adds confidence_score to debates

app/models/debate.rb

@@ -21,7 +21,7 @@ class Debate < ActiveRecord::Base
   before_validation :sanitize_description
   before_validation :sanitize_tag_list
 
-  before_save :calculate_hot_score
+  before_save :calculate_hot_score, :calculate_confidence_score
 
   scope :sort_for_moderation, -> { order(flags_count: :desc, updated_at: :desc) }
   scope :pending_flag_review, -> { where(ignored_flag_at: nil, hidden_at: nil) }
@@ -29,7 +29,7 @@ class Debate < ActiveRecord::Base
   scope :flagged, -> { where("flags_count > 0") }
   scope :for_render, -> { includes(:tags) }
   scope :sort_by_hot_score , -> { order(hot_score: :desc) }
-  scope :sort_by_score , -> { order(cached_votes_score: :desc) }
+  scope :sort_by_confidence_score , -> { order(confidence_score: :desc) }
   scope :sort_by_created_at, -> { order(created_at: :desc) }
   scope :sort_by_most_commented, -> { order(comments_count: :desc) }
   scope :sort_by_random, -> { order("RANDOM()") }
@@ -130,6 +130,11 @@ class Debate < ActiveRecord::Base
     self.hot_score = (age_in_units**3 + weighted_score * 1000).round
   end
 
+  def calculate_confidence_score
+    return unless cached_votes_total > 0
+    self.confidence_score = cached_votes_score * cached_votes_up / cached_votes_total
+  end
+
   def self.search(terms)
     terms.present? ? where("title ILIKE ? OR description ILIKE ?", "%#{terms}%", "%#{terms}%") : none
   end

db/migrate/20150908102936_add_confidence_score_to_debates.rb

@@ -0,0 +1,6 @@
+class AddConfidenceScoreToDebates < ActiveRecord::Migration
+  def change
+    add_column :debates, :confidence_score, :integer, default: 0
+    add_index :debates, :confidence_score
+  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: 20150907064631) do
+ActiveRecord::Schema.define(version: 20150908102936) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"
@@ -102,12 +102,14 @@ ActiveRecord::Schema.define(version: 20150907064631) do
     t.integer  "cached_anonymous_votes_total",            default: 0
     t.integer  "cached_votes_score",                      default: 0
     t.integer  "hot_score",                    limit: 8,  default: 0
+    t.integer  "confidence_score",                        default: 0
   end
 
   add_index "debates", ["cached_votes_down"], name: "index_debates_on_cached_votes_down", using: :btree
   add_index "debates", ["cached_votes_score"], name: "index_debates_on_cached_votes_score", using: :btree
   add_index "debates", ["cached_votes_total"], name: "index_debates_on_cached_votes_total", using: :btree
   add_index "debates", ["cached_votes_up"], name: "index_debates_on_cached_votes_up", using: :btree
+  add_index "debates", ["confidence_score"], name: "index_debates_on_confidence_score", using: :btree
   add_index "debates", ["hidden_at"], name: "index_debates_on_hidden_at", using: :btree
   add_index "debates", ["hot_score"], name: "index_debates_on_hot_score", using: :btree
 

spec/factories.rb

@@ -78,6 +78,10 @@ FactoryGirl.define do
       before(:save) { |d| d.calculate_hot_score }
     end
 
+    trait :with_confidence_score do
+      before(:save) { |d| d.calculate_confidence_score }
+    end
+
     trait :conflictive do
       after :create do |debate|
         Flag.flag(FactoryGirl.create(:user), debate)

spec/models/debate_spec.rb

@@ -236,6 +236,26 @@ describe Debate do
         expect(previous).to be < debate.hot_score
       end
     end
+  end
+
+  describe "#confidence_score" do
+
+    it "takes into account percentage of total votes and total_positive and total negative votes" do
+      debate = create(:debate, :with_confidence_score, cached_votes_up: 100, cached_votes_score: 100, cached_votes_total: 100)
+      expect(debate.confidence_score).to eq(100)
+
+      debate = create(:debate, :with_confidence_score, cached_votes_up: 0, cached_votes_score: -100, cached_votes_total: 100)
+      expect(debate.confidence_score).to eq(0)
+
+      debate = create(:debate, :with_confidence_score, cached_votes_up: 50, cached_votes_score: 50, cached_votes_total: 100)
+      expect(debate.confidence_score).to eq(25)
+
+      debate = create(:debate, :with_confidence_score, cached_votes_up: 500, cached_votes_score: 500, cached_votes_total: 1000)
+      expect(debate.confidence_score).to eq(250)
+
+      debate = create(:debate, :with_confidence_score, cached_votes_up: 10, cached_votes_score: -80, cached_votes_total: 100)
+      expect(debate.confidence_score).to eq(-8)
+    end
 
   end