new next and previous buttons

When selecting only one post buttons to select the previous and next
blog posts are added. These can then be used to read one blog post per
page.

controller/post.rb

@@ -1,29 +1,49 @@
 module Routes
   class Post < Controller
+    PREV_AND_NEXT_QUERY = <<SQL
+      select (
+        select id from posts where written < ? and released order by written desc limit 1
+      ) older,
+      (
+        select id from posts where written > ? and released order by written limit 1
+      ) younger
+SQL
+
     def self.get(session)
       define_posts(session)
       session.options[:render] = 'posts/index'
     end
 
     def self.define_posts(session)
-      # compute pages
-      page = session.request.params['page'].to_i
-      session.options[:page] = page if page
-      per_page = session.request.params['per_page'].to_i
-      per_page = 10 if per_page == 0
-      session.options[:per_page] = per_page if per_page
-      session.options[:pages] = DB[:posts].filter(:released => true).count / per_page
-
-      # fetch the posts to show
       posts = DB[:posts].
         filter(:released => true).
         select(:posts__id___post_id, :written, :title, :content, :username).
         join(:accounts, :id___account_id => :account_id).
         reverse_order(:written)
-      if session.options[:id]
-        posts = posts.where(:posts__id => session.options[:id]) 
-      end
+
+      # return when a single posts has to be shown
+      return load_previous_and_next_post(session, posts) if session.options[:id]
+      load_page_information(session, posts)
+    end
+
+    def self.load_page_information(session, posts)
+      # compute pages
+      page = session.request.params['page'].to_i
+      session.options[:page] = page if page
+      per_page = session.request.params['per_page'].to_i
+      per_page = 10 if per_page < 1
+      session.options[:per_page] = per_page if per_page
+      session.options[:pages] = DB[:posts].filter(:released => true).count / per_page
+
+      # fetch the posts to show
       session.options[:posts]  = posts.limit(per_page, page * per_page)
     end
+
+    def self.load_previous_and_next_post(session, posts)
+      posts = posts.filter(:posts__id => session.options[:id].to_i)
+      session.options[:posts] = posts
+      written = posts.first[:written]
+      session.options[:post_ids_pn] = DB[PREV_AND_NEXT_QUERY, written, written].first
+    end
   end
 end

templates/posts/index.html.slim

@@ -1,7 +1,11 @@
-- if 0 < fetch(:page)
+- if has_key?(:page) && 0 < fetch(:page)
   a.page.up(
     href="/post?page=#{fetch(:page) - 1}&per_page=#{fetch(:per_page)}"
     ) show newer
+- if has_key?(:post_ids_pn) && fetch(:post_ids_pn)[:younger]
+  a.page.up(
+    href="/post/#{fetch(:post_ids_pn)[:younger]}"
+    ) show newer
 
 - for post in fetch(:posts)
   article
@@ -14,7 +18,11 @@
       .time=  post[:written].strftime('%H-%M')
     section==Kramdown::Document.new(post[:content]).to_html
 
-- if fetch(:page) < fetch(:pages)
+- if has_key?(:page) && fetch(:page) < fetch(:pages)
   a.page.down(
     href="/post?page=#{fetch(:page) + 1}&per_page=#{fetch(:per_page)}"
     ) show older
+- if has_key?(:post_ids_pn) && fetch(:post_ids_pn)[:older]
+  a.page.down(
+    href="/post/#{fetch(:post_ids_pn)[:older]}"
+    ) show older