Bugfix for notification emails

The URLs in notification emails didn't get server URL prepended,
so users could not click on them.

Gemfile

@@ -50,6 +50,7 @@ gem 'redcarpet' # Markdown parser
 gem 'faker' # Generate fake data
 gem 'auto_strip_attributes', '~> 2.1' # Removes unnecessary whitespaces from ActiveRecord or ActiveModel attributes
 gem 'deface', '~> 1.0'
+gem 'nokogiri' # HTML/XML parser
 
 gem 'paperclip', '~> 4.3' # File attachment, image attachment library
 gem 'aws-sdk', '~> 2.2.8'

Gemfile.lock

@@ -255,6 +255,9 @@ GEM
       sprockets (>= 2.8, < 4.0)
       sprockets-rails (>= 2.0, < 4.0)
       tilt (>= 1.1, < 3)
+    scss_lint (0.50.2)
+      rake (>= 0.9, < 12)
+      sass (~> 3.4.20)
     sdoc (0.4.1)
       json (~> 1.7, >= 1.7.7)
       rdoc (~> 4.0)
@@ -346,6 +349,7 @@ DEPENDENCIES
   minitest-reporters (~> 1.1)
   momentjs-rails (>= 2.9.0)
   nested_form_fields
+  nokogiri
   paperclip (~> 4.3)
   pg
   puma
@@ -358,6 +362,7 @@ DEPENDENCIES
   rubocop
   ruby-graphviz (~> 1.2)
   sass-rails (~> 5.0)
+  scss_lint
   sdoc (~> 0.4.0)
   shoulda-context
   shoulda-matchers (>= 3.0.1)

app/helpers/mailer_helper.rb

@@ -0,0 +1,28 @@
+module MailerHelper
+  # This method receives a HTML (as String), and
+  # prepends the server URL in front of URLs/paths
+  def prepend_server_url_to_links(html)
+    html_doc = Nokogiri::HTML.fragment(html)
+    links = html_doc.search('a')
+    links.each do |link|
+      href = link.attribute('href')
+      href.value = prepend_server_url(href.value) if href.present?
+    end
+    html_doc.to_html
+  end
+
+  private
+
+  def prepend_server_url(href)
+    return href if href.start_with? ENV['MAIL_SERVER_URL']
+
+    new_href = ''
+    unless ENV['MAIL_SERVER_URL'].start_with?('http://', 'https://')
+      new_href += 'http://'
+    end
+    new_href += ENV['MAIL_SERVER_URL']
+    new_href += ((href.start_with? '/') ? '' : '/')
+    new_href += href
+    new_href
+  end
+end

app/mailers/app_mailer.rb

@@ -1,5 +1,5 @@
 class AppMailer < Devise::Mailer
-  helper :application
+  helper :application, :mailer
   include Devise::Controllers::UrlHelpers
   default template_path: 'users/mailer'
   default from: ENV["MAIL_FROM"]

app/views/users/mailer/notification.html.erb

@@ -4,6 +4,6 @@
 
 <p>Type: <%= I18n.t("notifications.types.#{@notification.type_of}") %></p>
 
-<p><%= @notification.title.html_safe %></p>
+<p><%= prepend_server_url_to_links(@notification.title.html_safe).html_safe %></p>
 
-<p><%= @notification.message.html_safe %></p>
+<p><%= prepend_server_url_to_links(@notification.message).html_safe %></p>