Show low-depth scores.

[remoteglot] / www / js / remoteglot.js

(function() {

/**
 * Version of this script. If the server returns a version larger than
 * this, it is a sign we should reload to upgrade ourselves.
 *
 * @type {Number}
 * @const
 * @private */
var SCRIPT_VERSION = 2021021300;

/**
 * The current backend URL.
 *
 * @type {!string}
 * @private
 */
var backend_url = "/analysis.pl";
var backend_hash_url = "/hash";

/** @type {window.ChessBoard} @private */
var board = null;

/** @type {boolean} @private */
var board_is_animating = false;

/**
 * The most recent analysis data we have from the server
 * (about the most recent position).
 *
 * @type {?Object}
 * @private */
var current_analysis_data = null;

/**
 * If we are displaying previous analysis or from hash, this is non-null,
 * and will override most of current_analysis_data.
 *
 * @type {?Object}
 * @private
 */
var displayed_analysis_data = null;

/**
 * Games currently in progress, if any.
 *
 * @type {?Array.<{
 *      name: string,
 *      url: string,
 *      hashurl: string,
 *      id: string,
 *      score: Object=,
 *      result: string=,
 * }>}
 * @private
 */
var current_games = null;

/** @type {Array.<{
 *      from_col: number,
 *      from_row: number,
 *      to_col: number,
 *      to_row: number,
 *      line_width: number,
 *      arrow_size: number,
 *      fg_color: string
 * }>}
 * @private
 */
var arrows = [];

/** @type {Array.<Array.<boolean>>} */
var occupied_by_arrows = [];

/** Currently displayed refutation lines (on-screen).
 * Can either come from the current_analysis_data, displayed_analysis_data,
 * or hash_refutation_lines.
 */
var refutation_lines = [];

/** Refutation lines from current hash probe.
 *
 * If non-null, will override refutation lines from the base position.
 * Note that these are relative to display_fen, not base_fen.
 */
var hash_refutation_lines = null;

/** @type {!number} @private */
var move_num = 1;

/** @type {!string} @private */
var toplay = 'W';

/** @type {number} @private */
var ims = 0;

/** @type {boolean} @private */
var truncate_display_history = true;

/** @type {!string|undefined} @private */
var highlight_from = undefined;

/** @type {!string|undefined} @private */
var highlight_to = undefined;

/** The HTML object of the move currently being highlighted (in red).
 * @type {?jQuery}
 * @private */
var highlighted_move = null;

/** Currently suggested/recommended move when dragging.
 * @type {?{from: !string, to: !string}}
 * @private
 */
var recommended_move = null;

/** If reverse-dragging (dragging from the destination square to the
 * source square), the destination square.
 * @type {?string}
 * @private
 */
var reverse_dragging_from = null;

/** @type {?number} @private */
var unique = null;

/** @type {boolean} @private */
var enable_sound = false;

/**
 * Our best estimate of how many milliseconds we need to add to 
 * new Date() to get the true UTC time. Calibrated against the
 * server clock.
 *
 * @type {?number}
 * @private
 */
var client_clock_offset_ms = null;

var clock_timer = null;

/** The current position being analyzed, represented as a FEN string.
 * Note that this is not necessarily the same as display_fen.
 * @type {?string}
 * @private
 */
var base_fen = null;

/** The current position on the board, represented as a FEN string.
 * Note that board.fen() does not contain e.g. who is to play.
 * @type {?string}
 * @private
 */
var display_fen = null;

/** @typedef {{
 *    start_fen: string,
 *    pv: Array.<string>,
 *    move_num: number,
 *    toplay: string,
 *    scores: Array<{first_move: number, score: Object}>,
 *    start_display_move_num: number
 * }} DisplayLine
 *
 * "start_display_move_num" is the (half-)move number to start displaying the PV at.
 * "score" is also evaluated at this point.
 */

/** All PVs that we currently know of.
 *
 * Element 0 is history (or null if no history).
 * Element 1 is current main PV, or explored line if nowhere else on the screen.
 * All remaining elements are refutation lines (multi-PV).
 *
 * @type {Array.<DisplayLine>}
 * @private
 */
var display_lines = [];

/** @type {?DisplayLine} @private */
var current_display_line = null;

/** @type {boolean} @private */
var current_display_line_is_history = false;

/** @type {?number} @private */
var current_display_move = null;

/**
 * The current backend request to get main analysis (not history), if any,
 * so that we can abort it.
 *
 * @type {?jqXHR}
 * @private
 */
var current_analysis_xhr = null;

/**
 * The current timer to fire off a request to get main analysis (not history),
 * if any, so that we can abort it.
 *
 * @type {?Number}
 * @private
 */
var current_analysis_request_timer = null;

/**
 * The current backend request to get historic data, if any.
 *
 * @type {?jqXHR}
 * @private
 */
var current_historic_xhr = null;

/**
 * The current backend request to get hash probes, if any, so that we can abort it.
 *
 * @type {?jqXHR}
 * @private
 */
var current_hash_xhr = null;

/**
 * The current timer to display hash probe information (it could be waiting on the
 * board to stop animating), if any, so that we can abort it.
 *
 * @type {?Number}
 * @private
 */
var current_hash_display_timer = null;

var supports_html5_storage = function() {
        try {
                return 'localStorage' in window && window['localStorage'] !== null;
        } catch (e) {
                return false;
        }
}

// Make the unique token persistent so people refreshing the page won't count twice.
// Of course, you can never fully protect against people deliberately wanting to spam.
var get_unique = function() {
        var use_local_storage = supports_html5_storage();
        if (use_local_storage && localStorage['unique']) {
                return localStorage['unique'];
        }
        var unique = Math.random();
        if (use_local_storage) {
                localStorage['unique'] = unique;
        }
        return unique;
}

var request_update = function() {
        current_analysis_request_timer = null;

        current_analysis_xhr = $.ajax({
                url: backend_url + "?ims=" + ims + "&unique=" + unique
        }).done(function(data, textstatus, xhr) {
                sync_server_clock(xhr.getResponseHeader('Date'));
                ims = xhr.getResponseHeader('X-RGLM');
                var num_viewers = xhr.getResponseHeader('X-RGNV');
                var new_data;
                if (Array.isArray(data)) {
                        new_data = JSON.parse(JSON.stringify(current_analysis_data));
                        JSON_delta.patch(new_data, data);
                } else {
                        new_data = data;
                }

                var minimum_version = xhr.getResponseHeader('X-RGMV');
                if (minimum_version && minimum_version > SCRIPT_VERSION) {
                        // Upgrade to latest version with a force-reload.
                        location.reload(true);
                }

                // Verify that the PV makes sense.
                var valid = true;
                if (new_data['pv']) {
                        var hiddenboard = new Chess(new_data['position']['fen']);
                        for (var i = 0; i < new_data['pv'].length; ++i) {
                                if (hiddenboard.move(new_data['pv'][i]) === null) {
                                        valid = false;
                                        break;
                                }
                        }
                }

                var timeout = 100;
                if (valid) {
                        possibly_play_sound(current_analysis_data, new_data);
                        current_analysis_data = new_data;
                        update_board();
                        update_num_viewers(num_viewers);
                } else {
                        console.log("Received invalid update, waiting five seconds and trying again.");
                        setTimeout(function() { location.reload(true); }, 5000);
                }

                // Next update.
                if (!backend_url.match(/history/)) {
                        current_analysis_request_timer = setTimeout(function() { request_update(); }, timeout);
                }
        }).fail(function(jqXHR, textStatus, errorThrown) {
                if (textStatus === "abort") {
                        // Aborted because we are switching backends. Abandon and don't retry,
                        // because another one is already started for us.
                } else {
                        // Backend error or similar. Wait ten seconds, then try again.
                        current_analysis_request_timer = setTimeout(function() { request_update(); }, 10000);
                }
        });
}

var possibly_play_sound = function(old_data, new_data) {
        if (!enable_sound) {
                return;
        }
        if (old_data === null) {
                return;
        }
        var ding = document.getElementById('ding');
        if (ding && ding.play) {
                if (old_data['position'] && old_data['position']['fen'] &&
                    new_data['position'] && new_data['position']['fen'] &&
                    (old_data['position']['fen'] !== new_data['position']['fen'] ||
                     old_data['position']['move_num'] !== new_data['position']['move_num'])) {
                        ding.play();
                }
        }
}

/**
 * @type {!string} server_date_string
 */
var sync_server_clock = function(server_date_string) {
        var server_time_ms = new Date(server_date_string).getTime();
        var client_time_ms = new Date().getTime();
        var estimated_offset_ms = server_time_ms - client_time_ms;

        // In order not to let the noise move us too much back and forth
        // (the server only has one-second resolution anyway), we only
        // change an existing skew if we are at least five seconds off.
        if (client_clock_offset_ms === null ||
            Math.abs(estimated_offset_ms - client_clock_offset_ms) > 5000) {
                client_clock_offset_ms = estimated_offset_ms;
        }
}

var clear_arrows = function() {
        for (var i = 0; i < arrows.length; ++i) {
                if (arrows[i].svg) {
                        if (arrows[i].svg.parentElement) {
                                arrows[i].svg.parentElement.removeChild(arrows[i].svg);
                        }
                        delete arrows[i].svg;
                }
        }
        arrows = [];

        occupied_by_arrows = [];
        for (var y = 0; y < 8; ++y) {
                occupied_by_arrows.push([false, false, false, false, false, false, false, false]);
        }
}

var redraw_arrows = function() {
        for (var i = 0; i < arrows.length; ++i) {
                position_arrow(arrows[i]);
        }
}

