function Segment(x, y) 
{
  if (x < y) {
    this.x = x;
    this.y = y;
  } else {
    this.x = y;
    this.y = x;
  }
}

Segment.prototype.length = function ()
{
  return (this.y - this.x);
}

Segment.prototype.before = function (s)
{
  return (this.x < s.x);
}

// Returns the intersection of segments s1 and s2
// or null is it doesn't exist
Segment.intersection = function (s1, s2)
{
  if (s2.before(s1)) {
    tmp = s1;
    s1 = s2; 
    s2 = tmp;
  }
  if (s1.y < s2.x) {
    // No intersection
    return null;
  } else {
    return new Segment(s2.x, Math.min(s1.y, s2.y));
  }
}

function Point(x, y) 
{
  this.x = x;
  this.y = y;
}

// A rectangle is defined by its left corner p0, 
// its length dx and high dy 
function Rectangle(p0, dx, dy) 
{
  this.p0 = p0;
  this.dx = dx;
  this.dy = dy;
}

Rectangle.prototype.lowerEdge = function ()
{
  return new Segment(this.p0.x, this.p0.x + this.dx);
}

Rectangle.prototype.leftEdge = function ()
{
  return new Segment(this.p0.y, this.p0.y + this.dy);
}

// s1 should be the lower edge and s2 the left one. 
// And they *must* shape a rectangle
Rectangle.fromSegments = function (s1, s2)
{
  return new Rectangle(new Point(s1.x, s2.x), s1.length(), s2.length());
}

// Return the intersection of r1 and r2
// or null is it doesn't exist
Rectangle.intersection = function (r1, r2)
{
  var sleft = Segment.intersection(r1.leftEdge(), r2.leftEdge());
  var slower = Segment.intersection(r1.lowerEdge(), r2.lowerEdge());
  if (sleft == null || slower == null) {
    return new Rectangle(new Point(0,0), 0, 0);
  } else {
    return Rectangle.fromSegments(slower, sleft);
  }
}

Rectangle.prototype.area = function ()
{
  return this.dx * this.dy;
}