add per-tag story hotness modifiers

app/models/story.rb

@@ -128,8 +128,13 @@ class Story < ActiveRecord::Base
   end
 
   def calculated_hotness
+    base = 10
+    self.tags.select{|t| t.hotness_mod != 0 }.each do |t|
+      base -= t.hotness_mod
+    end
+
     # don't immediately kill stories at 0 by bumping up score by one
-    order = Math.log([ (score + 1).abs + comments_count, 1 ].max, 10)
+    order = Math.log([ (score + 1).abs + comments_count, 1 ].max, base)
     if score > 0
       sign = 1
     elsif score < 0

db/migrate/20140825225915_add_tag_hotness_mod.rb

@@ -0,0 +1,5 @@
+class AddTagHotnessMod < ActiveRecord::Migration
+  def change
+    add_column :tags, :hotness_mod, :integer, :default => 0
+  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: 20140804005415) do
+ActiveRecord::Schema.define(version: 20140825225915) do
 
   create_table "comments", force: true do |t|
     t.datetime "created_at",                                                                    null: false
@@ -134,6 +134,7 @@ ActiveRecord::Schema.define(version: 20140804005415) do
     t.boolean "privileged",              default: false
     t.boolean "is_media",                default: false
     t.boolean "inactive",                default: false
+    t.integer "hotness_mod",             default: 0
   end
 
   add_index "tags", ["tag"], name: "tag", unique: true, using: :btree