QuickChess/src/index.js

import React from 'react';
import ReactDOM from 'react-dom';
import './index.css';

const BLACK = 0;
const WHITE = 1;

const PAWN = 0;
const ROOK = 1;
const KNIGHT = 2;
const BISHOP = 3;
const QUEEN = 4;
const KING = 5;

const Images = [
    './white_pawn.svg',
    './white_rook.svg',
    './white_knight.svg',
    './white_bishop.svg',
    './white_queen.svg',
    './white_king.svg',

    './black_pawn.svg',
    './black_rook.svg',
    './black_knight.svg',
    './black_bishop.svg',
    './black_queen.svg',
    './black_king.svg',
];

function range(n) {
  return Array.from(Array(n).keys());
}

function isBlack(piece) {
  return piece != null && piece.color === BLACK;
}

function isWhite(piece) {
  return piece != null && piece.color === WHITE;
}

function isPawn(piece) {
  return piece != null && piece.type === PAWN;
}

function isRook(piece) {
  return piece != null && piece.type === ROOK;
}

function isBishop(piece) {
  return piece != null && piece.type === BISHOP;
}

function isQueen(piece) {
  return piece != null && piece.type === QUEEN;
}

function isKnight(piece) {
  return piece != null && piece.type === KNIGHT;
}

function isKing(piece) {
  return piece != null && piece.type === KING;
}

function imageFromPiece(piece) {
  if (piece) {
    const image = piece.color === WHITE ? piece.type : piece.type + 6;
    return Images[image];
  }
  return null;
}

function Square(props) {
  return (
    <button
      className="square"
      onClick={props.onClick}
      style={{
        backgroundImage: `url(${imageFromPiece(props.piece)})`,
        backgroundSize: `100%`,
        backgroundColor: props.bgColor,
      }}
      title={props.piece == null ? "" : props.piece.getInfoText()}
    >
    </button>
  );
}

class Piece {
  constructor(color, type) {
    this.color = color;
    this.type = type;
    this.passantable = false;
    this.moves = 0;
  }

  setType(type) {
    this.type = type;
  }

  getInfoText() {
    if(this.moves === 1) {
      return "Has made 1 move"
    } else {
      return "Has made " + this.moves + " moves"
    }
  }
}

class Board extends React.Component {
  constructor(props) {
    super(props);
    this.state = {
      squares: this.reset(),
      blackIsNext: true,
      hand: {
        heldPiece: null,
      },
    };
  }

  setHand(hand) {
    this.setState({
      squares: this.state.squares,
      blackIsNext: this.state.blackIsNext,
      hand: hand,
    });
  }

  clone() {
    let board = new Board();
    board.state.squares = this.state.squares.slice();
    board.state.blackIsNext = this.state.blackIsNext;
    board.state.hand = {
      heldPiece: this.state.hand.heldPiece,
    };
    return board;
  }

  reset() {
    let squares = [];
    const mainRow = [ROOK, KNIGHT, BISHOP, QUEEN, KING, BISHOP, KNIGHT, ROOK];
    function add(num, color, type) {
      for(let i = 0; i < num; i++) {
        if(color != null && type != null) {
          squares.push(new Piece(color, type));
        } else {
          squares.push(null);
        }
      }
    }

    mainRow.forEach(type => add(1, WHITE, type));
    add(8, WHITE, PAWN);
    add(32, null, null);
    add(8, BLACK, PAWN);
    mainRow.forEach(type => add(1, BLACK, type));

    return squares;
  }

  getXandY(i) {
    const x = i % 8;
    const y = Math.floor(i / 8);
    return [x, y];
  }

  getIndex(x, y) {
    return x + (y * 8);
  }

  isValidXY(x, y) {
    return x < 8 && x >=0 && y < 8 && y >= 0;
  }

  squareCount() {
    return this.state.squares.length;
  }

  squareAt(i) {
    return i >= 0 && i < 64 ? this.state.squares[i] : null;
  }

  pieceAt(x, y) {
    if (this.isValidXY(x, y)) {
      return this.state.squares[this.getIndex(x, y)];
    } else {
      return null;
    }
  }

  whiteAt(x, y) {
    const square = this.pieceAt(x, y);
    if (square == null) {
      return false;
    }
    return isWhite(square);
  }

  blackAt(x, y) {
    const square = this.pieceAt(x, y);
    if (square == null) {
      return false;
    }
    return isBlack(square);
  }

  isEnemyOf(piece, x, y) {
    return isBlack(piece) ? this.whiteAt(x, y) : this.blackAt(x, y);
  }

  getValidMovesAt(piece, x, y) {
    let moves = [];
    const tryAddMove = (x, y) => {
      if (this.isValidXY(x, y)) {
        if(this.pieceAt(x, y) == null) {
          moves.push({x, y});
          // Keep searching
          return 0;
        } else if (this.isEnemyOf(piece, x, y)) {
          moves.push({x, y});
        }
        // Stop searching
        return 1;
      }
    };
    function addBunch(xFunc, yFunc, isUp) {
      for (let i = 1; i < 8; i++) {
        if(tryAddMove(xFunc(i), yFunc(i)) !== 0) {
          break;
        }
      }
    }

    if (isPawn(piece)) {
      const pieceIsBlack = isBlack(piece);
      const shift = pieceIsBlack ? -1 : 1;
      const startLine = pieceIsBlack ? 6 : 1;

