Add RevertDraftFormService

app/models/form.rb

@@ -31,6 +31,7 @@ class Form < ApplicationRecord
 
   after_create :set_external_id
   after_update :update_draft_form_document
+  ATTRIBUTES_NOT_IN_FORM_DOCUMENT = %i[state external_id pages question_section_completed declaration_section_completed share_preview_completed].freeze
 
   def save_draft!
     save!
@@ -148,7 +149,7 @@ def file_upload_question_count
 
   def as_form_document(live_at: nil)
     content = as_json(
-      except: %i[state external_id pages question_section_completed declaration_section_completed share_preview_completed],
+      except: ATTRIBUTES_NOT_IN_FORM_DOCUMENT,
       methods: %i[start_page steps],
     )
     content["form_id"] = content.delete("id").to_s

app/services/revert_draft_form_service.rb

@@ -0,0 +1,112 @@
+# This service reverts a draft form to a form_document with a given tag,
+# effectively discarding all draft changes
+class RevertDraftFormService
+  attr_reader :form
+
+  # A list of attributes on the Form model that should be not be reverted
+  FORM_ATTRIBUTES_TO_PRESERVE = %i[id created_at updated_at creator_id].freeze
+  ATTRIBUTES_TO_EXCLUDE = Form::ATTRIBUTES_NOT_IN_FORM_DOCUMENT + FORM_ATTRIBUTES_TO_PRESERVE
+
+  def initialize(form)
+    @form = form
+  end
+
+  # Discards draft changes by reverting the form and its associations
+  # to the state of the form_document with the given tag
+  # Returns true on success, false on failure
+  def revert_draft_from_form_document(tag)
+    # Return early if there's no draft to discard
+    form_document = FormDocument.find_by(form_id: form.id, tag:, language: "en")
+    return false if form_document.blank?
+
+    form_document_content = form_document.content
+
+    ActiveRecord::Base.transaction do
+      revert_form_attributes(form_document_content)
+      revert_pages_and_nested_associations(form_document_content["steps"])
+
+      form.delete_draft_from_live_form
+      form.save!
+    end
+
+    true
+  rescue ActiveRecord::RecordInvalid => e
+    Rails.logger.error("Failed to discard draft for form #{form.id}: #{e.message}")
+    false
+  end
+
+private
+
+  # revert the top-level attributes of the Form object
+  def revert_form_attributes(form_document_content)
+    attributes_to_update = Form.attribute_names - ATTRIBUTES_TO_EXCLUDE.map(&:to_s)
+
+    form.assign_attributes(form_document_content.slice(*attributes_to_update))
+  end
+
+  def revert_pages_and_nested_associations(steps_data)
+    form.pages.reload
+
+    revert_pages(steps_data)
+
+    # revert conditions after pages are created to make sure conditions don't
+    # have validation errors if the page hasn't been created yet
+    revert_routing_conditions(steps_data)
+  end
+
+  def revert_pages(steps_data)
+    form_document_step_ids = steps_data.pluck("id")
+
+    # delete any pages on the form that are not present in the form_document version
+    form.pages.where.not(id: form_document_step_ids).destroy_all
+
+    # iterate through the form_document steps data to create or update pages using the original ids
+    steps_data.each do |step_data|
+      page = form.pages.find_or_initialize_by(id: step_data["id"])
+
+      assign_page_attributes(page, step_data)
+
+      page.save!
+    end
+  end
+
+  # steps in a form_document store the page attributes under "data"
+  def assign_page_attributes(page, step_data)
+    page_data = step_data["data"]
+    page.assign_attributes(
+      position: step_data["position"],
+      question_text: page_data["question_text"],
+      hint_text: page_data["hint_text"],
+      answer_type: page_data["answer_type"],
+      is_optional: page_data["is_optional"],
+      answer_settings: page_data["answer_settings"],
+      page_heading: page_data["page_heading"],
+      guidance_markdown: page_data["guidance_markdown"],
+      is_repeatable: page_data["is_repeatable"],
+    )
+  end
+
+  def revert_routing_conditions(steps_data)
+    all_conditions_data = steps_data.flat_map { |step| step["routing_conditions"] || [] }
+    form_document_condition_ids = all_conditions_data.pluck("id")
+
+    # remove any conditions which have been added to the draft but are not in the form_document data
+    Condition.where(routing_page_id: form.pages.select(:id)).where.not(id: form_document_condition_ids).destroy_all
+
+    all_conditions_data.each do |condition_data|
+      condition = Condition.find_or_initialize_by(id: condition_data["id"])
+
+      assign_condition_attributes(condition, condition_data)
+      condition.save!
+    end
+  end
+
+  def assign_condition_attributes(condition, condition_data)
+    condition.assign_attributes(
+      answer_value: condition_data["answer_value"],
+      routing_page_id: condition_data["routing_page_id"],
+      check_page_id: condition_data["check_page_id"],
+      goto_page_id: condition_data["goto_page_id"],
+    )
+  end
+end

