Variation of RubyTapas episode "021 Domain Model Events" without using callbacks

tasks_controller_refactoring.rb

class TasksController < ApplicationController
  def update
    tracker = TaskTracker.new(@task)
    if @task.update_attributes(params[:task])
      TaskPusher.new(tracker, socket_id).push_changes
      TaskMailSender.new(tracker, current_user).deliver_email
      # success response
    else
      # failure respond
    end
  end
end

# This TaskTracker class isn't necessary since Rails dirty tracking has a previous_changes
# method that I overlooked. Thanks Jonas Nicklas for pointing this out and blowmage for
# making a fork using this: https://gist.github.com/4060224
#
# Update: One issue with previous_changes is if the TaskPusher saves the model the
# TaskMailSender would not have the original changes. I think this is good enough
# reason to stick with TaskTracker.
class TaskTracker
  attr_reader :task, :original_project_id, :original_status, :original_assignee

  def initialize(task)
    @task = task
    @original_project_id = task.project_id
    @original_status = task.status
    @original_assignee = task.assignee
  end

  def project_changed?
    original_project_id != task.project_id
  end

  def status_changed?
    original_status != task.status
  end

  def assignee_changed?
    original_assignee != task.assignee
  end
end

class TaskPusher < Struct.new(:task_tracker, :socket_id)
  def push_changes
    if task_tracker.assignee_changed?
      # push assignee changes
    end
    if task_tracker.project_changed?
      # push project changes
    end
  end
end

class TaskMailSender < Struct.new(:task_tracker, :recipient)
  def deliver_email
    if task_tracker.status_changed?
      # email status change
    end
    if task_tracker.assignee_changed?
      # email assignee change
    end
  end
end