feat: Add BE changes for captain pdf support for faq generation (#12113)

enterprise/app/services/captain/llm/pdf_processing_service.rb

@@ -0,0 +1,40 @@
+class Captain::Llm::PdfProcessingService < Llm::BaseOpenAiService
+  def initialize(document)
+    super()
+    @document = document
+  end
+
+  def process
+    return if document.openai_file_id.present?
+
+    file_id = upload_pdf_to_openai
+    raise CustomExceptions::PdfUploadError, I18n.t('captain.documents.pdf_upload_failed') if file_id.blank?
+
+    document.store_openai_file_id(file_id)
+  end
+
+  private
+
+  attr_reader :document
+
+  def upload_pdf_to_openai
+    with_tempfile do |temp_file|
+      response = @client.files.upload(
+        parameters: {
+          file: temp_file,
+          purpose: 'assistants'
+        }
+      )
+      response['id']
+    end
+  end
+
+  def with_tempfile(&)
+    Tempfile.create(['pdf_upload', '.pdf'], binmode: true) do |temp_file|
+      temp_file.write(document.pdf_file.download)
+      temp_file.close
+
+      File.open(temp_file.path, 'rb', &)
+    end
+  end
+end