Add email volume estimates to signup confirm page

Add very rough guesses about the weekly volume of email a user can
expect depending on which level of the taxonomy they sign up to. These
figures are based on analysis of historical email volume.

app/controllers/taxonomy_signups_controller.rb

@@ -10,6 +10,7 @@ def confirm
     redirect_to '/' and return unless valid_query_param?
 
     load_taxon
+    load_estimated_email_frequency
     load_breadcrumbs
   end
 
@@ -48,4 +49,8 @@ def load_breadcrumbs
     @breadcrumbs.last.merge!(is_current_page: false, url: @taxon['base_path'])
     @breadcrumbs << { title: 'Get email alerts', is_current_page: true }
   end
+
+  def load_estimated_email_frequency
+    @estimated_email_frequency = WeeklyEmailVolume.new(@taxon).estimate
+  end
 end

app/models/weekly_email_volume.rb

@@ -0,0 +1,35 @@
+class WeeklyEmailVolume
+  HIGH = '40-60'.freeze
+  MEDIUM = '0-20'.freeze
+  LOW = '0-5'.freeze
+
+  def initialize(taxon)
+    @taxon = taxon
+  end
+
+  def estimate
+    parent_taxon = extract_parent_from(@taxon)
+
+    # Is at the top of the taxonomy
+    return HIGH if parent_taxon.blank?
+
+    # Is a 2nd level taxon
+    grandparent_taxon = extract_parent_from(
+      fetch_content_item(parent_taxon.fetch('base_path'))
+    )
+    return MEDIUM if grandparent_taxon.blank?
+
+    # Is a 3rd level taxon or below
+    return LOW
+  end
+
+private
+
+  def extract_parent_from(content_item)
+    Array(content_item.dig('links', 'parent_taxons')).first
+  end
+
+  def fetch_content_item(base_path)
+    EmailAlertFrontend.services(:content_store).content_item(base_path)
+  end
+end

app/views/taxonomy_signups/confirm.html.erb

@@ -15,7 +15,7 @@
   </p>
 
   <p>
-    This might be from [number] updates a week.
+    This might be from <%= @estimated_email_frequency %> updates a week.
   </p>
 
   <p>

features/step_definitions/taxonomy_email_alert_steps.rb

@@ -34,6 +34,10 @@
   }
 
   content_store_has_item(@taxon[:base_path], @taxon)
+  content_store_has_item(
+    @taxon.dig(:links, :parent_taxons).first[:base_path],
+    @taxon.dig(:links, :parent_taxons).first
+  )
 end
 
 When(/^i visit its signup page$/) do
@@ -53,6 +57,8 @@
 
 Then(/^i see a confirmation page$/) do
   expect(page).to have_content("You can set your preferences once you've signed up.")
+  # Based on the position of this taxon in the taxonomy:
+  expect(page).to have_content("This might be from 0-20 updates a week")
   expect(page).to have_button('Sign up now')
 end
 

spec/models/weekly_email_volume_spec.rb

@@ -0,0 +1,50 @@
+require 'rails_helper'
+
+RSpec.describe WeeklyEmailVolume do
+  include GdsApi::TestHelpers::ContentStore
+
+  describe "#estimate" do
+    let(:top_taxon) do
+      { base_path: '/top', links: { parent_taxons: [] } }.deep_stringify_keys
+    end
+
+    let(:second_taxon) do
+      {
+        base_path: '/second', links: { parent_taxons: [ { base_path: '/top' } ] }
+      }.deep_stringify_keys
+    end
+
+    context 'given a top level taxon' do
+      it 'returns a HIGH range' do
+        expect(WeeklyEmailVolume.new(top_taxon).estimate).to eq WeeklyEmailVolume::HIGH
+      end
+    end
+
+    context 'given a 2nd level taxon' do
+
+      before do
+        content_store_has_item(top_taxon['base_path'], top_taxon)
+      end
+
+      it 'returns a MEDIUM range' do
+        expect(WeeklyEmailVolume.new(second_taxon).estimate).to eq WeeklyEmailVolume::MEDIUM
+      end
+    end
+
+    context 'given a 3rd level taxon' do
+      let(:third_taxon) do
+        {
+          base_path: '/third', links: { parent_taxons: [ { base_path: '/second' } ] }
+        }.deep_stringify_keys
+      end
+
+      before do
+        content_store_has_item(second_taxon['base_path'], second_taxon)
+      end
+
+      it 'returns a LOW range' do
+        expect(WeeklyEmailVolume.new(third_taxon).estimate).to eq WeeklyEmailVolume::LOW
+      end
+    end
+  end
+end