Refactor to extract common code from extensions.

Uses ActiveSupport::Concern to control the addition of methods.
The Kaminari public API (scope DSL, class methods for config)
was extracted to PageScopeMethods and ConfigurationMethods.
Shims to abstract the difference between Mongoid and ActiveRecord
were extracted to MongoidCriteriaMethods and ActiveRecordRelationMethods
respectively.

Also moved definition of common constants up to the railtie.

lib/kaminari/active_record_extension.rb

@@ -1,9 +1,8 @@
+require File.join(File.dirname(__FILE__), 'active_record_relation_methods')
 module Kaminari
-  DEFAULT_PER_PAGE = 25 unless defined? ::Kaminari::DEFAULT_PER_PAGE
-
   module ActiveRecordExtension
     extend ActiveSupport::Concern
-
+    include Kaminari::ConfigurationMethods
     included do
       def self.inherited(kls) #:nodoc:
         # TERRIBLE HORRIBLE NO GOOD VERY BAD HACK: inheritable_attributes is not yet set here on AR 3.0
@@ -20,39 +19,8 @@ module Kaminari
           scope :page, Proc.new {|num|
             limit(default_per_page).offset(default_per_page * ([num.to_i, 1].max - 1))
           } do
-            # Specify the <tt>per_page</tt> value for the preceding <tt>page</tt> scope
-            #   Model.page(3).per(10)
-            def per(num)
-              if (n = num.to_i) <= 0
-                self
-              else
-                limit(n).offset(offset_value / limit_value * n)
-              end
-            end
-
-            # Total number of pages
-            def num_pages
-              (except(:offset, :limit).count.to_f / limit_value).ceil
-            end
-
-            # Current page number
-            def current_page
-              (offset_value / limit_value) + 1
-            end
-          end
-
-          # Overrides the default per_page value per model
-          #   class Article < ActiveRecord::Base
-          #     paginates_per 10
-          #   end
-          def self.paginates_per(val)
-            @_default_per_page = val
-          end
-
-          # This model's default per_page value
-          # returns 25 unless explicitly overridden via <tt>paginates_per</tt>
-          def self.default_per_page
-            @_default_per_page || Kaminari::DEFAULT_PER_PAGE
+            include Kaminari::ActiveRecordRelationMethods
+            include Kaminari::PageScopeMethods
           end
         end
       end

lib/kaminari/active_record_relation_methods.rb

@@ -0,0 +1,10 @@
+module Kaminari
+  module ActiveRecordRelationMethods
+    extend ActiveSupport::Concern
+    module InstanceMethods
+      def pagination_count
+        except(:offset, :limit).count
+      end
+    end
+  end
+end

lib/kaminari/configuration_methods.rb

@@ -0,0 +1,20 @@
+module Kaminari
+  module ConfigurationMethods
+    extend ActiveSupport::Concern
+    module ClassMethods
+      # Overrides the default per_page value per model
+      #   class Article < ActiveRecord::Base
+      #     paginates_per 10
+      #   end
+      def paginates_per(val)
+        @_default_per_page = val
+      end
+
+      # This model's default per_page value
+      # returns 25 unless explicitly overridden via <tt>paginates_per</tt>
+      def default_per_page
+        @_default_per_page || Kaminari::DEFAULT_PER_PAGE
+      end
+    end
+  end
+end

lib/kaminari/mongoid_criteria_methods.rb

@@ -0,0 +1,16 @@
+module Kaminari
+  module MongoidCriteriaMethods
+    extend ActiveSupport::Concern
+    module InstanceMethods
+      def limit_value
+        options[:limit]
+      end
+      def offset_value
+        options[:skip]
+      end
+      def pagination_count
+        count
+      end
+    end
+  end
+end

lib/kaminari/mongoid_extension.rb

@@ -1,17 +1,17 @@
+require File.join(File.dirname(__FILE__), 'mongoid_criteria_methods')
 module Kaminari
-  DEFAULT_PER_PAGE = 25 unless defined? ::Kaminari::DEFAULT_PER_PAGE
-
   module MongoidExtension
     module Criteria
       extend ActiveSupport::Concern
 
       included do
-        delegate :page, :per, :num_pages, :current_page, :limit_value, :to => '@klass'
+        delegate :page, :per, :num_pages, :current_page, :limit_value, :offset_value, :pagination_count, :to => '@klass'
       end
     end
 
     module Document
       extend ActiveSupport::Concern
+      include Kaminari::ConfigurationMethods
 
       included do
         # Fetch the values at the specified page number
@@ -19,43 +19,8 @@ module Kaminari
         scope :page, Proc.new {|num|
           limit(default_per_page).offset(default_per_page * ([num.to_i, 1].max - 1))
         } do
-          # Specify the <tt>per_page</tt> value for the preceding <tt>page</tt> scope
-          #   Model.page(3).per(10)
-          def per(num)
-            if (n = num.to_i) <= 0
-              self
-            else
-              limit(n).offset(options[:skip] / options[:limit] * n)
-            end
-          end
-
-          # Total number of pages
-          def num_pages
-            (count.to_f / options[:limit]).ceil
-          end
-
-          # Current page number
-          def current_page
-            (options[:skip] / options[:limit]) + 1
-          end
-
-          def limit_value
-            options[:limit]
-          end
-        end
-
-        # Overrides the default per_page value per model
-        #   class Article < ActiveRecord::Base
-        #     paginates_per 10
-        #   end
-        def self.paginates_per(val)
-          @_default_per_page = val
-        end
-
-        # This model's default per_page value
-        # returns 25 unless explicitly overridden via <tt>paginates_per</tt>
-        def self.default_per_page
-          @_default_per_page || Kaminari::DEFAULT_PER_PAGE
+          include Kaminari::MongoidCriteriaMethods
+          include Kaminari::PageScopeMethods
         end
       end
     end

lib/kaminari/page_scope_methods.rb

@@ -0,0 +1,26 @@
+module Kaminari
+  module PageScopeMethods
+    extend ActiveSupport::Concern
+    module InstanceMethods
+      # Specify the <tt>per_page</tt> value for the preceding <tt>page</tt> scope
+      #   Model.page(3).per(10)
+      def per(num)
+        if (n = num.to_i) <= 0
+          self
+        else
+          limit(n).offset(offset_value / limit_value * n)
+        end
+      end
+
+      # Total number of pages
+      def num_pages
+        (pagination_count.to_f / limit_value).ceil
+      end
+
+      # Current page number
+      def current_page
+        (offset_value / limit_value) + 1
+      end
+    end
+  end
+end

lib/kaminari/railtie.rb

@@ -5,8 +5,11 @@ begin; require 'active_record'; rescue LoadError; end
 begin; require 'mongoid'; rescue LoadError; end
 
 require File.join(File.dirname(__FILE__), 'helpers')
+require File.join(File.dirname(__FILE__), 'page_scope_methods')
+require File.join(File.dirname(__FILE__), 'configuration_methods')
 
 module Kaminari
+  DEFAULT_PER_PAGE = 25 unless defined? ::Kaminari::DEFAULT_PER_PAGE
   class Railtie < ::Rails::Railtie #:nodoc:
     initializer 'kaminari' do |app|
       if defined? ::ActiveRecord