git.sesse.net Git - remoteglot-book/blob - www/js/book.js

   1 (function() {
   2
   3 var board = null;
   4 var game = new Chess();
   5 var fens = [];  // Position after each.
   6 var move_override = 0;
   7 var includetransp = true;
   8 var stockfish = new Worker('/js/stockfish.js');
   9 var engine_running = false;
  10 var engine_replacement_callback = null;
  11 var recommended_move = null;
  12 var reverse_dragging_from = null;
  13 var practice_mode = false;
  14 var practice_side = 'W';
  15
  16 // TODO: Make this configurable.
  17 var practice_top_moves_limit = 5;
  18 var practice_minimum_move_fraction_start = 0.05;
  19 var practice_minimum_move_fraction_move5 = 0.30;
  20
  21 var entity_map = {
  22         "&": "&amp;",
  23         "<": "&lt;",
  24         ">": "&gt;",
  25         '"': '&quot;',
  26         "'": '&#39;',
  27 };
  28
  29 function escape_html(string) {
  30         return String(string).replace(/[&<>"']/g, function (s) {
  31                 return entity_map[s];
  32         });
  33 }
  34
  35 var current_display_fen = function() {
  36         return fen_before_move(move_override);
  37 }
  38
  39 var fen_before_move = function(move_num) {
  40         if (move_num == 0) {
  41                 return 'rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1';
  42         } else {
  43                 return fens[move_num - 1];
  44         }
  45 }
  46
  47 var update = function() {
  48         var text = "";
  49         var history = game.history({ verbose: true });
  50         for (var i = 0; i < history.length; ++i) {
  51                 if (i % 2 == 0) {
  52                         text += (i/2 + 1) + ". ";
  53                 }
  54                 if (i + 1 == move_override) {
  55                         text += '<strong>' + history[i].san + '</strong>';
  56                 } else {
  57                         text += '<a href="javascript:set_move(' + (i + 1) + ')">' + history[i].san + '</a>';
  58                 }
  59                 text += " ";
  60         }
  61         $('#gamehistory').html(text);
  62
  63         if (board.fen() != current_display_fen()) {
  64                 board.position(current_display_fen());
  65         }
  66
  67         $("#board").find('.square-55d63').removeClass('nonuglyhighlight');
  68         if (move_override > 0) {
  69                 var last_move = history[move_override - 1];
  70                 var highlight_from = last_move.from;
  71                 var highlight_to = last_move.to;
  72                 $("#board").find('.square-' + highlight_from).addClass('nonuglyhighlight');
  73                 $("#board").find('.square-' + highlight_to).addClass('nonuglyhighlight');
  74         }
  75
  76         if (practice_mode) {
  77                 find_last_move_score();
  78                 var side_to_move = (move_override % 2 == 0) ? 'W' : 'B';
  79                 if (side_to_move !== practice_side) {
  80                         find_computer_move();
  81                 }
  82                 // Fall through to get the line name and such.
