Artificial-Intelligence-Nanodegree/Term-I – AI Foundations/02 - Game Playing Agent/isoviz/js/chessboard.js

/*!
 * chessboard.js v0.3.0
 *
 * Copyright 2013 Chris Oakman
 * Released under the MIT license
 * http://chessboardjs.com/license
 *
 * Date: 10 Aug 2013
 */

// start anonymous scope
;(function() {
'use strict';

//------------------------------------------------------------------------------
// Chess Util Functions
//------------------------------------------------------------------------------
var COLUMNS = 'abcdefg'.split('');

function validMove(move) {
  // move should be a string
  if (typeof move !== 'string') return false;

  // move should be in the form of "e2-e4", "f6-d5"
  var tmp = move.split('-');
  if (tmp.length !== 2) return false;

  return (validSquare(tmp[0]) === true && validSquare(tmp[1]) === true);
}

function validSquare(square) {
  if (typeof square !== 'string') return false;
  return (square.search(/^[a-h][1-7]$/) !== -1);
}

function validPieceCode(code) {
  if (typeof code !== 'string') return false;
  return (code.search(/^[bw][N]$/) !== -1);
}

// TODO: this whole function could probably be replaced with a single regex
function validFen(fen) {
  if (typeof fen !== 'string') return false;

  // cut off any move, castling, etc info from the end
  // we're only interested in position information
  fen = fen.replace(/ .+$/, '');

  // FEN should be 8 sections separated by slashes
  var chunks = fen.split('/');
  if (chunks.length !== 7) return false;

  // check the piece sections
  for (var i = 0; i < 7; i++) {
    if (chunks[i] === '' ||
        chunks[i].length > 7 ||
        chunks[i].search(/[^nN1-7]/) !== -1) {
      return false;
    }
  }

  return true;
}

function validPositionObject(pos) {
  if (typeof pos !== 'object') return false;

  for (var i in pos) {
    if (pos.hasOwnProperty(i) !== true) continue;

    if (validSquare(i) !== true || validPieceCode(pos[i]) !== true) {
      return false;
    }
  }

  return true;
}

// convert FEN piece code to bP, wK, etc
function fenToPieceCode(piece) {
  // black piece
  if (piece.toLowerCase() === piece) {
    return 'b' + piece.toUpperCase();
  }

  // white piece
  return 'w' + piece.toUpperCase();
}

// convert bP, wK, etc code to FEN structure
function pieceCodeToFen(piece) {
  var tmp = piece.split('');

  // white piece
  if (tmp[0] === 'w') {
    return tmp[1].toUpperCase();
  }

  // black piece
  return tmp[1].toLowerCase();
}

// convert FEN string to position object
// returns false if the FEN string is invalid
function fenToObj(fen) {
  if (validFen(fen) !== true) {
    return false;
  }

  // cut off any move, castling, etc info from the end
  // we're only interested in position information
  fen = fen.replace(/ .+$/, '');

  var rows = fen.split('/');
  var position = {};

  var currentRow = 7;
  for (var i = 0; i < 7; i++) {
    var row = rows[i].split('');
    var colIndex = 0;

    // loop through each character in the FEN section
    for (var j = 0; j < row.length; j++) {
      // number / empty squares
      if (row[j].search(/[1-7]/) !== -1) {
        var emptySquares = parseInt(row[j], 10);
        colIndex += emptySquares;
      }
      // piece
      else {
        var square = COLUMNS[colIndex] + currentRow;
        position[square] = fenToPieceCode(row[j]);
        colIndex++;
      }
    }

    currentRow--;
  }

  return position;
}

// position object to FEN string
// returns false if the obj is not a valid position object
function objToFen(obj) {
  if (validPositionObject(obj) !== true) {
    return false;
  }

  var fen = '';

  var currentRow = 7;
  for (var i = 0; i < 7; i++) {
    for (var j = 0; j < 7; j++) {
      var square = COLUMNS[j] + currentRow;