/** @param {!number} x
 * @return {!number}
 */
var sign = function(x) {
        if (x > 0) {
                return 1;
        } else if (x < 0) {
                return -1;
        } else {
                return 0;
        }
}

/** See if drawing this arrow on the board would cause unduly amount of confusion.
 * @param {!string} from The square the arrow is from (e.g. e4).
 * @param {!string} to The square the arrow is to (e.g. e4).
 * @return {boolean}
 */
var interfering_arrow = function(from, to) {
        var from_col = from.charCodeAt(0) - "a1".charCodeAt(0);
        var from_row = from.charCodeAt(1) - "a1".charCodeAt(1);
        var to_col   = to.charCodeAt(0) - "a1".charCodeAt(0);
        var to_row   = to.charCodeAt(1) - "a1".charCodeAt(1);

        occupied_by_arrows[from_row][from_col] = true;

        // Knight move: Just check that we haven't been at the destination before.
        if ((Math.abs(to_col - from_col) == 2 && Math.abs(to_row - from_row) == 1) ||
            (Math.abs(to_col - from_col) == 1 && Math.abs(to_row - from_row) == 2)) {
                return occupied_by_arrows[to_row][to_col];
        }

        // Sliding piece: Check if anything except the from-square is seen before.
        var dx = sign(to_col - from_col);
        var dy = sign(to_row - from_row);
        var x = from_col;
        var y = from_row;
        do {
                x += dx;
                y += dy;
                if (occupied_by_arrows[y][x]) {
                        return true;
                }
                occupied_by_arrows[y][x] = true;
        } while (x != to_col || y != to_row);

        return false;
}

/** Find a point along the coordinate system given by the given line,
 * <t> units forward from the start of the line, <u> units to the right of it.
 * @param {!number} x1
 * @param {!number} x2
 * @param {!number} y1
 * @param {!number} y2
 * @param {!number} t
 * @param {!number} u
 * @return {!string} The point in "x y" form, suitable for SVG paths.
 */
var point_from_start = function(x1, y1, x2, y2, t, u) {
        var dx = x2 - x1;
        var dy = y2 - y1;

        var norm = 1.0 / Math.sqrt(dx * dx + dy * dy);
        dx *= norm;
        dy *= norm;

        var x = x1 + dx * t + dy * u;
        var y = y1 + dy * t - dx * u;
        return x + " " + y;
}

/** Find a point along the coordinate system given by the given line,
 * <t> units forward from the end of the line, <u> units to the right of it.
 * @param {!number} x1
 * @param {!number} x2
 * @param {!number} y1
 * @param {!number} y2
 * @param {!number} t
 * @param {!number} u
 * @return {!string} The point in "x y" form, suitable for SVG paths.
 */
var point_from_end = function(x1, y1, x2, y2, t, u) {
        var dx = x2 - x1;
        var dy = y2 - y1;

        var norm = 1.0 / Math.sqrt(dx * dx + dy * dy);
        dx *= norm;
        dy *= norm;

        var x = x2 + dx * t + dy * u;
        var y = y2 + dy * t - dx * u;
        return x + " " + y;
}

var position_arrow = function(arrow) {
        if (arrow.svg) {
                if (arrow.svg.parentElement) {
                        arrow.svg.parentElement.removeChild(arrow.svg);
                }
                delete arrow.svg;
        }
        if (current_display_line !== null && !current_display_line_is_history) {
                return;
        }

        var zoom_factor = $("#board").width() / 400.0;
        var line_width = arrow.line_width * zoom_factor;
        var arrow_size = arrow.arrow_size * zoom_factor;

        var square_width = $(".square-a8").width();
        var pos, from_y, to_y, from_x, to_x;
        if (board.orientation() === 'black') {
                pos = $(".square-h1").position();
                from_y = (arrow.from_row + 0.5)*square_width;
                to_y = (arrow.to_row + 0.5)*square_width;
                from_x = (7 - arrow.from_col + 0.5)*square_width;
                to_x = (7 - arrow.to_col + 0.5)*square_width;
        } else {
                pos = $(".square-a8").position();
                from_y = (7 - arrow.from_row + 0.5)*square_width;
                to_y = (7 - arrow.to_row + 0.5)*square_width;
                from_x = (arrow.from_col + 0.5)*square_width;
                to_x = (arrow.to_col + 0.5)*square_width;
        }

        var SVG_NS = "http://www.w3.org/2000/svg";
        var XHTML_NS = "http://www.w3.org/1999/xhtml";
        var svg = document.createElementNS(SVG_NS, "svg");
        svg.setAttribute("width", /** @type{number} */ ($("#board").width()));
        svg.setAttribute("height", /** @type{number} */ ($("#board").height()));
        svg.setAttribute("style", "position: absolute");
        svg.setAttribute("position", "absolute");
        svg.setAttribute("version", "1.1");
        svg.setAttribute("class", "c1");
        svg.setAttribute("xmlns", XHTML_NS);

        var x1 = from_x;
        var y1 = from_y;
        var x2 = to_x;
        var y2 = to_y;

        // Draw the line.
        var outline = document.createElementNS(SVG_NS, "path");
        outline.setAttribute("d", "M " + point_from_start(x1, y1, x2, y2, arrow_size / 2, 0) + " L " + point_from_end(x1, y1, x2, y2, -arrow_size / 2, 0));
        outline.setAttribute("xmlns", XHTML_NS);
        outline.setAttribute("stroke", "#666");
        outline.setAttribute("stroke-width", line_width + 2);
        outline.setAttribute("fill", "none");
        svg.appendChild(outline);

        var path = document.createElementNS(SVG_NS, "path");
        path.setAttribute("d", "M " + point_from_start(x1, y1, x2, y2, arrow_size / 2, 0) + " L " + point_from_end(x1, y1, x2, y2, -arrow_size / 2, 0));
        path.setAttribute("xmlns", XHTML_NS);
        path.setAttribute("stroke", arrow.fg_color);
        path.setAttribute("stroke-width", line_width);
        path.setAttribute("fill", "none");
        svg.appendChild(path);

        // Then the arrow head.
        var head = document.createElementNS(SVG_NS, "path");
        head.setAttribute("d",
                "M " +  point_from_end(x1, y1, x2, y2, 0, 0) +
                " L " + point_from_end(x1, y1, x2, y2, -arrow_size, -arrow_size / 2) +
                " L " + point_from_end(x1, y1, x2, y2, -arrow_size * .623, 0.0) +
                " L " + point_from_end(x1, y1, x2, y2, -arrow_size, arrow_size / 2) +
                " L " + point_from_end(x1, y1, x2, y2, 0, 0));
        head.setAttribute("xmlns", XHTML_NS);
        head.setAttribute("stroke", "#000");
        head.setAttribute("stroke-width", "1");
        head.setAttribute("fill", arrow.fg_color);
        svg.appendChild(head);

        $(svg).css({ top: pos.top, left: pos.left, 'pointer-events': 'none' });
        document.body.appendChild(svg);
        arrow.svg = svg;
}

/**
 * @param {!string} from_square
 * @param {!string} to_square
 * @param {!string} fg_color
 * @param {number} line_width
 * @param {number} arrow_size
 */
var create_arrow = function(from_square, to_square, fg_color, line_width, arrow_size) {
        var from_col = from_square.charCodeAt(0) - "a1".charCodeAt(0);
        var from_row = from_square.charCodeAt(1) - "a1".charCodeAt(1);
        var to_col   = to_square.charCodeAt(0) - "a1".charCodeAt(0);
        var to_row   = to_square.charCodeAt(1) - "a1".charCodeAt(1);

        // Create arrow.
        var arrow = {
                from_col: from_col,
                from_row: from_row,
                to_col: to_col,
                to_row: to_row,
                line_width: line_width,
                arrow_size: arrow_size,
                fg_color: fg_color
        };

        position_arrow(arrow);
        arrows.push(arrow);
}

var compare_by_score = function(refutation_lines, invert, a, b) {
        var sa = compute_score_sort_key(refutation_lines[b]['score'], refutation_lines[b]['depth'], invert);
        var sb = compute_score_sort_key(refutation_lines[a]['score'], refutation_lines[a]['depth'], invert);
        return sa - sb;
}

