Add report download link to email notification

I added a system spec to verify that the download link can be generated
within the mailer in a background job. ActiveStorage is a bit particular
when it comes to genererating URLs and depending on the situation it may
generate a redirect URL, a proxy URL or link directly to the storage.
But we want a redirect URL here.

app/jobs/report_job.rb

@@ -13,10 +13,13 @@ class ReportJob < ApplicationJob
 
     execution_time = Time.zone.now - start_time
 
-    email_result if execution_time > NOTIFICATION_TIME
+    email_result(user, blob) if execution_time > NOTIFICATION_TIME
   end
 
-  def email_result
-    ReportMailer.report_ready.deliver_later
+  def email_result(user, blob)
+    ReportMailer.with(
+      to: user.email,
+      blob: blob,
+    ).report_ready.deliver_later
   end
 end

app/mailers/report_mailer.rb

@@ -2,6 +2,11 @@
 
 class ReportMailer < ApplicationMailer
   def report_ready
-    mail
+    # When we are in a background job then we don't have an HTTP request object
+    # and we need to tell ActiveStorage the hostname to generate URLs.
+    ActiveStorage::Current.url_options ||= url_options
+
+    @blob = params[:blob]
+    mail(params)
   end
 end

app/views/report_mailer/report_ready.html.haml

@@ -1 +1,5 @@
-%h3 TBC
+%h3= t(".heading")
+%p
+  = t(".intro")
+%ul
+  %li= link_to(t(".link_label", name: @blob.filename), @blob.url)

config/locales/en.yml

@@ -319,6 +319,13 @@ en:
     order_cycle:
       subject: "Order cycle report for %{producer}"
   provider_settings: "Provider settings"
+  report_mailer:
+    report_ready:
+      subject: "Report ready"
+      heading: "Report ready for download"
+      intro: |
+        The link below will expire after one month.
+      link_label: "%{name}"
   shipment_mailer:
     shipped_email:
       dear_customer: "Dear Customer,"

spec/jobs/report_job_spec.rb

@@ -40,7 +40,13 @@ describe ReportJob do
       # rspec-rails: https://github.com/rspec/rspec-rails/issues/2668
       ReportJob.perform_later(*report_args)
       perform_enqueued_jobs(only: ReportJob)
-    }.to enqueue_mail(ReportMailer, :report_ready)
+    }.to enqueue_mail(ReportMailer, :report_ready).with(
+      params: {
+        to: user.email,
+        blob: blob,
+      },
+      args: [],
+    )
   end
 
   it "triggers no email when the report is done quickly" do

spec/mailers/report_mailer_spec.rb

@@ -0,0 +1,31 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe ReportMailer do
+  describe "#report_ready" do
+    subject(:email) {
+      ReportMailer.with(
+        to: "current_user@example.net",
+        blob: blob,
+      ).report_ready
+    }
+    let(:blob) { ReportBlob.create_for_upload_later!("customers.csv") }
+
+    it "notifies about a report" do
+      expect(email.subject).to eq "Report ready"
+      expect(email.body).to have_content "Report ready for download"
+    end
+
+    it "notifies the user" do
+      expect(email.to).to eq ["current_user@example.net"]
+    end
+
+    it "contains a download link" do
+      expect(email.body).to have_link(
+        "customers.csv",
+        href: %r"^http://test\.host/rails/active_storage/disk/.*/customers\.csv$"
+      )
+    end
+  end
+end

spec/system/admin/reports_spec.rb

@@ -77,8 +77,10 @@ describe '
       visit admin_report_path(
         report_type: :customers, report_subtype: :mailing_list
       )
+      allow(ENV).to receive(:fetch).and_call_original
       expect(ENV).to receive(:fetch).with("RACK_TIMEOUT_SERVICE_TIMEOUT", "15")
         .and_return("-1") # Negative values time out immediately.
+      stub_const("ReportJob::NOTIFICATION_TIME", 0)
 
       click_button "Go"
 
@@ -92,6 +94,12 @@ describe '
 
       content = File.read(downloaded_filename)
       expect(content).to match "<th>\nFirst Name\n</th>"
+
+      # We also get an email.
+      perform_enqueued_jobs(only: ActionMailer::MailDeliveryJob)
+      email = ActionMailer::Base.deliveries.last
+      expect(email.body).to have_link "customers",
+        href: %r"^http://test\.host/rails/active_storage/disk/.*/customers_[0-9]+\.html$"
     end
   end