      // piece exists
      if (obj.hasOwnProperty(square) === true) {
        fen += pieceCodeToFen(obj[square]);
      }

      // empty space
      else {
        fen += '1';
      }
    }

    if (i !== 6) {
      fen += '/';
    }

    currentRow--;
  }

  // squeeze the numbers together
  // haha, I love this solution...
  fen = fen.replace(/1111111/g, '7');
  fen = fen.replace(/111111/g, '6');
  fen = fen.replace(/11111/g, '5');
  fen = fen.replace(/1111/g, '4');
  fen = fen.replace(/111/g, '3');
  fen = fen.replace(/11/g, '2');

  return fen;
}

window['ChessBoard'] = window['ChessBoard'] || function(containerElOrId, cfg) {
'use strict';

cfg = cfg || {};

//------------------------------------------------------------------------------
// Constants
//------------------------------------------------------------------------------

var MINIMUM_JQUERY_VERSION = '1.7.0',
  START_FEN = '7/7/7/7/7/7/7/7',
  START_POSITION = fenToObj(START_FEN);

// use unique class names to prevent clashing with anything else on the page
// and simplify selectors
var CSS = {
  alpha: 'alpha-d2270',
  black: 'black-3c85d',
  board: 'board-b72b1',
  chessboard: 'chessboard-63f37',
  clearfix: 'clearfix-7da63',
  highlight1: 'highlight1-32417',
  highlight2: 'highlight2-9c5d2',
  notation: 'notation-322f9',
  numeric: 'numeric-fc462',
  piece: 'piece-417db',
  row: 'row-5277c',
  sparePieces: 'spare-pieces-7492f',
  sparePiecesBottom: 'spare-pieces-bottom-ae20f',
  sparePiecesTop: 'spare-pieces-top-4028b',
  square: 'square-55d63',
  white: 'white-1e1d7'
};

//------------------------------------------------------------------------------
// Module Scope Variables
//------------------------------------------------------------------------------

// DOM elements
var containerEl,
  boardEl,
  draggedPieceEl,
  sparePiecesTopEl,
  sparePiecesBottomEl;

// constructor return object
var widget = {};

//------------------------------------------------------------------------------
// Stateful
//------------------------------------------------------------------------------

var ANIMATION_HAPPENING = false,
  BOARD_BORDER_SIZE = 2,
  CURRENT_ORIENTATION = 'white',
  CURRENT_POSITION = {},
  SQUARE_SIZE,
  DRAGGED_PIECE,
  DRAGGED_PIECE_LOCATION,
  DRAGGED_PIECE_SOURCE,
  DRAGGING_A_PIECE = false,
  SPARE_PIECE_ELS_IDS = {},
  SQUARE_ELS_IDS = {},
  SQUARE_ELS_OFFSETS;

//------------------------------------------------------------------------------
// JS Util Functions
//------------------------------------------------------------------------------

// http://stackoverflow.com/questions/105034/how-to-create-a-guid-uuid-in-javascript
function createId() {
  return 'xxxx-xxxx-xxxx-xxxx-xxxx-xxxx-xxxx-xxxx'.replace(/x/g, function(c) {
    var r = Math.random() * 16 | 0;
    return r.toString(16);
  });
}

function deepCopy(thing) {
  return JSON.parse(JSON.stringify(thing));
}

function parseSemVer(version) {
  var tmp = version.split('.');
  return {
    major: parseInt(tmp[0], 10),
    minor: parseInt(tmp[1], 10),
    patch: parseInt(tmp[2], 10)
  };
}

// returns true if version is >= minimum
function compareSemVer(version, minimum) {
  version = parseSemVer(version);
  minimum = parseSemVer(minimum);

  var versionNum = (version.major * 10000 * 10000) +
    (version.minor * 10000) + version.patch;
  var minimumNum = (minimum.major * 10000 * 10000) +
    (minimum.minor * 10000) + minimum.patch;

  return (versionNum >= minimumNum);
}

//------------------------------------------------------------------------------
// Validation / Errors
//------------------------------------------------------------------------------

function error(code, msg, obj) {
  // do nothing if showErrors is not set
  if (cfg.hasOwnProperty('showErrors') !== true ||
      cfg.showErrors === false) {
    return;
  }

  var errorText = 'ChessBoard Error ' + code + ': ' + msg;

