gmail_mailer.rb

require "nkf"
require 'google/apis/gmail_v1'
require 'googleauth'
require 'googleauth/stores/file_token_store'
require 'rmail'

require 'fileutils'

class GmailMailer

  OOB_URI = 'urn:ietf:wg:oauth:2.0:oob'
  APPLICATION_NAME = 'Gmail API Ruby Quickstart'
  CLIENT_SECRETS_PATH = 'client_secret.json'
  CREDENTIALS_PATH = File.join(Dir.home, '.credentials',
                               "gmail-ruby-quickstart.yaml")
  SCOPE = Google::Apis::GmailV1::AUTH_SCOPE

  MAIL_FROM_ALIAS = 'alias@example.com'
  
  ##
  # Ensure valid credentials, either by restoring from the saved credentials
  # files or intitiating an OAuth2 authorization. If authorization is required,
  # the user's default browser will be launched to approve the request.
  #
  # @return [Google::Auth::UserRefreshCredentials] OAuth2 credentials
  def authorize
    FileUtils.mkdir_p(File.dirname(CREDENTIALS_PATH))

    client_id = Google::Auth::ClientId.from_file(CLIENT_SECRETS_PATH)
    token_store = Google::Auth::Stores::FileTokenStore.new(file: CREDENTIALS_PATH)
    authorizer = Google::Auth::UserAuthorizer.new(
      client_id, SCOPE, token_store)
    user_id = 'default'
    credentials = authorizer.get_credentials(user_id)
    if credentials.nil?
      url = authorizer.get_authorization_url(
        base_url: OOB_URI)
      puts "Open the following URL in the browser and enter the " +
           "resulting code after authorization"
      puts url
      code = gets
      credentials = authorizer.get_and_store_credentials_from_code(
        user_id: user_id, code: code, base_url: OOB_URI)
    end
    credentials
  end
  def self.send(mail_to, mail_subject, mail_body)
    # Initialize the API
    service = Google::Apis::GmailV1::GmailService.new
    service.client_options.application_name = APPLICATION_NAME
    service.authorization = authorize()

    message = RMail::Message.new
    message.header['To'] = mail_to
    message.header['From'] = MAIL_FROM_ALIAS
    message.header['Subject'] = NKF.nkf('-WMjm0', mail_subject)
    message.body = mail_body
    service.send_user_message('me',
                            upload_source: StringIO.new(message.to_s),
                            content_type: 'message/rfc822')
  end
end