Only display paginator warning when relevant

If the user has configured a paginator, the warning about Kaminari and
WillPaginate both appearing in the Gemfile should not be printed.
Additionally, this moves loading of Kaminari and WillPaginate back into
`hooks.rb` with a warning printed if neither gem is included. This
warning still gets printed when the user's application starts. Finally,
add a note to the README saying that we basically aren't going to try to
deal with people's Kaminari/WillPaginate conflicts anymore. Let them
sort that out themselves. Sorry, folks!

Related: #18, #36

Signed-off-by: David Celis <me@davidcel.is>

Author: davidcelis

README.md

@@ -133,6 +133,25 @@ Per-Page: 10
 # ...
 ```
 
+## A Note on Kaminari and WillPaginate
+
+api-pagination requires either Kaminari or WillPaginate in order to function, but some users may find themselves in situations where their application includes both. For example, you may have included [ActiveAdmin][activeadmin] (which uses Kaminari for pagination) and WillPaginate to do your own pagination. While it's suggested that you remove one paginator gem or the other, if you're unable to do so, you _must_ configure api-pagination explicitly:
+
+```ruby
+ApiPagination.configure do |config|
+  config.paginator = :will_paginate
+end
+```
+
+If you don't do this, an annoying warning will print once your app starts seeing traffic. You should also configure Kaminari to use a different name for its `per_page` method (see https://github.com/activeadmin/activeadmin/wiki/How-to-work-with-will_paginate):
+
+```ruby
+Kaminari.configure do |config|
+  config.page_method_name = :per_page_kaminari
+end
+```
+
+[activeadmin]: https://github.com/activeadmin/activeadmin
 [kaminari]: https://github.com/amatsuda/kaminari
 [will_paginate]: https://github.com/mislav/will_paginate
 

lib/api-pagination/configuration.rb

@@ -18,7 +18,7 @@ def paginator
     end
 
     def paginator=(paginator)
-      case paginator
+      case paginator.to_sym
       when :kaminari
         use_kaminari
       when :will_paginate
@@ -35,41 +35,26 @@ def set_paginator
         Kernel.warn <<-WARNING
 Warning: api-pagination relies on either Kaminari or WillPaginate, but both are
 currently active. If possible, you should remove one or the other. If you can't,
-you must configure api-pagination on your own. For example:
+you _must_ configure api-pagination on your own. For example:
 
 ApiPagination.configure do |config|
-  config.paginator = Kaminari
+  config.paginator = :kaminari
+end
+
+You should also configure Kaminari to use a different `per_page` method name as
+using these gems together causes a conflict; some information can be found at
+https://github.com/activeadmin/activeadmin/wiki/How-to-work-with-will_paginate
+
+Kaminari.configure do |config|
+  config.page_method_name = :per_page_kaminari
 end
 
 WARNING
       elsif defined?(Kaminari)
-        use_kaminari and return
+        return use_kaminari
       elsif defined?(WillPaginate::CollectionMethods)
-        use_will_paginate and return
-      end
-
-      begin
-        require 'kaminari'
-        use_kaminari and return
-      rescue LoadError
-      end
-
-      begin
-        require 'will_paginate'
-        use_will_paginate and return
-      rescue LoadError
+        return use_will_paginate
       end
-
-      Kernel.warn <<-WARNING
-Warning: api-pagination relies on either Kaminari or WillPaginate. Please
-install either dependency by adding one of the following to your Gemfile:
-
-gem 'kaminari'
-gem 'will_paginate'
-
-WARNING
-
-      @paginator
     end
 
     def use_kaminari

lib/api-pagination/hooks.rb

@@ -15,3 +15,16 @@
   require 'grape/pagination'
   Grape::API.send(:include, Grape::Pagination)
 end
+
+begin; require 'kaminari';      rescue LoadError; end
+begin; require 'will_paginate'; rescue LoadError; end
+
+unless defined?(Kaminari) || defined?(WillPaginate::CollectionMethods)
+  Kernel.warn <<-WARNING.gsub(/^\s{4}/, '')
+    Warning: api-pagination relies on either Kaminari or WillPaginate. Please
+    install either dependency by adding one of the following to your Gemfile:
+
+    gem 'kaminari'
+    gem 'will_paginate'
+  WARNING
+end