Calculate age stats based on the participation date

We were calculating the age stats based on the age of the users who
participated... at the moment where we were calculating the stats. That
means that, if 20 years ago, 1000 people who were 16 years old
participated, they would be shown as having 36 years in the stats.

Instead, we want to show the stats at the time when the process took
place, so we're implementing a `participation_date` method.

Note that, for polls, we could actually use the `age` column in the
`poll_voters` table. However, doing so would be harder, would only work
for polls but not for budgets, and it wouldn't be statistically very
relevant, since the stats are shown by age groups, and only a small
percentage of people would change their age group (and only to the
nearest one) between the time they participate and the time the process
ends.

We might use the `poll_voters` table in the future, though, since we
have a similar issue with geozones and genders, and using the
information in `poll_voters` would solve it as well (only for polls,
though).

Also note that we're using the `ends_at` dates because some people but
be too young to vote when a process starts but old enough to vote when
the process ends.

Finally, note that we might need to change the way we calculate the
participation date for a budget, since some budgets might not enabled
every phase. Not sure how stats work in that scenario (even before these
changes).

app/models/budget/stats.rb

@@ -37,6 +37,10 @@ class Budget::Stats
     budget.finished?
   end
 
+  def participation_date
+    send("#{phases.last}_phase_participation_date")
+  end
+
   def total_participants
     participants.distinct.count
   end
@@ -98,6 +102,14 @@ class Budget::Stats
       phases.map { |phase| self.class.send("#{phase}_phase_methods") }.flatten
     end
 
+    def support_phase_participation_date
+      budget.phases.selecting.ends_at
+    end
+
+    def vote_phase_participation_date
+      budget.phases.balloting.ends_at
+    end
+
     def participant_ids
       phases.map { |phase| send("participant_ids_#{phase}_phase") }.flatten.uniq
     end

app/models/concerns/statisticable.rb

@@ -63,7 +63,11 @@ module Statisticable
   end
 
   def age?
-    participants.between_ages(age_groups.flatten.min, age_groups.flatten.max).any?
+    participants.between_ages(
+      age_groups.flatten.min,
+      age_groups.flatten.max,
+      at_time: participation_date
+    ).any?
   end
 
   def geozone?
@@ -96,7 +100,7 @@ module Statisticable
 
   def participants_by_age
     age_groups.to_h do |start, finish|
-      count = participants.between_ages(start, finish).count
+      count = participants.between_ages(start, finish, at_time: participation_date).count
 
       [
         "#{start} - #{finish}",

app/models/poll/stats.rb

@@ -21,6 +21,10 @@ class Poll::Stats
     total_participants_web + total_participants_booth
   end
 
+  def participation_date
+    poll.ends_at
+  end
+
   def channels
     CHANNELS.select { |channel| send(:"total_participants_#{channel}") > 0 }
   end

app/models/user.rb

@@ -119,11 +119,11 @@ class User < ApplicationRecord
     search = "%#{search_string.strip}%"
     where("username ILIKE ? OR email ILIKE ? OR document_number ILIKE ?", search, search, search)
   end
-  scope :between_ages, ->(from, to) do
+  scope :between_ages, ->(from, to, at_time: Time.current) do
     where(
       "date_of_birth > ? AND date_of_birth < ?",
-      to.years.ago.beginning_of_year,
-      from.years.ago.end_of_year
+      (at_time - to.years).beginning_of_year,
+      (at_time - from.years).end_of_year
     )
   end
 

spec/models/budget/stats_spec.rb

@@ -157,15 +157,13 @@ describe Budget::Stats do
   end
 
   describe "#participants_by_age" do
-    before do
+    it "returns the age groups hash" do
       [21, 22, 23, 23, 34, 42, 43, 44, 50, 51].each do |age|
         create(:user, date_of_birth: age.years.ago)
       end
 
