Allow users to explicitly specify the queue backend to use

* Add a configuration block for the main module
* Make backend auto detection more specific
* Refactor the job dispatching logic
* Add some basic specs
* Update the README with usage info
* Rearrange autoload to the top of the main module
* Suppress warning output in specs

README.md

@@ -33,6 +33,15 @@ gem 'carrierwave_backgrounder'
 
 ## Getting Started
 
+In an initializer:
+
+```ruby
+CarrierWave::Backgrounder.configure do |c|
+  # :delayed_job, :girl_friday, :sidekiq, :qu, :resque, or :qc
+  c.backend = :delayed_job 
+end
+```
+
 In your CarrierWave uploader file:
 
 ```ruby

lib/backgrounder/orm/base.rb

@@ -50,19 +50,7 @@ def set_#{column}_processing
             end
 
             def enqueue_#{column}_background_job
-              if defined? ::GirlFriday
-                CARRIERWAVE_QUEUE << { :worker => #{worker}.new(self.class.name, id, #{column}.mounted_as) }
-              elsif defined? ::Delayed::Job
-                ::Delayed::Job.enqueue #{worker}.new(self.class.name, id, #{column}.mounted_as)
-              elsif defined? ::Resque
-                ::Resque.enqueue #{worker}, self.class.name, id, #{column}.mounted_as
-              elsif defined? ::Qu
-                ::Qu.enqueue #{worker}, self.class.name, id, #{column}.mounted_as
-              elsif defined? ::Sidekiq
-                ::Sidekiq::Client.enqueue #{worker}, self.class.name, id, #{column}.mounted_as
-              elsif defined? ::QC
-                ::QC.enqueue "#{worker}.perform", self.class.name, id, #{column}.mounted_as.to_s
-              end
+              CarrierWave::Backgrounder.enqueue_for_backend(#{worker}, self.class.name, id, #{column}.mounted_as)
             end
 
             def trigger_#{column}_background_processing?
@@ -110,19 +98,7 @@ def store_#{column}!
             end
 
             def enqueue_#{column}_background_job
-              if defined? ::GirlFriday
-                CARRIERWAVE_QUEUE << { :worker => #{worker}.new(self.class.name, id, #{column}.mounted_as) }
-              elsif defined? ::Delayed::Job
-                ::Delayed::Job.enqueue #{worker}.new(self.class.name, id, #{column}.mounted_as)
-              elsif defined? ::Resque
-                ::Resque.enqueue #{worker}, self.class.name, id, #{column}.mounted_as
-              elsif defined? ::Qu
-                ::Qu.enqueue #{worker}, self.class.name, id, #{column}.mounted_as
-              elsif defined? ::Sidekiq
-                ::Sidekiq::Client.enqueue #{worker}, self.class.name, id, #{column}.mounted_as
-              elsif defined? ::QC
-                ::QC.enqueue "#{worker}.perform", self.class.name, id, #{column}.mounted_as.to_s
-              end
+              CarrierWave::Backgrounder.enqueue_for_backend(#{worker}, self.class.name, id, #{column}.mounted_as)
             end
 
             def trigger_#{column}_background_storage?

lib/carrierwave_backgrounder.rb

@@ -1,5 +1,6 @@
 module CarrierWave
   module Backgrounder
+
     Logger = Logger.new(STDOUT)
 
     autoload :Delay, 'backgrounder/delay'
@@ -8,6 +9,70 @@ module Backgrounder
     module ORM
       autoload :Base, 'backgrounder/orm/base'
     end
+
+    class << self
+      def backend=(value)
+        @backend = value
+        self.configure_backend
+      end
+
+      def backend
+        return @backend unless @backend.nil?
+        if available_backends.empty?
+          warn 'WARNING: No queue backends found to use for CarrierWave::Backgrounder'
+        elsif available_backends.size == 1
+          self.backend = available_backends.first
+        elsif available_backends.size > 1
+          warn 'WARNING: Multiple queue backends found for CarrierWave::Backgrounder. You need to set one explicitly.'
+        end
+      end
+
+      def configure
+        yield self
+      end
+
+      def available_backends
+        @available_backends ||= begin
+          backends = []
+          backends << :girl_friday if defined? ::GirlFriday
+          backends << :delayed_job if defined? ::Delayed::Job
+          backends << :resque      if defined? ::Resque
+          backends << :qu          if defined? ::Qu
+          backends << :sidekiq     if defined? ::Sidekiq
+          backends << :qc          if defined? ::QC
