Store report's filename within the blob

For future downloads outside the ReportsController.

app/controllers/admin/reports_controller.rb

@@ -57,7 +57,9 @@ module Admin
 
     def render_report_as(format)
       if OpenFoodNetwork::FeatureToggle.enabled?(:background_reports, spree_current_user)
-        blob = ReportBlob.create_for_upload_later!
+        filename = report_filename
+        filename = "#{filename}html" if report_format.blank?
+        blob = ReportBlob.create_for_upload_later!(filename)
         ReportJob.perform_later(
           report_class, spree_current_user, params, format, blob
         )

app/models/report_blob.rb

@@ -2,20 +2,24 @@
 
 # Stores a generated report.
 class ReportBlob < ActiveStorage::Blob
-  def self.create_for_upload_later!
+  def self.create_for_upload_later!(filename)
     # ActiveStorage discourages modifying a blob later but we need a blob
     # before we know anything about the report file. It enables us to use the
     # same blob in the controller to read the result.
     create_before_direct_upload!(
-      filename: "tbd",
+      filename: filename,
       byte_size: 0,
       checksum: "0",
-      content_type: "application/octet-stream",
+      content_type: content_type(filename),
     ).tap do |blob|
       ActiveStorage::PurgeJob.set(wait: 1.month).perform_later(blob)
     end
   end
 
+  def self.content_type(filename)
+    MIME::Types.of(filename).first&.to_s || "application/octet-stream"
+  end
+
   def store(content)
     io = StringIO.new(content)
     upload(io, identify: false)

spec/jobs/report_job_spec.rb

@@ -9,7 +9,7 @@ describe ReportJob do
   let(:enterprise) { create(:enterprise) }
   let(:params) { {} }
   let(:format) { :csv }
-  let(:blob) { ReportBlob.create_for_upload_later! }
+  let(:blob) { ReportBlob.create_for_upload_later!("report.csv") }
 
   it "generates a report" do
     job = perform_enqueued_jobs(only: ReportJob) do
@@ -29,6 +29,10 @@ describe ReportJob do
   end
 
   def expect_csv_report
+    blob.reload
+    expect(blob.filename.to_s).to eq "report.csv"
+    expect(blob.content_type).to eq "text/csv"
+
     table = CSV.parse(blob.result)
     expect(table[0][1]).to eq "Relationship"
     expect(table[1][1]).to eq "owns"