vote.js

// vote.js
//
// This is the Javascript support for the animated ballot. Rows are
// automatically resorted in ranking order, and buttons are provided
// for convenient manipulation of the ballot.

var rows = new Array;           // the actual DOM nodes for the table rows
var rank = new Array;           // the ranks of the table rows (1..num_choices)
var selected = new Array;
var preftable;                  // the ballot table
var prefsection;                // the parent node of the rows (a section)
var num_choices;

var cur_top;
var cur_bot;

var num_selected;
var selected_list;
var num_at_rank = new Array;

// Move the element of a currently at index i so it is just
// before the element currently at index j, while keeping
// all other elements in the same relative order. if
// j=num_choices then the element is put at the end.
function move_elem_to(a, i, j) {
    if (i == j) return;
    //alert("moving " + i + " to " + j);
    var src = a[i];
    if (i < j) {
        // move elems from i+1 to j-1 up one
        for (var k=i; k < j-1; k++) a[k] = a[k+1];
        a[j-1] = src;
    } else {
        // move elems from j to i-1 down one
        for (var k=i; k > j; k--) a[k] = a[k-1];
        a[j] = src;
    }
}

// return true if a later row moved into the row
// that moved.
function resort_row(i) {
    // figure out where it goes (j)
    var j = 0;
    while (j < num_choices && (j == i || rank[j] <= rank[i])) {
        j++;
    }
    if (i == j || i == j - 1) { // XXX is i==j test needed?
        //alert("no move needed for " + i);
        return false;
    }

    //alert("moving " + i + " to " + j);
    // fix UI
    if (j == num_choices) {
        prefsection.appendChild(rows[i]);
    } else {
        prefsection.insertBefore(rows[i], rows[j]);
    }

    // now fix rows, rank, and selected
    move_elem_to(rows, i, j);
    move_elem_to(rank, i, j);
    move_elem_to(selected, i, j);
    selected_list = null;

    return (i < j);
}

// stably sort rows by their rank
function sort_rows() {
    read_rows();
    //alert("sorting the rows of " + preftable);
    var permut = new Array;
    for (var i = 0; i < num_choices; i++) {
        permut[i] = i;
    }
    function compare(m,n) {
        if (rank[m] < rank[n]) return -1;
        if (rank[m] > rank[n]) return 1;
        if (m < n) return -1; // make it stable, please!
        if (m > n) return 1;
        return 0;
    }
    permut.sort(compare);
    diag = "";
    var newselected = new Array;
    for (var i = 0; i < permut.length; i++) {
        var j = permut[i];
        prefsection.appendChild(rows[j]);
        newselected[i] = selected[j];
        diag = diag + j;
    }
    selected = newselected;
    //alert("permutation: " + diag);
    read_rows();
    set_row_borders();
}

function set_row_borders() {
    for (var i = 0; i < num_choices; i++) {
	set_row_style(i);
    }
}

function set_row_style(i) {
    if (selected[i]) {
	if (i < num_choices-1 && rank[i] == rank[i+1]) {
	    rows[i].setAttribute('class', 'selected tied');
	} else {
	    rows[i].setAttribute('class', 'selected');
	}
    } else {
	if (i < num_choices-1 && rank[i] == rank[i+1]) {
	    rows[i].setAttribute('class', 'tied');
	} else {
	    rows[i].setAttribute('class', null);
	}
    }
}

// select the indicated row object. add is true
// if the user want to add to (or remove from)
// the current selection.
function select_row(row, add) {
    for (var i = 0; i < num_choices; i++) {
        if (!add) {
	    selected[i] = false;
        }
        if (rows[i] == row) {
	    selected[i] = !selected[i];
	}
	set_row_style(i);
    }
}

// Recompute the arrays "rows" and "rank" from the rows of the table.
function read_rows() {
    //alert("reading the rows, length = " + (preftable.rows.length - 1));
    for (var i = 0; i < num_choices; i++) {
        var row = rows[i] = preftable.rows[i+1];
        var s = row.getElementsByTagName("select")[0];
        rank[i] = s.selectedIndex + 1;
    }
}

// Compute the num_at_rank array
function scan_ranks() {
    var i;
    for (i = 1; i <= num_choices+1; i++) num_at_rank[i] = 0;
    for (i = 0; i < num_choices; i++) num_at_rank[rank[i]]++;
}

// minimum of ranks of selected items
// effect: updates num_selected, selected_list
function min_selected_rank() {
    var cur = num_choices + 1;
    num_selected = 0;
    selected_list = new Array;
    for (var i = 0; i < num_choices; i++) {
        if (selected[i]) {
            selected_list[num_selected++] = i;
            if (rank[i] < cur) cur = rank[i];
        }
    }
    return cur;
}

