require "aspect"

class Logging < Aspect
  def self.enable!
    super
    @logger = Logger.new
  end

  def self.tick; "#{Time.now.strftime('%Y-%m-%d %X')}"; end   

  pointcut(:log) { call(Product.setPrice($p)) }
  before(:log) { @logger.writeLog("#{context.self_obj.price} is changed to #{$p}") }
  after(:log) { @logger.writeLog("#{tick} #{context.class_name}##{context.method_name}: returned #{context.retval} and exited") }
end

class Product
  attr_reader :price
  def initialize
    @price = 0.0
    # logger = Logger.new
  end

  def setPrice(p)
    # @logger.writeLog("#{price} is changed to #{p}")
    @price = p
  end
end

class Logger  
  def initialize  
    # open log file  
  end  

  def writeLog(msg)  
    # write msg to log file  
    puts msg  
  end  
end  


Logging.enable!
product = Product.new
product.setPrice(13)  
product.setPrice(12)