Revert "Extract class to manage GeozoneStats"

Back in commit 383909e16, we said:

> Even if this class looks very simple now, we're trying a few things
> related to these stats. Having a class for it makes future changes
> easier and, if there weren't any future changes, at least it makes
> current experiments easier.

Since there haven't been any changes in the last 5 years and we've found
cases where using the GeozoneStats class results in a slightly worse
performance, we're removing this class. The code is now a bit easier to
read, and is consistent with the way we calculate participants by age.

This reverts commit 383909e16.

app/lib/geozone_stats.rb

@@ -1,24 +0,0 @@
-class GeozoneStats
-  attr_reader :geozone, :participants
-
-  def initialize(geozone, participants)
-    @geozone = geozone
-    @participants = participants
-  end
-
-  def geozone_participants
-    participants.where(geozone: geozone)
-  end
-
-  def name
-    geozone.name
-  end
-
-  def count
-    geozone_participants.count
-  end
-
-  def percentage
-    PercentageCalculator.calculate(count, participants.count)
-  end
-end

app/lib/percentage_calculator.rb

@@ -1,7 +0,0 @@
-module PercentageCalculator
-  def self.calculate(fraction, total)
-    return 0.0 if total.zero?
-
-    (fraction * 100.0 / total).round(3)
-  end
-end

app/models/concerns/statisticable.rb

@@ -114,19 +114,23 @@ module Statisticable
   end
 
   def participants_by_geozone
-    geozone_stats.to_h do |stats|
+    geozones.to_h do |geozone|
+      count = participants.where(geozone: geozone).count
+
       [
-        stats.name,
+        geozone.name,
         {
-          count: stats.count,
+          count: count,
-          percentage: stats.percentage
+          percentage: calculate_percentage(count, total_participants)
         }
       ]
     end
   end
 
   def calculate_percentage(fraction, total)
-    PercentageCalculator.calculate(fraction, total)
+    return 0.0 if total.zero?
+
+    (fraction * 100.0 / total).round(3)
   end
 
   def version
@@ -178,10 +182,6 @@ module Statisticable
       Geozone.order("name")
     end
 
-    def geozone_stats
-      geozones.map { |geozone| GeozoneStats.new(geozone, participants) }
-    end
-
     def range_description(start, finish)
       if finish > 200
         I18n.t("stats.age_more_than", start: start)

spec/lib/geozone_stats_spec.rb

@@ -1,44 +0,0 @@
-require "rails_helper"
-
-describe GeozoneStats do
-  let(:winterfell) { create(:geozone, name: "Winterfell") }
-  let(:riverlands) { create(:geozone, name: "Riverlands") }
-
-  describe "#name" do
-    let(:stats) { GeozoneStats.new(winterfell, []) }
-
-    it "returns the geozone name" do
-      expect(stats.name).to eq "Winterfell"
-    end
-  end
-
-  describe "#count" do
-    before do
-      2.times { create(:user, geozone: winterfell) }
-      1.times { create(:user, geozone: riverlands) }
-    end
-
-    let(:winterfell_stats) { GeozoneStats.new(winterfell, User.all) }
-    let(:riverlands_stats) { GeozoneStats.new(riverlands, User.all) }
-
-    it "counts participants from the geozone" do
-      expect(winterfell_stats.count).to eq 2
-      expect(riverlands_stats.count).to eq 1
-    end
-  end
-
-  describe "#percentage" do
-    before do
-      2.times { create(:user, geozone: winterfell) }
-      1.times { create(:user, geozone: riverlands) }
-    end
-
-    let(:winterfell_stats) { GeozoneStats.new(winterfell, User.all) }
-    let(:riverlands_stats) { GeozoneStats.new(riverlands, User.all) }
-
-    it "calculates percentage relative to the amount of participants" do
-      expect(winterfell_stats.percentage).to eq 66.667
-      expect(riverlands_stats.percentage).to eq 33.333
-    end
-  end
-end