      // Check for en passant
      const left = this.pieceAt(x - 1, y);
      const right = this.pieceAt(x + 1, y);
      if (left != null && left.passantable && left.color !== piece.color) {
        moves.push({x: x - 1, y: y + shift, passant: {x: x - 1, y}})
      }
      if (right != null && right.passantable && right.color !== piece.color) {
        moves.push({x: x + 1, y: y + shift, passant: {x: x + 1, y}})
      }

      if (this.pieceAt(x, y + shift) == null) {
        moves.push({x, y: y + shift});
        // Pawn moving two spaces becomes en-passantable
        if (y === startLine && this.pieceAt(x, y + (shift * 2)) == null) {
          moves.push({x, y: y + (shift * 2), passantable: true});
        }
      }
      [x + 1, x - 1].forEach(x => {
        if (this.isValidXY(x, y + shift) && this.isEnemyOf(piece, x, y + shift)) {
          moves.push({x, y: y + shift});
        }
      });
    } else if (isRook(piece)) {
      addBunch(n => {return x;}, n => {return y + n;});
      addBunch(n => {return x;}, n => {return y - n;});
      addBunch(n => {return x + n;}, n => {return y;});
      addBunch(n => {return x - n;}, n => {return y;});
    } else if (isBishop(piece)) {
      addBunch(n => {return x + n;}, n => {return y + n;});
      addBunch(n => {return x - n;}, n => {return y + n;});
      addBunch(n => {return x + n;}, n => {return y - n;});
      addBunch(n => {return x - n;}, n => {return y - n;});
    } else if (isQueen(piece)) {
      const [rook, bishop] =
        [new Piece(piece.color, ROOK), new Piece(piece.color, BISHOP)];
      moves = moves.concat(this.getValidMovesAt(rook, x, y));
      moves = moves.concat(this.getValidMovesAt(bishop, x, y));
    } else if (isKnight(piece)) {
      [
        [2, 1], [2, -1], [-2, 1], [-2, -1],
        [1, 2], [1, -2], [-1, 2], [-1, -2],
      ].forEach(delta => tryAddMove(x + delta[0], y + delta[1]));
    } else if (isKing(piece)) {
      [[1, 1], [1, -1], [-1, 1], [-1, -1], [0, 1], [0, -1], [1, 0], [-1, 0]]
        .forEach(delta => tryAddMove(x + delta[0], y + delta[1]));
      if (piece.moves === 0) {
        const [x, y] = this.getXandY(this.findIndex(piece));
        let leftRook = this.pieceAt(0, y);
        if(isRook(leftRook) && leftRook.moves === 0) {
          // Check if between space puts king in check
          // Check if spaces between rook and king are empty
          // add move(x: x - 2, y, castle: [x, y])
        }
        let rightRook = this.pieceAt(7, y);
        if(isRook(rightRook) && rightRook.moves === 0) {
          // Check if between space puts king in check
          // Check if spaces between rook and king are empty
          // add move(x: x + 2, y, castle: [x, y])
        }
      }
    }
    return moves;
  }

  findIndex(piece) {
    for(let i = 0; i < this.squareCount(); i++) {
      const check = this.state.squares[i];
      if(check && check.type === piece.type && check.color === piece.color) {
        return i;
      }
    }
    return null;
  }

  distanceBetween(i1, i2) {
    const [pos1X, pos1Y] = this.getXandY(i1);
    const [pos2X, pos2Y] = this.getXandY(i2);

    let a = pos1X - pos2X;
    a = a * a;

    let b = pos1Y - pos2Y;
    b = b * b;

    return Math.sqrt(a + b);
  }

  inCheck(piece) {
    const kingPos = this.getXandY(this.findIndex(piece));

    for(let i = 0; i < this.squareCount(); i++) {
      const [x, y] = this.getXandY(i);
      if(this.isEnemyOf(piece, x, y)) {
        const moves = this.getValidMoves(i);
        for(let j = 0; j < moves.length; j++) {
          if(moves[j].x === kingPos[0] && moves[j].y === kingPos[1]) {
            return piece;
          }
        }
      }
    }

