Add environment to the body of the monthly key metrics report (LG-11418)

app/assets/stylesheets/tables-report.css.scss

@@ -1,6 +1,7 @@
 @forward 'uswds-core';
 @forward 'usa-prose';
 @forward 'usa-table';
+@forward 'usa-alert';
 
 .table-number {
   font-variant-numeric: tabular-nums;

app/jobs/reports/monthly_key_metrics_report.rb

@@ -36,14 +36,30 @@ def perform(date = Time.zone.yesterday)
 
     # Explanatory text to go before the report in the email
     # @return [String]
-    def preamble
-      <<~HTML.html_safe # rubocop:disable Rails/OutputSafety
+    def preamble(env: Identity::Hostdata.env || 'local')
+      ERB.new(<<~ERB).result(binding).html_safe # rubocop:disable Rails/OutputSafety
+        <% if env != 'prod' %>
+          <div class="usa-alert usa-alert--info">
+            <div class="usa-alert__body">
+              <%#
+                NOTE: our AlertComponent doesn't support heading content like this uses,
+                so for a one-off outside the Rails pipeline it was easier to inline the HTML here.
+              %>
+              <h2 class="usa-alert__heading">
+                Non-Production Report
+              </h2>
+              <p class="usa-alert__text">
+                This was generated in the <strong><%= env %></strong> environment.
+              </p>
+            </div>
+          </div>
+        <% end %>
         <p>
           For more information on how each of these metrics are calculated, take a look at our
           <a href="https://handbook.login.gov/articles/monthly-key-metrics-explainer.html">
           Monthly Key Metrics Report Explainer document</a>.
         </p>
-      HTML
+      ERB
     end
 
     def reports

spec/jobs/reports/monthly_key_metrics_report_spec.rb

@@ -113,12 +113,26 @@
   end
 
   describe '#preamble' do
-    subject(:preamble) { report.preamble }
+    let(:env) { 'prod' }
+    subject(:preamble) { report.preamble(env:) }
 
     it 'has a preamble that is valid HTML' do
       expect(preamble).to be_html_safe
 
       expect { Nokogiri::XML(preamble) { |config| config.strict } }.to_not raise_error
     end
+
+    context 'in a non-prod environment' do
+      let(:env) { 'staging' }
+
+      it 'has an alert with the environment name' do
+        expect(preamble).to be_html_safe
+
+        doc = Nokogiri::XML(preamble)
+
+        alert = doc.at_css('.usa-alert')
+        expect(alert.text).to include(env)
+      end
+    end
   end
 end