Notification - Adding tokens {{diff_changed_from}} and {{diff_changed_to}} #3818

changedetectionio/diff/__init__.py

@@ -45,6 +45,36 @@ CHANGED_INTO_PLACEMARKER_CLOSED = '@changed_into_PLACEMARKER_CLOSED'
 # Compiled regex patterns for performance
 WHITESPACE_NORMALIZE_RE = re.compile(r'\s+')
 
+# Regexes built from the constants above — no brittle hardcoded strings
+_EXTRACT_REMOVED_RE = re.compile(
+    re.escape(REMOVED_PLACEMARKER_OPEN) + r'(.*?)' + re.escape(REMOVED_PLACEMARKER_CLOSED)
+    + r'|' +
+    re.escape(CHANGED_PLACEMARKER_OPEN) + r'(.*?)' + re.escape(CHANGED_PLACEMARKER_CLOSED)
+)
+_EXTRACT_ADDED_RE = re.compile(
+    re.escape(ADDED_PLACEMARKER_OPEN) + r'(.*?)' + re.escape(ADDED_PLACEMARKER_CLOSED)
+    + r'|' +
+    re.escape(CHANGED_INTO_PLACEMARKER_OPEN) + r'(.*?)' + re.escape(CHANGED_INTO_PLACEMARKER_CLOSED)
+)
+
+
+def extract_changed_from(raw_diff: str) -> str:
+    """Extract only the removed/changed-from fragments from a raw diff string.
+
+    Useful for {{diff_changed_from}} — gives just the old value (e.g. old price),
+    not the full surrounding line. Multiple fragments joined with newlines.
+    """
+    return '\n'.join(m.group(1) or m.group(2) for m in _EXTRACT_REMOVED_RE.finditer(raw_diff))
+
+
+def extract_changed_to(raw_diff: str) -> str:
+    """Extract only the added/changed-into fragments from a raw diff string.
+
+    Useful for {{diff_changed_to}} — gives just the new value (e.g. new price),
+    not the full surrounding line. Multiple fragments joined with newlines.
+    """
+    return '\n'.join(m.group(1) or m.group(2) for m in _EXTRACT_ADDED_RE.finditer(raw_diff))
+
 
 def render_inline_word_diff(before_line: str, after_line: str, ignore_junk: bool = False, markdown_style: str = None, tokenizer: str = 'words_and_html') -> tuple[str, bool]:
     """

changedetectionio/notification_service.py

@@ -88,6 +88,28 @@ class FormattableTimestamp(str):
             return self._dt.isoformat()
 
 
+class FormattableExtract(str):
+    """
+    A str subclass that holds only the extracted changed fragments from a diff.
+    Used for {{diff_changed_from}} and {{diff_changed_to}} tokens.
+
+        {{ diff_changed_from }}   → old value(s) only, e.g. "$99.99"
+        {{ diff_changed_to }}     → new value(s) only, e.g. "$109.99"
+
+    Multiple changed fragments are joined with newlines.
+    Being a str subclass means it is natively JSON serializable.
+    """
+    def __new__(cls, prev_snapshot, current_snapshot, extract_fn):
+        if prev_snapshot or current_snapshot:
+            from changedetectionio import diff as diff_module
+            raw = diff_module.render_diff(prev_snapshot, current_snapshot, word_diff=True)
+            extracted = extract_fn(raw)
+        else:
+            extracted = ''
+        instance = super().__new__(cls, extracted)
+        return instance
+
+
 class FormattableDiff(str):
     """
     A str subclass representing a rendered diff. As a plain string it renders
@@ -161,6 +183,8 @@ class NotificationContextData(dict):
             'diff_patch': FormattableDiff('', '', patch_format=True),
             'diff_removed': FormattableDiff('', '', include_added=False),
             'diff_removed_clean': FormattableDiff('', '', include_added=False, include_change_type_prefix=False),
+            'diff_changed_from': FormattableExtract('', '', extract_fn=lambda x: x),
+            'diff_changed_to': FormattableExtract('', '', extract_fn=lambda x: x),
             'diff_url': None,
             'markup_text_links_to_html_links': False, # If automatic conversion of plaintext to HTML should happen
             'notification_timestamp': time.time(),
@@ -244,16 +268,27 @@ def add_rendered_diff_to_notification_vars(notification_scan_text:str, prev_snap
         'diff_removed_clean': {'word_diff': word_diff, 'include_added': False, 'include_change_type_prefix': False},
     }
 
+    from changedetectionio.diff import extract_changed_from, extract_changed_to
+    extract_specs = {
+        'diff_changed_from': extract_changed_from,
+        'diff_changed_to':   extract_changed_to,
+    }
+
     ret = {}
     rendered_count = 0
-    # Only create FormattableDiff objects for diff keys actually used in the notification text
+    # Only create FormattableDiff/FormattableExtract objects for diff keys actually used in the notification text
     for key in NotificationContextData().keys():
-        if key.startswith('diff') and key in diff_specs:
+        if not key.startswith('diff'):
-            # Check if this placeholder is actually used in the notification text
+            continue
-            pattern = rf"(?<![A-Za-z0-9_]){re.escape(key)}(?![A-Za-z0-9_])"
+        pattern = rf"(?<![A-Za-z0-9_]){re.escape(key)}(?![A-Za-z0-9_])"
-            if re.search(pattern, notification_scan_text, re.IGNORECASE):
+        if not re.search(pattern, notification_scan_text, re.IGNORECASE):
-                ret[key] = FormattableDiff(prev_snapshot, current_snapshot, **diff_specs[key])
+            continue
-                rendered_count += 1
+        if key in diff_specs:
+            ret[key] = FormattableDiff(prev_snapshot, current_snapshot, **diff_specs[key])
+            rendered_count += 1
+        elif key in extract_specs:
+            ret[key] = FormattableExtract(prev_snapshot, current_snapshot, extract_fn=extract_specs[key])
+            rendered_count += 1
 