  // print to console
  if (cfg.showErrors === 'console' &&
      typeof console === 'object' &&
      typeof console.log === 'function') {
    console.log(errorText);
    if (arguments.length >= 2) {
      console.log(obj);
    }
    return;
  }

  // alert errors
  if (cfg.showErrors === 'alert') {
    if (obj) {
      errorText += '\n\n' + JSON.stringify(obj);
    }
    window.alert(errorText);
    return;
  }

  // custom function
  if (typeof cfg.showErrors === 'function') {
    cfg.showErrors(code, msg, obj);
  }
}

// check dependencies
function checkDeps() {
  // if containerId is a string, it must be the ID of a DOM node
  if (typeof containerElOrId === 'string') {
    // cannot be empty
    if (containerElOrId === '') {
      window.alert('ChessBoard Error 1001: ' +
        'The first argument to ChessBoard() cannot be an empty string.' +
        '\n\nExiting...');
      return false;
    }

    // make sure the container element exists in the DOM
    var el = document.getElementById(containerElOrId);
    if (! el) {
      window.alert('ChessBoard Error 1002: Element with id "' +
        containerElOrId + '" does not exist in the DOM.' +
        '\n\nExiting...');
      return false;
    }

    // set the containerEl
    containerEl = $(el);
  }

  // else it must be something that becomes a jQuery collection
  // with size 1
  // ie: a single DOM node or jQuery object
  else {
    containerEl = $(containerElOrId);

    if (containerEl.length !== 1) {
      window.alert('ChessBoard Error 1003: The first argument to ' +
        'ChessBoard() must be an ID or a single DOM node.' +
        '\n\nExiting...');
      return false;
    }
  }

  // JSON must exist
  if (! window.JSON ||
      typeof JSON.stringify !== 'function' ||
      typeof JSON.parse !== 'function') {
    window.alert('ChessBoard Error 1004: JSON does not exist. ' +
      'Please include a JSON polyfill.\n\nExiting...');
    return false;
  }

  // check for a compatible version of jQuery
  if (! (typeof window.$ && $.fn && $.fn.jquery &&
      compareSemVer($.fn.jquery, MINIMUM_JQUERY_VERSION) === true)) {
    window.alert('ChessBoard Error 1005: Unable to find a valid version ' +
      'of jQuery. Please include jQuery ' + MINIMUM_JQUERY_VERSION + ' or ' +
      'higher on the page.\n\nExiting...');
    return false;
  }

  return true;
}

function validAnimationSpeed(speed) {
  if (speed === 'fast' || speed === 'slow') {
    return true;
  }

  if ((parseInt(speed, 10) + '') !== (speed + '')) {
    return false;
  }

  return (speed >= 0);
}

// validate config / set default options
function expandConfig() {
  if (typeof cfg === 'string' || validPositionObject(cfg) === true) {
    cfg = {
      position: cfg
    };
  }

  // default for orientation is white
  if (cfg.orientation !== 'black') {
    cfg.orientation = 'white';
  }
  CURRENT_ORIENTATION = cfg.orientation;

  // default for showNotation is true
  if (cfg.showNotation !== false) {
    cfg.showNotation = true;
  }

  // default for draggable is false
  if (cfg.draggable !== true) {
    cfg.draggable = false;
  }

  // default for dropOffBoard is 'snapback'
  if (cfg.dropOffBoard !== 'trash') {
    cfg.dropOffBoard = 'snapback';
  }

  // default for sparePieces is false
  if (cfg.sparePieces !== true) {
    cfg.sparePieces = false;
  }

