invitation.rb

class InvitationRequest
  extend  ActiveModel::Naming
  include ActiveModel::Conversion
  include ActiveModel::Validations
  include ActiveModel::Serializers::JSON

  attr_reader :email, :url
  attr_writer :clock, :invitation_class, :mailer

  validates :email, presence: true

  def self.for attributes
    req = new attributes
    req.fulfill if req.valid? && !req.fulfilled?
    req
  end

  def initialize attributes = {}
    @email = attributes[:email]
    @url   = attributes[:url]

    @clock            = Time
    @invitation_class = Invitation
    @mailer           = InvitationMailer
  end

  def fulfill
    @mailer.deliver_request_confirmation invitation
  end

  def fulfilled?
    invitation.persisted?
  end

  def invitation
    @invitation ||= find_invitation || create_invitation
  end

  def attributes
    { email: email, url: url, fulfilled?: fulfilled? }
  end

  def persisted?
    false
  end

private

  def find_invitation
    @invitation_class.find_by_email email
  end

  def create_invitation
    @invitation_class.create email: email, url: url, requested_at: @clock.now.utc
  end
end

invitation_request_serializer.rb

class InvitationRequestSerializer < ActiveModel::Serializer
  attributes :email, :url, :fulfilled?
end

invitation_request_spec.rb

require 'spec_helper'

describe InvitationRequest do
  context 'when fulfilling for some attributes' do
    it 'does not fulfill the request if not valid' do
      req = double(:invitation_request, valid?: false)
      InvitationRequest.stub(:new).and_return req

      req.should_not_receive :fulfill

      InvitationRequest.for email: '[email protected]', url: 'test.com'
    end

    it 'does not fulfill the request if already fulfilled' do
      req = double(:invitation_request, valid?: true, fulfilled?: true)
      InvitationRequest.stub(:new).and_return req

      req.should_not_receive :fulfill

      InvitationRequest.for email: '[email protected]', url: 'test.com'
    end
  end

  it 'requires an email' do
    expect(InvitationRequest.new).to have(1).error_on :email
  end

  it 'sets the email from initializing attributes' do
    req = InvitationRequest.new email: '[email protected]'
    expect(req.email).to eq '[email protected]'
  end

  it 'sets the url from initializing attributes' do
    req = InvitationRequest.new url: 'test.com'
    expect(req.url).to eq 'test.com'
  end

  it 'deliver a confirmation when fulfilled' do
    req    = InvitationRequest.new
    mailer = double(:mailer).as_null_object

    req.mailer = mailer

    req.stub(:invitation).and_return 'fake invite'

    mailer.should_receive(:deliver_request_confirmation).with 'fake invite'

    req.fulfill
  end

  it 'is fulfilled if an invitation has already been created' do
    req        = InvitationRequest.new
    invitation = double :invitation, persisted?: true

    req.stub(:invitation).and_return invitation

    expect(req).to be_fulfilled
  end

  context 'when fulfilled' do
    it 'finds an invitation' do
      req = InvitationRequest.new email: '[email protected]'
      cls = double :invitation_class

      req.invitation_class = cls

      cls.should_receive(:find_by_email).with('[email protected]').and_return 'an invitation'

      expect(req.invitation).to eq 'an invitation'
    end
  end

  context 'when not fulfilled' do
    it 'creates an invitation' do
      req   = InvitationRequest.new email: '[email protected]', url: 'test.com'
      cls   = double :invitation_class
      clock = double :time

      clock.stub_chain('now.utc').and_return Time.new(1970, 1, 1)

      cls.stub(:find_by_email).and_return nil

      cls.should_receive(:create).with(
        hash_including({
          email: '[email protected]',
          url:   'test.com',
          requested_at: Time.new(1970, 1, 1)
        })
      ).and_return 'an invitation'

      req.invitation_class = cls
      req.clock            = clock

      expect(req.invitation).to eq 'an invitation'
    end
  end
end

invitation_requests_controller.rb

class InvitationRequestsController < ApplicationController
  respond_to :json, only: :create

  def new
    @invitation_request = InvitationRequest.new
  end

  def create
    respond_with InvitationRequest.for(valid_params), location: root_url
  end

private
  def valid_params
    params.fetch(:invitation_request).slice(:email, :url)
  end
end

invitation_requests_controller_spec.rb

require 'spec_helper'

describe InvitationRequestsController do
  describe 'GET new' do
    it 'assigns a new invitation request' do
      get:new
      expect(assigns(:invitation_request)).to be_instance_of InvitationRequest
    end

    it 'renders the new template' do
      get :new
      expect(response).to render_template 'new'
    end
  end

  describe 'POST create' do
    context 'when the invitation request has errors' do
      it 'renders the errors as json' do
        post :create, invitation_request: {}, format: :json
        expect(response.body).to match /^{\"errors\":/
      end
    end

    context 'when the invitation request is valid' do
      it 'renders the invitation request' do
        req = InvitationRequest.new email: '[email protected]'
        InvitationRequest.stub(:for).and_return req
        post :create, invitation_request: { email: '[email protected]' }, format: :json
        expect(response.body).to eq req.to_json
      end
    end
  end
end