add tag seq nav

app/logical/post_search_context.rb

@@ -0,0 +1,25 @@
+class PostSearchContext
+  attr_reader :params, :post_id
+  
+  def initialize(params)
+    @params = params
+    raise unless params[:seq].present?
+    raise unless params[:id].present?
+    
+    @post_id = find_post_id
+  end
+  
+  def find_post_id
+    if params[:seq] == "prev"
+      post = Post.tag_match(params[:tags]).where("posts.id > ?", params[:id].to_i).reorder("posts.id asc").first
+    else
+      post = Post.tag_match(params[:tags]).where("posts.id < ?", params[:id].to_i).reorder("posts.id desc").first
+    end
+
+    if post
+      post.id
+    else
+      nil
+    end
+  end
+end