I need advice on how to do collision in a clone of Pong - ruby

Question

Hi I am building a clone pong program with ruby and rubygame. My ain problem at the moment is the collision of the leftside. The collision happends backwards. The right works perfectly fine. I need help. Can anyone fix this?
Heres my code
require 'rubygems'
require 'rubygame'
Rubygame::TTF.setup
class Game
def initialize
#screen = Rubygame::Screen.new [640,480], 0,
[Rubygame::HWSURFACE, Rubygame::DOUBLEBUF]
#screen.title = "Pong"
#queue = Rubygame::EventQueue.new
#clock = Rubygame::Clock.new
#clock.target_framerate = 60
limit = #screen.height - 10
#player = Paddle.new 50, 10, Rubygame::K_W, Rubygame::K_S, 10, limit
#enemy = Paddle.new #screen.width-50-#player.width, 10,
Rubygame::K_UP, Rubygame::K_DOWN, 10, limit
#player.center_y #screen.height
#enemy.center_y #screen.height
#ball = Ball.new #screen.width/2, #screen.height/2
#background = Background.new #screen.width, #screen.height
end
def run!
loop do
update
draw
#clock.tick
end
end
def update
#player.update
#enemy.update
#ball.update #screen
#queue.each do |ev|
#player.handle_event ev
#enemy.handle_event ev
case ev
when Rubygame::QuitEvent
Rubygame.quit
exit
when Rubygame::KeyDownEvent
if ev.key==Rubygame::K_ESCAPE
#queue.push Rubygame::QuitEvent.new
end
end
end
if collision? #ball, #player
#ball.collision #player, #ball
elsif collision? #ball, #enemy
#ball.collision #enemy, #ball
end
end
def draw
#screen.fill [0,0,0]
#background.draw #screen
#player.draw #screen
#enemy.draw #screen
#ball.draw #screen
#screen.flip
end
def collision? obj1, obj2
if obj1.y + obj1.height < obj2.y ; return false ; end
if obj1.y > obj2.y + obj2.height ; return false ; end
if obj1.x + obj1.width < obj2.x ; return false ; end
if obj1.x > obj2.x + obj2.width ; return false ; end
return true
end
end
class GameObject
attr_accessor :x, :y, :width, :height, :surface
def initialize x, y, surface
#x = x
#y = y
#surface = surface
#width = surface.width
#height = surface.height
end
def update
end
def draw screen
#surface.blit screen, [#x, #y]
end
def handle_event event
end
end
class Paddle < GameObject
def initialize x,y,up_key,down_key,top_limit,bottom_limit
surface = Rubygame::Surface.new [20, 100]
surface.fill [255, 255, 255]
#up_key = up_key
#down_key = down_key
#moving_up = false
#moving_down = false
#top_limit = top_limit
#bottom_limit = bottom_limit
super x, y, surface
end
def center_y h
#y = h/2-#height/2
end
def handle_event event
case event
when Rubygame::KeyDownEvent
if event.key==#up_key
#moving_up = true
elsif event.key==#down_key
#moving_down = true
end
when Rubygame::KeyUpEvent
if event.key==#up_key
#moving_up = false
elsif event.key==#down_key
#moving_down = false
end
end
end
def update
if #moving_up and #y > #top_limit
#y -= 5
end
if #moving_down and #y+#height < #bottom_limit
#y += 5
end
end
end
class Background < GameObject
def initialize width, height
surface = Rubygame::Surface.new [width, height]
# Draw Background
white = [255, 255, 255]
#Top
surface.draw_box_s [0, 0], [surface.width, 10], white
#Left
surface.draw_box_s [0, 0], [10, surface.height], white
#Bottom
surface.draw_box_s [0, surface.height-10, 10],
[surface.width, surface.height], white
#Right
surface.draw_box_s [surface.width-10, 0],
[surface.width, surface.height], white
#Middle Divide
surface.draw_box_s [surface.width/2-5, 0],
[surface.width/2+5, surface.height], white
super 0, 0, surface
end
end
class Ball < GameObject
def initialize x, y
surface = Rubygame::Surface.load('Ball.png')
#vx = #vy = 5
super x, y, surface
end
def update screen
#x += #vx
#y += #vy
if #x <= 10 or #x+#width >= screen.width-10
#vx *= -1
end
if #y <= 10 or #y+#height >= screen.height-10
#vy *= -1
end
end
def collision paddle, screen
if paddle.x < screen.width/2
unless #x < paddle.x-5
#x = paddle.x+paddle.width+1
#vx *= -1
end
else
unless #x > paddle.x+5
#x = paddle.x-#width-1
#vx *= -1
end
end
end
end
class Text < GameObject
def initialize x=0, y=0, text="Hello, World!", size=40
#font = Rubygame::TTF.new "font.ttf", size
#text = textssssw
super x, y, #font.render(#text, true, [255,255,255])
end
end
g = Game.new
g.run! `