QuickChess/src/board.js

import React from 'react';
import Popup from './components/Popup';

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 EMPTY = -1;

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',
];

const SHUFFLING_ENABLED = 0;

function getAllSettings() {
  return [SHUFFLING_ENABLED];
}

function settingText(setting) {
  switch(setting) {
    case SHUFFLING_ENABLED:
      return "Shuffle Back Row";
    default:
      return "";
  }
}

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

function imageFromPiece(piece) {
  if (piece && piece.type >= 0) {
    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"
    }
  }

  isEmpty() {
    return this.type === EMPTY;
  }

  isFull() {
    return !this.isEmpty();
  }

  isBlack() {
    return this.color === BLACK;
  }

  isWhite() {
    return this.color === WHITE;
  }

  isEnemyOf(piece) {
    if (this.color === EMPTY || piece.color === EMPTY) {
      return false;
    } else {
      return this.color !== piece.color;
    }
  }

  isFriendOf(piece) {
    if (this.color === EMPTY || piece.color === EMPTY) {
      return false;
    } else {
      return this.color === piece.color;
    }
  }

  is(type) {
    return this.type === type;
  }

  hasMoved() {
    return this.moves !== 0;
  }

  hasntMoved() {
    return !this.hasMoved();
  }
}

class Board extends React.Component {
  constructor(props) {
    super(props);
    this.state = (props && props.text) ?
      this.stateFromText(props.text) : this.originalState();
  }

  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;
  }

  stateFromText(text) {
    text = text.replace(/[\n]+/g, '');
    const squares = text.substring(1);
    return {
      hand: {
        heldPiece: null,
      },
      blackIsNext: text[0].toUpperCase() === 'B',
      squares: squares.split('').map(c => {
        const type = c.toLowerCase();
        const color = c === type ? WHITE : BLACK;
        switch (type) {
          case 'r':
            return new Piece(color, ROOK);
          case 'n':
            return new Piece(color, KNIGHT);
          case 'b':
            return new Piece(color, BISHOP);
          case 'q':
            return new Piece(color, QUEEN);
          case 'k':
            return new Piece(color, KING);
          case 'p':
            return new Piece(color, PAWN);
          default:
            return new Piece(EMPTY, EMPTY);
        }
      }),
    };
  }

  shuffledBackRow() {
    return "rnbqkbnr".split('').sort(() => Math.random() - 0.5).join('');
  }

  shuffledBackRowState() {
    const backRow = this.shuffledBackRow();
    const text = ["B", backRow, "pppppppp",
      "________", "________", "________", "________",
      "PPPPPPPP", backRow.toUpperCase()].join('');
    return this.stateFromText(text);
  }

  textFromState() {
    const turn = (this.state.blackIsNext? 'B' : 'W');
    return turn + this.state.squares.map(square => {
      if (!square) {
        return '_';
      }
      let color = (c) => {
        return square.color === BLACK ? c.toUpperCase() : c;
      };
      switch (square.type) {
        case ROOK:
          return color('r');
        case KNIGHT:
          return color('n');
        case BISHOP:
          return color('b');
        case QUEEN:
          return color('q');
        case KING:
          return color('k');
        case PAWN:
          return color('p');
        default:
          return '_';
      }
    }).join('');;
  }

  doReset() {
    this.setState(this.getSetting(SHUFFLING_ENABLED) ?
      this.shuffledBackRowState() : this.originalState());
    this.setState({
      showPopup: false,
    });
  }

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

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

    return ({
      squares,
      blackIsNext: true,
      hand: {
        heldPiece: null,
      },
      showPopup: false,
      settings: {},
    });
  }

  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;
  }

  pieceAtIndex(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 new Piece(EMPTY, EMPTY);
    }
  }

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

    if (piece.is(PAWN)) {
      const pieceIsBlack = piece.isBlack();
      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 && left.passantable && left.isEnemyOf(piece)) {
        moves.push({x: x - 1, y: y + shift, passant: {x: x - 1, y}})
      }
      if (right && right.passantable && right.isEnemyOf(piece)) {
        moves.push({x: x + 1, y: y + shift, passant: {x: x + 1, y}})
      }

      if (this.pieceAt(x, y + shift).isEmpty()) {
        moves.push({x, y: y + shift});
        // Pawn moving two spaces becomes en-passantable
        if (y === startLine && this.pieceAt(x, y + (shift * 2)).isEmpty()) {
          moves.push({x, y: y + (shift * 2), passantable: true});
        }
      }
      [x + 1, x - 1].forEach(x => {
        const y2 = y + shift;
        if (this.isValidXY(x, y2) && piece.isEnemyOf(this.pieceAt(x, y2))) {
          moves.push({x, y: y2});
        }
      });
    } else if (piece.is(ROOK)) {
      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 (piece.is(BISHOP)) {
      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 (piece.is(QUEEN)) {
      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 (piece.is(KNIGHT)) {
      [
        [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 (piece.is(KING)) {
      [[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.hasntMoved()) {
        const kingIndex = this.findIndex(piece);
        const [x, y] = this.getXandY(kingIndex);

        let leftRook = this.pieceAt(0, y);
        if(leftRook.is(ROOK) && leftRook.hasntMoved()) {
          // Check if spaces between rook and king are empty
          if(this.pieceAt(1, y).isEmpty() &&
            this.pieceAt(2, y).isEmpty() &&
            this.pieceAt(3, y).isEmpty()) {
            // Check if between space puts king in check
            let board = this.clone();
            board.state.squares[board.getIndex(x - 1, y)] = piece;
            board.state.squares[kingIndex].isEmpty();
            if(board.inCheck(piece) == null) {
              moves.push({x: x - 2, y, castle: [x - 1, y]});
            }
          }
        }

