offset: 7, excludedFiles: [FILE.A] },
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{ offset: -8, excludedFiles: [] },
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{ offset: 1, excludedFiles: [FILE.H] },
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{ offset: 8, excludedFiles: [] },
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{ offset: -1, excludedFiles: [FILE.A] },
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],
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},
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});
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function generatePawnMoves(
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board: Readonly<Board>,
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position: number,
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color: Color
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): Move[] {
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if (board[position] == null) return [];
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const moves: Move[] = [];
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const generatePromotionMoves = (from: number, to: number) => {
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const fromAlgebraic = algebraic(from);
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const toAlgebraic = algebraic(to);
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PIECE_PROMOTION.forEach(piece =>
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moves.push({
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from: fromAlgebraic,
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to: toAlgebraic,
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promotion: piece,
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flag: MOVE_FLAGS.PROMOTION,
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})
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);
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};
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const offset = PAWN_MOVE_INFO[color].offset;
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const nextPosition = position + offset;
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if (board[nextPosition] == null) {
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if (rank(nextPosition) == PAWN_MOVE_INFO[color].promotion)
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generatePromotionMoves(position, nextPosition);
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else {
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moves.push({
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from: algebraic(position),
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to: algebraic(nextPosition),
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flag: MOVE_FLAGS.NORMAL,
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});
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const jumpPosition = nextPosition + offset;
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if (board[jumpPosition] == null)
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moves.push({
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from: algebraic(position),
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to: algebraic(jumpPosition),
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flag: MOVE_FLAGS.PAWN_JUMP,
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});
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}
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}
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PAWN_ATTACKS.forEach(({ offset, excludedFile }) => {
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const attackPosition = nextPosition + offset;
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if (file(position) != excludedFile && board[attackPosition] != null)
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moves.push({
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from: algebraic(position),
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to: algebraic(attackPosition),
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flag: MOVE_FLAGS.CAPTURE,
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});
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});
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return moves;
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}
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function generatePieceMoves(
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board: Readonly<Board>,
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position: number,
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piece: Piece
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): Move[] {
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if (piece.type == PIECE.PAWN)
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return generatePawnMoves(board, position, piece.color);
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const type = piece.type; // hacked the type system
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const generateOnce = () => {
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const moves: Move[] = [];
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PIECE_MOVE_INFO[type].moves.forEach(({ offset, excludedFiles }) => {
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const nextPosition = position + offset;
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if (nextPosition < 0 || nextPosition >= 64) return;
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if (excludedFiles.includes(file(nextPosition))) return;
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const attackedPiece = board[nextPosition];
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if (attackedPiece == null) {
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moves.push({
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from: algebraic(position),
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to: algebraic(nextPosition),
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flag: MOVE_FLAGS.NORMAL,
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});
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return;
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}
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if (attackedPiece.color == piece.color) return;
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moves.push({
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from: algebraic(position),
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to: algebraic(nextPosition),
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flag: MOVE_FLAGS.CAPTURE,
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});
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});
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return moves;
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};
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const generateMultiple = () => {
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const moves: Move[] = [];
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PIECE_MOVE_INFO[type].moves.forEach(({ offset, excludedFiles }) => {
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let nextPosition = position + offset;
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while (
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nextPosition >= 0 &&
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nextPosition < 64 &&
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!excludedFiles.includes(file(nextPosition))
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) {
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const attackedPiece = board[nextPosition];
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if (attackedPiece == null) {
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moves.push({
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from: algebraic(position),
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to: algebraic(nextPosition),
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flag: MOVE_FLAGS.NORMAL,
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});
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nextPosition += offset;
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continue;
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}
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if (attackedPiece.color != piece.color)
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moves.push({
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from: algebraic(position),
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to: algebraic(nextPosition),
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flag: MOVE_FLAGS.CAPTURE,
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});
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break;
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}
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});
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return moves;
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};
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return PIECE_MOVE_INFO[piece.type].generateMultiple
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? generateMultiple()
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: generateOnce();
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}
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export default class Chess {
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private _board: Board;
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private _turn: Color;
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@@ -471,7 +630,13 @@ export default class Chess {
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getMoves() {}
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getMovesForSquare(square: Square) {}
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getMovesForSquare(square: Square | number): Move[] {
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if (typeof square != "number") square = squareIndex(square);
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const piece = this.getPiece(square);
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return piece == null ? [] : generatePieceMoves(this._board, square, piece);
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}
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makeMove() {}
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