major refactoring of post sets and pagination, incomplete

app/logical/post_sets/sequential.rb

@@ -0,0 +1,29 @@
+module PostSets
+  module Sequential
+    attr_reader :before_id, :after_id
+    
+    def initialize(params)
+      super
+      @before_id = params[:before_id]
+      @after_id = params[:after_id]
+    end
+    
+    def slice(relation)
+      if before_id
+        relation.where("id < ?", before_id).all
+      elsif after_id
+        relation.where("id > ?", after_id).order("id asc").all.reverse
+      else
+        relation.all
+      end
+    end
+    
+    def pagination_options
+      {:before_id => before_id, :after_id => after_id}
+    end
+    
+    def is_first_page?
+      before_id.nil?
+    end
+  end
+end