/**
 * Fake multi-PV using the refutation lines. Find all “relevant” moves,
 * sorted by quality, descending.
 *
 * @param {!Object} data
 * @param {number} margin The maximum number of centipawns worse than the
 *     best move can be and still be included.
 * @param {boolean} invert Whether black is to play.
 * @return {Array.<string>} The FEN representation (e.g. Ne4) of all
 *     moves, in score order.
 */
var find_nonstupid_moves = function(data, margin, invert) {
        // First of all, if there are any moves that are more than 0.5 ahead of
        // the primary move, the refutation lines are probably bunk, so just
        // kill them all. 
        var best_score = undefined;
        var pv_score = undefined;
        for (var move in data['refutation_lines']) {
                var line = data['refutation_lines'][move];
                var score = compute_score_sort_key(line['score'], line['depth'], invert, false);
                if (move == data['pv'][0]) {
                        pv_score = score;
                }
                if (best_score === undefined || score > best_score) {
                        best_score = score;
                }
                if (line['depth'] < 8) {
                        return [];
                }
        }

        if (best_score - pv_score > 50) {
                return [];
        }

        // Now find all moves that are within “margin” of the best score.
        // The PV move will always be first.
        var moves = [];
        for (var move in data['refutation_lines']) {
                var line = data['refutation_lines'][move];
                var score = compute_score_sort_key(line['score'], line['depth'], invert);
                if (move != data['pv'][0] && best_score - score <= margin) {
                        moves.push(move);
                }
        }
        moves = moves.sort(function(a, b) { return compare_by_score(data['refutation_lines'], data['position']['toplay'] === 'B', a, b) });
        moves.unshift(data['pv'][0]);

        return moves;
}

/**
 * @param {number} x
 * @return {!string}
 */
var thousands = function(x) {
        return String(x).split('').reverse().join('').replace(/(\d{3}\B)/g, '$1,').split('').reverse().join('');
}

/**
 * @param {!string} start_fen
 * @param {Array.<string>} pv
 * @param {number} move_num
 * @param {!string} toplay
 * @param {Array<{ first_move: integer, score: Object }>} scores
 * @param {number} start_display_move_num
 * @param {number=} opt_limit
 * @param {boolean=} opt_showlast
 */
var add_pv = function(start_fen, pv, move_num, toplay, scores, start_display_move_num, opt_limit, opt_showlast) {
        display_lines.push({
                start_fen: start_fen,
                pv: pv,
                move_num: parseInt(move_num),
                toplay: toplay,
                scores: scores,
                start_display_move_num: start_display_move_num
        });
        var splicepos = null;
        if (scores !== null && scores.length >= 1 &&
            scores[scores.length - 1].score !== undefined &&
            scores[scores.length - 1].score !== null &&
            (scores[scores.length - 1].score[0] === 'T' ||
             scores[scores.length - 1].score[0] === 't')) {
                splicepos = scores[scores.length - 1].score[1];
        }
        return print_pv(display_lines.length - 1, splicepos, opt_limit, opt_showlast);
}

/**
 * @param {number} line_num
 * @param {?number} splicepos If non-null, where the tablebase-spliced portion of the TB starts.
 * @param {number=} opt_limit If set, show at most this number of moves.
 * @param {boolean=} opt_showlast If limit is set, show the last moves instead of the first ones.
 */
var print_pv = function(line_num, splicepos, opt_limit, opt_showlast) {
        var display_line = display_lines[line_num];
        var pv = display_line.pv;
        var move_num = display_line.move_num;
        var toplay = display_line.toplay;

        // Truncate PV at the start if needed.
        var start_display_move_num = display_line.start_display_move_num;
        if (start_display_move_num > 0) {
                pv = pv.slice(start_display_move_num);
                var to_add = start_display_move_num;
                if (toplay === 'B') {
                        ++move_num;
                        toplay = 'W';
                        --to_add;
                }
                if (to_add % 2 == 1) {
                        toplay = 'B';
                        --to_add;
                }
                move_num += to_add / 2;
                if (splicepos !== null && splicepos > 0) {
                        --splicepos;
                }
        }

        var ret = '';
        var i = 0;
        var in_tb = false;
        if (opt_limit && opt_showlast && pv.length > opt_limit) {
                // Truncate the PV at the beginning (instead of at the end).
                // We assume here that toplay is 'W'. We also assume that if
                // opt_showlast is set, then it is the history, and thus,
                // the UI should be to expand the history.
                ret = '(<a class="move" href="javascript:collapse_history(false)">…</a>) ';
                i = pv.length - opt_limit;
                if (i % 2 == 1) {
                        ++i;
                }
                move_num += i / 2;
        } else if (toplay == 'B' && pv.length > 0) {
                var move = "";
                if (splicepos === 0) {
                        move += "(TB: ";
                        in_tb = true;
                }
                move += "<a class=\"move\" id=\"automove" + line_num + "-0\" href=\"javascript:show_line(" + line_num + ", " + 0 + ");\">" + pv[0] + "</a>";
                ret = move_num + '. … ' + move;
                toplay = 'W';
                ++i;
                ++move_num;
        }
        for ( ; i < pv.length; ++i) {
                var move = "<a class=\"move\" id=\"automove" + line_num + "-" + i + "\" href=\"javascript:show_line(" + line_num + ", " + i + ");\">" + pv[i] + "</a>";
                if (splicepos === i) {
                        ret += " (TB: ";
                        in_tb = true;
                }

                if (toplay == 'W') {
                        if (i > opt_limit && !opt_showlast) {
                                if (in_tb) {
                                        ret += ")";
                                }
                                return ret + ' (…)';
                        }
                        if (ret != '') {
                                ret += ' ';
                        }
                        ret += move_num + '. ' + move;
                        ++move_num;
                        toplay = 'B';
                } else {
                        ret += ' ' + move;
                        toplay = 'W';
                }
        }
        if (in_tb) {
                ret += ")";
        }
        return ret;
}

/** Update the highlighted to/from squares on the board.
 * Based on the global "highlight_from" and "highlight_to" variables.
 */
var update_board_highlight = function() {
        $("#board").find('.square-55d63').removeClass('nonuglyhighlight');
        if ((current_display_line === null || current_display_line_is_history) &&
            highlight_from !== undefined && highlight_to !== undefined) {
                $("#board").find('.square-' + highlight_from).addClass('nonuglyhighlight');
                $("#board").find('.square-' + highlight_to).addClass('nonuglyhighlight');
        }
}

var update_history = function() {
        if (display_lines[0] === null || display_lines[0].pv.length == 0) {
                $("#history").html("No history");
        } else if (truncate_display_history) {
                $("#history").html(print_pv(0, null, 8, true));
        } else {
                $("#history").html(
                        '(<a class="move" href="javascript:collapse_history(true)">collapse</a>) ' +
                        print_pv(0, null));
        }
}

/**
 * @param {!boolean} truncate_history
 */
var collapse_history = function(truncate_history) {
        truncate_display_history = truncate_history;
        update_history();
}
window['collapse_history'] = collapse_history;

/** Update the HTML display of multi-PV from the global "refutation_lines".
 *
 * Also recreates the global "display_lines".
 */
var update_refutation_lines = function() {
        if (base_fen === null) {
                return;
        }
        if (display_lines.length > 2) {
                // Truncate so that only the history and PV is left.
                display_lines = [ display_lines[0], display_lines[1] ];
        }
        var tbl = $("#refutationlines");
        tbl.empty();

        if (display_lines.length < 2) {
                return;
        }

        // Find out where the lines start from.
        var base_line = [];
        var base_scores = display_lines[1].scores;
        var start_display_move_num = 0;
        if (hash_refutation_lines) {
                base_line = current_display_line.pv.slice(0, current_display_move + 1);
                base_scores = current_display_line.scores;
                start_display_move_num = base_line.length;
        }

        var moves = [];
        for (var move in refutation_lines) {
                moves.push(move);
        }

        var invert = (toplay === 'B');
        if (current_display_line && current_display_move % 2 == 0 && !current_display_line_is_history) {
                invert = !invert;
        }
        moves = moves.sort(function(a, b) { return compare_by_score(refutation_lines, invert, a, b) });
        for (var i = 0; i < moves.length; ++i) {
                var line = refutation_lines[moves[i]];

                var tr = document.createElement("tr");

                var move_td = document.createElement("td");
                tr.appendChild(move_td);
                $(move_td).addClass("move");

                var scores = base_scores.concat([{ first_move: start_display_move_num, score: line['score'] }]);

                if (line['pv'].length == 0) {
                        // Not found, so just make a one-move PV.
                        var move = "<a class=\"move\" href=\"javascript:show_line(" + display_lines.length + ", " + 0 + ");\">" + line['move'] + "</a>";
                        $(move_td).html(move);
                        var score_td = document.createElement("td");

                        $(score_td).addClass("score");
                        $(score_td).text("—");
                        tr.appendChild(score_td);

                        var depth_td = document.createElement("td");
                        tr.appendChild(depth_td);
                        $(depth_td).addClass("depth");
                        $(depth_td).text("—");

                        var pv_td = document.createElement("td");
                        tr.appendChild(pv_td);
                        $(pv_td).addClass("pv");
                        $(pv_td).html(add_pv(base_fen, base_line.concat([ line['move'] ]), move_num, toplay, scores, start_display_move_num));

