Add EmailNormalizer (LG-10313)

app/services/email_normalizer.rb

@@ -0,0 +1,41 @@
+require 'resolv'
+
+# Class to help normalize email addresses for services like Gmail that let users
+# add extra things after a +
+class EmailNormalizer
+  attr_reader :email
+
+  # @param [#to_s] email
+  def initialize(email)
+    @email = Mail::Address.new(email.to_s)
+  end
+
+  # @return [String]
+  def normalized_email
+    if gmail?
+      before_plus, _after_plus = email.local.split('+', 2)
+      [before_plus.tr('.', ''), email.domain].join('@')
+    else
+      email.to_s
+    end
+  end
+
+  private
+
+  def gmail?
+    email.domain == 'gmail.com' || google_mx_record?
+  end
+
+  def google_mx_record?
+    return false if ENV['RAILS_OFFLINE']
+
+    mx_records(email.domain).any? { |domain| domain.end_with?('google.com') }
+  end
+
+  def mx_records(domain)
+    Resolv::DNS.open do |dns|
+      dns.getresources(domain, Resolv::DNS::Resource::IN::MX).
+        map { |r| r.exchange.to_s }
+    end
+  end
+end

spec/services/email_normalizer_spec.rb

@@ -0,0 +1,44 @@
+require 'rails_helper'
+
+RSpec.describe EmailNormalizer do
+  subject(:normalizer) { EmailNormalizer.new(email) }
+
+  describe '#normalized_email' do
+    subject(:normalized_email) { normalizer.normalized_email }
+
+    context 'with a non-gmail domain' do
+      let(:email) { 'foobar+123@example.com' }
+
+      it 'is the same email' do
+        expect(normalized_email).to eq(email)
+      end
+    end
+
+    context 'with a gmail domain' do
+      let(:email) { 'foo.bar+123@gmail.com' }
+
+      it 'removes . and anything after the +' do
+        expect(normalized_email).to eq('foobar@gmail.com')
+      end
+    end
+
+    context 'with a Google Apps domain' do
+      let(:email) { 'foo.bar.baz+123@example.com' }
+
+      before do
+        dns = instance_double(
+          'Resolv::DNS',
+          getresources: [
+            Resolv::DNS::Resource::IN::MX.new(1, Resolv::DNS::Name.new(%w[abcd l google com])),
+          ],
+        )
+
+        allow(Resolv::DNS).to receive(:open).and_yield(dns)
+      end
+
+      it 'still removes . and anything after the +' do
+        expect(normalized_email).to eq('foobarbaz@example.com')
+      end
+    end
+  end
+end