Add MessageData module to include sparkpost_data in Mail::Message

Gemfile.lock

@@ -1,7 +1,7 @@
 PATH
   remote: .
   specs:
-    sparkpost_rails (1.5.1)
+    sparkpost_rails (1.5.2)
       rails (>= 4.0, < 5.3)
 
 GEM

lib/sparkpost_rails.rb

@@ -1,6 +1,7 @@
 require "sparkpost_rails/data_options"
 require "sparkpost_rails/delivery_method"
 require "sparkpost_rails/exceptions"
+require "sparkpost_rails/message_data"
 require "sparkpost_rails/railtie"
 
 module SparkPostRails

lib/sparkpost_rails/data_options.rb

@@ -14,7 +14,9 @@ def mail(headers={}, &block)
           sparkpost_data = headers.delete(:sparkpost_data)
           sparkpost_data ||= {}
           super(headers, &block).tap do |message|
-            message.singleton_class.class_eval { attr_accessor "sparkpost_data" }
+            unless message.respond_to?(:sparkpost_data=)
+              message.singleton_class.class_eval { attr_accessor "sparkpost_data" }
+            end
             message.sparkpost_data = sparkpost_data
           end
         end

lib/sparkpost_rails/message_data.rb

@@ -0,0 +1,15 @@
+module SparkPostRails
+  module MessageData
+
+    def self.included(base)
+      base.class_eval do
+        attr_writer :sparkpost_data
+
+        def sparkpost_data
+          @sparkpost_data ||= {}
+        end
+      end
+    end
+
+  end
+end

lib/sparkpost_rails/railtie.rb

@@ -11,5 +11,11 @@ class Railtie < Rails::Railtie
         ActionMailer::Base.send :include, SparkPostRails::DataOptions
       end
     end
+
+    initializer 'sparkpost_rails.include_message_data' do
+      ActiveSupport.on_load :action_mailer do
+        Mail::Message.send :include, SparkPostRails::MessageData
+      end
+    end
   end
 end

lib/sparkpost_rails/version.rb

@@ -1,4 +1,4 @@
 module SparkPostRails
-  VERSION = "1.5.1"
+  VERSION = "1.5.2"
 end
 

spec/spec_helper.rb

@@ -7,6 +7,7 @@
 
   config.before(:all) do
     ActionMailer::Base.send :include, SparkPostRails::DataOptions
+    Mail::Message.send :include, SparkPostRails::MessageData
   end
 
   config.before(:each) do |example|