Add score, percent_rank to topics. Adds HotTopic model and consolidated job to calculate

hotness. Note: People on Heroku will have to update their jobs to the new structure
in Heroku.md

app/models/hot_topic.rb

@@ -0,0 +1,60 @@
+class HotTopic < ActiveRecord::Base
+
+  belongs_to :topic
+  belongs_to :category
+
+
+  # Here's the current idea behind the implementaiton of hot: random can produce good results!
+  # Hot is currently made up of a random selection of high percentile topics. It includes mostly
+  # new topics, but also some old ones for variety.
+  def self.refresh!
+    transaction do
+      exec_sql "DELETE FROM hot_topics"
+
+      # TODO, move these to site settings once we're sure this is how we want to figure out hot
+      max_hot_topics = 200        # how many hot topics we want
+      hot_percentile = 0.2        # What percentile of topics we consider good
+      older_percentage = 0.2      # how many old topics we want as a percentage
+      new_days = 21               # how many days old we consider old
+
+      exec_sql("INSERT INTO hot_topics (topic_id, category_id, score)
+                SELECT t.id,
+                       t.category_id,
+                       RANDOM()
+                FROM topics AS t
+                WHERE t.deleted_at IS NULL
+                  AND t.visible
+                  AND (NOT t.closed)
+                  AND (NOT t.archived)
+                  AND t.archetype <> :private_message
+                  AND created_at >= (CURRENT_TIMESTAMP - INTERVAL ':days_ago' DAY)
+                  AND t.percent_rank < :hot_percentile
+                ORDER BY 3 DESC
+                LIMIT :limit",
+                hot_percentile: hot_percentile,
+                limit: ((1.0 - older_percentage) * max_hot_topics).round,
+                private_message: Archetype::private_message,
+                days_ago: new_days)
+
+      # Add a sprinkling of random older topics
+      exec_sql("INSERT INTO hot_topics (topic_id, category_id, score)
+                SELECT t.id,
+                       t.category_id,
+                       RANDOM()
+                FROM topics AS t
+                WHERE t.deleted_at IS NULL
+                  AND t.visible
+                  AND (NOT t.closed)
+                  AND (NOT t.archived)
+                  AND t.archetype <> :private_message
+                  AND created_at < (CURRENT_TIMESTAMP - INTERVAL ':days_ago' DAY)
+                  AND t.percent_rank < :hot_percentile
+                LIMIT :limit",
+                hot_percentile: hot_percentile,
+                limit: (older_percentage * max_hot_topics).round,
+                private_message: Archetype::private_message,
+                days_ago: new_days)
+    end
+  end
+
+end

app/models/topic.rb

@@ -38,6 +38,8 @@ class Topic < ActiveRecord::Base
   has_many :posts
   has_many :topic_allowed_users
   has_many :allowed_users, through: :topic_allowed_users, source: :user
+
+  has_one :hot_topic
   belongs_to :user
   belongs_to :last_poster, class_name: 'User', foreign_key: :last_post_user_id
   belongs_to :featured_user1, class_name: 'User', foreign_key: :featured_user1_id