  // draggable must be true if sparePieces is enabled
  if (cfg.sparePieces === true) {
    cfg.draggable = true;
  }

  // default piece theme is wikipedia
  if (cfg.hasOwnProperty('pieceTheme') !== true ||
      (typeof cfg.pieceTheme !== 'string' &&
       typeof cfg.pieceTheme !== 'function')) {
    cfg.pieceTheme = 'img/chesspieces/wikipedia/{piece}.png';
  }

  // animation speeds
  if (cfg.hasOwnProperty('appearSpeed') !== true ||
      validAnimationSpeed(cfg.appearSpeed) !== true) {
    cfg.appearSpeed = 200;
  }
  if (cfg.hasOwnProperty('moveSpeed') !== true ||
      validAnimationSpeed(cfg.moveSpeed) !== true) {
    cfg.moveSpeed = 200;
  }
  if (cfg.hasOwnProperty('snapbackSpeed') !== true ||
      validAnimationSpeed(cfg.snapbackSpeed) !== true) {
    cfg.snapbackSpeed = 50;
  }
  if (cfg.hasOwnProperty('snapSpeed') !== true ||
      validAnimationSpeed(cfg.snapSpeed) !== true) {
    cfg.snapSpeed = 25;
  }
  if (cfg.hasOwnProperty('trashSpeed') !== true ||
      validAnimationSpeed(cfg.trashSpeed) !== true) {
    cfg.trashSpeed = 100;
  }

  // make sure position is valid
  if (cfg.hasOwnProperty('position') === true) {
    if (cfg.position === 'start') {
      CURRENT_POSITION = deepCopy(START_POSITION);
    }

    else if (validFen(cfg.position) === true) {
      CURRENT_POSITION = fenToObj(cfg.position);
    }

    else if (validPositionObject(cfg.position) === true) {
      CURRENT_POSITION = deepCopy(cfg.position);
    }

    else {
      error(7263, 'Invalid value passed to config.position.', cfg.position);
    }
  }

  return true;
}

//------------------------------------------------------------------------------
// DOM Misc
//------------------------------------------------------------------------------

// calculates square size based on the width of the container
// got a little CSS black magic here, so let me explain:
// get the width of the container element (could be anything), reduce by 1 for
// fudge factor, and then keep reducing until we find an exact mod 8 for
// our square size
function calculateSquareSize() {
  var containerWidth = parseInt(containerEl.css('width'), 10);

  // defensive, prevent infinite loop
  if (! containerWidth || containerWidth <= 0) {
    return 0;
  }

  // pad one pixel
  var boardWidth = containerWidth - 1;

  while (boardWidth % 7 !== 0 && boardWidth > 0) {
    boardWidth--;
  }

  return (boardWidth / 7);
}

// create random IDs for elements
function createElIds() {
  // squares on the board
  for (var i = 0; i < COLUMNS.length; i++) {
    for (var j = 1; j <= 7; j++) {
      var square = COLUMNS[i] + j;
      SQUARE_ELS_IDS[square] = square + '-' + createId();
    }
  }
}

//------------------------------------------------------------------------------
// Markup Building
//------------------------------------------------------------------------------

function buildBoardContainer() {
  var html = '<div class="' + CSS.chessboard + '">';

  html += '<div class="' + CSS.board + '"></div>';

  html += '</div>';

  return html;
}

/*
var buildSquare = function(color, size, id) {
  var html = '<div class="' + CSS.square + ' ' + CSS[color] + '" ' +
  'style="width: ' + size + 'px; height: ' + size + 'px" ' +
  'id="' + id + '">';

  if (cfg.showNotation === true) {

  }

  html += '</div>';

  return html;
};
*/

function buildBoard(orientation) {
  if (orientation !== 'black') {
    orientation = 'white';
  }

  var html = '';