  83         }
  84
  85         fetch_analysis();
  86 }
  87
  88 var get_history_url = function() {
  89         var history = game.history({ verbose: true }).map(function(x) { return x.san; });
  90         history.length = move_override;
  91         return '/?' + history.join(',');
  92 }
  93
  94 var fetch_analysis = function() {
  95         var fen = current_display_fen();
  96         $.ajax({
  97                 url: "/opening-stats.pl?fen=" + encodeURIComponent(fen) +
  98                         ";includetransp=" + (includetransp ? 1 : 0)
  99         }).done(function(data, textstatus, xhr) {
 100                 show_lines(data, game);
 101         });
 102 }
 103
 104 var find_last_move_score = function() {
 105         var history = game.history({ verbose: true });
 106         var side_to_move = (move_override % 2 == 0) ? 'W' : 'B';
 107         var move_num = (side_to_move === practice_side) ? (move_override - 2) : (move_override - 1);
 108         if (move_num < 0) {
 109                 $("#yourmove").text("(none)");
 110                 $("#yourfraction").text("N/A");
 111                 $("#yourrank").text("N/A");
 112                 $("#yourawin").text("??.?%");
 113                 $("#yourawindiff").text("+?.?%");
 114                 return;
 115         }
 116
 117         var chosen_move = history[move_num].san;
 118         $("#yourmove").text(chosen_move);
 119         $.ajax({
 120                 url: "/opening-stats.pl?fen=" + encodeURIComponent(fen_before_move(move_num)) +
 121                         ";includetransp=0"
 122         }).done(function(data, textstatus, xhr) {
 123                 var moves = data['moves'];
 124                 var root_move = sort_move_by_frequency(moves, data);
 125                 var your_move, your_index;
 126
 127                 for (var i = 0; i < moves.length; ++i) {
 128                         var move = moves[i];
 129                         if (move['move'] === chosen_move) {
 130                                 your_move = move;
 131                                 your_index = i;
 132                         }
 133                 }
 134
 135                 if (your_move) {
 136                         $("#yourfraction").text(format_fraction(your_move['fraction']));
 137                         $("#yourawin").text(format_fraction(your_move['corrected_win_ratio']));
 138                         $("#yourrank").text(format_ordinal(your_index + 1) + ", based on " + root_move['num'] + " games");
 139                         var diff = your_move['corrected_win_ratio'] - root_move['corrected_win_ratio'];
 140                         $("#yourawindiff").css("color", "black");
 141                         if (diff === 0) {
 142                                 $("#yourawindiff").text("0.0%");
 143                         } else if (diff > 0) {
 144                                 $("#yourawindiff").text("+" + format_fraction(diff));
 145                                 $("#yourawindiff").css("color", "green");
 146                         } else {
 147                                 $("#yourawindiff").text(format_fraction(diff));
 148                                 if (diff < -0.02) {
 149                                         $("#yourawindiff").css("color", "red");
 150                                 }
 151                         }
 152                 } else {
 153                         $("#yourfraction").text("??.?%");
 154                         $("#yourrank").text("?th");
 155                         $("#yourawin").text("??.?%");
 156                         $("#yourawindiff").text("+?.?%");
 157                 }
 158         });
 159 }
 160
 161 var candidate_moves = [];
 162 var chosen_index = null;
 163
 164 var find_computer_move = function() {
 165         var fen = current_display_fen();
 166         $.ajax({
 167                 url: "/opening-stats.pl?fen=" + encodeURIComponent(fen) + ";includetransp=0"
 168         }).done(function(data, textstatus, xhr) {
 169                 candidate_moves = [];
 170
 171                 var moves = data['moves'];
 172                 var root_move = sort_move_by_frequency(moves, data);
 173
 174                 var practice_minimum_move_fraction;
 175                 if (move_override > 20) {
 176                         practice_minimum_move_fraction = practice_minimum_move_fraction_move5;
 177                 } else {
 178                         practice_minimum_move_fraction = practice_minimum_move_fraction_start +
 179                                 ((move_override-1)/10.0) * (practice_minimum_move_fraction_move5 - practice_minimum_move_fraction_start);
 180                 }
 181                 console.log(practice_minimum_move_fraction);
 182
 183                 for (var i = 0; i < Math.min(moves.length, practice_top_moves_limit); ++i) {
 184                         var move = moves[i];
 185                         if (i == 0 || move['fraction'] >= practice_minimum_move_fraction) {
 186                                 candidate_moves.push(move);
 187                         }
 188                 }
 189
 190                 // Pick one at random.
 191                 choose_move(Math.floor(Math.random() * candidate_moves.length));
 192         });
 193 }
 194
 195 var choose_move = function(idx) {
 196         chosen_index = idx;
 197         var chosen = candidate_moves[chosen_index];
 198         $("#compmove").text(chosen['move']);
 199         $("#compfraction").text((100.0 * chosen['fraction']).toFixed(1) + "%");
 200         if (candidate_moves.length == 1) {
 201                 $("#comprank").text("only candidate move");
 202         } else {
 203                 $("#comprank").text(format_ordinal(chosen_index + 1) + " out of " + candidate_moves.length + " candidate moves, j/k to switch");
 204         }
 205         make_move(chosen['move']);
 206 }
 207
 208 var prev_variant = function() {
 209         if (chosen_index !== null) {
 210                 --move_override;
 211                 choose_move((chosen_index + candidate_moves.length - 1) % candidate_moves.length);
 212         }
 213 }
 214
 215 var next_variant = function() {
 216         if (chosen_index !== null) {
 217                 --move_override;
 218                 choose_move((chosen_index + 1) % candidate_moves.length);
 219         }
 220 }
 221
 222 // Add deried data and then sort moves to get the most common ones (in-place).
