# Allows you to declare an alias_method_chain before the original 
# method has been defined.
#
#   class A
#     delayed_method_chain :name, :hello
#       
#     def name_with_hello
#       "Hello #{name_without_hello}"
#     end
#     
#     # This method is immediately chained when defined
#     def name
#       'Bill'
#     end
#   end
#
#   A.new.name #=> "Hello Bill"
#
module DelayedMethodChain
  def delayed_method_chain(name, suffix)
    # if both methods already exist, just chain and forget the method_added stuff
    if method_defined?(name.to_sym) && method_defined?(DelayedMethodChain.suffixed_name(name, 'with', suffix))
      alias_method DelayedMethodChain.suffixed_name(name, 'without', suffix), name.to_sym
      alias_method name.to_sym, DelayedMethodChain.suffixed_name(name, 'with', suffix)
      return
    end
    
    (class << self; self; end).class_eval do
      @@delayed_methods ||= []
      @@delayed_methods << [name, suffix]
      return if method_defined?(:method_added_with_delay_chain)
      
      def method_added_with_delay_chain(added_name)
        # prevent infinite looping of method_added when aliasing method
        @currently_being_delayed_methods ||= {}
        return if @currently_being_delayed_methods[added_name]
        
        # listen for both methods, only chain if both are defined
        @@delayed_methods.select {|name, suffix| [name.to_sym, DelayedMethodChain.suffixed_name(name, 'with', suffix)].include?(added_name.to_sym)}.each do |name, suffix|
          next unless method_defined?(name.to_sym) && method_defined?(DelayedMethodChain.suffixed_name(name, 'with', suffix))
          
          @currently_being_delayed_methods[name] = :aliasing
          alias_method DelayedMethodChain.suffixed_name(name, 'without', suffix), name.to_sym
          alias_method name.to_sym, DelayedMethodChain.suffixed_name(name, 'with', suffix)
          @currently_being_delayed_methods[name] = nil
        end
        
        if respond_to?(:method_added_without_delay_chain) 
          method_added_without_delay_chain(added_name)
        end
      end
      
      # chain method_added if this class already had one
      if method_defined?(:method_added)
        alias_method :method_added_without_delay_chain, :method_added
      end
      alias_method :method_added, :method_added_with_delay_chain
    end
  end

  # takes query, bang and setter method names into account
  def self.suffixed_name(name, with, suffix)
    if m = name.to_s.match(/(.*)([\?!=])$/)
      "#{m[1]}_#{with}_#{suffix}#{m[2]}".to_sym
    else
      "#{name}_#{with}_#{suffix}".to_sym
    end
  end

end

Object.send :extend, DelayedMethodChain