feat: new background work process

This removes all previous dependencies on RabbitMQ and the need to run separate cron and requeueing processes.

lib/worker/jobs/process_webhook_requests_job.rb

@@ -0,0 +1,48 @@
+# frozen_string_literal: true
+
+module Worker
+  module Jobs
+    class ProcessWebhookRequestsJob < BaseJob
+
+      def call
+        @lock_time = Time.current
+        @locker = Postal.locker_name_with_suffix(SecureRandom.hex(8))
+
+        lock_request_for_processing
+        obtain_locked_requests
+        process_requests
+      end
+
+      private
+
+      # Obtain a webhook request from the database for processing
+      #
+      # @return [void]
+      def lock_request_for_processing
+        WebhookRequest.unlocked
+                      .ready
+                      .limit(1)
+                      .update_all(locked_by: @locker, locked_at: @lock_time)
+      end
+
+      # Get a full list of all webhooks which we can process (i.e. those which have just
+      # been locked by us for processing)
+      #
+      # @return [void]
+      def obtain_locked_requests
+        @requests_to_process = WebhookRequest.where(locked_by: @locker, locked_at: @lock_time)
+      end
+
+      # Process the webhook requests we obtained from the database
+      #
+      # @return [void]
+      def process_requests
+        @requests_to_process.each do |request|
+          work_completed!
+          request.deliver
+        end
+      end
+
+    end
+  end
+end