Guess = function(points)
{
    this.points = points;
    this.position = [0,0];
    this.dragDiff = [0,0];
    this.handles = [new Handle(this.position)];
}

Guess.prototype = inherit([Draggable]);

Guess.RADIUS = 10;
Guess.DRAW_NUMBERS = false;

Guess.prototype.clickIn = function(screenloc)
{
    var canvasLoc = worldToCanvas(this.position);

    var dx = screenloc[0] - canvasLoc[0];
    var dy = screenloc[1] - canvasLoc[1];

    return dx < Guess.RADIUS && dx > -Guess.RADIUS &&
           dy < Guess.RADIUS && dy > -Guess.RADIUS;
}

Guess.prototype.draw = function(ctx, info)
{
    var points = this.points;
    var n = points.length;
    if( n == 0 )
    {
        return;
    }

    var p = this.position;
    if( n == 1 )
    {
        p[0] = points[0].point[0];
        p[1] = points[0].point[1];
    }

    var convert = info.convert;
    ctx.beginPath();
    ctx.lineWidth = 2;
    ctx.strokeStyle = "rgba(40, 200, 250, 0.6)";
    ctx.fillStyle = "rgba(40, 200, 250, 1.0)";

    var a = convert(p);
    for ( var i = 0; i < n; i++ )
    {
        var b = convert(points[i].point);
        ctx.beginPath();
        ctx.moveTo(a[0], a[1]);
        ctx.lineTo(b[0], b[1]);
        ctx.stroke();
    }

    ctx.beginPath();
    ctx.ellipse(a[0], a[1], Guess.RADIUS, Guess.RADIUS, 0, 0, 2 * Math.PI);
    ctx.fill();
    ctx.closePath();

    if (Guess.DRAW_NUMBERS)
    {
        var td = 0.0;
        for ( var i = 0; i < n; i++ )
        {
            var q = points[i].point;
            var d0 = q[0] - p[0];
            var d1 = q[1] - p[1];
            td += Math.sqrt(d0*d0 + d1*d1);
        }

        ctx.font = "20px Arial";
        ctx.fillStyle = "rgba(40, 200, 250, 0.4)"
        ctx.lineWidth = 1;

        ctx.fillText(td.toFixed(2), a[0]+10, a[1]-10);
    }
}

Guess.prototype.step = function(ctx, info)
{
    if( this.isDragging )
    {
        return;
    }

    var points = this.points;
    var p = this.position;

    var n = points.length;
    if( n == 0 )
    {
        p[0] = 0;
        p[1] = 0;
        return;
    }

    if( n == 1 )
    {
        p[0] = points[0].point[0];
        p[1] = points[0].point[1];
        return;
    }

    var g = [0, 0];
    var k = 10.0/n;
    for ( var i = 0; i < n; i++ )
    {
        var q = points[i].point;
        var d0 = q[0] - p[0];
        var d1 = q[1] - p[1];
        var d = Math.sqrt(d0*d0 + d1*d1);
        if (d > 0.0)
        {
            g[0] -= k*d0/d;
            g[1] -= k*d1/d;
        }
    }

    p[0] -= g[0];
    p[1] -= g[1];
}