Guides: procedures written and read inside ShopDB

plugins/guides/services/blocks.py

@@ -17,6 +17,7 @@ Storing text verbatim keeps what the author typed recoverable even if the
 rendering rules change later.
 """
 
+import hashlib
 import json
 
 from ..models import BLOCKTYPES
@@ -129,3 +130,23 @@ def checklistitemcount(blocks):
         if isinstance(block, dict) and block.get('type') == 'checklist':
             total += len(block.get('items') or [])
     return total
+
+
+def contenthash(title, summary, tags, blocks):
+    """sha256 over everything a reader would notice changing.
+
+    Title, summary and tags are included, not just the blocks: renaming a guide
+    or retagging it is a change worth a revision, and hashing only the body
+    would silently drop it from the history.
+
+    Canonical by construction - the blocks are re-serialized with sorted keys
+    and no whitespace, so the same content saved twice hashes the same however
+    the editor happened to order its JSON that day.
+    """
+    canonical = json.dumps({
+        'title': (title or '').strip(),
+        'summary': (summary or '').strip(),
+        'tags': sorted(t.strip().lower() for t in (tags or '').split(',') if t.strip()),
+        'blocks': blocks or [],
+    }, sort_keys=True, separators=(',', ':'))
+    return hashlib.sha256(canonical.encode('utf-8')).hexdigest()