Move backend logic from model to a serializer

As suggested in maintainer review of a previous MR, the logic to
display a JSON format used by the frontend should not be put in the
model. Instead, using a serializer is better separation of concerns.

app/models/service.rb

@@ -171,20 +171,6 @@ class Service < ApplicationRecord
     fields
   end
 
-  def global_fields_json
-    global_fields.map do |field|
-      value = send(field[:name]) # rubocop:disable GitlabSecurity/PublicSend
-      public_value =
-        if field[:type] == 'password' && value.present?
-          'true'
-        else
-          value
-        end
-
-      field.merge(value: public_value)
-    end.to_json
-  end
-
   def configurable_events
     events = self.class.supported_events
 

app/serializers/service_field_entity.rb

+# frozen_string_literal: true
+
+class ServiceFieldEntity < Grape::Entity
+  include RequestAwareEntity
+
+  expose :type, :name, :title, :placeholder, :required, :choices, :help
+
+  expose :value do |field|
+    value = service.send(field[:name]) # rubocop:disable GitlabSecurity/PublicSend
+    if field[:type] == 'password' && value.present?
+      'true'
+    else
+      value
+    end
+  end
+
+  private
+
+  alias_method :field, :object
+
+  def service
+    request.service
+  end
+end

app/serializers/service_field_serializer.rb

+# frozen_string_literal: true
+
+class ServiceFieldSerializer < BaseSerializer
+  entity ServiceFieldEntity
+end

app/views/shared/_service_settings.html.haml

 = form_errors(@service)
 - trigger_events = Feature.enabled?(:integration_form_refactor) ? ServiceEventSerializer.new(service: @service).represent(@service.configurable_events).to_json : []
-- fields = Feature.enabled?(:integration_form_refactor) ? @service.global_fields_json : []
+- fields = Feature.enabled?(:integration_form_refactor) ? ServiceFieldSerializer.new(service: @service).represent(@service.global_fields).to_json : []
 
 - if lookup_context.template_exists?('help', "projects/services/#{@service.to_param}", true)
   = render "projects/services/#{@service.to_param}/help", subject: @service

spec/serializers/service_field_entity_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe ServiceFieldEntity do
+  let(:service) { create(:jira_service) }
+  let(:request) { double('request') }
+
+  subject { described_class.new(field, request: request, service: service).as_json }
+
+  before do
+    allow(request).to receive(:service).and_return(service)
+  end
+
+  describe '#as_json' do
+    context 'field with type text' do
+      let(:field) { service.global_fields.find { |field| field[:name] == 'username' } }
+
+      it 'exposes correct attributes' do
+        expect(subject[:type]).to eq('text')
+        expect(subject[:name]).to eq('username')
+        expect(subject[:title]).to eq('Username or Email')
+        expect(subject[:placeholder]).to eq('Use a username for server version and an email for cloud version')
+        expect(subject[:required]).to eq(true)
+        expect(subject[:choices]).to eq(nil)
+        expect(subject[:help]).to eq(nil)
+        expect(subject[:value]).to eq('jira_username')
+      end
+    end
+
+    context 'field with type password' do
+      let(:field) { service.global_fields.find { |field| field[:name] == 'password' } }
+
+      it 'exposes correct attributes but hides password' do
+        expect(subject[:type]).to eq('password')
+        expect(subject[:name]).to eq('password')
+        expect(subject[:title]).to eq('Password or API token')
+        expect(subject[:placeholder]).to eq('Use a password for server version and an API token for cloud version')
+        expect(subject[:required]).to eq(true)
+        expect(subject[:choices]).to eq(nil)
+        expect(subject[:help]).to eq(nil)
+        expect(subject[:value]).to eq('true')
+      end
+    end
+  end
+end