imagestack: add validate_imagestack

derivermodule/imagestack.py

 from pathlib import Path
+from os.path import splitext
+
 from subprocess import check_call
 from time import time
 
 import zipfile
 import tarfile
 
+
 from .logger import logger
 
 def get_imagestack_info(task_info):
@@ -79,6 +82,7 @@ def unpack_and_validate_imagestack(imagestack_path, imagestack_info, dst):
 
     return str(img_dir), image_count
 
+
 def iterate_imagestack(imagestack_path, imagestack_info, sort=True):
     """Unpack and validate an imagestack
 
@@ -140,3 +144,18 @@ def iterate_imagestack(imagestack_path, imagestack_info, sort=True):
         raise ValueError('Cannot extract archive_type %s' % imagestack_info['archive_type'])
 
     return
+
+
+def validate_imagestack(imagestack_path, imagestack_info):
+    image_count = 0
+
+    for img_path, _ in iterate_imagestack(imagestack_path, imagestack_info):
+        _, file_extension = splitext(img_path)
+
+        if file_extension[1:] == imagestack_info['image_type']:
+            image_count += 1
+
+    if image_count == 0:
+        raise Exception('Imagestack contains no valid images.')
+
+    return