Expose age_range instead of date_of_birth for Voter/User class

app/models/user.rb

@@ -244,6 +244,10 @@ class User < ActiveRecord::Base
   end
   delegate :can?, :cannot?, to: :ability
 
+  def age_range
+    AgeRangeCalculator::range_from_birthday(self.date_of_birth).to_s
+  end
+
   private
 
     def clean_document_number

config/initializers/graphql.rb

@@ -5,7 +5,7 @@ API_TYPE_DEFINITIONS = {
   },
   Voter => {
     gender:     :string,
-    date_of_birth:  :string,
+    age_range:  :string,
     geozone_id: :integer,
     geozone:     Geozone
   },

lib/age_range_calculator.rb

@@ -0,0 +1,15 @@
+class AgeRangeCalculator
+
+  MIN_AGE = 16
+  MAX_AGE = 1.0/0.0 # Infinity
+  RANGES = [ (MIN_AGE..25), (26..40), (41..60), (61..MAX_AGE) ]
+
+  def self.range_from_birthday(dob)
+    # Inspired by: http://stackoverflow.com/questions/819263/get-persons-age-in-ruby/2357790#2357790
+    now = Time.current.to_date
+    age = now.year - dob.year - ((now.month > dob.month || (now.month == dob.month && now.day >= dob.day)) ? 0 : 1)
+
+    index = RANGES.find_index { |range| range.include?(age) }
+    index ? RANGES[index] : nil
+  end
+end

spec/lib/age_range_calculator_spec.rb

@@ -0,0 +1,14 @@
+require 'rails_helper'
+
+describe AgeRangeCalculator do
+  subject { AgeRangeCalculator }
+
+  describe '::range_from_birthday' do
+    it 'returns the age range' do
+      expect(subject::range_from_birthday(Time.current - 1.year)).to eq(nil)
+      expect(subject::range_from_birthday(Time.current - 26.year)).to eq(26..40)
+      expect(subject::range_from_birthday(Time.current - 60.year)).to eq(41..60)
+      expect(subject::range_from_birthday(Time.current - 200.year)).to eq(61..subject::MAX_AGE)
+    end
+  end
+end

spec/models/user_spec.rb

@@ -469,4 +469,10 @@ describe User do
 
   end
 
+  describe "#age_range" do
+    it 'returns string representation of age range' do
+      user = create(:user, date_of_birth: Time.current - 41.years)
+      expect(user.age_range).to eq('41..60')
+    end
+  end
 end