Riparian is a partial workflow system built with Delayed Job and Paperclip. It consists of Flow Tasks, which are tasks to be performed by Delayed Job, and Flow Task Resources, which constitute input and output data of the tasks. Flow Task Resources can have an attached file, or a polymorphic relationship to an ActiveRecord resource.

To make your own tasks, subclass FlowTask and implement the run method. Tasks will be executed whenever Delayed Job gets to them.

If you need to alter Paperclip's path and url settings, you can add a riparian.yml file to your config folder with the following settings:

flow_task_resource_file_path: paperclip/interpolation/string
flow_task_resource_file_url: paperclip/interpolation/string

Similarly you can set the max and min file sizes in bytes for file attachments:

flow_task_resource_file_size_greater_than: 1 # Default: 1 byte
flow_task_resource_file_size_less_than: 1024 # Default: 10 megabytes

# generate controller, helper, and migration
rails generate riparian

# subclass FlowTask
class MyTask < FlowTask
  def run
    open(inputs.first.file.path) do |f|
      txt = f.read
      txt.gsub! 'foo', 'bar'
      Tempfile.open('bar') do |tf|
        tf.write(txt)
        outputs.create(:file => tf)
      end
    end
  end
end

Start POSTing stuff to /flow_tasks!