A way to extend an exiting API via concern

Sometimes, it's needed to extend an existing controller method with additional
parameters (usually when extending exiting API from plugins/rails engines).
The concern can be also used for this purposed, using `update_api` method.
The params defined in this block are merged with the params of the original method
in the controller this concern is included to.

```ruby
module Concerns
  module OauthConcern
    extend Apipie::DSL::Concern

    update_api(:create, :update) do
 param :user, Hash do
   param :oauth, String, :desc => 'oauth param'
 end
    end
  end
end
```

The concern needs to be included to the controller after the methods are defined
(either at the end of the class, or by using `Controller.send(:include, Concerns::OauthConcern)`.

README.rst

@@ -504,6 +504,32 @@ Example
    end
 
 
+Sometimes, it's needed to extend an existing controller method with additional
+parameters (usually when extending exiting API from plugins/rails engines).
+The concern can be also used for this purposed, using `update_api` method.
+The params defined in this block are merged with the params of the original method
+in the controller this concern is included to.
+
+Example
+~~~~~~~
+
+.. code:: ruby
+
+   module Concerns
+     module OauthConcern
+       extend Apipie::DSL::Concern
+
+       update_api(:create, :update) do
+         param :user, Hash do
+           param :oauth, String, :desc => 'oauth param'
+         end
+       end
+     end
+   end
+
+The concern needs to be included to the controller after the methods are defined
+(either at the end of the class, or by using
+``Controller.send(:include, Concerns::OauthConcern)``.
 
 =========================
  Configuration Reference
@@ -1231,7 +1257,7 @@ one example per method) by adding a 'title' attribute.
          - recorded: true
 
 In RSpec you can add metadata to examples. We can use that feature
-to mark selected examples – the ones that perform the requests that we want to
+to mark selected examples - the ones that perform the requests that we want to
 show as examples in the documentation.
 
 For example, we can add ``show_in_doc`` to examples, like this:

lib/apipie/dsl_definition.rb

@@ -8,6 +8,14 @@ module DSL
     module Base
       attr_reader :apipie_resource_descriptions, :api_params
 
+      def _apipie_eval_dsl(*args, &block)
+        raise 'The Apipie DLS data need to be cleared before evaluating new block' if @_apipie_dsl_data
+        instance_exec(*args, &block)
+        return _apipie_dsl_data
+      ensure
+        _apipie_dsl_data_clear
+      end
+
       private
 
       def _apipie_dsl_data
@@ -381,6 +389,37 @@ def apipie_concern_subst(subst_hash)
         _apipie_concern_subst.merge!(subst_hash)
       end
 
+      # Allows to update existing params after definition was made (usually needed
+      # when extending the API form plugins).
+      #
+      #     UsersController.apipie_update_params([:create, :update]) do
+      #       param :user, Hash do
+      #         param :oauth, String
+      #       end
+      #      end
+      #
+      # The block is evaluated in scope of the controller. Ohe can pass some additional
+      # objects via additional arguments like this:
+      #
+      #     UsersController.apipie_update_params([:create, :update], [:name, :secret]) do |param_names|
+      #       param :user, Hash do
+      #         param_names.each { |p| param p, String }
+      #       end
+      #      end
+      def apipie_update_params(methods, *args, &block)
+        methods.each do |method|
+          method_description = Apipie.get_method_description(self, method)
+          unless method_description
+            raise "Could not find method description for #{self}##{method}. Was the method defined?"
+          end
+          dsl_data = _apipie_eval_dsl(*args, &block)
+          params_ordered = dsl_data[:params].map do |args|
+            Apipie::ParamDescription.from_dsl_data(method_description, args)
+          end
+          ParamDescription.unify(method_description.params_ordered_self + params_ordered)
+        end
+      end
+
       def _apipie_concern_subst
         @_apipie_concern_subst ||= {:controller_path => self.controller_path,
                                     :resource_id => Apipie.get_resource_name(self)}
@@ -428,12 +467,19 @@ def included(controller)
           description = Apipie.define_method_description(controller, method_name, _apipie_dsl_data)
           controller._apipie_define_validators(description)
         end
+        _apipie_concern_update_api_blocks.each do |(methods, block)|
+          controller.apipie_update_params(methods, &block)
+        end
       end
 
       def _apipie_concern_data
         @_apipie_concern_data ||= []
       end
 
+      def _apipie_concern_update_api_blocks
+        @_apipie_concern_update_api_blocks ||= []
+      end
+
       def apipie_concern?
         true
       end
@@ -449,6 +495,10 @@ def method_added(method_name) #:doc:
         _apipie_dsl_data_clear
       end
 
