models: factor out concerns to app/logical/concerns.

app/logical/concerns/mentionable.rb

@@ -0,0 +1,41 @@
+module Mentionable
+  extend ActiveSupport::Concern
+
+  included do
+    attr_accessor :skip_mention_notifications
+  end
+
+  module ClassMethods
+    # options:
+    # - message_field
+    # - user_field
+    def mentionable(options = {})
+      @mentionable_options = options
+
+      message_field = mentionable_option(:message_field)
+      after_save :queue_mention_messages
+    end
+
+    def mentionable_option(key)
+      @mentionable_options[key]
+    end
+  end
+
+  def queue_mention_messages
+    message_field = self.class.mentionable_option(:message_field)
+    return if !send(:saved_change_to_attribute?, message_field)
+    return if self.skip_mention_notifications
+
+    text = send(message_field)
+    text_was = send(:attribute_before_last_save, message_field)
+
+    names = DText.parse_mentions(text) - DText.parse_mentions(text_was)
+
+    names.uniq.each do |name|
+      body  = self.instance_exec(name, &self.class.mentionable_option(:body))
+      title = self.instance_exec(name, &self.class.mentionable_option(:title))
+
+      Dmail.create_automated(to_name: name, title: title, body: body)
+    end
+  end
+end