method hook filter for ruby

method_filter.rb

module MethodFilter
  
  def before(hook_method, target_methods)
    wrap target_methods do |instance, method, args|
      instance.send hook_method
      instance.send method, *args
    end
  end

  def after(hook_method, target_methods)
    wrap target_methods do |instance, method, args|
      instance.send method, *args
      instance.send hook_method
    end
  end

  private
  
  def wrap(target_methods, &block)
    target_methods.each do |target_method|
      if method_defined?(target_method)
        define_wrap_method(target_method, &block)
      else
        enqueue target_method, ->{ define_wrap_method(target_method, &block) }
      end
    end
  end
  
  def define_wrap_method(target_method, &block)
    renamed_method = rename_original_method(target_method)

    alias_method renamed_method, target_method unless method_defined?(renamed_method)

    define_method(target_method) do |*args|
      instance_eval { block.call(self, renamed_method, args) }
    end
  end

  def method_added(name)
    dequeue(name).call if queue.key?(name)
  end
  
  def queue
    @queue ||= {}
  end

  def enqueue(name, method)
    queue.store(name, method)
  end
  
  def dequeue(name)
    queue.delete(name)
  end

  def rename_original_method(method)
    "__#{method}"
  end
end