Manage correctly results and stats for open-ended questions

Note that we are not including Poll::PartialResults for open-ended
questions resutls. The reason is that we do not contemplate the
possibility of there being open questions in booths. Manually
counting and introducing the votes in the system is not feasible.

app/models/poll/question.rb

@@ -87,6 +87,26 @@ class Poll::Question < ApplicationRecord
     answer
   end
 
+  def open_ended_valid_answers_count
+    answers.count
+  end
+
+  def open_ended_blank_answers_count
+    poll.voters.count - open_ended_valid_answers_count
+  end
+
+  def open_ended_valid_percentage
+    return 0.0 if open_ended_total_answers.zero?
+
+    (open_ended_valid_answers_count * 100.0) / open_ended_total_answers
+  end
+
+  def open_ended_blank_percentage
+    return 0.0 if open_ended_total_answers.zero?
+
+    (open_ended_blank_answers_count * 100.0) / open_ended_total_answers
+  end
+
   private
 
     def find_by_attributes(user, option_id)
@@ -96,4 +116,8 @@ class Poll::Question < ApplicationRecord
         { author: user }
       end
     end
+
+    def open_ended_total_answers
+      open_ended_valid_answers_count + open_ended_blank_answers_count
+    end
 end