Only finalize metadata if the current file content is different than …

…the new metadata.

This will prevent an annoying behavior where a post that hasn't changed at all
gets rewritten because the finalization plugin *always* writes the file if it's turned
on.

engineer/models.py

@@ -42,6 +42,7 @@ class Post(object):
     # Make _content_raw only settable once. This is just to help prevent data loss that might be caused by
     # inadvertantly messing with this property.
     _content_raw = setonce()
+    _file_contents_raw = setonce()
 
     @staticmethod
     def convert_to_html(content):
@@ -214,6 +215,7 @@ def _parse_source(self):
             with open(self.source, mode='r', encoding='UTF-8') as file:
                 item = file.read()
 
+        self._file_contents_raw = item
         parsed_content = re.match(self._regex, item)
 
         if parsed_content is None or parsed_content.group('metadata') is None:

engineer/plugins/bundled.py

@@ -76,12 +76,29 @@ def preprocess(cls, post, metadata):
     def postprocess(cls, post):
         from engineer.conf import settings
 
+        logger = cls.get_logger()
         if settings.FINALIZE_METADATA:
             output = cls.render_markdown(post)
-            with open(post.source, mode='wb', encoding='UTF-8') as file:
-                file.write(output)
+            if cls.need_update(post, output):
+                logger.debug("Finalizing metadata for post '%s'" % post)
+                with open(post.source, mode='wb', encoding='UTF-8') as file:
+                    file.write(output)
+            else:
+                logger.debug("No metadata finalization needed for post '%s'" % post)
         return post
 
+    @classmethod
+    def need_update(cls, post, new_post_content):
+        from engineer.models import Post
+
+        old_content = Post._regex.match(post._file_contents_raw).group('metadata').strip()
+        new_content = Post._regex.match(new_post_content).group('metadata').strip()
+
+        if new_content == old_content:
+            return False
+        else:
+            return True
+
     @staticmethod
     def render_markdown(post):
         """
@@ -103,7 +120,7 @@ def render_markdown(post):
         # set of metadata that was in the file originally.
         metadata_to_finalize = set([m for m, s in settings.FINALIZE_METADATA.iteritems() if post.status in s])
         metadata_to_finalize.update(post.metadata_original)
-        
+
         if 'title' in metadata_to_finalize:
             # insert at the top of the list
             d.insert(0, ('title', post.title))