       allow(stats).to receive(:participants).and_return(User.all)
-    end
 
-    it "returns the age groups hash" do
       expect(stats.participants_by_age["16 - 19"][:count]).to eq 0
       expect(stats.participants_by_age["20 - 24"][:count]).to eq 4
       expect(stats.participants_by_age["25 - 29"][:count]).to eq 0
@@ -179,6 +177,60 @@ describe Budget::Stats do
       expect(stats.participants_by_age["65 - 69"][:count]).to eq 0
       expect(stats.participants_by_age["70 - 74"][:count]).to eq 0
     end
+
+    it "returns stats based on what happened when the voting took place" do
+      travel_to(50.years.ago) do
+        [21, 22, 23, 23, 34, 42, 43, 44, 50, 51].each do |age|
+          create(:user, date_of_birth: age.years.ago)
+        end
+
+        create(:budget, :finished)
+      end
+
+      stats = Budget::Stats.new(Budget.last)
+      allow(stats).to receive(:participants).and_return(User.all)
+
+      expect(stats.participants_by_age["16 - 19"][:count]).to eq 0
+      expect(stats.participants_by_age["20 - 24"][:count]).to eq 4
+      expect(stats.participants_by_age["25 - 29"][:count]).to eq 0
+      expect(stats.participants_by_age["30 - 34"][:count]).to eq 1
+      expect(stats.participants_by_age["35 - 39"][:count]).to eq 0
+      expect(stats.participants_by_age["40 - 44"][:count]).to eq 3
+      expect(stats.participants_by_age["45 - 49"][:count]).to eq 0
+      expect(stats.participants_by_age["50 - 54"][:count]).to eq 2
+      expect(stats.participants_by_age["55 - 59"][:count]).to eq 0
+      expect(stats.participants_by_age["60 - 64"][:count]).to eq 0
+      expect(stats.participants_by_age["65 - 69"][:count]).to eq 0
+      expect(stats.participants_by_age["70 - 74"][:count]).to eq 0
+    end
+  end
+
+  describe "#participation_date", :with_frozen_time do
+    let(:budget) do
+      create(:budget).tap do |budget|
+        budget.phases.informing.update!(starts_at: 10.months.ago, ends_at: 9.months.ago)
+        budget.phases.accepting.update!(starts_at: 9.months.ago, ends_at: 8.months.ago)
+        budget.phases.reviewing.update!(starts_at: 8.months.ago, ends_at: 7.months.ago)
+        budget.phases.selecting.update!(starts_at: 7.months.ago, ends_at: 6.months.ago)
+        budget.phases.valuating.update!(starts_at: 6.months.ago, ends_at: 5.months.ago)
+        budget.phases.publishing_prices.update!(starts_at: 5.months.ago, ends_at: 4.months.ago)
+        budget.phases.balloting.update!(starts_at: 4.months.ago, ends_at: 3.months.ago)
+        budget.phases.reviewing_ballots.update!(starts_at: 3.months.ago, ends_at: 2.months.ago)
+        budget.phases.finished.update!(starts_at: 2.months.ago, ends_at: 1.month.ago)
+      end
+    end
+
+    it "returns the date when balloting ended on finished budgets" do
+      budget.update!(phase: "finished")
+
+      expect(stats.participation_date).to eq 3.months.ago
+    end
+
+    it "returns the date when selecting ended on unfinished budgets" do
+      budget.update!(phase: "reviewing_ballots")
+
+      expect(stats.participation_date).to eq 6.months.ago
+    end
   end
 
