denyago/remote_association

module RemoteAssociation
  module HasOneRemote
      # Specifies a one-to-one association with another class. This method should only be used
      # if this class is a kind of ActiveResource::Base and service for this resource can
      # return some kind of foreign key.
      #
      # Methods will be added for retrieval and query for a single associated object, for which
      # this object holds an id:
      #
      # [association()]
      #   Returns the associated object. +nil+ is returned if none is found.
      # [association=(associate)]
      #   Just setter, no saves.
      #
      # (+association+ is replaced with the symbol passed as the first argument, so
      # <tt>has_one_remote :author</tt> would add among others <tt>author.nil?</tt>.)
      #
      # === Example
      #
      # A Author class declares <tt>has_one_remote :profile</tt>, which will add:
      # * <tt>Author#profile</tt> (similar to <tt>Profile.find(:first, params: { author_id: [author.id]})</tt>)
      # * <tt>Author#profile=(profile)</tt> (will set @profile instance variable of Author# to profile value)
      # The declaration can also include an options hash to specialize the behavior of the association.
      #
      # === Options
      #
      # [:class_name]
      #   Specify the class name of the association. Use it only if that name can't be inferred
      #   from the association name. So <tt>has_one_remote :profile</tt> will by default be linked to the Profile class, but
      #   if the real class name is SocialProfile, you'll have to specify it with this option.
      # [:foreign_key]
      #   Specify the foreign key used for searching association on remote service. By default this is guessed to be the name
      #   of the current class with an "_id" suffix. So a class Author that defines a <tt>has_one_remote :profile</tt>
      #   association will use "author_id" as the default <tt>:foreign_key</tt>.
      #   This key will be used in :get request. Example: <tt>GET http://example.com/profiles?author_id[]=1</tt>
      #
      # Option examples:
      #   has_one_remote :firm, :foreign_key => "client_of"
      #   has_one_remote :author, :class_name => "Person", :foreign_key => "author_id"
      def has_one_remote(remote_rel, options ={})
        rel_options = {
                       class_name: remote_rel.to_s.classify,
                       foreign_key: self.model_name.to_s.foreign_key,
                       association_type: :has_one_remote
                      }.merge(options.symbolize_keys)

        add_activeresource_relation(remote_rel.to_sym, rel_options)

        class_eval <<-RUBY, __FILE__, __LINE__+1

          attr_accessor :#{remote_rel}

          def #{remote_rel}
            if remote_resources_loaded?
              @#{remote_rel} ? @#{remote_rel}.first : nil
            else
              join_key = self.class.primary_key
              @#{remote_rel} ||= #{rel_options[:class_name]}.find(:first, params: self.class.build_params_hash_for_#{remote_rel}(self.send(join_key)))
            end
          end

          ##
          # Returns Hash with HTTP parameters to query remote API
          def self.build_params_hash_for_#{remote_rel}(keys)
            keys = [keys] unless keys.kind_of?(Array)
            {"#{rel_options[:foreign_key]}" => keys}
          end

        RUBY

      end

  end
end