 223 // Remove the root mode and return it. Currently usable for practice mode only!
 224 var sort_move_by_frequency = function(moves, data)
 225 {
 226         var total_num = find_total_games(moves);
 227         var root_move;
 228         for (var i = 0; i < moves.length; ++i) {
 229                 var move = moves[i];
 230                 calc_move_derived_data(move, total_num, data, (practice_side === 'W'));
 231                 if (!move['move']) {
 232                         root_move = (moves.splice(i, 1))[0];
 233                         --i;
 234                 }
 235         }
 236         moves.sort(function(a, b) { return b['num'] - a['num'] });
 237         return root_move;
 238 }
 239
 240 var add_td = function(tr, value) {
 241         var td = document.createElement("td");
 242         tr.appendChild(td);
 243         $(td).addClass("num");
 244         $(td).text(value);
 245 }
 246
 247 var format_ordinal = function(x) {
 248         var tens = Math.floor(x / 10) % 10;
 249         if (tens == 1) {
 250                 return x + "th";
 251         } else {
 252                 var ones = x % 10;
 253                 if (ones == 1) return x + "st";
 254                 if (ones == 2) return x + "nd";
 255                 if (ones == 3) return x + "rd";
 256                 return x + "th";
 257         }
 258 }
 259
 260 var format_fraction = function(x) {
 261         return (100.0 * x).toFixed(1) + '%';
 262 }
 263
 264 var TYPE_MOVE = 0;
 265 var TYPE_INTEGER = 1;
 266 var TYPE_FLOAT = 2;
 267 var TYPE_RATIO = 3;
 268
 269 var headings = [
 270         [ "Move", TYPE_MOVE ],
 271         [ "Games", TYPE_INTEGER ],
 272         [ "%", TYPE_RATIO ],
 273         [ "CGames", TYPE_INTEGER ],
 274         [ "Hum", TYPE_RATIO ],
 275         [ "Win%", TYPE_RATIO ],
 276         [ "WWin", TYPE_INTEGER ],
 277         [ "%WW", TYPE_RATIO ],
 278         [ "Bwin", TYPE_INTEGER ],
 279         [ "%BW", TYPE_RATIO ],
 280         [ "Draw", TYPE_INTEGER ],
 281         [ "Draw%", TYPE_RATIO ],
 282         [ "AvWElo", TYPE_FLOAT ],
 283         [ "AvBElo", TYPE_FLOAT ],
 284         [ "EloVar", TYPE_FLOAT ],
 285         [ "AWin%", TYPE_RATIO ],
 286 ];
 287 var sort_by = 1;
 288 var direction = 1;
 289
 290 var show_lines = function(data, game) {
 291         var moves = data['moves'];
 292         $('#numviewers').text(data['opening']);
 293
 294         if (data['root_game']) {
 295                 var text = escape_html(data['root_game']['white']);
 296                 if (data['root_game']['white_elo']) {
 297                         text += " (" + escape_html(data['root_game']['white_elo']) + ")";
 298                 }
 299                 text += " &ndash; " + escape_html(data['root_game']['black']);
 300                 if (data['root_game']['black_elo']) {
 301                         text += " (" + escape_html(data['root_game']['black_elo']) + ")";
 302                 }
 303                 text += " &nbsp;" + escape_html(data['root_game']['result']).replace(/-/, "&ndash;") + "<br />";
 304                 if (data['root_game']['eco']) {
 305                         text += "[" + escape_html(data['root_game']['eco']) + "] ";
 306                 }
 307                 text += "(" + data['root_game']['moves'] + ") ";
 308                 text += escape_html(data['root_game']['event']) + " &nbsp;" + escape_html(data['root_game']['date']);
 309                 $('#gamesummary').html(text);
 310         }
 311
 312         var total_num = find_total_games(moves);
 313
 314         var headings_tr = $("#headings");
 315         headings_tr.empty();
 316         for (var i = 0; i < headings.length; ++i) {
 317                 var th = document.createElement("th");
 318                 headings_tr.append(th);
 319                 $(th).text(headings[i][0]);
 320                 (function(new_sort_by) {
 321                         $(th).click(function() {
 322                                 if (sort_by == new_sort_by) {
 323                                         direction = -direction;
 324                                 } else {
 325                                         sort_by = new_sort_by;
 326                                         direction = 1;
 327                                 }
 328                                 show_lines(data, game);
 329                         });
 330                 })(i);
 331         }
 332
 333         var lines = [];
 334         var transpose_only = [];
 335         for (var i = 0; i < moves.length; ++i) {
 336                 var move = moves[i];
 337                 var line = [];
 338
 339                 calc_move_derived_data(move, total_num, data, (move_override % 2 == 0));
 340
 341                 var white = move['white'];
 342                 var draw = move['draw'];
 343                 var black = move['black'];
 344                 var computer = move['computer'];
 345
 346                 line.push(move['move']);  // Move.
