Serialize incidents for the Status Page MVC

This commit enables serializing of GitLab's issues as incidents
for the upcoming Status Page MVC.

Future MRs will utilize this functionality.

ee/app/serializers/status_page/incident_comment_entity.rb

+# frozen_string_literal: true
+
+module StatusPage
+  class IncidentCommentEntity < Grape::Entity
+    expose :note_html, as: :note
+    expose :created_at
+  end
+end

ee/app/serializers/status_page/incident_entity.rb

+# frozen_string_literal: true
+
+module StatusPage
+  class IncidentEntity < Grape::Entity
+    expose :iid, as: :id
+    expose :state
+    expose :title_html, as: :title
+    expose :description_html, as: :description
+    expose :updated_at
+    expose :created_at
+    expose :user_notes, as: :comments, using: IncidentCommentEntity
+
+    private
+
+    def user_notes
+      Array(options[:user_notes])
+    end
+  end
+end

ee/app/serializers/status_page/incident_serializer.rb

+# frozen_string_literal: true
+
+module StatusPage
+  class IncidentSerializer < BaseSerializer
+    entity IncidentEntity
+
+    def represent_list(resource)
+      represent(resource, except: [:comments])
+    end
+
+    def represent_details(resource, user_notes)
+      represent(resource, user_notes: user_notes)
+    end
+
+    private :represent
+  end
+end

ee/spec/fixtures/api/schemas/status_page/basic_incident.json

+{
+  "type": "object",
+  "required": [
+    "id",
+    "state",
+    "title",
+    "description",
+    "updated_at",
+    "created_at"
+  ],
+  "properties": {
+    "id": { "type": "integer" },
+    "state": {
+      "type": "string",
+      "enum": ["opened", "closed"]
+    },
+    "title": { "type": "string" },
+    "description": { "type": "string" },
+    "updated_at": { "type": "date" },
+    "created_at": { "type": "date" }
+  }
+}

ee/spec/fixtures/api/schemas/status_page/incident_details.json

+{
+  "type": "object",
+  "allOf": [
+    { "$ref": "basic_incident.json" },
+    {
+      "required": ["comments"],
+      "properties": {
+        "type": "object",
+        "items": {
+          "required": ["note", "created_at"],
+          "properties": {
+            "note": { "type": "string" },
+            "created_at": { "type": "date" }
+          },
+          "additionalProperties": false
+        }
+      }
+    }
+  ]
+}

ee/spec/fixtures/api/schemas/status_page/incident_list.json

+{
+  "type": "array",
+  "items": { "$ref": "basic_incident.json" },
+  "additionalProperties": false
+}

ee/spec/serializers/status_page/incident_comment_entity_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe StatusPage::IncidentCommentEntity do
+  let_it_be(:note) { create(:note, note: ':ok:') }
+  let(:json) { subject.as_json }
+
+  subject { described_class.new(note) }
+
+  it 'exposes JSON fields' do
+    expect(json).to eq(
+      note: note.note_html,
+      created_at: note.created_at
+    )
+  end
+end

ee/spec/serializers/status_page/incident_entity_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe StatusPage::IncidentEntity do
+  let_it_be(:issue) do
+    create(:issue, title: ':ok:', description: ':tada:')
+  end
+
+  let(:json) { subject.as_json }
+
+  subject { described_class.new(issue) }
+
+  it 'exposes JSON fields' do
+    expect(json).to eq(
+      id: issue.iid,
+      state: issue.state,
+      title: issue.title_html,
+      description: issue.description_html,
+      updated_at: issue.updated_at,
+      created_at: issue.created_at,
+      comments: []
+    )
+  end
+
+  context 'with user notes' do
+    let(:user_notes) do
+      create_list(:note, 1, noteable: issue, project: issue.project)
+    end
+
+    subject { described_class.new(issue, user_notes: user_notes) }
+
+    it 'exposes comments' do
+      expect(json).to include(:comments)
+      expect(json[:comments].size).to eq(1)
+    end
+  end
+end

ee/spec/serializers/status_page/incident_serializer_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe StatusPage::IncidentSerializer do
+  let_it_be(:issue) { create(:issue) }
+
+  shared_examples 'valid JSON schema' do |schema:|
+    it 'matches JSON schema' do
+      expect(json_entity).to match_schema(schema, dir: 'ee')
+    end
+  end
+
+  describe '.represent_list' do
+    let(:resource) { [issue] }
+    let(:json_entity) do
+      subject.represent_list(resource).map(&:with_indifferent_access)
+    end
+
+    it_behaves_like 'valid JSON schema', schema: 'status_page/incident_list'
+
+    it 'returns a list with one entity' do
+      expect(json_entity.size).to eq(1)
+    end
+
+    it 'does not contain comments' do
+      expect(json_entity).to be_none(include(:comments))
+    end
+  end
+
+  describe '.represent_details' do
+    let(:resource) { issue }
+    let_it_be(:user_notes) do
+      create_list(:note, 1, noteable: issue, project: issue.project)
+    end
+
+    let(:json_entity) do
+      subject
+        .represent_details(resource, user_notes)
+        .with_indifferent_access
+    end
+
+    it_behaves_like 'valid JSON schema', schema: 'status_page/incident_details'
+  end
+end