Added an UrlBuilder for building rails named routes

Signed-off-by: Jeroen van Baarsen <jeroenvanbaarsen@gmail.com>

app/services/issues/base_service.rb

 module Issues
   class BaseService < ::BaseService
-    include Rails.application.routes.url_helpers
     private
@@ -10,9 +9,7 @@ module Issues
     def execute_hooks(issue, action = 'open')
       issue_data = issue.to_hook_data
-      issue_url = project_issue_url(id: issue.iid,
-                                    project_id: issue.project,
-                                    host: Settings.gitlab['url'])
+      issue_url = Gitlab::UrlBuilder.new(:issue).build(issue.id)
       issue_data[:object_attributes].merge!(url: issue_url, action: action)
       issue.project.execute_hooks(issue_data, :issue_hooks)
     end

lib/gitlab/url_builder.rb

+module Gitlab
+  class UrlBuilder
+    include Rails.application.routes.url_helpers
+
+    def initialize(type)
+      @type = type
+    end
+
+    def build(id)
+      case @type
+      when :issue
+        issue_url(id)
+      end
+    end
+
+    private
+
+    def issue_url(id)
+      issue = Issue.find(id)
+      project_issue_url(id: issue.iid,
+                        project_id: issue.project,
+                        host: Settings.gitlab['url'])
+    end
+  end
+end

spec/lib/gitlab/url_builder_spec.rb

+require 'spec_helper'
+
+describe Gitlab::UrlBuilder do
+  describe 'When asking for an issue' do
+    it 'returns the issue url' do
+      issue = create(:issue)
+      url = Gitlab::UrlBuilder.new(:issue).build(issue.id)
+      expect(url).to eq "#{Settings.gitlab['url']}/namespace1/gitlabhq/issues/#{issue.iid}"
+    end
+  end
+end