heartcombo--devise/app/mailers/devise/mailer.rb

class Devise::Mailer < ::ActionMailer::Base
  include Devise::Controllers::ScopedViews
  attr_reader :scope_name, :resource

  def confirmation_instructions(record)
    setup_mail(record, :confirmation_instructions)
  end

  def reset_password_instructions(record)
    setup_mail(record, :reset_password_instructions)
  end

  def unlock_instructions(record)
    setup_mail(record, :unlock_instructions)
  end

  private

  # Configure default email options
  def setup_mail(record, action)
    initialize_from_record(record)
    mail headers_for(action)
  end

  def initialize_from_record(record)
    @scope_name = Devise::Mapping.find_scope!(record)
    @resource   = instance_variable_set("@#{devise_mapping.name}", record)
  end

  def devise_mapping
    @devise_mapping ||= Devise.mappings[scope_name]
  end

  def headers_for(action)
    headers = {
      :subject       => translate(devise_mapping, action),
      :from          => mailer_sender(devise_mapping),
      :to            => resource.email,
      :template_path => template_paths
    }

    if resource.respond_to?(:headers_for)
      headers.merge!(resource.headers_for(action))
    end

    unless headers.key?(:reply_to)
      headers[:reply_to] = headers[:from]
    end

    headers
  end

  def mailer_sender(mapping)
    if Devise.mailer_sender.is_a?(Proc)
      Devise.mailer_sender.call(mapping.name)
    else
      Devise.mailer_sender
    end
  end

  def template_paths
    template_path = [self.class.mailer_name]
    template_path.unshift "#{@devise_mapping.scoped_path}/mailer" if self.class.scoped_views?
    template_path
  end

  # Setup a subject doing an I18n lookup. At first, it attemps to set a subject
  # based on the current mapping:
  #
  #   en:
  #     devise:
  #       mailer:
  #         confirmation_instructions:
  #           user_subject: '...'
  #
  # If one does not exist, it fallbacks to ActionMailer default:
  #
  #   en:
  #     devise:
  #       mailer:
  #         confirmation_instructions:
  #           subject: '...'
  #
  def translate(mapping, key)
    I18n.t(:"#{mapping.name}_subject", :scope => [:devise, :mailer, key],
      :default => [:subject, key.to_s.humanize])
  end
end