Add background job for sending files to print services

app/jobs/send_file_to_print_host_job.rb

@@ -0,0 +1,11 @@
+class SendFileToPrintHostJob < ApplicationJob
+  queue_as :low
+  unique :until_executed
+
+  def perform(print_host:, file:)
+    service = print_host.service
+    # Check print host is OK before sending, otherwise raise an ArgumentError to try again later
+    raise PrintHost::NotReady unless service.ok?
+    service.upload(file: file, start_print: true)
+  end
+end

app/models/print_host.rb

@@ -3,6 +3,9 @@ class PrintHost < ApplicationRecord
 
   PROTOCOLS = Print.constants.map { [const_get("Print::#{it}::PROTOCOL"), const_get("Print::#{it}")] }.to_h.freeze
 
+  class NotReady < RuntimeError
+  end
+
   validates :name, presence: true
   validates :endpoint, presence: true
   validates :protocol, presence: true, inclusion: {in: PROTOCOLS.keys}

spec/jobs/send_file_to_print_host_job_spec.rb

@@ -0,0 +1,23 @@
+require "rails_helper"
+
+RSpec.describe SendFileToPrintHostJob do
+  let(:print_host) { create(:print_host) }
+  let(:file) { create(:model_file, filename: "test.gcode") }
+
+  it "raises PrintHost::NotReady if printer is not ok" do
+    stub_service = instance_double(Print::MoonrakerService)
+    allow(stub_service).to receive(:ok?).and_return(false)
+    allow(print_host).to receive(:service).and_return(stub_service)
+
+    expect { described_class.perform_now(print_host: print_host, file: file) }.to raise_error PrintHost::NotReady
+  end
+
+  it "calls upload method in relevant print service" do # rubocop:disable RSpec/ExampleLength
+    stub_service = instance_double(Print::MoonrakerService)
+    allow(stub_service).to receive(:ok?).and_return(true)
+    allow(stub_service).to receive(:upload)
+    allow(print_host).to receive(:service).and_return(stub_service)
+    described_class.perform_now(print_host: print_host, file: file)
+    expect(stub_service).to have_received(:upload).with(file: file, start_print: true).once
+  end
+end