function screen_col_detect(object, display)
  if not (object.x >= -1 and 
    object.x <= (display.width - object.width)) then
    return false
  end 

  if not (object.y >= -1 and 
     object.y <= (display.height - object.height)) then
     return false
  end 

  return true
end




function create_object(start_x, start_y, width, height, speed)
  local	object = {}
	object.x = start_x
	object.y = start_y
	object.width = width
	object.height = height
	object.speed = speed
	return object
end

function num_is_pos(number)
	if number > 0 then
		return true
	else return false
	end
end


-- Inspired by https://love2d.org/wiki/BoundingBox.lua
-- Returns true if boxes overlap

function hitbox_collision(x1, y1, width1, height1,
                          x2, y2, width2, height2)
	return x1 < x2 + width2 and
  	     x2 < x1 + width1 and
    	   y1 < y2 + height2 and
      	 y2 < y1 + height1
end


--Takes a string "left" or "right"
function bounce(str, ball)
	if str == "right" and
		 not num_is_pos(ball.x_speed) then
		 ball.x_speed = ball.x_speed *-1

	elseif
		str == "left" and
		num_is_pos(ball.x_speed) then
		ball.x_speed = ball.x_speed *-1
	end
	return ball
end



function ball_bounce(player, ball, dt)
	local paddle_hit = false
	ball.x = ball.x + (ball.x_speed *dt)
	ball.y = ball.y + (ball.y_speed *dt)

	--If ball hits screen wall
	if ball.x >= screen.width or ball.x < 0 then
		ball.x_speed = ball.x_speed * -1
	end

	--If ball hits screen top
	if ball.y >= screen.height then
		ball.y_speed = ball.y_speed * -1
		ball.score = ball.score + 1
	end
	--If ball hits screen bottom
	if ball.y <= 0 then
		ball.y_speed = ball.y_speed * -1
	end

	

	--If ball hits paddle 
	
	if hitbox_collision(ball.x, ball.y, ball.width, ball.height,
											player.x, player.y, player.width, player.height) then

		
		-- We don't need to check left limits because we already know
		-- there was a collision, so just bounce left if the ball is
		-- left of center on the paddle
		if ball.x < player.x + (player.width /2) then
			bounce("left", ball)
		
		-- If the ball is on the right side, bounce right
		elseif ball.x > player.x +(player.width /2) then
			bounce("right", ball)
		end

		-- We don't really need to worry about the center
		-- so we won't modify it.

		-- Bounce
		ball.y_speed = ball.y_speed *-1
	end
	return ball
end