                        tbl.append(tr);
                        continue;
                }

                var move = "<a class=\"move\" href=\"javascript:show_line(" + display_lines.length + ", " + 0 + ");\">" + line['move'] + "</a>";
                $(move_td).html(move);

                var score_td = document.createElement("td");
                tr.appendChild(score_td);
                $(score_td).addClass("score");
                $(score_td).text(format_short_score(line['score']));

                var depth_td = document.createElement("td");
                tr.appendChild(depth_td);
                $(depth_td).addClass("depth");
                if (line['depth'] && line['depth'] >= 0) {
                        $(depth_td).text("d" + line['depth']);
                } else {
                        $(depth_td).text("—");
                }

                var pv_td = document.createElement("td");
                tr.appendChild(pv_td);
                $(pv_td).addClass("pv");
                $(pv_td).html(add_pv(base_fen, base_line.concat(line['pv']), move_num, toplay, scores, start_display_move_num, 10));

                tbl.append(tr);
        }

        // Update the move highlight, as we've rewritten all the HTML.
        update_move_highlight();
}

/**
 * Create a Chess.js board object, containing the given position plus the given moves,
 * up to the given limit.
 *
 * @param {?string} fen
 * @param {Array.<string>} moves
 * @param {number} last_move
 */
var chess_from = function(fen, moves, last_move) {
        var hiddenboard = new Chess();
        if (fen !== null && fen !== undefined) {
                hiddenboard.load(fen);
        }
        for (var i = 0; i <= last_move; ++i) {
                if (moves[i] === '0-0') {
                        hiddenboard.move('O-O');
                } else if (moves[i] === '0-0-0') {
                        hiddenboard.move('O-O-O');
                } else {
                        hiddenboard.move(moves[i]);
                }
        }
        return hiddenboard;
}

var update_game_list = function(games) {
        $("#games").text("");
        if (games === null) {
                return;
        }

        var games_div = document.getElementById('games');
        for (var game_num = 0; game_num < games.length; ++game_num) {
                var game = games[game_num];
                var game_span = document.createElement("span");
                game_span.setAttribute("class", "game");

                var game_name = document.createTextNode(game['name']);
                if (game['url'] === backend_url) {
                        // This game.
                        game_span.appendChild(game_name);

                        if (current_analysis_data && current_analysis_data['position']) {
                                var score;
                                if (current_analysis_data['position']['result']) {
                                        score = " (" + current_analysis_data['position']['result'] + ")";
                                } else {
                                        score = " (" + format_short_score(current_analysis_data['score']) + ")";
                                }
                                game_span.appendChild(document.createTextNode(score));
                        }
                } else {
                        // Some other game.
                        var game_a = document.createElement("a");
                        game_a.setAttribute("href", "#" + game['id']);
                        game_a.appendChild(game_name);
                        game_span.appendChild(game_a);

                        var score;
                        if (game['result']) {
                                score = " (" + game['result'] + ")";
                        } else {
                                score = " (" + format_short_score(game['score']) + ")";
                        }
                        game_span.appendChild(document.createTextNode(score));
                }

                games_div.appendChild(game_span);
        }
}

/**
 * Try to find a running game that matches with the current hash,
 * and switch to it if we're not already displaying it.
 */
var possibly_switch_game_from_hash = function() {
        var history_match = window.location.hash.match(/^#history=([a-zA-Z0-9_-]+)/);
        if (history_match !== null) {
                var game_id = history_match[1];
                var fake_game = {
                        url: '/history/' + game_id + '.json',
                        hashurl: '',
                        id: 'history=' + game_id
                };
                switch_backend(fake_game);
                return;
        }

        if (current_games === null) {
                return;
        }

        var hash = window.location.hash.replace(/^#/,'');
        for (var i = 0; i < current_games.length; ++i) {
                if (current_games[i]['id'] === hash) {
                        if (backend_url !== current_games[i]['url']) {
                                switch_backend(current_games[i]);
                        }
                        return;
                }
        }
}

/**
 * If this is a Chess960 castling which doesn't move the king,
 * move the rook instead.
*/
var patch_move = function(move) {
        if (move === null) return null;
        if (move.from !== move.to) return move;

        var f = move.rook_sq & 15;
        var r = move.rook_sq >> 4;
        var from = ('abcdefgh'.substring(f,f+1) + '87654321'.substring(r,r+1));
        var to = move.to;

        if (move.to === 'g1') {
                to = 'f1';
        } else if (move.to === 'g8') {
                to = 'f8';
        } else if (move.to === 'b1') {
                to = 'c1';
        } else if (move.to === 'b8') {
                to = 'c8';
        }

        return { from: from, to: to };
}

/** Update all the HTML on the page, based on current global state.
 */
var update_board = function() {
        var data = displayed_analysis_data || current_analysis_data;
        var current_data = current_analysis_data;  // Convenience alias.

        display_lines = [];

        // Print the history. This is pretty much the only thing that's
        // unconditionally taken from current_data (we're not interested in
        // historic history).
        if (current_data['position']['history']) {
                var start = (current_data['position'] && current_data['position']['start_fen']) ? current_data['position']['start_fen'] : 'start';
                add_pv(start, current_data['position']['history'], 1, 'W', null, 0, 8, true);
        } else {
                display_lines.push(null);
        }
        update_history();

        // Games currently in progress, if any.
        if (current_data['games']) {
                current_games = current_data['games'];
                possibly_switch_game_from_hash();
        } else {
                current_games = null;
        }
        update_game_list(current_games);

        // The headline. Names are always fetched from current_data;
        // the rest can depend a bit.
        var headline;
        if (current_data &&
            current_data['position']['player_w'] && current_data['position']['player_b']) {
                headline = current_data['position']['player_w'] + '–' +
                        current_data['position']['player_b'] + ', analysis';
        } else {
                headline = 'Analysis';
        }

        // Credits, where applicable. Note that we don't want the footer to change a lot
        // when e.g. viewing history, so if any of these changed during the game,
        // use the current one still.
        if (current_data['using_lomonosov']) {
                $("#lomonosov").show();
        } else {
                $("#lomonosov").hide();
        }

        // Credits: The engine name/version.
        if (current_data['engine'] && current_data['engine']['name'] !== null) {
                $("#engineid").text(current_data['engine']['name']);
        }

        // Credits: The engine URL.
        if (current_data['engine'] && current_data['engine']['url']) {
                $("#engineid").attr("href", current_data['engine']['url']);
        } else {
                $("#engineid").removeAttr("href");
        }

        // Credits: Engine details.
        if (current_data['engine'] && current_data['engine']['details']) {
                $("#enginedetails").text(" (" + current_data['engine']['details'] + ")");
        } else {
                $("#enginedetails").text("");
        }

        // Credits: Move source, possibly with URL.
        if (current_data['move_source'] && current_data['move_source_url']) {
                $("#movesource").text("Moves provided by ");
                var movesource_a = document.createElement("a");
                movesource_a.setAttribute("href", current_data['move_source_url']);
                var movesource_text = document.createTextNode(current_data['move_source']);
                movesource_a.appendChild(movesource_text);
                var movesource_period = document.createTextNode(".");
                document.getElementById("movesource").appendChild(movesource_a);
                document.getElementById("movesource").appendChild(movesource_period);
        } else if (current_data['move_source']) {
                $("#movesource").text("Moves provided by " + current_data['move_source'] + ".");
        } else {
                $("#movesource").text("");
        }

        var last_move;
        if (displayed_analysis_data) {
                // Displaying some non-current position, pick out the last move
                // from the history. This will work even if the fetch failed.
                if (current_display_move !== -1) {
                        last_move = format_halfmove_with_number(
                                current_display_line.pv[current_display_move],
                                current_display_move);
                        headline += ' after ' + last_move;
                }
        } else if (data['position']['last_move'] !== 'none') {
                // Find the previous move.
                var previous_move_num, previous_toplay;
                if (data['position']['toplay'] == 'B') {
                        previous_move_num = data['position']['move_num'];
                        previous_toplay = 'W';
                } else {
                        previous_move_num = data['position']['move_num'] - 1;
                        previous_toplay = 'B';
                }

                last_move = format_move_with_number(
                        data['position']['last_move'],
                        previous_move_num,
                        previous_toplay == 'W');
                headline += ' after ' + last_move;
        } else {
                last_move = null;
        }
        $("#headline").text(headline);

        // The <title> contains a very brief headline.
        var title_elems = [];
        if (data['position'] && data['position']['result']) {
                title_elems.push(data['position']['result']);
        } else if (data['score']) {
                title_elems.push(format_short_score(data['score']));
        }
        if (last_move !== null) {
                title_elems.push(last_move);
        }

        if (title_elems.length != 0) {
                document.title = '(' + title_elems.join(', ') + ') analysis.sesse.net';
        } else {
                document.title = 'analysis.sesse.net';
        }

        // The last move (shown by highlighting the from and to squares).
        if (data['position'] && data['position']['last_move_uci']) {
                highlight_from = data['position']['last_move_uci'].substr(0, 2);
                highlight_to = data['position']['last_move_uci'].substr(2, 2);
        } else if (current_display_line_is_history && current_display_line && current_display_move >= 0) {
                // We don't have historic analysis for this position, but we
                // can reconstruct what the last move was by just replaying
                // from the start.
                var position = (data['position'] && data['position']['start_fen']) ? data['position']['start_fen'] : null;
                var hiddenboard = chess_from(position, current_display_line.pv, current_display_move);
                var moves = hiddenboard.history({ verbose: true });
                last_move = moves.pop();
                highlight_from = last_move.from;
                highlight_to = last_move.to;
        } else {
                highlight_from = highlight_to = undefined;
        }
        update_board_highlight();

        if (data['failed']) {
                $("#score").text("No analysis for this move");
                $("#pvtitle").text("PV:");
                $("#pv").empty();
                $("#searchstats").html("&nbsp;");
                $("#refutationlines").empty();
                $("#whiteclock").empty();
                $("#blackclock").empty();
                refutation_lines = [];
                update_refutation_lines();
                clear_arrows();
                update_displayed_line();
                update_move_highlight();
                return;
        }

        update_clock();