// maximum of ranks of selected items
// effect: updates num_selected, selected_list
function max_selected_rank() {
    var cur = 1;
    num_selected = 0;
    selected_list = new Array;
    for (var i = 0; i < num_choices; i++) {
        if (selected[i]) {
            selected_list[num_selected++] = i;
            if (rank[i] > cur) cur = rank[i];
        }
    }
    return cur;
}

function num_sel_by_rank(r) {
    var c = 0;
    for (var i = 0; i < num_selected; i++) {
        if (rank[selected_list[i]] == r) c++;
    }
    return c;
}

function selector(r) {
    return r.getElementsByTagName('select')[0];
}


// return true if it had to be moved
function set_rank(i, r) {
    //alert("Setting rank of " + i + " to " + r);
    if (rank[i] == r) return false;
    rank[i] = r;
    selector(rows[i]).selectedIndex = r - 1;
    return resort_row(i);
}

// set multiple choices to have the same rank
function do_make_tie() {
    var min_rank = min_selected_rank();
    if (num_selected < 2) {
        alert("Not enough choices were selected. "+
              "Shift-click to select two or more choices");
        return;
    }
    for (var i = 0; i < num_choices; i++) {
        if (selected[i])
            if (set_rank(i, min_rank)) i--;
    }
    set_row_borders();
}

// move the selected choices up
function do_move_up () {
    var min_rank = min_selected_rank();
    if (num_selected < 1) {
        alert("No choices were selected. "+
              "Click (or shift-click) to select choices");
        return;
    }
    if (min_rank == 1) return;
    scan_ranks();
    var nr = num_sel_by_rank(min_rank);
    var new_rank = min_rank - 1;
    var split = (num_at_rank[min_rank] > nr);
    if (!split) { // moving whole rank
        while (new_rank > 1 && !num_at_rank[new_rank])
            new_rank--; // find prev full rank to jump past
        // should check here whether new_rank = num_choices
        // and do a "push up" if so.
    } else if (num_at_rank[new_rank]) {
        // an additional rank is being occupied and we
        // don't have a place to put it. Try shifting
        // others up first.
        var j = new_rank;
        //alert("trying to shift up");
        while (j >= 1 && num_at_rank[j]) j--;
        if (j >= 1) { // nothing at j: can shift up
            for (var i = 0; i < num_choices; i++) {
                if (rank[i] > j && rank[i] <= new_rank)
                    set_rank(i, rank[i] - 1); // should not change position
            }
        } else { // must shift down
            new_rank++;
            var j = new_rank;
            //alert("shifting down");
            while (j <= num_choices && num_at_rank[j]) j++;
                // note: don't shift choices down to "no opinion"
            if (j <= num_choices) { // nothing at j: can shift down
                for (var i = num_choices; i >= 0; i--) {
                    if (rank[i] >= new_rank && rank[i] < j)
                        set_rank(i, rank[i] + 1); // should not change posn
                }
            }
        }
    }
    //alert("updating ranks");
    for (var i = 0; i < num_choices; i++) {
        if (selected[i]) {
            if (set_rank(i, new_rank)) i--;
        }
        else if (!split && rank[i] == new_rank && new_rank < num_choices)
            // we have an empty rank to push the old rank down to
            if (set_rank(i, rank[i]+1)) i--;
    }
    set_row_borders();
}

// move the selected choices down
function do_move_down () {
    var max_rank = max_selected_rank();
    if (num_selected < 1) {
        alert("No choices were selected. "+
              "Click (or shift-click) to select choices");
        return;
    }
    if (max_rank == num_choices + 1) {
        alert("Use pulldown to change the rank from \"No opinion\"");
        return;
    }
    var new_rank = max_rank + 1;
    if (new_rank == num_choices + 1) {
        new_rank = max_rank;
        //alert("moving bottom-ranked item down " + new_rank);
    }
    scan_ranks();
    var nr = num_sel_by_rank(max_rank);
    var split = (num_at_rank[max_rank] > nr);
    if (!split) { // moving whole rank
        while (new_rank < num_choices && !num_at_rank[new_rank])
            new_rank++; // find next full rank to jump past
    } else if (num_at_rank[new_rank]) {
        // an additional rank is being occupied and we
        // don't have a place to put it. Try shifting
        // others down first.
        var j = new_rank;
        //alert("trying to shift down");
        while (j <= num_choices && num_at_rank[j]) j++;
        if (j <= num_choices) { // nothing at j: can shift down
            // note: won't shift choices down to "no opinion"
            for (var i = num_choices-1; i >= 0; i--) {
                if (rank[i] < j && rank[i] >= new_rank)
                    set_rank(i, rank[i] + 1); // should not change position
            }
        } else { // must shift up
            if (new_rank != max_rank) new_rank--;
            var j = new_rank;
            while (j >= 1 && num_at_rank[j]) j--;
            //alert("shifting up to " + j);
            if (j >= 1) { // nothing at j: can shift up
                for (var i = 0; i < num_choices; i++) {
                    if (rank[i] <= new_rank && rank[i] > j) {
            //alert("moving " + i + " from " + rank[i] + " to " + (rank[i]-1));
                        set_rank(i, rank[i] - 1); // should not change posn
                    }
                }
            }
        }
    }
    for (var i = 0; i < num_choices; i++) {
        if (selected[i]) {
            //alert("now moving " + i + " from " + rank[i] + " to " + new_rank);
            if (set_rank(i, new_rank)) i--;
        } else if (!split && rank[i] == new_rank && new_rank > 1) {
            if (set_rank(i, rank[i] - 1)) i--;
        }
    }
    set_row_borders();
}

