optimize for large files

app/controllers/api/templates_documents_controller.rb

@@ -16,6 +16,7 @@ module Api
       render json: {
         schema:,
         documents: documents.as_json(
+          methods: [:metadata],
           include: {
             preview_images: { methods: %i[url metadata filename] }
           }

app/controllers/preview_document_page_controller.rb

@@ -0,0 +1,52 @@
+# frozen_string_literal: true
+
+class PreviewDocumentPageController < ActionController::API
+  include ActiveStorage::SetCurrent
+
+  FORMAT = Templates::ProcessDocument::FORMAT
+
+  def show
+    if Docuseal.multitenant?
+      Rollbar.warning('load page')
+
+      return head :not_found
+    end
+
+    attachment = ActiveStorage::Attachment.find_by(uuid: params[:attachment_uuid])
+
+    return head :not_found unless attachment
+
+    preview_image = attachment.preview_images.joins(:blob).find_by(blob: { filename: "#{params[:id]}#{FORMAT}" })
+
+    return redirect_to preview_image.url, allow_other_host: true if preview_image
+
+    file_path =
+      if attachment.service.name == :disk
+        ActiveStorage::Blob.service.path_for(attachment.key)
+      else
+        find_or_create_document_tempfile_path(attachment)
+      end
+
+    io = Templates::ProcessDocument.generate_pdf_preview_from_file(attachment, file_path, params[:id].to_i)
+
+    render plain: io.tap(&:rewind).read
+  end
+
+  def find_or_create_document_tempfile_path(attachment)
+    file_path = "#{Dir.tmpdir}/#{attachment.uuid}"
+
+    File.open(file_path, File::RDWR | File::CREAT, 0o644) do |f|
+      f.flock(File::LOCK_EX)
+
+      # rubocop:disable Style/ZeroLengthPredicate
+      if f.size.zero?
+        f.binmode
+
+        f.write(attachment.download)
+      end
+      # rubocop:enable Style/ZeroLengthPredicate
+    end
+
+    file_path
+  end
+end

app/controllers/submissions_controller.rb

@@ -6,12 +6,24 @@ class SubmissionsController < ApplicationController
 
   load_and_authorize_resource :submission, only: %i[show destroy]
 
+  PRELOAD_ALL_PAGES_AMOUNT = 200
+
   def show
     ActiveRecord::Associations::Preloader.new(
       records: [@submission],
-      associations: [:template, { template_schema_documents: [:blob, { preview_images_attachments: :blob }] }]
+      associations: [:template, { template_schema_documents: :blob }]
     ).call
 
+    total_pages =
+      @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: @submission.template_schema_documents,
+        associations: [:blob, { preview_images_attachments: :blob }]
+      ).call
+    end
+
     render :show, layout: 'plain'
   end
 

app/controllers/submit_form_controller.rb

@@ -6,15 +6,28 @@ class SubmitFormController < ApplicationController
   skip_before_action :authenticate_user!
   skip_authorization_check
 
+  PRELOAD_ALL_PAGES_AMOUNT = 200
+
   def show
-    @submitter =
-      Submitter.preload(submission: [
-                          :template, { template_schema_documents: [:blob, { preview_images_attachments: :blob }] }
-                        ])
-               .find_by!(slug: params[:slug])
+    @submitter = Submitter.find_by!(slug: params[:slug])
 
     return redirect_to submit_form_completed_path(@submitter.slug) if @submitter.completed_at?
 
+    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
+
     Submitters::MaybeUpdateDefaultValues.call(@submitter, current_user)
 
     cookies[:submitter_sid] = @submitter.signed_id

app/controllers/templates_controller.rb

@@ -30,6 +30,14 @@ class TemplatesController < ApplicationController
       associations: [schema_documents: { preview_images_attachments: :blob }]
     ).call
 
+    @template_data =
+      @template.as_json.merge(
+        documents: @template.schema_documents.as_json(
+          methods: [:metadata],
+          include: { preview_images: { methods: %i[url metadata filename] } }
+        )
+      ).to_json
+
     render :edit, layout: 'plain'
   end