  // algebraic notation / orientation
  var alpha = deepCopy(COLUMNS);
  var row = 7;
  if (orientation === 'black') {
    alpha.reverse();
    row = 1;
  }

  var squareColor = 'white';
  for (var i = 0; i < 7; i++) {
    html += '<div class="' + CSS.row + '">';
    for (var j = 0; j < 7; j++) {
      var square = alpha[j] + row;

      html += '<div class="' + CSS.square + ' ' + CSS[squareColor] + ' ' +
        'square-' + square + '" ' +
        'style="width: ' + SQUARE_SIZE + 'px; height: ' + SQUARE_SIZE + 'px" ' +
        'id="' + SQUARE_ELS_IDS[square] + '" ' +
        'data-square="' + square + '">';

      if (cfg.showNotation === true) {
        // alpha notation
        if ((orientation === 'white' && row === 1) ||
            (orientation === 'black' && row === 7)) {
          html += '<div class="' + CSS.notation + ' ' + CSS.alpha + '">' +
            '</div>';
        }

        // numeric notation
        if (j === 0) {
          html += '<div class="' + CSS.notation + ' ' + CSS.numeric + '">' +
            '</div>';
        }
      }

      html += '</div>'; // end .square

      squareColor = (squareColor === 'white' ? 'black' : 'white');
    }
    html += '<div class="' + CSS.clearfix + '"></div></div>';

    squareColor = (squareColor === 'white' ? 'white' : 'black');

    if (orientation === 'white') {
      row--;
    }
    else {
      row++;
    }
  }

  return html;
}

function buildPieceImgSrc(piece) {
  if (typeof cfg.pieceTheme === 'function') {
    return cfg.pieceTheme(piece);
  }

  if (typeof cfg.pieceTheme === 'string') {
    return cfg.pieceTheme.replace(/{piece}/g, piece);
  }

  // NOTE: this should never happen
  error(8272, 'Unable to build image source for cfg.pieceTheme.');
  return '';
}

function buildPiece(piece, hidden, id) {
  var html = '<img src="' + buildPieceImgSrc(piece) + '" ';
  if (id && typeof id === 'string') {
    html += 'id="' + id + '" ';
  }
  html += 'alt="" ' +
  'class="' + CSS.piece + '" ' +
  'data-piece="' + piece + '" ' +
  'style="width: ' + SQUARE_SIZE + 'px;' +
  'height: ' + SQUARE_SIZE + 'px;';
  if (hidden === true) {
    html += 'display:none;';
  }
  html += '" />';

  return html;
}

//------------------------------------------------------------------------------
// Animations
//------------------------------------------------------------------------------

function animateSquareToSquare(src, dest, piece, completeFn) {
  // get information about the source and destination squares
  var srcSquareEl = $('#' + SQUARE_ELS_IDS[src]);
  var srcSquarePosition = srcSquareEl.offset();
  var destSquareEl = $('#' + SQUARE_ELS_IDS[dest]);
  var destSquarePosition = destSquareEl.offset();

  // create the animated piece and absolutely position it
  // over the source square
  var animatedPieceId = createId();
  $('body').append(buildPiece(piece, true, animatedPieceId));
  var animatedPieceEl = $('#' + animatedPieceId);
  animatedPieceEl.css({
    display: '',
    position: 'absolute',
    top: srcSquarePosition.top,
    left: srcSquarePosition.left
  });

  // remove original piece from source square
  srcSquareEl.find('.' + CSS.piece).remove();

  // on complete
  var complete = function() {
    // add the "real" piece to the destination square
    destSquareEl.append(buildPiece(piece));

    // remove the animated piece
    animatedPieceEl.remove();

    // run complete function
    if (typeof completeFn === 'function') {
      completeFn();
    }
  };

  // animate the piece to the destination square
  var opts = {
    duration: cfg.moveSpeed,
    complete: complete
  };
  animatedPieceEl.animate(destSquarePosition, opts);
}

// execute an array of animations
function doAnimations(a, oldPos, newPos) {
  ANIMATION_HAPPENING = true;

  var numFinished = 0;
  function onFinish() {
    numFinished++;

