class Class # :nodoc:
  
  def cattr_reader(*syms)
    syms.flatten.each do |sym|
      class_eval(<<-EOS, __FILE__, __LINE__)
        unless defined? @@#{sym}
          @@#{sym} = nil
        end

        def self.#{sym}
          @@#{sym}
        end

        def #{sym}
          @@#{sym}
        end
      EOS
    end
  end

  def cattr_writer(*syms)
    syms.flatten.each do |sym|
      class_eval(<<-EOS, __FILE__, __LINE__)
        unless defined? @@#{sym}
          @@#{sym} = nil
        end

        def self.#{sym}=(obj)
          @@#{sym} = obj
        end

        def #{sym}=(obj)
          @@#{sym} = obj
        end
      EOS
    end
  end

  def cattr_accessor(*syms)
    cattr_reader(*syms)
    cattr_writer(*syms)
  end
  
  def shared_reader(*syms)
    syms.each do |sym|
      class_eval <<-EOS
        def self.#{sym}
          read_shared_attribute(:#{sym})
        end

        def #{sym}
          self.class.#{sym}
        end
      EOS
    end
  end

  def shared_writer(*syms)
    syms.each do |sym|
      class_eval <<-EOS
        def self.#{sym}=(obj)
          write_shared_attribute(:#{sym}, obj)
        end

        def #{sym}=(obj)
          self.class.#{sym} = obj
        end
      EOS
    end
  end

  def shared_accessor(*syms)
    shared_reader(*syms)
    shared_writer(*syms)
  end

  def shared_attributes
    @shared_attributes ||= {}
  end
  
  def write_shared_attribute(key, value)
    shared_attributes[key] = value
  end

  def read_shared_attribute(key)
    shared_attributes[key]
  end
  
  def reset_shared_attributes
    shared_attributes.clear
  end

  private 
    def inherited_with_shared_attributes(child)
      inherited_without_shared_attributes(child) if respond_to?(:inherited_without_shared_attributes)
      
      new_shared_attributes = shared_attributes.inject({}) do |memo, (key, value)|
        memo.update(key => (value.dup rescue value))
      end
      
      child.instance_variable_set('@shared_attributes', new_shared_attributes)
    end

    alias inherited_without_shared_attributes inherited
    alias inherited inherited_with_shared_attributes
end