zip up course files

closes OFFW-49

test plan:
- Sign in as a user in a course that has Offline Web Downloads turned on
- navigate to the modules page
- Click on 'Download Course Content'
- go to the Rails Console
  - type: `Attachment.all.last.id`
  - take the ID it spits out
- request that file through the API
- ** if the URL attribute has epub_export/:id/ before files/:id/...
  then delete that part (expub_export/:id/) so that it reads
  something like localhost:3000/files/:id/download?download_frd=blahblah
- in a course without any course files, export the course content
  and you should get an empty zip file (you need to do all the stuff above)

Change-Id: I91fcbf35a1c482eab476dbcf4565f3499453253a
Reviewed-on: https://gerrit.instructure.com/97849
Tested-by: Jenkins
Reviewed-by: Mysti Sadler <mysti@instructure.com>
QA-Review: Nathan Rogowski <nathan@instructure.com>
Product-Review: Cameron Sutter <csutter@instructure.com>

app/models/web_zip_export.rb

@@ -1,4 +1,5 @@
 class WebZipExport < EpubExport
+  include CC::Exporter::WebZip::Exportable
 
   def export
     MustViewModuleProgressor.new(user, course).make_progress
@@ -12,19 +13,23 @@ class WebZipExport < EpubExport
   end
   handle_asynchronously :generate, priority: Delayed::LOW_PRIORITY, max_attempts: 1
 
+  # WebZip Exportable overrides
+  def content_cartridge
+    self.content_export.attachment
+  end
+
   def convert_to_offline_web_zip
     begin
       set_locale
-      # TODO: connect to cameron's patchset
-      # file_path = super
-      file_path = "/Users/mysti/canvas/chaos.mov.zip"
+      file_path = super
       I18n.locale = :en
+
+      create_attachment_from_path!(file_path)
     rescue => e
       mark_as_failed
       raise e
     end
 
-    create_attachment_from_path!(file_path)
     mark_as_generated
     cleanup_file_path!(file_path)
   end

lib/cc/exporter/web_zip/exportable.rb

@@ -7,9 +7,9 @@ module CC::Exporter::WebZip
     def convert_to_offline_web_zip
       exporter = CC::Exporter::WebZip::Exporter.new(content_cartridge.open, false)
       zip = CC::Exporter::WebZip::ZipPackage.new(exporter)
-      result = zip.create
+      file_path = zip.create || zip.empty_zip_file
       exporter.cleanup_files
-      result
+      file_path
     end
   end
 end

lib/cc/exporter/web_zip/zip_package.rb

@@ -1,5 +1,22 @@
 module CC::Exporter::WebZip
   class ZipPackage < CC::Exporter::Epub::FilesDirectory
+    def initialize(exporter)
+      @files = exporter.unsupported_files + exporter.cartridge_json[:files]
+      @filename_prefix = exporter.filename_prefix
+    end
+    attr_reader :files
+
+    def empty_zip_file
+      zip_file = Zip::File.new(
+        File.join(export_directory, filename),
+        Zip::File::CREATE
+      )
+      tempfile = 'empty.txt'
+      f = File.new(tempfile, "w+")
+      zip_file.add(tempfile, f) { f.close }
+      zip_file.close
+      zip_file.name
+    end
 
   end
 end

spec/models/web_zip_export_spec.rb

@@ -24,5 +24,14 @@ describe WebZipExport do
       web_zip_export.generate_without_send_later
       expect(web_zip_export.generating?).to be_truthy
     end
+
+    it 'should create and associate an attachment' do
+      web_zip_export.export_without_send_later
+      web_zip_export.content_export.export_without_send_later
+      expect(web_zip_export.zip_attachment).to be_nil, 'precondition'
+      expect{web_zip_export.convert_to_offline_web_zip_without_send_later}.to change{Attachment.count}.by(1)
+      web_zip_export.reload
+      expect(web_zip_export.zip_attachment).not_to be_nil
+    end
   end
 end