    // exit if all the animations aren't finished
    if (numFinished !== a.length) return;

    drawPositionInstant();
    ANIMATION_HAPPENING = false;

    // run their onMoveEnd function
    if (cfg.hasOwnProperty('onMoveEnd') === true &&
      typeof cfg.onMoveEnd === 'function') {
      cfg.onMoveEnd(deepCopy(oldPos), deepCopy(newPos));
    }
  }

  for (var i = 0; i < a.length; i++) {
    // clear a piece
    if (a[i].type === 'clear') {
      $('#' + SQUARE_ELS_IDS[a[i].square] + ' .' + CSS.piece)
        .fadeOut(cfg.trashSpeed, onFinish);
    }

    // add a piece (no spare pieces)
    if (a[i].type === 'add' && cfg.sparePieces !== true) {
      $('#' + SQUARE_ELS_IDS[a[i].square])
        .append(buildPiece(a[i].piece, true))
        .find('.' + CSS.piece)
        .fadeIn(cfg.appearSpeed, onFinish);
    }

    // add a piece from a spare piece
    if (a[i].type === 'add' && cfg.sparePieces === true) {
      animateSparePieceToSquare(a[i].piece, a[i].square, onFinish);
    }

    // move a piece
    if (a[i].type === 'move') {
      animateSquareToSquare(a[i].source, a[i].destination, a[i].piece,
        onFinish);
    }
  }
}

// returns the distance between two squares
function squareDistance(s1, s2) {
  s1 = s1.split('');
  var s1x = COLUMNS.indexOf(s1[0]) + 1;
  var s1y = parseInt(s1[1], 10);

  s2 = s2.split('');
  var s2x = COLUMNS.indexOf(s2[0]) + 1;
  var s2y = parseInt(s2[1], 10);

  var xDelta = Math.abs(s1x - s2x);
  var yDelta = Math.abs(s1y - s2y);

  if (xDelta >= yDelta) return xDelta;
  return yDelta;
}

// returns an array of closest squares from square
function createRadius(square) {
  var squares = [];

  // calculate distance of all squares
  for (var i = 0; i < 7; i++) {
    for (var j = 0; j < 7; j++) {
      var s = COLUMNS[i] + (j + 1);

      // skip the square we're starting from
      if (square === s) continue;

      squares.push({
        square: s,
        distance: squareDistance(square, s)
      });
    }
  }

  // sort by distance
  squares.sort(function(a, b) {
    return a.distance - b.distance;
  });

  // just return the square code
  var squares2 = [];
  for (var i = 0; i < squares.length; i++) {
    squares2.push(squares[i].square);
  }

  return squares2;
}

// returns the square of the closest instance of piece
// returns false if no instance of piece is found in position
function findClosestPiece(position, piece, square) {
  // create array of closest squares from square
  var closestSquares = createRadius(square);

  // search through the position in order of distance for the piece
  for (var i = 0; i < closestSquares.length; i++) {
    var s = closestSquares[i];

    if (position.hasOwnProperty(s) === true && position[s] === piece) {
      return s;
    }
  }

  return false;
}

// calculate an array of animations that need to happen in order to get
// from pos1 to pos2
function calculateAnimations(pos1, pos2) {
  // make copies of both
  pos1 = deepCopy(pos1);
  pos2 = deepCopy(pos2);

  var animations = [];
  var squaresMovedTo = {};

  // remove pieces that are the same in both positions
  for (var i in pos2) {
    if (pos2.hasOwnProperty(i) !== true) continue;

    if (pos1.hasOwnProperty(i) === true && pos1[i] === pos2[i]) {
      delete pos1[i];
      delete pos2[i];
    }
  }

  // find all the "move" animations
  for (var i in pos2) {
    if (pos2.hasOwnProperty(i) !== true) continue;

    var closestPiece = findClosestPiece(pos1, pos2[i], i);
    if (closestPiece !== false) {
      animations.push({
        type: 'move',
        source: closestPiece,
        destination: i,
        piece: pos2[i]
      });

      delete pos1[closestPiece];
      delete pos2[i];
      squaresMovedTo[i] = true;
    }
  }

