Don't load both Kaminari and will_paginate

It's possible users will have both `will_paginate` and `kaminari` as
dependencies. Because the two are incompatible, avoid loading both and
instead first attempt to load Kaminari. If that cannot load, then
attempt to load will_paginate. Fixes #18.

Signed-off-by: David Celis <[email protected]>

Author: davidcelis

lib/api-pagination/hooks.rb

@@ -1,6 +1,6 @@
 module ApiPagination
   class Hooks
-    def self.init
+    def self.init!
       begin; require 'rails'; rescue LoadError; end
       if defined?(ActionController::Base)
         require 'rails/pagination'
@@ -19,22 +19,28 @@ def self.init
         Grape::API.send(:include, Grape::Pagination)
       end
 
-      begin; require 'will_paginate'; rescue LoadError; end
-      if defined?(WillPaginate::CollectionMethods)
-        WillPaginate::CollectionMethods.module_eval do
-          def first_page?() !previous_page end
-          def last_page?() !next_page end
-        end
+      # Kaminari and will_paginate conflict with each other, so we should check
+      # to see if either is already active before attempting to load them.
+      if defined?(Kaminari)
+        initialize_kaminari! and return
+      elsif defined?(WillPaginate::CollectionMethods)
+        initialize_will_paginate! and return
+      end
 
-        ApiPagination.instance_variable_set(:@paginator, :will_paginate)
+      # If neither is loaded, we can safely attempt these requires.
+      begin
+        require 'kaminari'
+        initialize_kaminari! and return
+      rescue LoadError
       end
 
-      begin; require 'kaminari'; rescue LoadError; end
-      if defined?(Kaminari)
-        ApiPagination.instance_variable_set(:@paginator, :kaminari)
+      begin
+        require 'will_paginate'
+        initialize_will_paginate! and return
+      rescue LoadError
       end
 
-      STDERR.puts <<-EOC unless defined?(Kaminari) || defined?(WillPaginate)
+      STDERR.puts <<-EOC
 Warning: api-pagination relies on either Kaminari or WillPaginate. Please
 install either dependency by adding one of the following to your Gemfile:
 
@@ -43,7 +49,20 @@ def last_page?() !next_page end
 
 EOC
     end
+
+    def self.initialize_kaminari!
+      ApiPagination.instance_variable_set(:@paginator, :kaminari)
+    end
+
+    def self.initialize_will_paginate!
+      WillPaginate::CollectionMethods.module_eval do
+        def first_page?() !previous_page end
+        def last_page?() !next_page end
+      end
+
+      ApiPagination.instance_variable_set(:@paginator, :will_paginate)
+    end
   end
 end
 
-ApiPagination::Hooks.init
+ApiPagination::Hooks.init!