Improve sequential paginator

fixes #2044, fixes #1298

lib/danbooru/paginator/active_record_extension.rb

@@ -31,7 +31,7 @@ module Danbooru
         end
 
         def paginate_sequential_before(before_id = nil)
-          c = limit(records_per_page)
+          c = limit(records_per_page + 1)
 
           if before_id.to_i > 0
             c = c.where("#{table_name}.id < ?", before_id.to_i)
@@ -44,7 +44,7 @@ module Danbooru
         end
 
         def paginate_sequential_after(after_id)
-          limit(records_per_page).where("#{table_name}.id > ?", after_id.to_i).reorder("#{table_name}.id asc").tap do |obj|
+          limit(records_per_page + 1).where("#{table_name}.id > ?", after_id.to_i).reorder("#{table_name}.id asc").tap do |obj|
             obj.extend(SequentialCollectionExtension)
             obj.sequential_paginator_mode = :after
           end

lib/danbooru/paginator/sequential_collection_extension.rb

@@ -4,18 +4,26 @@ module Danbooru
       attr_accessor :sequential_paginator_mode
 
       def is_first_page?
-        size == 0
+        if sequential_paginator_mode == :before
+          false
+        else
+          size <= records_per_page
+        end
       end
 
       def is_last_page?
-        size == 0
+        if sequential_paginator_mode == :after
+          false
+        else
+          size <= records_per_page
+        end
       end
 
       def to_a
         if sequential_paginator_mode == :before
-          super
+          super.first(records_per_page)
         else
-          super.reverse
+          super.first(records_per_page).reverse
         end
       end
     end