    return null;
  }

  whoInCheck() {
    const blackKing = this.inCheck(new Piece(BLACK, KING));
    return blackKing ? blackKing : this.inCheck(new Piece(WHITE, KING));
  }

  checkmate() {
    const checkedKing = this.whoInCheck();
    if (checkedKing != null) {
      // For each square
      for(let i = 0; i < this.squareCount(); i++) {
        const piece = this.squareAt(i);
        // If that piece is on the checked team
        if (piece != null && isBlack(piece) === isBlack(checkedKing)) {
          // For each move of the above piece
          const moves = this.getValidMoves(i)
          for(const move of moves) {
            // Copy the board
            const board = this.clone();
            board.state.squares[board.getIndex(move.x, move.y)] = board.state.squares[i];
            board.state.squares[i] = null;
            const check = board.inCheck(checkedKing);
            if (check == null || check.color !== checkedKing.color) {
              return false;
            }
          }
        }
      }
      return true;
    }

    return false;
  }

  getValidMoves(source) {
    const [x, y] = this.getXandY(source);

    const piece = this.squareAt(source);
    return this.getValidMovesAt(piece, x, y);
  }

  isValidMove(source, dest) {
    const [destX, destY] = this.getXandY(dest);

    for (const move of this.getValidMoves(source)) {
      if (destX === move.x && destY === move.y) {
        return move;
      }
    }

    return null;
  }

  isHoldingPiece() {
    return this.heldPiece() != null;
  }

  heldPiece() {
    return this.state.hand.heldPiece;
  }

  makeMove(from, to) {
    const squares = this.state.squares.slice();
    const move = this.isValidMove(from, to)
    if (move) {
      if (move.passant) {
        squares[this.getIndex(move.passant.x, move.passant.y)] = null;
      }
      // Remove existing passantable states
      squares.forEach(square => {
        if (square) {
          square.passantable = false;
        }
      });
      if (move.passantable) {
        squares[from].passantable = true;
      }
      const y = this.getXandY(to)[1];
      squares[to] = squares[from];
      squares[from] = null;
      if (squares[to].type === PAWN && (y === 0 || y === 7)) {
        squares[to].setType(QUEEN);
      }
      squares[to].moves++;
      this.setState({
        squares: squares,
        blackIsNext: !this.state.blackIsNext,
        hand: {
          heldPiece: null,
        }
      });
      return 0;
    }
    return 1;
  }

  handleClick(i) {
    if (this.checkmate()) {
      return;
    }
    if (this.isHoldingPiece()) {
      // Copy the board
      let board = this.clone();
      board.state.squares[i] = board.state.squares[board.heldPiece()];
      board.state.squares[this.heldPiece()] = null;

      const moversKing = this.state.blackIsNext ?
        new Piece(BLACK, KING) : new Piece(WHITE, KING);
      if (board.inCheck(moversKing) != null) {
        return;
      }
      if (this.makeMove(this.heldPiece(), i) !== 0) {
        this.setHand({
            heldPiece: null,
        });
      }
    } else if (this.state.squares[i] != null) {
      const isSquareBlack = isBlack(this.state.squares[i]);
      if(isSquareBlack === this.state.blackIsNext) {
        this.setHand({
            heldPiece: i,
        });
      }
    }
  }

  renderSquare(i) {
    const plainBg = (i + (Math.floor(i / 8))) % 2 === 0 ? "white" : "#666";
    const bgColor = this.heldPiece() === i ? "#5D98E6" : plainBg;
    return (
      <Square
        key={"square-" + i}
        piece={this.state.squares[i]}
        onClick={() => this.handleClick(i)}
        bgColor={bgColor}
      />
    );
  }

  row(r) {
    const i = r * 8;
    return (
      <div className="board-row" key={"row=" + r}>
        {range(8).map(n => this.renderSquare(n + i))}
      </div>
    );
  }

  render() {
    const checkMsg = this.whoInCheck() ? "Check! " : "";
    const isCheckmate = this.checkmate();
    const namedPlayer = isCheckmate ?
      !this.state.blackIsNext : this.state.blackIsNext
    const color = namedPlayer ? 'Black' : 'White';

    const status = isCheckmate ? "Checkmate! " + color + " Wins!" :
      checkMsg + color + "'s Turn";

    return (
      <div style={{textAlign: `center`,}}>
        <div className="status"><h1>{status}</h1></div>
        {range(8).map(n => this.row(n))}
      </div>
    );
  }
}

class Game extends React.Component {
  render() {
    return (
      <div className="game">
        <div className="game-board">
          <Board />
        </div>
      </div>
    );
  }
}

// ========================================

ReactDOM.render(
  <Game />,
  document.getElementById('root')
);