        // The score.
        if (current_display_line && !current_display_line_is_history) {
                var score;
                if (current_display_line.scores && current_display_line.scores.length > 0) {
                        for (var i = 0; i < current_display_line.scores.length; ++i) {
                                if (current_display_move < current_display_line.scores[i].first_move) {
                                        break;
                                }
                                score = current_display_line.scores[i].score;
                        }
                }
                if (score) {
                        $("#score").text(format_long_score(score));
                } else {
                        $("#score").text("No score for this line");
                }
        } else if (data['score']) {
                $("#score").text(format_long_score(data['score']));
        }

        // Low depth.
        var lowdepth = '';
        if (data['lowdepth']) {
                lowdepth = 'Quick look: ';
                var lds = [];
                Object.keys(data['lowdepth']).forEach(function(depth) {
                        lds.push([parseInt(depth), format_short_score(data['lowdepth'][depth])]);
                });
                lds.sort(function(a, b) { return a[0] - b[0]; });
                for (var i = 0; i < lds.length; ++i) {
                        lowdepth += '<span class="depth">d' + lds[i][0] + ':</span> ' + lds[i][1];
                        if (i != lds.length - 1) {
                                lowdepth += ', ';
                        }
                }
        }
        $("#lowdepth").html(lowdepth);

        // The search stats.
        if (data['searchstats']) {
                $("#searchstats").html(data['searchstats']);
        } else if (data['tablebase'] == 1) {
                $("#searchstats").text("Tablebase result");
        } else if (data['nodes'] && data['nps'] && data['depth']) {
                var stats = thousands(data['nodes']) + ' nodes, ' + thousands(data['nps']) + ' nodes/sec, depth ' + data['depth'] + ' ply';
                if (data['seldepth']) {
                        stats += ' (' + data['seldepth'] + ' selective)';
                }
                if (data['tbhits'] && data['tbhits'] > 0) {
                        if (data['tbhits'] == 1) {
                                stats += ', one Syzygy hit';
                        } else {
                                stats += ', ' + thousands(data['tbhits']) + ' Syzygy hits';
                        }
                }

                $("#searchstats").text(stats);
        } else {
                $("#searchstats").text("");
        }

        // Update the board itself.
        base_fen = data['position']['fen'];
        update_displayed_line();

        // Print the PV.
        $("#pvtitle").text("PV:");

        var scores = [{ first_move: -1, score: data['score'] }];
        $("#pv").html(add_pv(data['position']['fen'], data['pv'], data['position']['move_num'], data['position']['toplay'], scores, 0));

        // Update the PV arrow.
        clear_arrows();
        if (data['pv'].length >= 1) {
                var hiddenboard = new Chess(base_fen);

                // draw a continuation arrow as long as it's the same piece
                var last_to;
                for (var i = 0; i < data['pv'].length; i += 2) {
                        var move = patch_move(hiddenboard.move(data['pv'][i]));

                        if ((i >= 2 && move.from != last_to) ||
                             interfering_arrow(move.from, move.to)) {
                                break;
                        }
                        create_arrow(move.from, move.to, '#f66', 6, 20);
                        last_to = move.to;
                        hiddenboard.move(data['pv'][i + 1]);  // To keep continuity.
                }

                var alt_moves = find_nonstupid_moves(data, 30, data['position']['toplay'] === 'B');
                for (var i = 1; i < alt_moves.length && i < 3; ++i) {
                        hiddenboard = new Chess(base_fen);
                        var move = patch_move(hiddenboard.move(alt_moves[i]));
                        if (move !== null) {
                                create_arrow(move.from, move.to, '#f66', 1, 10);
                        }
                }
        }

        // See if all semi-reasonable moves have only one possible response.
        if (data['pv'].length >= 2) {
                var nonstupid_moves = find_nonstupid_moves(data, 300, data['position']['toplay'] === 'B');
                var response;
                {
                        var hiddenboard = new Chess(base_fen);
                        hiddenboard.move(data['pv'][0]);
                        response = hiddenboard.move(data['pv'][1]);
                }
                for (var i = 0; i < nonstupid_moves.length; ++i) {
                        if (nonstupid_moves[i] == data['pv'][0]) {
                                // ignore the PV move for refutation lines.
                                continue;
                        }
                        if (!data['refutation_lines'] ||
                            !data['refutation_lines'][nonstupid_moves[i]] ||
                            !data['refutation_lines'][nonstupid_moves[i]]['pv'] ||
                            data['refutation_lines'][nonstupid_moves[i]]['pv'].length < 2) {
                                // Incomplete PV, abort.
                                response = undefined;
                                break;
                        }
                        var line = data['refutation_lines'][nonstupid_moves[i]];
                        hiddenboard = new Chess(base_fen);
                        hiddenboard.move(line['pv'][0]);
                        var this_response = hiddenboard.move(line['pv'][1]);
                        if (this_response === null) {
                                console.log("BUG: ", i);
                                console.log(data);
                                console.log(line['pv']);
                        }
                        if (response.from !== this_response.from || response.to !== this_response.to) {
                                // Different response depending on lines, abort.
                                response = undefined;
                                break;
                        }
                }

                if (nonstupid_moves.length > 0 && response !== undefined) {
                        create_arrow(response.from, response.to, '#66f', 6, 20);
                }
        }

        // Update the refutation lines.
        base_fen = data['position']['fen'];
        move_num = parseInt(data['position']['move_num']);
        toplay = data['position']['toplay'];
        refutation_lines = hash_refutation_lines || data['refutation_lines'];
        update_refutation_lines();

        // Update the sparkline last, since its size depends on how everything else reflowed.
        update_sparkline(data);
}

var update_sparkline = function(data) {
        if (data && data['score_history']) {
                var first_move_num = undefined;
                for (var halfmove_num in data['score_history']) {
                        halfmove_num = parseInt(halfmove_num);
                        if (first_move_num === undefined || halfmove_num < first_move_num) {
                                first_move_num = halfmove_num;
                        }
                }
                if (first_move_num !== undefined) {
                        var last_move_num = data['position']['move_num'] * 2 - 3;
                        if (data['position']['toplay'] === 'B') {
                                ++last_move_num;
                        }

                        // Possibly truncate some moves if we don't have enough width.
                        // FIXME: Sometimes width() for #scorecontainer (and by extent,
                        // #scoresparkcontainer) on Chrome for mobile seems to start off
                        // at something very small, and then suddenly snap back into place.
                        // Figure out why.
                        var max_moves = Math.floor($("#scoresparkcontainer").width() / 5) - 5;
                        if (last_move_num - first_move_num > max_moves) {
                                first_move_num = last_move_num - max_moves;
                        }

                        var min_score = -100;
                        var max_score = 100;
                        var last_score = null;
                        var scores = [];
                        for (var halfmove_num = first_move_num; halfmove_num <= last_move_num; ++halfmove_num) {
                                if (data['score_history'][halfmove_num]) {
                                        var score = compute_plot_score(data['score_history'][halfmove_num]);
                                        last_score = score;
                                        if (score < min_score) min_score = score;
                                        if (score > max_score) max_score = score;
                                }
                                scores.push(last_score);
                        }
                        if (data['score']) {
                                scores.push(compute_plot_score(data['score']));
                        }
                        // FIXME: at some widths, calling sparkline() seems to push
                        // #scorecontainer under the board.
                        $('#scorespark').unbind('sparklineClick');
                        $("#scorespark").sparkline(scores, {
                                type: 'bar',
                                zeroColor: 'gray',
                                chartRangeMin: min_score,
                                chartRangeMax: max_score,
                                tooltipFormatter: function(sparkline, options, fields) {
                                        // score_history contains the Nth _position_, but format_tooltip
                                        // wants to format the Nth _move_; thus the -1.
                                        return format_tooltip(data, fields[0].offset + first_move_num - 1);
                                }
                        });
                        $('#scorespark').unbind('sparklineClick');
                        $('#scorespark').bind('sparklineClick', function(event) {
                                var sparkline = event.sparklines[0];
                                var region = sparkline.getCurrentRegionFields();
                                if (region[0].offset !== undefined) {
                                        show_line(0, first_move_num + region[0].offset - 1);
                                }
                        });
                } else {
                        $("#scorespark").text("");
                }
        } else {
                $("#scorespark").text("");
        }
}