   describe "#headings" do

spec/models/poll/stats_spec.rb

@@ -165,6 +165,46 @@ describe Poll::Stats do
     end
   end
 
+  describe "#participants_by_age" do
+    it "returns stats based on what happened when the voting took place" do
+      travel_to(100.years.ago) do
+        [16, 18, 32, 32, 33, 34, 64, 65, 71, 73, 90, 99, 105].each do |age|
+          create(:user, date_of_birth: age.years.ago)
+        end
+
+        create(:poll, starts_at: 1.minute.from_now, ends_at: 2.minutes.from_now)
+      end
+
+      stats = Poll::Stats.new(Poll.last)
+      allow(stats).to receive(:participants).and_return(User.all)
+
+      expect(stats.participants_by_age["16 - 19"][:count]).to eq 2
+      expect(stats.participants_by_age["20 - 24"][:count]).to eq 0
+      expect(stats.participants_by_age["25 - 29"][:count]).to eq 0
+      expect(stats.participants_by_age["30 - 34"][:count]).to eq 4
+      expect(stats.participants_by_age["35 - 39"][:count]).to eq 0
+      expect(stats.participants_by_age["40 - 44"][:count]).to eq 0
+      expect(stats.participants_by_age["45 - 49"][:count]).to eq 0
+      expect(stats.participants_by_age["50 - 54"][:count]).to eq 0
+      expect(stats.participants_by_age["55 - 59"][:count]).to eq 0
+      expect(stats.participants_by_age["60 - 64"][:count]).to eq 1
+      expect(stats.participants_by_age["65 - 69"][:count]).to eq 1
+      expect(stats.participants_by_age["70 - 74"][:count]).to eq 2
+      expect(stats.participants_by_age["75 - 79"][:count]).to eq 0
+      expect(stats.participants_by_age["80 - 84"][:count]).to eq 0
+      expect(stats.participants_by_age["85 - 89"][:count]).to eq 0
+      expect(stats.participants_by_age["90 - 300"][:count]).to eq 3
+    end
+  end
+
+  describe "#participation_date", :with_frozen_time do
+    let(:poll) { create(:poll, starts_at: 3.years.ago, ends_at: 2.years.ago) }
+
+    it "returns the date when the poll finishes" do
+      expect(stats.participation_date).to eq 2.years.ago
+    end
+  end
+
   describe "#participants_by_geozone" do
     it "groups by geozones in alphabetic order" do
       %w[Oceania Eurasia Eastasia].each { |name| create(:geozone, name: name) }

spec/models/statisticable_spec.rb

@@ -8,6 +8,10 @@ describe Statisticable do
       def participants
         User.all
       end
+
+      def participation_date
+        Time.current
+      end
     end
 
     stub_const("DummyStats", dummy_stats)
@@ -80,6 +84,17 @@ describe Statisticable do
         expect(stats.age?).to be true
       end
     end
+
+    context "Partipation took place a long time ago" do
+      before do
+        create(:user, date_of_birth: 2000.years.ago)
+        allow(stats).to receive(:participation_date).and_return(1900.years.ago)
+      end
+
+      it "is true" do
+        expect(stats.age?).to be true
+      end
+    end
   end
 
   describe "#geozone?" do

spec/models/user_spec.rb

@@ -437,6 +437,26 @@ describe User do
         expect(User.between_ages(41, 45).count).to eq 3
         expect(User.between_ages(51, 100).count).to eq 1
       end
+
+      it "returns users between certain ages on a reference date" do
+        reference_date = 20.years.ago
+
+        travel_to(reference_date) do
+          [21, 22, 23, 23, 34, 42, 43, 44, 50, 51].each do |age|
+            create(:user, date_of_birth: age.years.ago)
+          end
+        end
+
+        expect(User.between_ages(0, 20, at_time: reference_date).count).to eq 0
+        expect(User.between_ages(21, 25, at_time: reference_date).count).to eq 4
+        expect(User.between_ages(25, 30, at_time: reference_date).count).to eq 0
+        expect(User.between_ages(30, 34, at_time: reference_date).count).to eq 1
+        expect(User.between_ages(35, 39, at_time: reference_date).count).to eq 0
+        expect(User.between_ages(40, 44, at_time: reference_date).count).to eq 3
+        expect(User.between_ages(45, 49, at_time: reference_date).count).to eq 0
+        expect(User.between_ages(50, 54, at_time: reference_date).count).to eq 2
+        expect(User.between_ages(55, 100, at_time: reference_date).count).to eq 0
+      end
     end
   end