 347                 transpose_only.push(move['transpose_only']);
 348                 line.push(move['num']);  // N.
 349                 line.push(move['fraction']);  // %.
 350                 line.push(computer);  // CGames.
 351                 line.push(move['human_index']);  // Hum.
 352                 line.push(move['win_ratio']);  // Win%.
 353
 354                 line.push(white);                // WWin.
 355                 line.push(white / move['num']);  // %WW.
 356                 line.push(black);                // BWin.
 357                 line.push(black / move['num']);  // %BW.
 358                 line.push(draw);                 // Draw.
 359                 line.push(draw / move['num']);   // %Draw.
 360
 361                 if (move['num_elo'] >= 10) {
 362                         // Elo.
 363                         line.push(move['white_avg_elo']);
 364                         line.push(move['black_avg_elo']);
 365                         line.push(move['white_avg_elo'] - move['black_avg_elo']);
 366                 } else {
 367                         line.push(null);
 368                         line.push(null);
 369                         line.push(null);
 370                 }
 371
 372                 line.push(move['corrected_win_ratio'] || null);
 373                 lines.push(line);
 374         }
 375
 376         lines.sort(function(a, b) { return direction * ( b[sort_by] - a[sort_by]); });
 377
 378         var tbl = $("#lines");
 379         tbl.empty();
 380
 381         for (var i = 0; i < moves.length; ++i) {
 382                 var line = lines[i];
 383                 var tr = document.createElement("tr");
 384
 385                 if (line[0] === undefined) {
 386                         $(tr).addClass("totals");
 387                 } else if (transpose_only[i]) {
 388                         $(tr).addClass("transponly");
 389                 }
 390
 391                 for (var j = 0; j < line.length; ++j) {
 392                         if (line[j] === null) {
 393                                 add_td(tr, "");
 394                         } else if (headings[j][1] == TYPE_MOVE) {
 395                                 var td = document.createElement("td");
 396                                 tr.appendChild(td);
 397                                 $(td).addClass("move");
 398                                 if (line[j] !== undefined) {
 399                                         if (move_override % 2 == 0) {
 400                                                 $(td).text(((move_override / 2) + 1) + ". ");
 401                                         } else {
 402                                                 $(td).text(((move_override / 2) + 0.5) + "…");
 403                                         }
 404                                 }
 405
 406                                 if (line[j] === '1-0' || line[j] === '1/2-1/2' || line[j] === '0-1') {
 407                                         $(td).text($(td).text() + line[j]);
 408                                 } else {
 409                                         var move_a = document.createElement("a");
 410                                         move_a.href = "javascript:make_move('" + line[j] + "')";
 411                                         td.appendChild(move_a);
 412                                         $(move_a).text(line[j]);
 413                                 }
 414                         } else if (headings[j][1] == TYPE_INTEGER) {
 415                                 add_td(tr, line[j] || 0);
 416                         } else if (headings[j][1] == TYPE_FLOAT) {
 417                                 if (isNaN(line[j]) || !isFinite(line[j])) {
 418                                         add_td(tr, '');
 419                                 } else {
 420                                         add_td(tr, line[j].toFixed(1));
 421                                 }
 422                         } else {
 423                                 if (isNaN(line[j]) || !isFinite(line[j])) {
 424                                         add_td(tr, '');
 425                                 } else {
 426                                         add_td(tr, format_fraction(line[j]));
 427                                 }
 428                         }
 429                 }
 430
 431                 tbl.append(tr);
 432         }
 433 }
 434
 435 var find_total_games = function(moves) {
 436         var total_num = 0;
 437         for (var i = 0; i < moves.length; ++i) {
 438                 var move = moves[i];
 439                 if (move['move']) {
 440                         total_num += move['white'];
 441                         total_num += move['draw'];
 442                         total_num += move['black'];
 443                 }
 444         }
 445         return total_num;
 446 }
 447
 448 var calc_move_derived_data = function(move, total_num, data, is_white) {
 449         var white = move['white'];
 450         var draw = move['draw'];
 451         var black = move['black'];
 452         var computer = move['computer'];
 453
 454         var num = white + draw + black;
 455         move['num'] = num;
 456         move['fraction'] = num / total_num;
 457
 458         // Adjust so that the human index is 50% overall.
