Ruby logging wrapper. Allow: Add interceptor

log.rb

require 'logger'

module Log
  class << self
    def log
      @logger ||= Logger.new($stdout)
      @logger.formatter = proc do |severity, datetime, progname, msg|
         if(@interceptors)
           @interceptors.each { |interceptor|
             interceptor.call(severity, msg)
           }
         end
         
        "#{severity}> #{msg}\n"
      end
      @logger
    end

    def set_interceptors(it)
      @interceptors = it
    end
    
    def log=(logger)
      @logger = logger
    end
  end

  # Addition
  def self.included(base)
    class << base
      def logger
        Log.log.level = Logger::DEBUG if $debug == true
        Log.log
      end
    end
  end

  def log
    Log.log
  end
  
  # Register interceptor
  def interceptors(interceptors)
    return if interceptors.size == 0
    raise 'Interceptors must be an array' unless interceptors.class == Array
    raise "Interceptor must be lambda expression" unless interceptors.first.class == Proc
    Log.set_interceptors(interceptors)
  end
end

log_spec.rb

require_relative 'lib/log'

describe 'Log utility' do

  # Do not pass if included in a regression
  it 'Interceptor pattern' do

    class ILog
      include Log

      def initialize()
        log.warn('Hello world') # Not added to the stack
      end

      def log_hello_world
        log.warn('Hello world') # Add to the stack
      end

    end

    Log.log = Logger.new($stdout)

    # Keep track of the message
    stash = []
    interceptor = lambda do |level, msg|
       stash << msg 
    end

    # Create custom logger
    ilog = ILog.new()

    # Register interceptor
    ilog.interceptors([interceptor])
    
    expect(stash.size).to eq(0)

    # Log something
    ilog.log_hello_world
    
    expect(stash.size).to eq(1)
  end
  
end

usage.rb

class Cat
  include Log
  
  def initialize()
    log.info('the cat is born')
  end
end