1 files changed, 73 insertions, 0 deletions
diff --git a/actionmailer/lib/action_mailer/preview.rb b/actionmailer/lib/action_mailer/preview.rb
new file mode 100644
index 0000000000..ecceaf8c70
--- /dev/null
+++ b/actionmailer/lib/action_mailer/preview.rb
@@ -0,0 +1,73 @@
+require 'active_support/descendants_tracker'
+
+module ActionMailer
+  module Previews #:nodoc:
+    extend ActiveSupport::Concern
+
+    included do
+      # Set the location of mailer previews through app configuration:
+      #
+      #     config.action_mailer.preview_path = "#{Rails.root}/lib/mailer_previews"
+      #
+      class_attribute :preview_path, instance_writer: false
+    end
+  end
+
+  class Preview
+    extend ActiveSupport::DescendantsTracker
+
+    class << self
+      # Returns all mailer preview classes
+      def all
+        load_previews if descendants.empty?
+        descendants
+      end
+
+      # Returns the mail object for the given email name
+      def call(email)
+        preview = self.new
+        preview.public_send(email)
+      end
+
+      # Returns all of the available email previews
+      def emails
+        public_instance_methods(false).map(&:to_s).sort
+      end
+
+      # Returns true if the email exists
+      def email_exists?(email)
+        emails.include?(email)
+      end
+
+      # Returns true if the preview exists
+      def exists?(preview)
+        all.any?{ |p| p.preview_name == preview }
+      end
+
+      # Find a mailer preview by its underscored class name
+      def find(preview)
+        all.find{ |p| p.preview_name == preview }
+      end
+
+      # Returns the underscored name of the mailer preview without the suffix
+      def preview_name
+        name.sub(/Preview$/, '').underscore
+      end
+
+      protected
+        def load_previews #:nodoc:
+          if preview_path?
+            Dir["#{preview_path}/**/*_preview.rb"].each{ |file| require_dependency file }
+          end
+        end
+
+        def preview_path #:nodoc:
+          Base.preview_path
+        end
+
+        def preview_path? #:nodoc:
+          Base.preview_path?
+        end
+    end
+  end
+end