a_controller.rb

Wf.new
  .chain  { CloseProject.new(project) }
  .chain  { NotifyProjectClosed(project) }
  .chain  { Log.new(:project_closed, project) }
  .chain  { render json: project }
  .on_dam { |error_pool| render json: {errors: error_pool}, status: 422 }
  

close_project.rb

class CloseProject
  include Waterfall
  attr_reader :project
  def initialize(project)
    @project = project
  end
  
  def call
    self
      .chain { CreditTransaction.new({ payable: project.owner, amount: project.cost, source: project }) }
      .chain { close }
      .chain { project }
  end
  
  def close
    dam project.errors unless project.close
  end
  
end
  

credit_transaction.rb

class CreditTransaction
  include Waterfall
  attr_reader :payable, :amount, :source
  def initialize(options)
    source  = options.fetch(:source)
    payable = options.fetch(:payable)
    amount  = options.fetch(:amount)
  end
  
  def call
    self
      .when_falsy { credit.save }
        .dam { credit.errors } 
      .chain { credit }
  end
  
  def credit
    @credit ||= payable.credit_transactions.create(amount: amount, source: source})
  end
end

notify_project_closed.rb

class NotifyProjectClosed
  include Waterfall
  attr_reader :project
  def initialize(project)
    @project = project
  end
  
  def call
    self
      .chain { notify_owner }
      .chain { notify_manager }
  end
  
  def notify_owner
    ProjectMailer.delay.notify_owner_on_close(project)
  end
  
  def notify_manager
    ProjectMailer.delay.notify_manager_on_close(project)
  end
end