/**
 * @param {number} num_viewers
 */
var update_num_viewers = function(num_viewers) {
        var text = "";
        if (num_viewers === null) {
                text = "";
        } else if (num_viewers == 1) {
                text = "You are the only current viewer";
        } else {
                text = num_viewers + " current viewers";
        }
        if (display_fen !== null) {
                var counter = Math.floor(display_fen.split(" ")[4] / 2);
                if (counter >= 20) {
                        text = text.replace("current ", "");
                        text += " | 50-move rule: " + counter;
                }
        }
        $("#numviewers").text(text);
}

var update_clock = function() {
        clearTimeout(clock_timer);

        var data = displayed_analysis_data || current_analysis_data;
        if (!data) return;

        if (data['position']) {
                var result = data['position']['result'];
                if (result === '1-0') {
                        $("#whiteclock").text("1");
                        $("#blackclock").text("0");
                        $("#whiteclock").removeClass("running-clock");
                        $("#blackclock").removeClass("running-clock");
                        return;
                }
                if (result === '1/2-1/2') {
                        $("#whiteclock").text("1/2");
                        $("#blackclock").text("1/2");
                        $("#whiteclock").removeClass("running-clock");
                        $("#blackclock").removeClass("running-clock");
                        return;
                }       
                if (result === '0-1') {
                        $("#whiteclock").text("0");
                        $("#blackclock").text("1");
                        $("#whiteclock").removeClass("running-clock");
                        $("#blackclock").removeClass("running-clock");
                        return;
                }
        }

        var white_clock_ms = null;
        var black_clock_ms = null;

        // Static clocks.
        if (data['position'] &&
            data['position']['white_clock'] &&
            data['position']['black_clock']) {
                white_clock_ms = data['position']['white_clock'] * 1000;
                black_clock_ms = data['position']['black_clock'] * 1000;
        }

        // Dynamic clock (only one, obviously).
        var color;
        if (data['position']['white_clock_target']) {
                color = "white";
                $("#whiteclock").addClass("running-clock");
                $("#blackclock").removeClass("running-clock");
        } else if (data['position']['black_clock_target']) {
                color = "black";
                $("#whiteclock").removeClass("running-clock");
                $("#blackclock").addClass("running-clock");
        } else {
                $("#whiteclock").removeClass("running-clock");
                $("#blackclock").removeClass("running-clock");
        }
        var remaining_ms;
        if (color) {
                var now = new Date().getTime() + client_clock_offset_ms;
                remaining_ms = data['position'][color + '_clock_target'] * 1000 - now;
                if (color === "white") {
                        white_clock_ms = remaining_ms;
                } else {
                        black_clock_ms = remaining_ms;
                }
        }

        if (white_clock_ms === null || black_clock_ms === null) {
                $("#whiteclock").empty();
                $("#blackclock").empty();
                return;
        }

        // If either player has twenty minutes or less left, add the second counters.
        // This matches what DGT clocks do.
        var show_seconds = (white_clock_ms < 60 * 20 * 1000 || black_clock_ms < 60 * 20 * 1000);

        if (color) {
                // See when the clock will change next, and update right after that.
                var next_update_ms;
                if (show_seconds) {
                        next_update_ms = remaining_ms % 1000 + 100;
                } else {
                        next_update_ms = remaining_ms % 60000 + 100;
                }
                clock_timer = setTimeout(update_clock, next_update_ms);
        }

        $("#whiteclock").text(format_clock(white_clock_ms, show_seconds));
        $("#blackclock").text(format_clock(black_clock_ms, show_seconds));
}

/**
 * @param {Number} remaining_ms
 * @param {boolean} show_seconds
 */
var format_clock = function(remaining_ms, show_seconds) {
        if (remaining_ms <= 0) {
                if (show_seconds) {
                        return "00:00:00";
                } else {
                        return "00:00";
                }
        }

        var remaining = Math.floor(remaining_ms / 1000);
        var seconds = remaining % 60;
        remaining = (remaining - seconds) / 60;
        var minutes = remaining % 60;
        remaining = (remaining - minutes) / 60;
        var hours = remaining;
        if (show_seconds) {
                return format_2d(hours) + ":" + format_2d(minutes) + ":" + format_2d(seconds);
        } else {
                return format_2d(hours) + ":" + format_2d(minutes);
        }
}

/**
 * @param {Number} x
 */
var format_2d = function(x) {
        if (x >= 10) {
                return x;
        } else {
                return "0" + x;
        }
}

/**
 * @param {string} move
 * @param {Number} move_num Move number of this move.
 * @param {boolean} white_to_play Whether white is to play this move.
 */
var format_move_with_number = function(move, move_num, white_to_play) {
        var ret;
        if (white_to_play) {
                ret = move_num + '. ';
        } else {
                ret = move_num + '… ';
        }
        ret += move;
        return ret;
}

/**
 * @param {string} move
 * @param {Number} halfmove_num Half-move number that is to be played,
 *   starting from 0.
 */
var format_halfmove_with_number = function(move, halfmove_num) {
        return format_move_with_number(
                move,
                Math.floor(halfmove_num / 2) + 1,
                halfmove_num % 2 == 0);
}

/**
 * @param {Object} data
 * @param {Number} halfmove_num
 */
var format_tooltip = function(data, halfmove_num) {
        if (data['score_history'][halfmove_num + 1] ||
            (halfmove_num + 1) === data['position']['history'].length) {
                // Position is in the history, or it is the current position
                // (which is implicitly tacked onto the history).
                var move;
                var short_score;
                if ((halfmove_num + 1) === data['position']['history'].length) {
                        move = data['position']['last_move'];
                        short_score = format_short_score(data['score']);
                } else {
                        move = data['position']['history'][halfmove_num];
                        short_score = format_short_score(data['score_history'][halfmove_num + 1]);
                }
                if (halfmove_num === -1) {
                        return "Start position: " + short_score;
                } else {
                        var move_with_number = format_halfmove_with_number(move, halfmove_num);
                        return "After " + move_with_number + ": " + short_score;
                }
        } else {
                for (var i = halfmove_num; i --> -1; ) {
                        if (data['score_history'][i]) {
                                var move = data['position']['history'][i];
                                if (i === -1) {
                                        return "[Analysis kept from start position]";
                                } else {
                                        return "[Analysis kept from " + format_halfmove_with_number(move, i) + "]";
                                }
                        }
                }
        }
}

/**
 * @param {boolean} truncate_history
 */
var set_truncate_history = function(truncate_history) {
        truncate_display_history = truncate_history;
        update_refutation_lines();
}
window['set_truncate_history'] = set_truncate_history;

/**
 * @param {number} line_num
 * @param {number} move_num
 */
var show_line = function(line_num, move_num) {
        if (line_num == -1) {
                current_display_line = null;
                current_display_move = null;
                hash_refutation_lines = null;
                if (displayed_analysis_data) {
                        // TODO: Support exiting to history position if we are in an
                        // analysis line of a history position.
                        displayed_analysis_data = null;
                }
                update_board();
                return;
        } else {
                current_display_line = jQuery.extend({}, display_lines[line_num]);  // Shallow clone.
                current_display_move = move_num + current_display_line.start_display_move_num;
        }
        current_display_line_is_history = (line_num == 0);

        update_historic_analysis();
        update_displayed_line();
        update_board_highlight();
        update_move_highlight();
        redraw_arrows();
}
window['show_line'] = show_line;

var prev_move = function() {
        if (current_display_line &&
            current_display_move >= current_display_line.start_display_move_num) {
                --current_display_move;
        }
        update_historic_analysis();
        update_displayed_line();
        update_move_highlight();
}
window['prev_move'] = prev_move;

var next_move = function() {
        if (current_display_line &&
            current_display_move < current_display_line.pv.length - 1) {
                ++current_display_move;
        }
        update_historic_analysis();
        update_displayed_line();
        update_move_highlight();
}
window['next_move'] = next_move;

var next_game = function() {
        if (current_games === null) {
                return;
        }

        // Try to find the game we are currently looking at.
        for (var game_num = 0; game_num < current_games.length; ++game_num) {
                var game = current_games[game_num];
                if (game['url'] === backend_url) {
                        var next_game_num = (game_num + 1) % current_games.length;
                        switch_backend(current_games[next_game_num]);
                        return;
                }
        }

        // Couldn't find it; give up.
}

var update_historic_analysis = function() {
        if (!current_display_line_is_history) {
                return;
        }
        if (current_display_move == current_display_line.pv.length - 1) {
                displayed_analysis_data = null;
                update_board();
        }

        // Fetch old analysis for this line if it exists.
        var hiddenboard = chess_from(current_display_line.start_fen, current_display_line.pv, current_display_move);
        var filename = "/history/move" + (current_display_move + 1) + "-" +
                hiddenboard.fen().replace(/ /g, '_').replace(/\//g, '-') + ".json";

        current_historic_xhr = $.ajax({
                url: filename
        }).done(function(data, textstatus, xhr) {
                displayed_analysis_data = data;
                update_board();
        }).fail(function(jqXHR, textStatus, errorThrown) {
                if (textStatus === "abort") {
                        // Aborted because we are switching backends. Don't do anything;
                        // we will already have been cleared.
                } else {
                        displayed_analysis_data = {'failed': true};
                        update_board();
                }
        });
}

