Add FoiAttachmentMaskJob uniqueness methods

Instead of locking jobs to prevent them from running add checks for
existing jobs before performing/enqueuing attempting to ensure we
execute once only.

These methods only work if Sidekiq is used as the ActiveJob adapter.

app/controllers/attachment_masks_controller.rb

@@ -15,7 +15,7 @@ def wait
       )
 
     else
-      FoiAttachmentMaskJob.perform_later(@attachment)
+      FoiAttachmentMaskJob.perform_once_later(@attachment)
     end
   end
 

app/controllers/attachments_controller.rb

@@ -22,7 +22,7 @@ def show
     if @attachment.masked?
       render body: @attachment.body, content_type: content_type
     else
-      FoiAttachmentMaskJob.perform_later(@attachment)
+      FoiAttachmentMaskJob.perform_once_later(@attachment)
 
       Timeout.timeout(5) do
         until @attachment.masked?

app/jobs/foi_attachment_mask_job.rb

@@ -6,6 +6,8 @@
 #   FoiAttachmentMaskJob.perform(FoiAttachment.first)
 #
 class FoiAttachmentMaskJob < ApplicationJob
+  include Uniqueness
+
   queue_as :default
 
   attr_reader :attachment

app/jobs/foi_attachment_mask_job/uniqueness.rb

@@ -0,0 +1,34 @@
+##
+# Module to add methods to check for existing jobs before performing/enqueuing
+# attempting to ensure we execute once only.
+#
+# These methods only work if Sidekiq is used as the ActiveJob adapter.
+#
+module FoiAttachmentMaskJob::Uniqueness
+  def self.included(base)
+    base.extend ClassMethods
+  end
+
+  module ClassMethods
+    def perform_once_later(attachment)
+      perform_later(attachment) unless existing_job(attachment)
+    end
+
+    def perform_once_now(attachment)
+      existing_job(attachment)&.delete
+      perform_now(attachment)
+    end
+
+    def existing_job(attachment)
+      return unless queue_adapter.is_a?(
+        ActiveJob::QueueAdapters::SidekiqAdapter
+      )
+
+      queue = Sidekiq::Queue.new(queue_name)
+      queue.find do |j|
+        gid = j.display_args.first['_aj_globalid']
+        gid == attachment.to_gid.to_s
+      end
+    end
+  end
+end

app/models/foi_attachment.rb

@@ -107,7 +107,7 @@ def body
     if masked?
       @cached_body = file.download
     elsif persisted?
-      FoiAttachmentMaskJob.perform_now(self)
+      FoiAttachmentMaskJob.perform_once_now(self)
       reload
       body
     end

spec/jobs/foi_attachment_mask_job_spec.rb

@@ -139,4 +139,57 @@ def perform
       expect(new_attachment.body).to include 'Banana'
     end
   end
+
+  describe '.perform_once_later' do
+    it 'call perform_later' do
+      expect(FoiAttachmentMaskJob).to receive(:perform_later)
+      FoiAttachmentMaskJob.perform_once_later(attachment)
+    end
+
+    it 'does not call perform_later if existing job is present' do
+      allow(FoiAttachmentMaskJob).to receive(:existing_job).and_return(double)
+      expect(FoiAttachmentMaskJob).to_not receive(:perform_later)
+      FoiAttachmentMaskJob.perform_once_later(attachment)
+    end
+  end
+
+  describe '.perform_once_now' do
+    it 'deleted existing job if present' do
+      job = double(:job)
+      allow(FoiAttachmentMaskJob).to receive(:existing_job).and_return(job)
+      expect(job).to receive(:delete)
+      FoiAttachmentMaskJob.perform_once_now(attachment)
+    end
+
+    it 'calls perform_now' do
+      expect(FoiAttachmentMaskJob).to receive(:perform_now)
+      FoiAttachmentMaskJob.perform_once_now(attachment)
+    end
+  end
+
+  describe '.existing_job' do
+    around do |example|
+      adapter = ActiveJob::Base.queue_adapter
+      ActiveJob::Base.queue_adapter = :sidekiq
+      example.call
+      ActiveJob::Base.queue_adapter = adapter
+    end
+
+    before do
+      allow(FoiAttachmentMaskJob).to receive(:queue_name).and_return('test')
+    end
+
+    after do
+      Sidekiq::Queue.new('test').clear
+    end
+
+    it 'return nil if existing job is not present' do
+      expect(FoiAttachmentMaskJob.existing_job(attachment)).to be_nil
+    end
+
+    it 'return existing job if present' do
+      FoiAttachmentMaskJob.perform_later(attachment)
+      expect(FoiAttachmentMaskJob.existing_job(attachment)).to_not be_nil
+    end
+  end
 end