app/state_machines/form_state_machine.rb

@@ -58,6 +58,10 @@ module FormStateMachine
         transitions from: :live, to: :archived
         transitions from: :live_with_draft, to: :archived_with_draft
       end
+
+      event :delete_draft_from_live_form do
+        transitions from: %i[live_with_draft live], to: :live
+      end
     end
   end
 end

spec/services/revert_draft_form_service_spec.rb

@@ -0,0 +1,147 @@
+require "rails_helper"
+
+describe RevertDraftFormService do
+  subject(:revert_draft_form_service) { described_class.new(form) }
+
+  let(:form) { create(:form, :live_with_draft) }
+  let(:tag) { :live }
+
+  RSpec::Matchers.define :be_reverted_to_state do |expected_state|
+    match do |form|
+      # reload the form to get the latest state from the database
+      reloaded_form = form.reload
+
+      # the form should be live
+      # is_live = reloaded_form.live?
+      state_matches = reloaded_form.state == expected_state.to_s
+
+      # We convert the form to a form document and compare the content
+      # to the live form document content and check they match baring the live_at times
+      # this is the closest we can get to saying there is no changes to the form
+      form_document = FormDocument.find_by(form_id: form.id, tag:, language: "en")
+      document_matches = reloaded_form.as_form_document.except("live_at") == form_document.content.except("live_at")
+
+      state_matches && document_matches
+    end
+  end
+
+  def revert_draft_to_live
+    revert_draft_form_service.revert_draft_from_form_document(tag)
+  end
+
+  # we use `freeze_time` to freeze the timestamps of the form and its pages
+  # reverting a draft will not keep the timestamps from the live version
+  around { |example| freeze_time { example.run } }
+
+  context "when the draft has no changes" do
+    it "reverts the form to its live state" do
+      revert_draft_to_live
+      expect(form).to be_reverted_to_state(:live)
+    end
+  end
+
+  context "when a form attribute is changed in the draft" do
+    before do
+      form.update!(name: "A new draft name")
+    end
+
+    it "reverts the attribute change" do
+      revert_draft_to_live
+      expect(form).to be_reverted_to_state(:live)
+    end
+  end
+
+  context "when a page attribute is changed in the draft" do
+    before do
+      form.pages.first.update!(question_text: "A new draft question text")
+    end
+
+    it "reverts the page change" do
+      revert_draft_to_live
+      expect(form).to be_reverted_to_state(:live)
+    end
+  end
+
+  context "when a page is added to the draft" do
+    before do
+      form.pages.create!(answer_type: "text", question_text: "A new page added to the draft", is_optional: false)
+    end
+
+    it "removes the added page" do
+      revert_draft_to_live
+      expect(form).to be_reverted_to_state(:live)
+    end
+  end
+
+  context "when a page is removed from the draft" do
+    before do
+      form.pages.last.destroy!
+    end
+
+    it "re-adds the removed page" do
+      revert_draft_to_live
+      expect(form).to be_reverted_to_state(:live)
+    end
+  end
+
+  context "with routing conditions" do
+    let(:form) { create(:form, :ready_for_live, pages_count: 2) }
+
+    before do
+      # live version with a routing condition
+      form.pages.first.routing_conditions.create!(
+        answer_value: "Yes",
+        goto_page_id: form.pages.last.id,
+        routing_page_id: form.pages.first.id,
+      )
+      FormDocument.create!(form:, tag: "live", content: form.as_form_document(live_at: form.updated_at))
+      form.update!(state: :live_with_draft)
+    end
+
+    context "when a routing condition is added to the draft" do
+      before do
+        form.pages.first.routing_conditions.create!(
+          answer_value: "No",
+          goto_page_id: form.pages.last.id,
+          routing_page_id: form.pages.first.id,
+        )
+      end
+
+      it "removes the added routing condition" do
+        revert_draft_to_live
+        expect(form).to be_reverted_to_state(:live)
+      end
+    end
+
+    context "when a routing condition is removed from the draft" do
+      before do
+        form.pages.first.routing_conditions.first.destroy!
+      end
+
+      it "re-adds the removed routing condition" do
+        revert_draft_to_live
+        expect(form).to be_reverted_to_state(:live)
+      end
+    end
+
+    context "when a routing condition is changed in the draft" do
+      before do
+        form.pages.first.routing_conditions.first.update!(answer_value: "Maybe")
+      end
+
+      it "reverts the changed routing condition" do
+        revert_draft_to_live
+        expect(form).to be_reverted_to_state(:live)
+      end
+    end
+  end
+
+  context "when reverting to an archived form_document" do
+    let(:form) { create(:form, :archived) }
+    let(:tag) { :archived }
+
+    it "reverts the form to its live state" do
+      expect(form).to be_reverted_to_state(:archived)
+    end
+  end
+end