gistfile1.rb

# Oauth-specific user methods
class User::Oauth2Service
  def initialize(auth, user = nil)
    @policy  = policy(auth)
    @user    = user || User.where(email: @policy.email).first_or_initialize
    @account = Oauth2::Account.where(provider: @policy.provider, uid: @policy.uid).first_or_initialize
  end

  def workflow(controller, &block)
    @controller = controller
    instance_eval(&block) if block_given?

    # User found by email or already logged in
    if @user.persisted?
      # User already linked with account
      if @account.persisted?
        refresh_tokens!
        run(on_sign_in, @account, @policy.provider_title)
      else # User haven't account for current provider
        create_account!
        run(on_sign_in, @account, @policy.provider_title)
      end
    # Oauth2 provider does not provide email, or user not logged in
    else
      # Generate passwords for user
      password = Devise.friendly_token.first(8)
      @user.password ||= password
      @user.password_confirmation ||= password

      # FIXME: Should not confirm users automatically when user enter his email in form by hands
      if @user.valid?
        @user.skip_confirmation!
        @user.save!
        create_account!
        run(on_sign_in, @account, @policy.provider_title)
      else
        # Ask user for required info
        @user.name = @policy.username
        @user.errors.clear
        run(on_invalid_credentials, @user, @policy.provider_title)
      end
    end
  end

  def on_invalid_credentials(&block)
    @on_invalid_credentials ||= block
  end

  def on_sign_in(&block)
    @on_sign_in ||= block
  end

  protected

  def create_account!
    @account = @user.oauth2_accounts.create!(
      provider:           @policy.provider,
      uid:                @policy.uid,
      oauth_token:        @policy.oauth_token,
      oauth_expires:      @policy.oauth_expires,
      oauth_secret:       @policy.oauth_secret,
      username:           @policy.username,
      remote_userpic_url: @policy.userpic_url,
      profile_url:        @policy.profile_url
    )
  end

  def refresh_tokens!
    @account.update_attributes(
      oauth_token:   @policy.oauth_token,
      oauth_expires: @policy.oauth_expires,
      oauth_secret:  @policy.oauth_secret
    )
  end

  def policy(auth)
    "Oauth2::Policy::#{auth.provider.classify}".constantize.new(auth)
  end

  # Execute proc in context of controller and pass account into it
  def run(proc, *args)
    @controller.instance_exec(*args, &proc)
  end
end