// move the suggested choices to the top ranking (1)
function do_move_top() {
    var min_rank = min_selected_rank();
    if (num_selected < 1) {
        alert("No choices were selected. "+
              "Click (or shift-click) to select choices");
        return;
    }
    //if (min_rank <= cur_top)
    cur_top = 1;
    scan_ranks();
    var collision = num_at_rank[min_rank];
    for (var i = 0; i < num_choices; i++) {
        if (selected[i]) {
            if (set_rank(i, cur_top)) i--;
        } else if (collision && rank[i] >= cur_top &&
                    rank[i] < min_rank &&
                    rank[i] < num_choices) {
            set_rank(i, rank[i] + 1);
        }
    }
    cur_top++;
    set_row_borders();
}

// move the suggested choices to the bottom possible ranking
function do_move_bottom() {
    var max_rank = max_selected_rank();
    if (num_selected < 1) {
        alert("No choices were selected. "+
              "Click (or shift-click) to select choices");
        return;
    }
    //if (max_rank >= cur_bot)
    cur_bot = num_choices;
    scan_ranks();
    var collision = num_at_rank[max_rank];
    for (var i = 0; i < num_choices; i++) {
        if (selected[i]) {
            if (set_rank(i, cur_bot)) i--;
        } else if (collision && rank[i] <= cur_bot
                             && rank[i] > max_rank
                             && rank[i] > 1) {
            set_rank(i, rank[i] - 1);
        }
    }
    cur_bot--;
    set_row_borders();
}

// Correct the ranks of the rows after a row is dragged.
function drag_update(e, u) {
    var this_select = u.item.find('select')[0];
    var rownum = 0;
    read_rows();
    var i;
    var selected;
    for (i = 0; i < num_choices; i++) {
        if (selector(rows[i]) == this_select) {
            selected = i;
        }
    }
    selector(rows[selected]).selectedIndex = selected;
    i = selected-1;
    var last_dest = selected;
    var last_src = -1;

    while (i >= 0) {
        // three cases: 1. rank[i] is the same as the rank of the
        // previous one. In this case map it to last_dest.
        // 2. Or it is less than last_dest, in which keep it the same.
        // 3. Otherwise map it to last_used - 1;
        if (rank[i] != last_src) {
            last_src = rank[i];
            if (rank[i]-1 < last_dest) break;
            else last_dest--;
        }
        selector(rows[i]).selectedIndex = last_dest;
        i--;
    }
    i = selected+1;
    last_src = -1;
    last_dest = selected;
    while (i < num_choices) {
        if (rank[i] != last_src) {
            last_src = rank[i];
            if (rank[i]-1 > last_dest) break;
            else last_dest++;
        }
        selector(rows[i]).selectedIndex = last_dest;
        i++;
    }
    read_rows();
    set_row_borders();
}

// initialize the UI

if (window.navigator.appName != "Microsoft Internet Explorer") {
    Element.prototype.app = function(c) {
	this.appendChild(c);
	return this;
    }
}

function el(t) {
    return document.createElement(t);
}
function tx(t) {
    return document.createTextNode(t);
}

function setup() {
    var button = document.getElementById("sort_button");
    if (button != null) {
	button.parentNode.removeChild(button);
    }


    var jsnohelp = document.getElementById("jsnohelp");
    var jshelp = document.getElementById("jshelp");

    if (jshelp != null) {
	var curtext = jshelp.childNodes[0];

	jsnohelp.style.display = 'none';
	jshelp.style.display = 'block';

	document.CastVote.move_top.disabled = false;
	document.CastVote.move_up.disabled = false;
	document.CastVote.make_tie.disabled = false;
	document.CastVote.move_down.disabled = false;
	document.CastVote.move_bottom.disabled = false;
    }

    preftable = document.getElementById("preftable");
    prefsection = preftable.rows[0].parentNode;
    num_choices = preftable.rows.length - 1;

    cur_top = 1;
    cur_bot = num_choices;

    sort_rows();

    $('#preftable tbody').sortable({'items':'tr:not(.heading)',
			'axis':'y', 
			'update':drag_update});
}
//vim: sw=4 ts=8