utilize reddit rank

app/controllers/items_controller.rb

@@ -4,7 +4,7 @@ class ItemsController < ApplicationController
   before_action :set_user_item, only: [:edit, :update, :toggle]
 
   def index
-    order = params[:newest] ? {created_at: :desc} : {score: :desc}
+    order = params[:newest] ? {created_at: :desc} : {rank: :desc}
 
     @items = Item.order(order).includes(:user)
     @votes = @items.includes(:votes).each_with_object({}) do |item, object|

app/controllers/user_item_votes_controller.rb

@@ -1,5 +1,5 @@
 class UserItemVotesController < ApplicationController
-  before_action :set_item
+  before_action :set_item, :require_login
 
   def create
     if current_user.votes.build(vote_params).save

app/models/vote.rb

@@ -22,9 +22,20 @@ def get_object
   def update_votes
     attrs = self.attributes.with_indifferent_access.slice(:votable_id, :votable_type)
     count = Vote.where(attrs).count
-    get_object.update(
+    item = get_object
+
+    # Hot Score is a function defined inside:
+    # db/migrate/20150405200823_add_hot_score_function.rb
+
+    rank = item.class.where(id: item.id)
+             .select("id, hot_score(#{count}, 0, created_at) as hot_score")
+             .first.hot_score.to_i
+
+    item.update(
+      downvotes_count: 0,
       upvotes_count: count,
-      score: count
+      score: count,
+      rank: rank
     )
   end
 end

db/migrate/20150405200823_add_hot_score_function.rb

@@ -0,0 +1,18 @@
+class AddHotScoreFunction < ActiveRecord::Migration
+  # This is some sql borrowed from reddit:
+  # https://github.com/reddit/reddit/blob/master/sql/functions.sql
+  def up
+    execute <<-SQL
+      create or replace function
+        hot_score(ups integer, downs integer, date timestamp with time zone)
+        returns numeric as $$
+        select round(cast(log(greatest(abs($1 - $2), 1)) * sign($1 - $2) +
+          (date_part('epoch', $3) - 1134028003) / 45000.0 as numeric), 7)
+      $$ language sql immutable;
+    SQL
+  end
+
+  def down
+    execute "DROP FUNCTION IF EXISTS hot_score(integer, integer, timestamp);"
+  end
+end

db/schema.rb

@@ -11,7 +11,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 20150216170958) do
+ActiveRecord::Schema.define(version: 20150405200823) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"