adds confidence_score capacity to the comment model

app/models/comment.rb

@@ -17,10 +17,13 @@ class Comment < ActiveRecord::Base
   belongs_to :commentable, -> { with_hidden }, polymorphic: true, counter_cache: true
   belongs_to :user, -> { with_hidden }
 
+  before_save :calculate_confidence_score
+
   scope :recent, -> { order(id: :desc) }
   scope :for_render, -> { with_hidden.includes(user: :organization) }
   scope :with_visible_author, -> { joins(:user).where("users.hidden_at IS NULL") }
   scope :sort_by_flags, -> { order(flags_count: :desc, updated_at: :desc) }
+  scope :sort_by_confidence_score , -> { order(confidence_score: :desc) }
   scope :sort_by_created_at, -> { order(created_at: :desc) }
 
   after_create :call_after_commented
@@ -88,6 +91,11 @@ class Comment < ActiveRecord::Base
     1000
   end
 
+  def calculate_confidence_score
+    self.confidence_score = ScoreCalculator.confidence_score(cached_votes_total,
+                                                             cached_votes_up)
+  end
+
   private
 
     def validate_body_length

spec/factories.rb

@@ -216,6 +216,10 @@ FactoryGirl.define do
         Flag.flag(FactoryGirl.create(:user), debate)
       end
     end
+
+    trait :with_confidence_score do
+      before(:save) { |d| d.calculate_confidence_score }
+    end
   end
 
   factory :administrator do

spec/models/comment_spec.rb

@@ -39,6 +39,44 @@ describe Comment do
     end
   end
 
+  describe "#confidence_score" do
+
+    it "takes into account percentage of total votes and total_positive and total negative votes" do
+      comment = create(:comment, :with_confidence_score, cached_votes_up: 100, cached_votes_total: 100)
+      expect(comment.confidence_score).to eq(10000)
+
+      comment = create(:comment, :with_confidence_score, cached_votes_up: 0, cached_votes_total: 100)
+      expect(comment.confidence_score).to eq(0)
+
+      comment = create(:comment, :with_confidence_score, cached_votes_up: 75, cached_votes_total: 100)
+      expect(comment.confidence_score).to eq(3750)
+
+      comment = create(:comment, :with_confidence_score, cached_votes_up: 750, cached_votes_total: 1000)
+      expect(comment.confidence_score).to eq(37500)
+
+      comment = create(:comment, :with_confidence_score, cached_votes_up: 10, cached_votes_total: 100)
+      expect(comment.confidence_score).to eq(-800)
+    end
+
+    describe 'actions which affect it' do
+      let(:comment) { create(:comment, :with_confidence_score) }
+
+      it "increases with like" do
+        previous = comment.confidence_score
+        5.times { comment.vote_by(voter: create(:user), vote: true) }
+        expect(previous).to be < comment.confidence_score
+      end
+
+      it "decreases with dislikes" do
+        comment.vote_by(voter: create(:user), vote: true)
+        previous = comment.confidence_score
+        3.times { comment.vote_by(voter: create(:user), vote: false) }
+        expect(previous).to be > comment.confidence_score
+      end
+    end
+
+  end
+
   describe "cache" do
     let(:comment) { create(:comment) }