add preview url to attachments graphql response

fixes COMMS-2099

TEST PLAN
* Create a course.
* Add two or more students to the course.
* Create an assignment with file upload submission type. Note the
  assignemnt id in the url.
* Masquerade as one of the users and submit the assignment. Use a zip
  file and an image file (or any other canvadocable mime type) as the
  submission files.
* Masquerade and submit the assignment as your other students, using
  different canvadocable file types (e.g. pdf, png, jpeg).
* As the instructor/site admin Navigate to the /graphiql endpoint.
* run the following query substituting in the assignment id:

  {
    assignment(id: "<your_assignment_id>") {
      submissionsConnection {
        nodes {
          _id
          user {
            name
          }
        }
      }
    }
  }

* Using those submission ids, run the following query for each
  submission id to view the submission preview urls:

  {
    assignment(id: "<your_assignment_id>") {
      submissionsConnection {
        nodes {
          _id
          user {
            name
          }
          attachments {
            submissionPreviewUrl(submissionId: "<submission_id>")
            displayName
          }
        }
      }
    }
  }

* Note that the zip file does not have a preview url and verify that the
  other attachments do.

Change-Id: Ic8e8c0be994f1d6e4979755674a9e8c3d35c038a
Reviewed-on: https://gerrit.instructure.com/196418
Tested-by: Jenkins
Reviewed-by: Cameron Matheson <cameron@instructure.com>
Reviewed-by: Landon Gilbert-Bland <lbland@instructure.com>
QA-Review: Steven Burnett <sburnett@instructure.com>
Product-Review: Steven Burnett <sburnett@instructure.com>

app/graphql/types/file_type.rb

@@ -60,5 +60,59 @@ module Types
       opts[:verifier] = object.uuid if context[:in_app]
       GraphQLHelpers::UrlHelpers.file_download_url(object, opts)
     end
+
+    field :submission_preview_url, Types::UrlType, null: true do
+      argument :submission_id, ID, required: true, prepare: GraphQLHelpers.relay_or_legacy_id_prepare_func("Submission")
+    end
+    def submission_preview_url(submission_id:)
+      return if object.locked_for?(current_user, check_policies: true)
+
+      Loaders::IDLoader.for(Submission).load(submission_id).then do |submission|
+        next unless submission.grants_right?(current_user, session, :read)
+
+        # We are checking first to see if the attachment is associated with the given submission id
+        # to potentially avoid needing to load submission histories which is expensive.
+        if submission.attachment_ids_for_version.include?(object.id)
+          load_submission_associations(submission) do |course, assignment|
+            get_canvadoc_url(course, assignment, submission)
+          end
+        else
+          load_submission_history_associations(submission) do |course, assignment|
+            attachment_ids = submission.submission_history.map(&:attachment_ids_for_version).flatten
+            next unless attachment_ids.include?(object.id)
+            get_canvadoc_url(course, assignment, submission)
+          end
+        end
+      end
+    end
+
+    private
+
+    def load_submission_associations(submission)
+      Loaders::AssociationLoader.for(Submission, :assignment).load(submission).then do |assignment|
+        Loaders::AssociationLoader.for(Assignment, :context).load(assignment).then do |course|
+          yield(course, assignment)
+        end
+      end
+    end
+
+    def load_submission_history_associations(submission)
+      load_submission_associations(submission) do |course, assignment|
+        Loaders::AssociationLoader.for(Submission, :versions).load(submission).then do
+          yield(course, assignment)
+        end
+      end
+    end
+
+    def get_canvadoc_url(course, assignment, submission)
+      opts = {
+        anonymous_instructor_annotations: course.grants_right?(current_user, :manage_grade) && assignment.anonymous_instructor_annotations,
+        moderated_grading_whitelist: submission.moderated_grading_whitelist,
+        submission_id: submission.id,
+        enable_annotations: true,
+        enrollment_type: CoursesHelper.user_type(course, current_user)
+      }
+      object.canvadoc_url(current_user, opts)
+    end
   end
 end

app/helpers/courses_helper.rb

@@ -120,6 +120,7 @@ module CoursesHelper
 
     type
   end
+  module_function :user_type
 
   def why_cant_i_enable_master_course(course)
     return nil if MasterCourses::MasterTemplate.is_master_course?(course)

schema.graphql

@@ -1052,6 +1052,7 @@ type File implements ModuleItemInterface & Node & Timestamped {
   id: ID!
   mimeClass: String
   modules: [Module!]
+  submissionPreviewUrl(submissionId: ID!): URL
   thumbnailUrl: URL
   updatedAt: DateTime
   url: URL

spec/graphql/types/file_type_spec.rb

@@ -61,4 +61,64 @@ describe Types::FileType do
       file_type.resolve('url', request: ActionDispatch::TestRequest.create, current_user: @student)
     ).to be_nil
   end
+
+  context 'submission preview url' do
+    before(:once) do
+      @assignment = assignment_model(course: @course)
+      @student_file = attachment_with_context(@student, content_type: "application/pdf")
+      @submission = @assignment.submit_homework(
+        @student,
+        body: 'Attempt 1',
+        submitted_at: 2.hours.ago,
+        submission_type: "online_upload",
+        attachments: [@student_file]
+      )
+      AttachmentAssociation.create!(attachment: @student_file, context: @submission, context_type: "Submission")
+      @resolver = GraphQLTypeTester.new(@student_file, current_user: @student)
+    end
+
+    it 'returns nil if the the file is locked' do
+      file.update!(locked: true)
+      expect(
+        file_type.resolve(
+          'submissionPreviewUrl(submissionId: "' + @submission.id.to_s + '")',
+          request: ActionDispatch::TestRequest.create,
+          current_user: @student
+        )
+      ).to be_nil
+    end
+
+    it 'returns nil if the file is not a canvadocable type' do
+      allow(Canvadocs).to receive(:enabled?).and_return true
+      @student_file.update!(content_type: 'application/loser')
+      expect(
+        @resolver.resolve('submissionPreviewUrl(submissionId: "' + @submission.id.to_s + '")')
+      ).to be_nil
+    end
+
+    it 'returns nil if canvadocs is not enabled' do
+      allow(Canvadocs).to receive(:enabled?).and_return false
+      expect(
+        @resolver.resolve('submissionPreviewUrl(submissionId: "' + @submission.id.to_s + '")')
+      ).to be_nil
+    end
+
+    it 'returns nil if the given submission id is not associated with the attachment' do
+      other_assignment = assignment_model(course: @course)
+      other_submission = other_assignment.submit_homework(
+        @student,
+        body: 'Attempt 1',
+        submitted_at: 2.hours.ago,
+      )
+      resp = @resolver.resolve('submissionPreviewUrl(submissionId: "' + other_submission.id.to_s + '")')
+      expect(resp).to be_nil
+    end
+
+    it 'returns the submission preview url' do
+      allow(Canvadocs).to receive(:enabled?).and_return true
+      resp = @resolver.resolve('submissionPreviewUrl(submissionId: "' + @submission.id.to_s + '")')
+      expect(resp).not_to be_nil
+      expect(resp.start_with?('/api/v1/canvadoc_session')).to be true
+    end
+  end
 end