+      def update_api(*methods, &block)
+        _apipie_concern_update_api_blocks << [methods, block]
+      end
+
     end
 
     class ResourceDescriptionDsl
@@ -461,14 +511,9 @@ def initialize(controller)
         @controller = controller
       end
 
-      def _eval_dsl(&block)
-        instance_eval(&block)
-        return _apipie_dsl_data
-      end
-
       # evaluates resource description DSL and returns results
       def self.eval_dsl(controller, &block)
-        dsl_data  = self.new(controller)._eval_dsl(&block)
+        dsl_data  = self.new(controller)._apipie_eval_dsl(&block)
         if dsl_data[:api_versions].empty?
           dsl_data[:api_versions] = Apipie.controller_versions(controller)
         end

lib/apipie/method_description.rb

@@ -65,6 +65,10 @@ def params
       params_ordered.reduce(ActiveSupport::OrderedHash.new) { |h,p| h[p.name] = p; h }
     end
 
+    def params_ordered_self
+      @params_ordered
+    end
+
     def params_ordered
       all_params = []
       parent = Apipie.get_resource_description(@resource.controller.superclass)

lib/apipie/param_description.rb

@@ -21,6 +21,19 @@ def self.from_dsl_data(method_description, args)
                                    &block)
     end
 
+    def to_s
+      "ParamDescription: #{method_description.id}##{name}"
+    end
+
+    def ==(other)
+      return false unless self.class == other.class
+      if method_description == other.method_description && @options == other.options
+        true
+      else
+        false
+      end
+    end
+
     def initialize(method_description, name, validator, desc_or_options = nil, options = {}, &block)
 
       if desc_or_options.is_a?(Hash)
@@ -146,7 +159,7 @@ def merge_with(other_param_desc)
       self
     end
 
-    # merge param descripsiont. Allows defining hash params on more places
+    # merge param descriptions. Allows defining hash params on more places
     # (e.g. in param_groups). For example:
     #
     #     def_param_group :user do

lib/apipie/validator.rb

@@ -13,6 +13,16 @@ def initialize(param_description)
         @param_description = param_description
       end
 
+      def inspected_fields
+        [:param_description]
+      end
+
+      def inspect
+        string = "#<#{self.class.name}:#{self.object_id} "
+        fields = inspected_fields.map {|field| "#{field}: #{self.send(field)}"}
+        string << fields.join(", ") << ">"
+      end
+
       def self.inherited(subclass)
         @validators ||= []
         @validators.insert 0, subclass
@@ -67,13 +77,22 @@ def expected_type
       end
 
       def merge_with(other_validator)
-        raise NotImplementedError, "Dont know how to merge #{self.inspect} with #{other_validator.inspect}"
+        return self if self == other_validator
+        raise NotImplementedError, "Don't know how to merge #{self.inspect} with #{other_validator.inspect}"
       end
 
       def params_ordered
         nil
       end
 
+      def ==(other)
+        return false unless self.class == other.class
+        if param_description == other.param_description
+          true
+        else
+          false
+        end
+      end
     end
 
     # validate arguments type

spec/controllers/extended_controller_spec.rb

@@ -0,0 +1,10 @@
+require "spec_helper"
+
+describe ExtendedController do
+
+  it 'should include params from both original controller and extending concern' do
+    user_param = Apipie["extended#create"].params[:user]
+    expect(user_param.validator.params_ordered.map(&:name)).to eq [:name, :password, :from_concern]
+  end
+end
+

spec/dummy/app/controllers/concerns/extending_concern.rb

@@ -0,0 +1,11 @@
+module Concerns
+  module ExtendingConcern
+    extend Apipie::DSL::Concern
+
+    update_api(:create) do
+      param :user, Hash do
+        param :from_concern, String, :desc => 'param from concern', :allow_nil => false
+      end
+    end
+  end
+end

spec/dummy/app/controllers/extended_controller.rb

@@ -0,0 +1,12 @@
+class ExtendedController < ApplicationController
+
+  api :POST, '/extended'
+  param :user, Hash do
+    param :name, String
+    param :password, String
+  end
+  def create
+  end
+
+  include Concerns::ExtendingConcern
+end