Variation of RubyTapas episode "021 Domain Model Events" without callbacks, using dirty, and keeping the tracker object.

tasks_controller_refactoring.rb

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

class TaskTracker
  attr_reader :task

  def initialize(task)
    @task = task
  end

  def project_changed?
    changed?("project")
  end

  def status_changed?
    changed?("status")
  end

  def assignee_changed?
    changed?("assignee")
  end

  def changed?(attribute)
    if changed_attribute = changes[attribute]
      changes.first != changes.last
    end
  end
  
  def changes
    task.changed_attributes
  end
end

class PostSaveTaskTracker < TaskTracker
  def changes
    task.previous_changes
  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