        let rightRook = this.pieceAt(7, y);
        if(rightRook.is(ROOK) && rightRook.hasntMoved()) {
          // Check if spaces between rook and king are empty
          if(this.pieceAt(5, y).isEmpty() &&
            this.pieceAt(6, y).isEmpty()) {
            // Check if between space puts king in check
            let board = this.clone();
            board.state.squares[board.getIndex(x + 1, y)] = piece;
            board.state.squares[kingIndex].isEmpty();
            if(board.inCheck(piece) == null) {
              moves.push({x: x + 2, y, castle: [x + 1, y]});
            }
          }
        }
      }
    }
    return moves;
  }

  findIndex(piece) {
    for(let i = 0; i < this.squareCount(); i++) {
      const check = this.state.squares[i];
      if(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++) {
      if(piece.isEnemyOf(this.pieceAtIndex(i))) {
        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.pieceAtIndex(i);
        // If that piece is on the checked team
        if (piece != null && piece.isFriendOf(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();
            const moveIndex = board.getIndex(move.x, move.y);
            board.state.squares[moveIndex] = board.state.squares[i];
            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.pieceAtIndex(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 && this.state.hand) ? this.state.hand.heldPiece : null;
  }

  makeMove(from, to) {
    const squares = this.state.squares.slice();
    const move = this.isValidMove(from, to)
    if (move) {
      if (move.passant) {
        const i = this.getIndex(move.passant.x, move.passant.y);
        squares[i] = new Piece(EMPTY, EMPTY);
      }
      if (move.castle) {
        // .castle holds the position where the rook should end up
        // King moved left
        const rookX = move.castle[0] > move.x ? 0 : 7;
        console.log("Replace " + move.castle + " with " + [rookX, move.castle[1]]);
        const rookStart = this.getIndex(rookX, move.castle[1]);
        const rookLanding = this.getIndex(move.castle[0], move.castle[1]);
        squares[rookLanding] = squares[rookStart];
        squares[rookStart] = new Piece(EMPTY, EMPTY);
      }
      // 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] = new Piece(EMPTY, EMPTY);
      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()] = new Piece(EMPTY, EMPTY);

      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].isFull()) {
      const isSquareBlack = this.state.squares[i].isBlack();
      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>
    );
  }

  togglePopup() {
    this.setState({
      showPopup: !this.state.showPopup
    });
  }

  setSetting(name, value) {
    let settings = this.state.settings;
    settings[name] = value;
    this.setState({
      settings
    });
  }

  getSetting(name) {
    return this.state.settings[name];
  }

  toggleSetting(name) {
    console.log("toggle " + settingText(name));
    let settings = this.state.settings;
    settings[name] = !settings[name];
    console.log(settings[name]);
    this.setState({
      settings: settings,
    });
  }

  renderPopup() {
    return (this.state.showPopup ?
     <Popup
      header='QuickChess'
      closePopup={this.togglePopup.bind(this)}
      body={<div>

        <p>This is a simple implementation of the classic board game,
        implemented in React. It supports all possible moves, including
        castling, and <em>en passant</em> (both explained below).</p>

        <p>At the moment there is no support for online play, or even a simple
        AI opponent, but both options are currently being examined.</p>

        <h2>Castling</h2>
        <p>Castling is a special move that allows a king and a rook to move at
        the same time, under certain circumstances:</p>
        <ul>
          <li>The king cannot be in check</li>
          <li>The space the king skips over cannot be in check</li>
          <li>The spaces between the king and the rook must be empty</li>
          <li>Neither the king nor the rook have already moved this game</li>
        </ul>
        <p>If these conditions are met, the king can move 2 spaces toward the
        rook, and the rook moves into the space the king skipped over.</p>

        <h2><em>En Passant</em></h2>

        <p>Most people know that a pawn can jump two spaces the first time
        it moves. <em>En passant</em> (French for "in passing") is a rare move
        that can counter such a double-jump.</p>

        <p>For example, say a white pawn double-jumps, and lands side-by-side
        with a black pawn. That black pawn can then move into the space that
        was jumped over (right behind the white pawn), and capture its
        enemy!</p>

        <p>It's not useful every game, but is very powerful in the right
        situation!</p>

        <h2>Settings</h2>
        <div className="settings-buttons">{
          getAllSettings().map(setting => {
            return (
              <div>
              <button onClick={this.toggleSetting.bind(this, setting)}>
                {
                  settingText(setting) +
                  (this.getSetting(setting) ? " On" : " Off")
                }
              </button>
              </div>
            );
          })
        }</div>

        <p><em>Assets have been borrowed from Wikipedia.</em></p>

        <div style={{float: "right", marginBottom: "0.5em"}}>
          <button onClick={this.doReset.bind(this)}>Reset Game</button>
          <span> </span>
          <button onClick={this.togglePopup.bind(this)}>Close</button>
        </div>

      </div>}
      />
      : null
    );
  }

  /* Board class can't (always) include a settings button if used as a demo. */
  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>
        <div className="status">
          <h1 style={{display: "inline-block", margin: "0"}}>{status}</h1>
          <img
            className="icon"
            alt="Settings icon: a gear"
            style={{height: "2em", float: "right", }}
            src="./gear.svg" onClick={this.togglePopup.bind(this)}>
          </img>
        </div>
        <div>
          {range(8).map(n => this.row(n))}
        </div>
        {this.renderPopup()}
      </div>
    );
  }
}

export default Board;
export {Piece};
export { BLACK, WHITE, PAWN, ROOK, KNIGHT, BISHOP, QUEEN, KING, EMPTY };