 459         var exp = Math.log(0.5) / Math.log(data['computer_games'] / data['total_games']);
 460         move['human_index'] = 1.0 - Math.pow(computer / num, exp);
 461
 462         // Win%.
 463         var white_win_ratio = (white + 0.5 * draw) / num;
 464         var win_ratio = is_white ? white_win_ratio : 1.0 - white_win_ratio;
 465         move['win_ratio'] = win_ratio;
 466
 467         if (move['num_elo'] >= 10) {
 468                 // Win% corrected for Elo.
 469                 var win_elo = -400.0 * Math.log(1.0 / white_win_ratio - 1.0) / Math.LN10;
 470                 win_elo -= (move['white_avg_elo'] - move['black_avg_elo']);
 471                 white_win_ratio = 1.0 / (1.0 + Math.pow(10, win_elo / -400.0));
 472                 win_ratio = is_white ? white_win_ratio : 1.0 - white_win_ratio;
 473                 move['corrected_win_ratio'] = win_ratio;
 474         }
 475 };
 476
 477 var set_includetransp = function(value) {
 478         includetransp = value;
 479         update();
 480 }
 481 window['set_includetransp'] = set_includetransp;
 482
 483 var set_flipboard = function(value) {
 484         board.orientation(value ? 'black' : 'white');
 485 }
 486 window['set_flipboard'] = set_flipboard;
 487
 488 var set_practice = function(value) {
 489         practice_mode = value;
 490         if (practice_mode) {
 491                 practice_side = (move_override % 2 == 0) ? 'W' : 'B';
 492                 find_last_move_score();
 493                 $("#stats").hide();
 494                 $("#practiceoutput").show();
 495                 document.getElementById("includetransp").checked = false;
 496                 set_includetransp(false);
 497         } else {
 498                 $("#stats").show();
 499                 $("#practiceoutput").hide();
 500         }
 501         update();
 502 }
 503 window['set_practice'] = set_practice;
 504
 505 var make_move = function(move, do_update) {
 506         var history = game.history({ verbose: true });
 507         if (move_override < history.length && history[move_override].san == move) {
 508                 // User effectively only moved forward in history.
 509                 ++move_override;
 510         } else {
 511                 var moves = game.history();
 512                 // Truncate the history if needed.