+          backends
+        end
+      end
+
+      def configure_backend
+        if backend == :girl_friday
+          require 'girl_friday'
+          @girl_friday_queue = GirlFriday::WorkQueue.new(:carrierwave) do |msg|
+            worker = msg[:worker]
+            worker.perform
+          end
+        end
+      end
+
+      def enqueue_for_backend(worker, class_name, subject_id, mounted_as)
+        case backend
+        when :girl_friday
+          @girl_friday_queue << { :worker => worker.new(self.class.name, subject_id, mounted_as) }
+        when :delayed_job
+          ::Delayed::Job.enqueue worker.new(class_name, subject_id, mounted_as)
+        when :resque
+          ::Resque.enqueue worker, class_name, subject_id, mounted_as
+        when :qu
+          ::Qu.enqueue worker, class_name, subject_id, column.mounted_as
+        when :sidekiq
+          ::Sidekiq::Client.enqueue worker, class_name, subject_id, mounted_as
+        when :qc
+          ::QC.enqueue "#{worker.name}.perform", class_name, subject_id, mounted_as.to_s
+        end
+      end
+
+    end
+
   end
 end
 
@@ -35,11 +100,3 @@ class Railtie < Rails::Railtie
   end
 end
 
-if defined?(GirlFriday)
-  require 'girl_friday'
-
-  CARRIERWAVE_QUEUE = GirlFriday::WorkQueue.new(:carrierwave) do |msg|
-    worker = msg[:worker]
-    worker.perform
-  end
-end

spec/backgrounder/backends_spec.rb

@@ -0,0 +1,67 @@
+require 'spec_helper'
+require 'carrierwave_backgrounder'
+
+describe CarrierWave::Backgrounder do
+
+  describe 'enumerating available backends' do
+
+    it 'detects GirlFriday' do
+      CarrierWave::Backgrounder.available_backends.should include(:girl_friday)
+    end
+    it 'detects Delayed::Job' do
+      CarrierWave::Backgrounder.available_backends.should include(:delayed_job)
+    end
+    it 'detects Resque' do
+      CarrierWave::Backgrounder.available_backends.should include(:resque)
+    end
+    it 'detects Qu' do
+      CarrierWave::Backgrounder.available_backends.should include(:qu)
+    end
+    it 'detects Sidekiq' do
+      CarrierWave::Backgrounder.available_backends.should include(:sidekiq)
+    end
+    it 'detects QC' do
+      CarrierWave::Backgrounder.available_backends.should include(:qc)
+    end
+  end
+
+  describe 'automatically setting backends' do
+
+    before do
+      CarrierWave::Backgrounder.instance_variable_set('@backend', nil)
+    end
+
+    it 'does not set a backend if none are available' do
+      suppress_warnings do
+        CarrierWave::Backgrounder.stubs(:available_backends).returns([])
+        CarrierWave::Backgrounder.backend.should be_nil
+      end
+    end
+    it 'sets a backend automatically if only one is available' do
+      CarrierWave::Backgrounder.stubs(:available_backends).returns([ :qu ])
+      CarrierWave::Backgrounder.backend.should eq(:qu)
+    end
+    it 'does not set a backend if more than one is available' do
+      suppress_warnings do
+        CarrierWave::Backgrounder.stubs(:available_backends).returns([:qu, :resque])
+        CarrierWave::Backgrounder.backend.should be_nil
+      end
+    end
+
+    it 'does not clobber a manually set backend' do
+      CarrierWave::Backgrounder.backend = :not_a_backend
+      CarrierWave::Backgrounder.backend.should eq(:not_a_backend)
+    end
+
+    it 'calls configure_backend when setting the backend' do
+      CarrierWave::Backgrounder.stubs(:available_backends).returns([ :qu ])
+      CarrierWave::Backgrounder.expects(:configure_backend).once
+      CarrierWave::Backgrounder.backend.should eq(:qu)
+    end
+
+  end
+
+
+
+end
+

spec/spec_helper.rb

@@ -1,7 +1,21 @@
 # encoding: utf-8
 require 'rubygems'
 require 'bundler/setup'
+require 'support/backend_constants'
+require 'logger'
+
+module WarningSuppression
+  def suppress_warnings
+    original_verbosity = $VERBOSE
+    $VERBOSE = nil
+    result = yield
+    $VERBOSE = original_verbosity
+    return result
+  end
+end
 
 RSpec.configure do |c|
   c.mock_with :mocha
-end
+  c.include WarningSuppression
+end
+

spec/support/backend_constants.rb

@@ -0,0 +1,23 @@
+# Fixture module declarations for backend detection testing
+
+module GirlFriday
+end
+
+module Delayed
+  module Job
+  end
+end
+
+module Resque
+end
+
+module Qu
+end
+
+module Sidekiq
+  module Worker
+  end
+end
+
+module QC
+end