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-- Below there are 2 auxiliary functions

function Distance(x1,y1, x2,y2)
  return (x2-x1)^2+(y2-y1)^2
end

function Lerp(a, b, t)
  return a + t * (b - a)
end


-- In order to encapsulate the of following the mouse, we are
-- going to create class FollowSprite that is derived from Sprite class.


-- Pay attention to line below. It shows you how to extend a class in Gideros.
FollowSprite = Core.class(Sprite)

-- init() method is the constructor of our class. It will be called when one
-- instantiates FollowSprite (it's done by calling function new()).
--
-- speed parameter adjusts how fast sprite will follow mouse.
-- distance parameter sets how far from mouse sprite will be.
-- texture expects the

function FollowSprite:init(speed, distance, image)
  self.bmp = Bitmap.new(Texture.new(image))
  self.bmp:setAnchorPoint(.5,.5)
  self:addChild(self.bmp)
  self.tx = 0
  self.ty = 0
  self.speed = speed
  self.dist = distance
end

function FollowSprite:follow(x, y)
  self.tx = x
  self.ty = y
end

function FollowSprite:update(dt)
  local x, y = self:getPosition()
  local distSq = Distance(x, y, self.tx, self.ty)

  if (distSq > self.dist^2) then
    local t = 0.1
    x = Lerp(x, self.tx, t)
    y = Lerp(y, self.ty, t)
    self:setPosition(x, y)
  end
end

-- Here we instantiate FollowSprite. Note that it calls init().
local obj = FollowSprite.new(300, 20, 'gideros.png')

stage:addChild(obj)

-- On ENTER_FRAME event we update sprite's position.
stage:addEventListener(Event.ENTER_FRAME, function(e)
                       local dt = e.deltaTime
                       obj:update(dt)
                       end)

-- On MOUSE_HOVER event, we update sprite position when mouse moves.
stage:addEventListener(Event.MOUSE_HOVER, function(e)
                       obj:follow(e.x, e.y)
                       end)