convert app/models/mailer.rb for rails3

fixes CNVS-8732

makes Mailer#message act in the rails3 style, but then provides
scaffolding so that it produces the necessary rails2 behavior when
running under rails2

test-plan:
 * email delivery needs to be configured
 * set up an email communication channel for a student
 * configure to receive conversation alerts at that channel
 * have a teacher send a conversation message to that student
 * confirm receipt of the email at the student's address

Change-Id: I7f027a0a9a9dfd0231847017c888f1003b38d948
Reviewed-on: https://gerrit.instructure.com/25035
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Cody Cutrer <cody@instructure.com>
QA-Review: Jeremy Putnam <jeremyp@instructure.com>
Product-Review: Jacob Fugal <jacob@instructure.com>

app/models/communication_channel.rb

@@ -192,7 +192,7 @@ class CommunicationChannel < ActiveRecord::Base
     m = self.messages.new
     m.to = self.path
     m.body = t :body, "Your Canvas verification code is %{verification_code}", :verification_code => code
-    Mailer.deliver_message(m) rescue nil # omg! just ignore delivery failures
+    Mailer.message(m).deliver rescue nil # omg! just ignore delivery failures
   end
 
   # If you are creating a new communication_channel, do nothing, this just

app/models/mailer.rb

@@ -20,24 +20,87 @@ class Mailer < ActionMailer::Base
 
   attr_reader :email
 
-  def message(m)
-    headers({
-      # notifications have context, bounce replies don't.
-      'Auto-Submitted' => m.context ? 'auto-generated' : 'auto-replied'
-      })
-    recipients m.to
-    bcc m.bcc if m.bcc
-    cc m.cc if m.cc
-    from ("#{m.from_name || HostUrl.outgoing_email_default_name} <" + HostUrl.outgoing_email_address + ">")
-    reply_to ReplyToAddress.new(m).address
-    subject m.subject
-    if m.html_body
-      content_type 'multipart/alternative'
+  if CANVAS_RAILS2
+    # yielded to the block given to #mail as called from #message in order to
+    # perform the appropriate rails2-style ActionMailer actions on @target.
+    class Formatter
+      def initialize(target)
+        @target = target
+      end
 
-      part :content_type => 'text/plain; charset=utf-8', :body => m.body
-      part :content_type => 'text/html; charset=utf-8',  :body => m.html_body
-    else
-      body m.body
+      # e.g. the "render text: ..." in format.html{ render text: ... }
+      def render(params)
+        params[:text]
+      end
+
+      # e.g. format.html{ render text: ... }
+      def html
+        body = yield self
+        @hasHTML = true
+        @target.content_type 'multipart/alternative'
+        @target.part content_type: 'text/html; charset=utf-8', body: body
+      end
+
+      # e.g. format.text{ render text: ... }
+      def text
+        body = yield self
+        if @hasHTML
+          @target.part content_type: 'text/plain; charset=utf-8', body: body
+        else
+          @target.body body
+        end
+      end
+    end
+
+    # now define #mail -- as called from #message -- to perform the appropriate
+    # rails2-style ActionMailer actions
+    def mail(params)
+      recipients params[:to]
+      bcc params[:bcc] if params[:bcc]
+      cc params[:cc] if params[:cc]
+      from params[:from]
+      reply_to params[:reply_to]
+      subject params[:subject]
+      yield Formatter.new(self)
+      self
+    end
+
+    # finally, define a proxy so that the rails3-style
+    # Mailer.message(m).deliver syntax works to invoke deliver_message(m) as
+    # expected by the rails2-implementation of ActionMailer
+    class Proxy
+      def initialize(message)
+        @message = message
+      end
+
+      def deliver
+        Mailer.deliver_message(@message)
+      end
+    end
+
+    def self.message(m)
+      Proxy.new(m)
+    end
+  end
+
+  # define in rails3-style
+  def message(m)
+    # notifications have context, bounce replies don't.
+    headers('Auto-Submitted' => m.context ? 'auto-generated' : 'auto-replied')
+
+    params = {
+      from: "#{m.from_name || HostUrl.outgoing_email_default_name} <" + HostUrl.outgoing_email_address + ">",
+      reply_to: ReplyToAddress.new(m).address,
+      to: m.to,
+      subject: m.subject
+    }
+
+    params[:cc] = m.cc if m.cc
+    params[:bcc] = m.bcc if m.bcc
+
+    mail(params) do |format|
+      format.html{ render text: m.html_body } if m.html_body
+      format.text{ render text: m.body }
     end
   end
 end

app/models/message.rb

@@ -603,7 +603,7 @@ class Message < ActiveRecord::Base
     logger.info "Delivering mail: #{self.inspect}"
 
     begin
-      res = Mailer.deliver_message(self)
+      res = Mailer.message(self).deliver
     rescue Net::SMTPServerBusy => e
       @exception = e
       logger.error "Exception: #{e.class}: #{e.message}\n\t#{e.backtrace.join("\n\t")}"