Appearance: Fix form CSS media rendering

Fix the way the form CSS contained in the media attribute
is rendered. This is now an interator and not a single value.
Replace the current method with a for loop.

Signed-off-by: Roberto Rosario <roberto.rosario.gonzalez@gmail.com>

mayan/apps/document_states/models.py

@@ -6,6 +6,7 @@ import logging
 from graphviz import Digraph
 
 from django.conf import settings
+from django.core.files.base import ContentFile
 from django.core.exceptions import PermissionDenied, ValidationError
 from django.db import IntegrityError, models
 from django.db.models import F, Max, Q
@@ -26,6 +27,7 @@ from .literals import (
 )
 from .managers import WorkflowManager
 from .permissions import permission_workflow_transition
+from .storages import storage_workflowimagecache
 
 logger = logging.getLogger(__name__)
 
@@ -62,6 +64,22 @@ class Workflow(models.Model):
     def __str__(self):
         return self.label
 
+    def generate_image(self):
+        cache_filename = '{}'.format(self.id)
+        image = self.render()
+
+        # Since open "wb+" doesn't create files, check if the file
+        # exists, if not then create it
+        if not storage_workflowimagecache.exists(cache_filename):
+            storage_workflowimagecache.save(
+                name=cache_filename, content=ContentFile(content='')
+            )
+
+        with storage_workflowimagecache.open(cache_filename, 'wb+') as file_object:
+            file_object.write(image)
+
+        return cache_filename
+
     def get_document_types_not_in_workflow(self):
         return DocumentType.objects.exclude(pk__in=self.document_types.all())