  // add pieces to pos2
  for (var i in pos2) {
    if (pos2.hasOwnProperty(i) !== true) continue;

    animations.push({
      type: 'add',
      square: i,
      piece: pos2[i]
    })

    delete pos2[i];
  }

  // clear pieces from pos1
  for (var i in pos1) {
    if (pos1.hasOwnProperty(i) !== true) continue;

    // do not clear a piece if it is on a square that is the result
    // of a "move", ie: a piece capture
    if (squaresMovedTo.hasOwnProperty(i) === true) continue;

    animations.push({
      type: 'clear',
      square: i,
      piece: pos1[i]
    });

    delete pos1[i];
  }

  return animations;
}

//------------------------------------------------------------------------------
// Control Flow
//------------------------------------------------------------------------------

function drawPositionInstant() {
  // clear the board
  boardEl.find('.' + CSS.piece).remove();

  // add the pieces
  for (var i in CURRENT_POSITION) {
    if (CURRENT_POSITION.hasOwnProperty(i) !== true) continue;

    $('#' + SQUARE_ELS_IDS[i]).append(buildPiece(CURRENT_POSITION[i]));
  }
}

function drawBoard() {
  boardEl.html(buildBoard(CURRENT_ORIENTATION));
  drawPositionInstant();
}

// given a position and a set of moves, return a new position
// with the moves executed
function calculatePositionFromMoves(position, moves) {
  position = deepCopy(position);

  for (var i in moves) {
    if (moves.hasOwnProperty(i) !== true) continue;

    // skip the move if the position doesn't have a piece on the source square
    if (position.hasOwnProperty(i) !== true) continue;

    var piece = position[i];
    delete position[i];
    position[moves[i]] = piece;
  }

  return position;
}

function setCurrentPosition(position) {
  var oldPos = deepCopy(CURRENT_POSITION);
  var newPos = deepCopy(position);
  var oldFen = objToFen(oldPos);
  var newFen = objToFen(newPos);

  // do nothing if no change in position
  if (oldFen === newFen) return;

  // run their onChange function
  if (cfg.hasOwnProperty('onChange') === true &&
    typeof cfg.onChange === 'function') {
    cfg.onChange(oldPos, newPos);
  }

  // update state
  CURRENT_POSITION = position;
}

function isXYOnSquare(x, y) {
  for (var i in SQUARE_ELS_OFFSETS) {
    if (SQUARE_ELS_OFFSETS.hasOwnProperty(i) !== true) continue;

    var s = SQUARE_ELS_OFFSETS[i];
    if (x >= s.left && x < s.left + SQUARE_SIZE &&
        y >= s.top && y < s.top + SQUARE_SIZE) {
      return i;
    }
  }

  return 'offboard';
}

// records the XY coords of every square into memory
function captureSquareOffsets() {
  SQUARE_ELS_OFFSETS = {};

  for (var i in SQUARE_ELS_IDS) {
    if (SQUARE_ELS_IDS.hasOwnProperty(i) !== true) continue;

    SQUARE_ELS_OFFSETS[i] = $('#' + SQUARE_ELS_IDS[i]).offset();
  }
}

function removeSquareHighlights() {
  boardEl.find('.' + CSS.square)
    .removeClass(CSS.highlight1 + ' ' + CSS.highlight2);
}

//------------------------------------------------------------------------------
// Public Methods
//------------------------------------------------------------------------------

// clear the board
widget.clear = function(useAnimation) {
  widget.position({}, useAnimation);
};

/*
// get or set config properties
// TODO: write this, GitHub Issue #1
widget.config = function(arg1, arg2) {
  // get the current config
  if (arguments.length === 0) {
    return deepCopy(cfg);
  }
};
*/

// remove the widget from the page
widget.destroy = function() {
  // remove markup
  containerEl.html('');
  draggedPieceEl.remove();