 513                 if (move_override < moves.length) {
 514                         game = new Chess();
 515                         for (var i = 0; i < move_override; ++i) {
 516                                 game.move(moves[i]);
 517                         }
 518                         fens.length = move_override;
 519                 }
 520                 game.move(move);
 521                 fens.push(game.fen());
 522                 ++move_override;
 523         }
 524
 525         if (do_update !== false) {
 526                 update();
 527                 window.history.pushState(null, null, get_history_url());
 528         }
 529 }
 530 window['make_move'] = make_move;
 531
 532 var prev_move = function() {
 533         var moves_to_skip = practice_mode ? 2 : 1;
 534         if (move_override >= moves_to_skip) {
 535                 move_override -= moves_to_skip;
 536                 update();
 537                 window.history.replaceState(null, null, get_history_url());
 538         }
 539 }
 540 window['prev_move'] = prev_move;
 541
 542 var next_move = function() {
 543         if (move_override < game.history().length) {
 544                 ++move_override;
 545                 update();
 546                 window.history.replaceState(null, null, get_history_url());
 547         }
 548 }
 549 window['next_move'] = next_move;
 550
 551 var set_move = function(n, do_update) {
 552         move_override = n;
 553         if (do_update !== false) {
 554                 update();
 555                 window.history.replaceState(null, null, get_history_url());
 556         }
 557 }
 558 window['set_move'] = set_move;
 559
 560 // almost all of this stuff comes from the chessboard.js example page
 561 var onDragStart = function(source, piece, position, orientation) {
 562         var pseudogame = new Chess(current_display_fen());
 563         if (pseudogame.game_over() === true ||
 564             (pseudogame.turn() === 'w' && piece.search(/^b/) !== -1) ||
 565             (pseudogame.turn() === 'b' && piece.search(/^w/) !== -1)) {
 566                 return false;
 567         }
 568
 569         recommended_move = null;
 570         get_best_dest(pseudogame, source, null, function(src, dest) {
 571                 $("#board").find('.square-55d63').removeClass('nonuglyhighlight');
 572                 if (dest !== null) {
 573                         var squareEl = $('#board .square-' + dest);
 574                         squareEl.addClass('highlight1-32417');
 575                         recommended_move = [src, dest];
 576                 }
 577         });
 578 }
 579
 580 var mousedownSquare = function(e) {
 581         reverse_dragging_from = null;
 582         var square = $(this).attr('data-square');
 583
 584         var pseudogame = new Chess(current_display_fen());
 585         if (pseudogame.game_over() === true) {
 586                 return;
 587         }
 588
 589         // If the square is empty, or has a piece of the side not to move,
 590         // we handle it. If not, normal piece dragging will take it.
 591         var position = board.position();
 592         if (!position.hasOwnProperty(square) ||
 593             (pseudogame.turn() === 'w' && position[square].search(/^b/) !== -1) ||
 594             (pseudogame.turn() === 'b' && position[square].search(/^w/) !== -1)) {
 595                 reverse_dragging_from = square;
 596                 get_best_dest(pseudogame, null, square, function(src, dest) {
 597                         if (src !== null) {
 598                                 var squareEl = $('#board .square-' + src);
 599                                 squareEl.addClass('highlight1-32417');
 600                                 squareEl = $('#board .square-' + dest);
 601                                 squareEl.addClass('highlight1-32417');
 602                                 recommended_move = [src, dest];
 603                         }
 604                 });
 605         } else {
 606                 recommended_src = null;
 607         }
 608 }
 609
 610 var mouseupSquare = function(e) {
 611         if (reverse_dragging_from === null) {
 612                 return;
 613         }
 614         var source = $(this).attr('data-square');
 615         var target = reverse_dragging_from;
 616         reverse_dragging_from = null;
 617         if (onDrop(source, target) !== 'snapback') {
 618                 onSnapEnd(source, target);
 619         }
 620         $("#board").find('.square-55d63').removeClass('highlight1-32417');
 621 }
 622
 623 var get_best_dest = function(game, source, target, cb) {
 624         var moves = game.moves({ verbose: true });
 625         if (source !== null) {
 626                 moves = moves.filter(function(move) { return move.from == source; });
 627         }
 628         if (target !== null) {
 629                 moves = moves.filter(function(move) { return move.to == target; });
 630         }
 631         if (moves.length == 0) {
 632                 cb(null, null);
 633                 return;
 634         }
 635         if (moves.length == 1) {
 636                 cb(moves[0].from, moves[0].to);
 637                 return;
 638         }
 639
 640         // More than one move. Ask the engine to disambiguate.
 641         var uci_moves = moves.map(function(m) { return m.from + m.to; });
 642         var when_engine_is_ready = function() {
 643                 engine_running = true;
 644                 stockfish.onmessage = function(event) {
 645                         var res = event.data.match(/^bestmove (\S\S)(\S\S)/);
 646                         if (res !== null) {
 647                                 engine_running = false;
 648                                 if (engine_replacement_callback !== null) {
 649                                         // We are no longer interested in this query,
 650                                         // so just discard it and call this other callback.
