Format numbers as millions or billions

This matches the existing performance platform page, and I think is a
bit easier to read for high-level numbers where you don’t need to see
that they’re changing second-by-second.

app/__init__.py

@@ -38,6 +38,7 @@ from app.config import configs
 from app.extensions import antivirus_client, redis_client, zendesk_client
 from app.formatters import (
     convert_to_boolean,
+    format_billions,
     format_date,
     format_date_human,
     format_date_normal,
@@ -527,6 +528,7 @@ def setup_event_handlers():
 
 def add_template_filters(application):
     for fn in [
+        format_billions,
         format_datetime,
         format_datetime_24h,
         format_datetime_normal,

app/formatters.py

@@ -515,3 +515,7 @@ def format_mobile_network(network):
     if network in ('three', 'vodafone', 'o2'):
         return network.capitalize()
     return 'EE'
+
+
+def format_billions(count):
+    return humanize.intword(count)

app/templates/views/performance.html

@@ -22,28 +22,28 @@
   <div class="govuk-grid-row">
     <div class="govuk-grid-column-one-half">
       <h3 class="govuk-visually-hidden">Total messages</h3>
-      <div class="product-page-big-number">{{ total_notifications }}</div>
+      <div class="product-page-big-number">{{ total_notifications|format_billions }}</div>
       total
     </div>
     <div class="govuk-grid-column-one-half">
       <div class="govuk-grid-row govuk-!-padding-top-4">
         <div class="govuk-grid-column-one-third">
           {{ big_number(
-            email_notifications,
+            email_notifications|format_billions,
             label=email_notifications|message_count_noun('email'),
             smallest=True,
           ) }}
         </div>
         <div class="govuk-grid-column-one-third">
           {{ big_number(
-            sms_notifications,
+            sms_notifications|format_billions,
             label=sms_notifications|message_count_noun('sms'),
             smallest=True,
           ) }}
         </div>
         <div class="govuk-grid-column-one-third">
           {{ big_number(
-            letter_notifications,
+            letter_notifications|format_billions,
             label=letter_notifications|message_count_noun('letter'),
             smallest=True,
           ) }}

tests/app/main/views/test_performance.py

@@ -117,10 +117,10 @@ def test_should_render_performance_page(
         ''
         'Messages sent since May 2016 '
         'Total messages '
-        '1789000000 total '
-        '1,123,000,000 emails '
-        '987,654,321 text messages '
-        '1,234,567 letters '
+        '1.8 billion total '
+        '1.1 billion emails '
+        '987.7 million text messages '
+        '1.2 million letters '
         ''
         'Date Emails Text messages Letters '
         '21 February 2021 1,234,567 123,456 123 '