Add preview example and supporting code

docassemble/AssemblyLine/data/questions/al_document.yml

@@ -100,6 +100,8 @@ code: |
   from_file = action_argument('from_file')
   background_response(ocrmypdf_task(from_file, to_pdf))
 ---
+############## Background document assembly #################
+---
 generic object: ALDocumentBundle
 code: |
   x.generate_downloads_task = background_action(x.attr_name('create_downloads'))
@@ -137,4 +139,34 @@ subquestion: |
       <span class="sr-only">Making documents...</span>
   </div>
 event: al_download_waiting_screen
+reload: True
+---
+########## Background preview assembly ################
+---
+generic object: ALDocumentBundle
+code: |
+  x.generate_preview_task = background_action(x.attr_name('generate_preview_event'))
+---
+generic object: ALDocumentBundle
+event: x.generate_preview_event
+code: |
+  preview_response = x.as_pdf(key="preview")
+  background_response_action(x.attr_name('save_preview'), preview_response=preview_response)
+---
+generic object: ALDocumentBundle
+event: x.save_preview
+code: |
+  x._preview_file = action_argument('preview_response')
+  background_response()
+---
+id: preview waiting screen
+question: |
+  Please wait while we generate a preview of your document
+subquestion: |
+  This can take a few minutes.
+
+  <div class="spinner-border text-primary d-flex justify-content-center" role="status">
+      <span class="sr-only">Generating preview...</span>
+  </div>
+event: al_preview_waiting_screen
 reload: True

docassemble/AssemblyLine/data/questions/test_aldocument_background_assembly.yml

@@ -8,6 +8,9 @@ metadata:
 mandatory: True
 code: |
   intro_screen
+  if not al_user_bundle.generate_preview_task.ready():
+    al_preview_waiting_screen
+  preview_screen
   # if not al_user_bundle.generate_downloads_task.ready(): # Without DOCX
   if not al_user_bundle.generate_downloads_with_docx_task.ready(): # With DOCX
     al_download_waiting_screen
@@ -17,6 +20,17 @@ continue button field: intro_screen
 question: |
   Intro screen
 ---
+id: preview_screen
+continue button field: preview_screen
+question: |
+  Preview the documents
+subquestion: |
+  Your documents are ready for preview.
+
+  Click the thumbnail below to view the preview of your documents. It will open in a new tab.
+
+  ${ al_user_bundle._preview_file }
+---
 id: download
 event: download_screen
 question: |