/**
 * @param {string} fen
 */
var update_imbalance = function(fen) {
        var hiddenboard = new Chess(fen);
        var imbalance = {'k': 0, 'q': 0, 'r': 0, 'b': 0, 'n': 0, 'p': 0};
        for (var row = 0; row < 8; ++row) {
                for (var col = 0; col < 8; ++col) {
                        var col_text = String.fromCharCode('a1'.charCodeAt(0) + col);
                        var row_text = String.fromCharCode('a1'.charCodeAt(1) + row);
                        var square = col_text + row_text;
                        var contents = hiddenboard.get(square);
                        if (contents !== null) {
                                if (contents.color === 'w') {
                                        ++imbalance[contents.type];
                                } else {
                                        --imbalance[contents.type];
                                }
                        }
                }
        }
        var white_imbalance = '';
        var black_imbalance = '';
        for (var piece in imbalance) {
                for (var i = 0; i < imbalance[piece]; ++i) {
                        white_imbalance += '<img src="img/chesspieces/wikipedia/w' + piece.toUpperCase() + '.png" alt="" style="width: 15px;height: 15px;">';
                }
                for (var i = 0; i < -imbalance[piece]; ++i) {
                        black_imbalance += '<img src="img/chesspieces/wikipedia/b' + piece.toUpperCase() + '.png" alt="" style="width: 15px;height: 15px;">';
                }
        }
        $('#whiteimbalance').html(white_imbalance);
        $('#blackimbalance').html(black_imbalance);
}

/** Mark the currently selected move in red.
 * Also replaces the PV with the current displayed line if it's not shown
 * anywhere else on the screen.
 */
var update_move_highlight = function() {
        if (highlighted_move !== null) {
                highlighted_move.removeClass('highlight'); 
        }
        if (current_display_line) {
                var display_line_num = find_display_line_matching_num();
                if (display_line_num === null) {
                        // Replace the PV with the (complete) line.
                        $("#pvtitle").text("Exploring:");
                        current_display_line.start_display_move_num = 0;
                        display_lines.push(current_display_line);
                        $("#pv").html(print_pv(display_lines.length - 1, null));  // FIXME
                        display_line_num = display_lines.length - 1;

                        // Clear out the PV, so it's not selected by anything later.
                        display_lines[1].pv = [];
                }

                highlighted_move = $("#automove" + display_line_num + "-" + (current_display_move - current_display_line.start_display_move_num));
                highlighted_move.addClass('highlight');
        }
}

/**
 * See if the current displayed line is identical to any of the ones
 * we have on screen. (It might not be if e.g. the analysis reloaded
 * since we started looking.)
 *
 * @return {?number}
 */
var find_display_line_matching_num = function() {
        for (var i = 0; i < display_lines.length; ++i) {
                var line = display_lines[i];
                if (line.start_display_move_num > 0) continue;
                if (current_display_line.start_fen !== line.start_fen) continue;
                if (current_display_line.pv.length !== line.pv.length) continue;
                var ok = true;
                for (var j = 0; j < line.pv.length; ++j) {
                        if (current_display_line.pv[j] !== line.pv[j]) {
                                ok = false;
                                break;
                        }
                }
                if (ok) {
                        return i;
                }
        }
        return null;
}

/** Update the board based on the currently displayed line.
 * 
 * TODO: This should really be called only whenever something changes,
 * instead of all the time.
 */
var update_displayed_line = function() {
        if (current_display_line === null) {
                $("#linenav").hide();
                $("#linemsg").show();
                display_fen = base_fen;
                set_board_position(base_fen);
                update_imbalance(base_fen);
                return;
        }

        $("#linenav").show();
        $("#linemsg").hide();

        if (current_display_move <= 0) {
                $("#prevmove").html("Previous");
        } else {
                $("#prevmove").html("<a href=\"javascript:prev_move();\">Previous</a></span>");
        }
        if (current_display_move == current_display_line.pv.length - 1) {
                $("#nextmove").html("Next");
        } else {
                $("#nextmove").html("<a href=\"javascript:next_move();\">Next</a></span>");
        }

        var hiddenboard = chess_from(current_display_line.start_fen, current_display_line.pv, current_display_move);
        set_board_position(hiddenboard.fen());
        if (display_fen !== hiddenboard.fen() && !current_display_line_is_history) {
                // Fire off a hash request, since we're now off the main position
                // and it just changed.
                explore_hash(hiddenboard.fen());
        }
        display_fen = hiddenboard.fen();
        update_imbalance(hiddenboard.fen());
}

var set_board_position = function(new_fen) {
        board_is_animating = true;
        var old_fen = board.fen();
        board.position(new_fen);
        if (board.fen() === old_fen) {
                board_is_animating = false;
        }
}

/**
 * @param {boolean} param_enable_sound
 */
var set_sound = function(param_enable_sound) {
        enable_sound = param_enable_sound;
        if (enable_sound) {
                $("#soundon").html("<strong>On</strong>");
                $("#soundoff").html("<a href=\"javascript:set_sound(false)\">Off</a>");

                // Seemingly at least Firefox prefers MP3 over Opus; tell it otherwise,
                // and also preload the file since the user has selected audio.
                var ding = document.getElementById('ding');
                if (ding && ding.canPlayType && ding.canPlayType('audio/ogg; codecs="opus"') === 'probably') {
                        ding.src = 'ding.opus';
                        ding.load();
                }
        } else {
                $("#soundon").html("<a href=\"javascript:set_sound(true)\">On</a>");
                $("#soundoff").html("<strong>Off</strong>");
        }
        if (supports_html5_storage()) {
                localStorage['enable_sound'] = enable_sound ? 1 : 0;
        }
}
window['set_sound'] = set_sound;

/** Send off a hash probe request to the backend.
 * @param {string} fen
 */
var explore_hash = function(fen) {
        // If we already have a backend response going, abort it.
        if (current_hash_xhr) {
                current_hash_xhr.abort();
        }
        if (current_hash_display_timer) {
                clearTimeout(current_hash_display_timer);
                current_hash_display_timer = null;
        }
        $("#refutationlines").empty();
        current_hash_xhr = $.ajax({
                url: backend_hash_url + "?fen=" + fen
        }).done(function(data, textstatus, xhr) {
                show_explore_hash_results(data, fen);
        });
}

/** Process the JSON response from a hash probe request.
 * @param {!Object} data
 * @param {string} fen
 */
var show_explore_hash_results = function(data, fen) {
        if (board_is_animating) {
                // Updating while the animation is still going causes
                // the animation to jerk. This is pretty crude, but it will do.
                current_hash_display_timer = setTimeout(function() { show_explore_hash_results(data, fen); }, 100);
                return;
        }
        current_hash_display_timer = null;
        hash_refutation_lines = data['lines'];
        update_board();
}

// almost all of this stuff comes from the chessboard.js example page
var onDragStart = function(source, piece, position, orientation) {
        var pseudogame = new Chess(display_fen);
        if (pseudogame.game_over() === true ||
            (pseudogame.turn() === 'w' && piece.search(/^b/) !== -1) ||
            (pseudogame.turn() === 'b' && piece.search(/^w/) !== -1)) {
                return false;
        }

        recommended_move = get_best_move(pseudogame, source, null, pseudogame.turn() === 'b');
        if (recommended_move) {
                var squareEl = $('#board .square-' + recommended_move.to);
                squareEl.addClass('highlight1-32417');
        }
        return true;
}

var mousedownSquare = function(e) {
        reverse_dragging_from = null;
        var square = $(this).attr('data-square');

        var pseudogame = new Chess(display_fen);
        if (pseudogame.game_over() === true) {
                return;
        }

        // If the square is empty, or has a piece of the side not to move,
        // we handle it. If not, normal piece dragging will take it.
        var position = board.position();
        if (!position.hasOwnProperty(square) ||
            (pseudogame.turn() === 'w' && position[square].search(/^b/) !== -1) ||
            (pseudogame.turn() === 'b' && position[square].search(/^w/) !== -1)) {
                reverse_dragging_from = square;
                recommended_move = get_best_move(pseudogame, null, square, pseudogame.turn() === 'b');
                if (recommended_move) {
                        var squareEl = $('#board .square-' + recommended_move.from);
                        squareEl.addClass('highlight1-32417');
                        squareEl = $('#board .square-' + recommended_move.to);
                        squareEl.addClass('highlight1-32417');
                }
        }
}

var mouseupSquare = function(e) {
        if (reverse_dragging_from === null) {
                return;
        }
        var source = $(this).attr('data-square');
        var target = reverse_dragging_from;
        reverse_dragging_from = null;
        if (onDrop(source, target) !== 'snapback') {
                onSnapEnd(source, target);
        }
        $("#board").find('.square-55d63').removeClass('highlight1-32417');
}

var get_best_move = function(game, source, target, invert) {
        var moves = game.moves({ verbose: true });
        if (source !== null) {
                moves = moves.filter(function(move) { return move.from == source; });
        }
        if (target !== null) {
                moves = moves.filter(function(move) { return move.to == target; });
        }
        if (moves.length == 0) {
                return null;
        }
        if (moves.length == 1) {
                return moves[0];
        }

        // More than one move. Use the display lines (if we have them)
        // to disambiguate; otherwise, we have no information.
        var move_hash = {};
        for (var i = 0; i < moves.length; ++i) {
                move_hash[moves[i].san] = moves[i];
        }

