SVG.Gradient = SVG.invent({
  // Initialize node
  create: function(type) {
    this.constructor.call(this, SVG.create(type + 'Gradient'))
    
    // store type 
    this.type = type
  }

  // Inherit from
, inherit: SVG.Container

  // Add class methods
, extend: {
    // Add a color stop
    at: function(offset, color, opacity) {
      return this.put(new SVG.Stop).update(offset, color, opacity)
    }
    // Update gradient
  , update: function(block) {
      // remove all stops 
      this.clear()
      
      // invoke passed block 
      if (typeof block == 'function')
        block.call(this, this)
      
      return this
    }
    // Return the fill id
  , fill: function() {
      return 'url(#' + this.id() + ')'
    }
    // Alias string convertion to fill
  , toString: function() {
      return this.fill()
    }
    // custom attr to handle transform
  , attr: function(a, b, c) {
      if(a == 'transform') a = 'gradientTransform'
      return SVG.Container.prototype.attr.call(this, a, b, c)
    }
  }
  
  // Add parent method
, construct: {
    // Create gradient element in defs
    gradient: function(type, block) {
      return this.defs().gradient(type, block)
    }
  }
})

// Add animatable methods to both gradient and fx module
SVG.extend(SVG.Gradient, SVG.FX, {
  // From position
  from: function(x, y) {
    return (this.target || this).type == 'radial' ?
      this.attr({ fx: new SVG.Number(x), fy: new SVG.Number(y) }) :
      this.attr({ x1: new SVG.Number(x), y1: new SVG.Number(y) })
  }
  // To position
, to: function(x, y) {
    return (this.target || this).type == 'radial' ?
      this.attr({ cx: new SVG.Number(x), cy: new SVG.Number(y) }) :
      this.attr({ x2: new SVG.Number(x), y2: new SVG.Number(y) })
  }
})

// Base gradient generation
SVG.extend(SVG.Defs, {
  // define gradient
  gradient: function(type, block) {
    return this.put(new SVG.Gradient(type)).update(block)
  }
  
})

SVG.Stop = SVG.invent({
  // Initialize node
  create: 'stop'

  // Inherit from
, inherit: SVG.Element

  // Add class methods
, extend: {
    // add color stops
    update: function(o) {
      if (typeof o == 'number' || o instanceof SVG.Number) {
        o = {
          offset:  arguments[0]
        , color:   arguments[1]
        , opacity: arguments[2]
        }
      }

      // set attributes 
      if (o.opacity != null) this.attr('stop-opacity', o.opacity)
      if (o.color   != null) this.attr('stop-color', o.color)
      if (o.offset  != null) this.attr('offset', new SVG.Number(o.offset))

      return this
    }
  }

})