  // remove event handlers
  containerEl.unbind();
};

// flip orientation
widget.flip = function() {
  widget.orientation('flip');
};

/*
// TODO: write this, GitHub Issue #5
widget.highlight = function() {

};
*/

// move pieces
widget.move = function() {
  // no need to throw an error here; just do nothing
  if (arguments.length === 0) return;

  var useAnimation = true;

  // collect the moves into an object
  var moves = {};
  for (var i = 0; i < arguments.length; i++) {
    // any "false" to this function means no animations
    if (arguments[i] === false) {
      useAnimation = false;
      continue;
    }

    // skip invalid arguments
    if (validMove(arguments[i]) !== true) {
      error(2826, 'Invalid move passed to the move method.', arguments[i]);
      continue;
    }

    var tmp = arguments[i].split('-');
    moves[tmp[0]] = tmp[1];
  }

  // calculate position from moves
  var newPos = calculatePositionFromMoves(CURRENT_POSITION, moves);

  // update the board
  widget.position(newPos, useAnimation);

  // block the square
  for (var m in moves) {
    var el = document.getElementById(SQUARE_ELS_IDS[m]);
    el.classList.add("blocked");
  }
  
  // return the new position object
  return newPos;
};

widget.position = function(position, useAnimation) {
  // no arguments, return the current position
  if (arguments.length === 0) {
    return deepCopy(CURRENT_POSITION);
  }

  // get position as FEN
  if (typeof position === 'string' && position.toLowerCase() === 'fen') {
    return objToFen(CURRENT_POSITION);
  }

  // default for useAnimations is true
  if (useAnimation !== false) {
    useAnimation = true;
  }

  // start position
  if (typeof position === 'string' && position.toLowerCase() === 'start') {
    position = deepCopy(START_POSITION);
  }

  // convert FEN to position object
  if (validFen(position) === true) {
    position = fenToObj(position);
  }

  // validate position object
  if (validPositionObject(position) !== true) {
    error(6482, 'Invalid value passed to the position method.', position);
    return;
  }

  if (useAnimation === true) {
    // start the animations
    doAnimations(calculateAnimations(CURRENT_POSITION, position),
      CURRENT_POSITION, position);

    // set the new position
    setCurrentPosition(position);
  }
  // instant update
  else {
    setCurrentPosition(position);
    drawPositionInstant();
  }
};

widget.resize = function() {
  // calulate the new square size
  SQUARE_SIZE = calculateSquareSize();

  // set board width
  boardEl.css('width', (SQUARE_SIZE * 7) + 'px');

  // redraw the board
  drawBoard();
};

widget.finalize = function(winCell, lossCell) {

  var el;
  
  el = document.getElementById(SQUARE_ELS_IDS[winCell]);
  el.classList.add("win");

  el = document.getElementById(SQUARE_ELS_IDS[lossCell]);
  el.classList.add("lose");
};

// set the starting position
widget.start = function(useAnimation) {
  widget.position('start', useAnimation);
};

//------------------------------------------------------------------------------
// Browser Events
//------------------------------------------------------------------------------


function stopDefault(e) {
  e.preventDefault();
}

//------------------------------------------------------------------------------
// Initialization
//------------------------------------------------------------------------------

function initDom() {
  // build board and save it in memory
  containerEl.html(buildBoardContainer());
  boardEl = containerEl.find('.' + CSS.board);

  // get the border size
  BOARD_BORDER_SIZE = parseInt(boardEl.css('borderLeftWidth'), 10);

  // set the size and draw the board
  widget.resize();
}

function init() {
  if (checkDeps() !== true ||
      expandConfig() !== true) return;

  // create unique IDs for all the elements we will create
  createElIds();

  initDom();
}

// go time
init();

// return the widget object
return widget;

}; // end window.ChessBoard

// expose util functions
window.ChessBoard.fenToObj = fenToObj;
window.ChessBoard.objToFen = objToFen;

})(); // end anonymous wrapper