        // See if we're already exploring some line.
        if (current_display_line &&
            current_display_move < current_display_line.pv.length - 1) {
                var first_move = current_display_line.pv[current_display_move + 1];
                if (move_hash[first_move]) {
                        return move_hash[first_move];
                }
        }

        // History and PV take priority over the display lines.
        for (var i = 0; i < 2; ++i) {
                var line = display_lines[i];
                var first_move = line.pv[line.start_display_move_num];
                if (move_hash[first_move]) {
                        return move_hash[first_move];
                }
        }

        var best_move = null;
        var best_move_score = null;

        for (var move in refutation_lines) {
                var line = refutation_lines[move];
                if (!line['score']) {
                        continue;
                }
                var first_move = line['pv'][0];
                if (move_hash[first_move]) {
                        var score = compute_score_sort_key(line['score'], line['depth'], invert);
                        if (best_move_score === null || score > best_move_score) {
                                best_move = move_hash[first_move];
                                best_move_score = score;
                        }
                }
        }
        return best_move;
}

var onDrop = function(source, target) {
        if (source === target) {
                if (recommended_move === null) {
                        return 'snapback';
                } else {
                        // Accept the move. It will be changed in onSnapEnd.
                        return;
                }
        } else {
                // Suggestion not asked for.
                recommended_move = null;
        }

        // see if the move is legal
        var pseudogame = new Chess(display_fen);
        var move = pseudogame.move({
                from: source,
                to: target,
                promotion: 'q' // NOTE: always promote to a queen for example simplicity
        });

        // illegal move
        if (move === null) return 'snapback';
}

var onSnapEnd = function(source, target) {
        if (source === target && recommended_move !== null) {
                source = recommended_move.from;
                target = recommended_move.to;
        }
        recommended_move = null;
        var pseudogame = new Chess(display_fen);
        var move = pseudogame.move({
                from: source,
                to: target,
                promotion: 'q' // NOTE: always promote to a queen for example simplicity
        });

        if (current_display_line &&
            current_display_move < current_display_line.pv.length - 1 &&
            current_display_line.pv[current_display_move + 1] === move.san) {
                next_move();
                return;
        }

        // Walk down the displayed lines until we find one that starts with
        // this move, then select that. Note that this gives us a good priority
        // order (history first, then PV, then multi-PV lines).
        for (var i = 0; i < display_lines.length; ++i) {
                if (i == 1 && current_display_line) {
                        // Do not choose PV if not on it.
                        continue;
                }
                var line = display_lines[i];
                if (line.pv[line.start_display_move_num] === move.san) {
                        show_line(i, 0);
                        return;
                }
        }

        // Shouldn't really be here if we have hash probes, but there's really
        // nothing we can do.
}
// End of dragging-related code.

var fmt_cp = function(v) {
        if (v === 0) {
                return "0.00";
        } else if (v > 0) {
                return "+" + (v / 100).toFixed(2);
        } else {
                v = -v;
                return "-" + (v / 100).toFixed(2);
        }
}

var format_short_score = function(score) {
        if (!score) {
                return "???";
        }
        if (score[0] === 'T' || score[0] === 't') {
                var ret = "TB\u00a0";
                if (score[2]) {  // Is a bound.
                        ret = score[2] + "\u00a0TB\u00a0";
                }
                if (score[0] === 'T') {
                        return ret + Math.ceil(score[1] / 2);
                } else {
                        return ret + "-" + Math.ceil(score[1] / 2);
                }
        } else if (score[0] === 'M' || score[0] === 'm') {
                var sign = (score[0] === 'm') ? '-' : '';
                if (score[2]) {  // Is a bound.
                        return score[2] + "\u00a0M " + sign + score[1];
                } else {
                        return "M " + sign + score[1];
                }
        } else if (score[0] === 'd') {
                return "TB =0";
        } else if (score[0] === 'cp') {
                if (score[2]) {  // Is a bound.
                        return score[2] + "\u00a0" + fmt_cp(score[1]);
                } else {
                        return fmt_cp(score[1]);
                }
        }
        return null;
}

var format_long_score = function(score) {
        if (!score) {
                return "???";
        }
        if (score[0] === 'T') {
                if (score[1] == 0) {
                        return "Won for white (tablebase)";
                } else {
                        return "White wins in " + Math.ceil(score[1] / 2);
                }
        } else if (score[0] === 't') {
                if (score[1] == -1) {
                        return "Won for black (tablebase)";
                } else {
                        return "Black wins in " + Math.ceil(score[1] / 2);
                }
        } else if (score[0] === 'M') {
                if (score[1] == 0) {
                        return "White wins by checkmate";
                } else {
                        return "White mates in " + score[1];
                }
        } else if (score[0] === 'm') {
                if (score[1] == 0) {
                        return "Black wins by checkmate";
                } else {
                        return "Black mates in " + score[1];
                }
        } else if (score[0] === 'd') {
                return "Theoretical draw";
        } else if (score[0] === 'cp') {
                return "Score: " + format_short_score(score);
        }
        return null;
}

var compute_plot_score = function(score) {
        if (score[0] === 'M' || score[0] === 'T') {
                return 500;
        } else if (score[0] === 'm' || score[0] === 't') {
                return -500;
        } else if (score[0] === 'd') {
                return 0;
        } else if (score[0] === 'cp') {
                if (score[1] > 500) {
                        return 500;
                } else if (score[1] < -500) {
                        return -500;
                } else {
                        return score[1];
                }
        }
        return null;
}

/**
 * @param score The score digest tuple.
 * @param {?number} depth Depth the move has been computed to, or null.
 * @param {boolean} invert Whether black is to play.
 * @param {boolean=} depth_secondary_key
 * @return {number}
 */
var compute_score_sort_key = function(score, depth, invert, depth_secondary_key) {
        var s;
        if (!score) {
                return -10000000;
        }
        if (score[0] === 'T') {
                // White reaches TB win.
                s = 89999 - score[1];
        } else if (score[0] === 't') {
                // Black reaches TB win.
                s = -(89999 - score[1]);
        } else if (score[0] === 'M') {
                // White mates.
                s = 99999 - score[1];
        } else if (score[0] === 'm') {
                // Black mates.
                s = -(99999 - score[1]);
        } else if (score[0] === 'd') {
                s = 0;
        } else if (score[0] === 'cp') {
                s = score[1];
        }
        if (s) {
                if (invert) s = -s;
                if (depth_secondary_key) {
                        return s * 200 + (depth || 0);
                } else {
                        return s;
                }
        } else {
                return null;
        }
}

/**
 * @param {Object} game
 */
var switch_backend = function(game) {
        // Stop looking at historic data.
        current_display_line = null;
        current_display_move = null;
        displayed_analysis_data = null;
        if (current_historic_xhr) {
                current_historic_xhr.abort();
        }

        // If we already have a backend response going, abort it.
        if (current_analysis_xhr) {
                current_analysis_xhr.abort();
        }
        if (current_hash_xhr) {
                current_hash_xhr.abort();
        }

        // Otherwise, we should have a timer going to start a new one.
        // Kill that, too.
        if (current_analysis_request_timer) {
                clearTimeout(current_analysis_request_timer);
                current_analysis_request_timer = null;
        }
        if (current_hash_display_timer) {
                clearTimeout(current_hash_display_timer);
                current_hash_display_timer = null;
        }

        // Request an immediate fetch with the new backend.
        backend_url = game['url'];
        backend_hash_url = game['hashurl'];
        window.location.hash = '#' + game['id'];
        current_analysis_data = null;
        ims = 0;
        request_update();
}
window['switch_backend'] = switch_backend;

window['flip'] = function() { board.flip(); redraw_arrows(); };

var init = function() {
        unique = get_unique();

        // Load settings from HTML5 local storage if available.
        if (supports_html5_storage() && localStorage['enable_sound']) {
                set_sound(parseInt(localStorage['enable_sound']));
        } else {
                set_sound(false);
        }

        // Create board.
        board = new window.ChessBoard('board', {
                onMoveEnd: function() { board_is_animating = false; },

                draggable: true,
                onDragStart: onDragStart,
                onDrop: onDrop,
                onSnapEnd: onSnapEnd
        });
        $("#board").on('mousedown', '.square-55d63', mousedownSquare);
        $("#board").on('mouseup', '.square-55d63', mouseupSquare);

        request_update();
        $(window).resize(function() {
                board.resize();
                update_sparkline(displayed_analysis_data || current_analysis_data);
                update_board_highlight();
                redraw_arrows();
        });
        $(window).keyup(function(event) {
                if (event.which == 39) {  // Left arrow.
                        next_move();
                } else if (event.which == 37) {  // Right arrow.
                        prev_move();
                } else if (event.which >= 49 && event.which <= 57) {  // 1-9.
                        var num = event.which - 49;
                        if (current_games && current_games.length >= num) {
                                switch_backend(current_games[num]);
                        }
                } else if (event.which == 78) {  // N.
                        next_game();
                }
        });
        window.addEventListener('hashchange', possibly_switch_game_from_hash, false);
        possibly_switch_game_from_hash();
};
$(document).ready(init);

})();