 651                                         engine_replacement_callback();
 652                                         engine_replacement_callback = null;
 653                                 } else {
 654                                         cb(res[1], res[2]);
 655                                 }
 656                         }
 657                 };
 658                 stockfish.postMessage("position fen " + game.fen());
 659                 stockfish.postMessage("go depth 6 searchmoves " + uci_moves.join(" "));
 660         };
 661         if (engine_running) {
 662                 engine_replacement_callback = when_engine_is_ready;
 663         } else {
 664                 when_engine_is_ready();
 665         }
 666 }
 667
 668 var onDrop = function(source, target) {
 669         if (engine_running) {
 670                 // Snap end before the engine came back.
 671                 // Discard the result when it does.
 672                 engine_replacement_callback = function() {};
 673         }
 674         if (source == target) {
 675                 if (recommended_move === null) {
 676                         return 'snapback';
 677                 } else {
 678                         // Accept the move. It will be changed in onSnapEnd.
 679                         return;
 680                 }
 681         } else {
 682                 // Suggestion not asked for.
 683                 recommended_move = null;
 684         }
 685
 686         // see if the move is legal
 687         var pseudogame = new Chess(current_display_fen());
 688         var move = pseudogame.move({
 689                 from: source,
 690                 to: target,
 691                 promotion: 'q' // NOTE: always promote to a queen for example simplicity
 692         });
 693
 694         // illegal move
 695         if (move === null) return 'snapback';
 696 }
 697
 698 var onSnapEnd = function(source, target) {
 699         if (source == target && recommended_move !== null) {
 700                 source = recommended_move[0];
 701                 target = recommended_move[1];
 702         }
 703         recommended_move = null;
 704         var pseudogame = new Chess(current_display_fen());
 705         var move = pseudogame.move({
 706                 from: source,
 707                 to: target,
 708                 promotion: 'q' // NOTE: always promote to a queen for example simplicity
 709         });
 710
 711         make_move(pseudogame.history({ verbose: true }).pop().san);
 712 }
 713
 714 var onpopstate = function() {
 715         var old_moves = game.history({ verbose: true }).map(function(x) { return x.san; });
 716         var new_moves = document.location.search.replace(/^\?/, "").split(",");
 717
 718         if (new_moves.length == 1 && new_moves[0] == "") {
 719                 new_moves = [];
 720         }
 721
 722         var num_shared_moves;
 723         for (num_shared_moves = 0; num_shared_moves < Math.min(old_moves.length, new_moves.length); ++num_shared_moves) {
 724                 if (old_moves[i] != new_moves[i]) {
 725                         break;
 726                 }
 727         }
 728
 729         set_move(num_shared_moves, false);
 730         for (var i = num_shared_moves; i < new_moves.length; ++i) {
 731                 make_move(new_moves[i], false);
 732         }
 733         update();
 734         window.history.replaceState(null, null, get_history_url());
 735 }
 736
 737 var init = function() {
 738         // Create board.
 739         board = new window.ChessBoard('board', {
 740                 draggable: true,
 741                 position: 'start',
 742                 onDragStart: onDragStart,
 743                 onDrop: onDrop,
 744                 onSnapEnd: onSnapEnd
 745         });
 746         $("#board").on('mousedown', '.square-55d63', mousedownSquare);
 747         $("#board").on('mouseup', '.square-55d63', mouseupSquare);
 748
 749         window.onpopstate = onpopstate;
 750         onpopstate();
 751         set_practice(false);
 752
 753         $(window).keyup(function(event) {
 754                 if (event.which == 39) {
 755                         next_move();
 756                 } else if (event.which == 37) {
 757                         prev_move();
 758                 } else if (event.which == 74) {  // j
 759                         if (practice_mode) next_variant();
 760                 } else if (event.which == 75) {  // k
 761                         if (practice_mode) prev_variant();
 762                 }
 763         });
 764
 765         // Seemingly the web worker is not started before we send it a message.
 766         stockfish.postMessage("uci");
 767 }
 768
 769 $(document).ready(init);
 770
 771 })();