add form preview

app/controllers/templates_form_preview_controller.rb

@@ -0,0 +1,38 @@
+# frozen_string_literal: true
+
+class TemplatesFormPreviewController < ApplicationController
+  PRELOAD_ALL_PAGES_AMOUNT = 200
+
+  layout 'form'
+
+  load_and_authorize_resource :template
+
+  def show
+    @submitter = Submitter.new(uuid: params[:uuid] || @template.submitters.first['uuid'],
+                               account: current_account,
+                               submission: @template.submissions.new(template_submitters: @template.submitters,
+                                                                     account: current_account))
+
+    @submitter.submission.submitters = @template.submitters.map { |item| Submitter.new(uuid: item['uuid']) }
+
+    ActiveRecord::Associations::Preloader.new(
+      records: [@submitter],
+      associations: [submission: [:template, { template_schema_documents: :blob }]]
+    ).call
+
+    total_pages =
+      @submitter.submission.template_schema_documents.sum { |e| e.metadata.dig('pdf', 'number_of_pages').to_i }
+
+    if total_pages < PRELOAD_ALL_PAGES_AMOUNT
+      ActiveRecord::Associations::Preloader.new(
+        records: @submitter.submission.template_schema_documents,
+        associations: [:blob, { preview_images_attachments: :blob }]
+      ).call
+    end
+
+    @attachments_index = ActiveStorage::Attachment.where(record: @submitter.submission.submitters, name: :attachments)
+                                                  .preload(:blob).index_by(&:uuid)
+
+    @form_configs = Submitters::FormConfigs.call(@submitter)
+  end
+end