     if rendered_count:
         logger.trace(f"Rendered {rendered_count} diff placeholder(s) {sorted(ret.keys())} in {time.time() - now:.3f}s")

changedetectionio/templates/_common_fields.html

@@ -98,6 +98,14 @@
                 <td><code>{{ '{{diff_patch}}' }}</code></td>
                 <td>{{ _('The diff output - patch in unified format') }}</td>
             </tr>
+            <tr>
+                <td><code>{{ '{{diff_changed_from}}' }}</code></td>
+                <td>{{ _('Only the changed fragments from the previous version — e.g. the old price. Multiple changes joined by newline.') }}</td>
+            </tr>
+            <tr>
+                <td><code>{{ '{{diff_changed_to}}' }}</code></td>
+                <td>{{ _('Only the changed fragments from the new version — e.g. the new price. Multiple changes joined by newline.') }}</td>
+            </tr>
             <tr>
                 <td><code>{{ '{{current_snapshot}}' }}</code></td>
                 <td>{{ _('The current snapshot text contents value, useful when combined with JSON or CSS filters') }}

changedetectionio/tests/smtp/test_notification_smtp.py

@@ -11,10 +11,10 @@ from changedetectionio.tests.util import set_original_response, set_modified_res
     set_longer_modified_response, delete_all_watches
 
 import logging
-
+import os
 
 # NOTE - RELIES ON mailserver as hostname running, see github build recipes
-smtp_test_server = 'mailserver'
+smtp_test_server = os.getenv('SMTP_TEST_MAILSERVER', 'mailserver')
 
 ALL_MARKUP_TOKENS = ''.join(f"TOKEN: '{t}'\n{{{{{t}}}}}\n" for t in NotificationContextData().keys())
 

changedetectionio/tests/unit/test_notification_diff.py

@@ -15,7 +15,9 @@ from changedetectionio.diff import (
     CHANGED_PLACEMARKER_OPEN,
     CHANGED_PLACEMARKER_CLOSED,
     CHANGED_INTO_PLACEMARKER_OPEN,
-    CHANGED_INTO_PLACEMARKER_CLOSED
+    CHANGED_INTO_PLACEMARKER_CLOSED,
+    extract_changed_from,
+    extract_changed_to,
 )
 
 
@@ -381,5 +383,72 @@ Line 3 with tabs and spaces"""
         self.assertNotIn('[-Line 2-]', output)
         self.assertNotIn('[+Line 2+]', output)
 
+    def test_diff_changed_from_to_word_level(self):
+        """Primary use case: extract just the old/new value from a changed line (e.g. price monitoring)"""
+        before = "Widget costs $99.99 per month"
+        after  = "Widget costs $109.99 per month"
+
+        raw = diff.render_diff(before, after, word_diff=True)
+
+        self.assertEqual(extract_changed_from(raw), "$99.99")
+        self.assertEqual(extract_changed_to(raw),   "$109.99")
+
+    def test_diff_changed_from_to_multiple_changes(self):
+        """Multiple changed fragments on different lines are joined with newline.
+        An unchanged line between the two changes ensures each is a 1-to-1 replace,
+        so word_diff fires per line rather than falling back to multi-line block mode."""
+        before = "Price $99\nunchanged\nTax $5"
+        after  = "Price $149\nunchanged\nTax $12"
+
+        raw = diff.render_diff(before, after, word_diff=True)
+
+        self.assertEqual(extract_changed_from(raw), "$99\n$5")
+        self.assertEqual(extract_changed_to(raw),   "$149\n$12")
+
+    def test_diff_changed_from_to_pure_insert_delete(self):
+        """Pure line additions/deletions (no inline word diff) are also captured"""
+        before = "old line"
+        after  = "new line"
+
+        # word_diff=False forces line-level CHANGED markers
+        raw = diff.render_diff(before, after, word_diff=False)
+
+        self.assertEqual(extract_changed_from(raw), "old line")
+        self.assertEqual(extract_changed_to(raw),   "new line")
+
+    def test_diff_changed_from_to_similar_numbers(self):
+        """$90.00 → $9.00 must not produce a partial match like '0.00'.
+        The tokenizer splits on whitespace only, so '$90.00' and '$9.00' are
+        each a single atomic token — diff never sees their internal characters."""
+        before = "for sale $90.00"
+        after  = "for sale $9.00"
+
+        raw = diff.render_diff(before, after, word_diff=True)
+
+        self.assertEqual(extract_changed_from(raw), "$90.00")
+        self.assertEqual(extract_changed_to(raw),   "$9.00")
+
+    def test_diff_changed_from_to_whole_line_replaced(self):
+        """When every token on the line changed (no common tokens), render_inline_word_diff
+        takes the whole_line_replaced path using CHANGED/CHANGED_INTO markers instead of
+        REMOVED/ADDED. Extraction must still work via the alternation in the regex."""
+        before = "$99"
+        after  = "$109"
+
+        raw = diff.render_diff(before, after, word_diff=True)
+
+        self.assertEqual(extract_changed_from(raw), "$99")
+        self.assertEqual(extract_changed_to(raw),   "$109")
+
+    def test_diff_changed_from_to_no_change(self):
+        """No changes → empty string"""
+        content = "nothing changed here"
+
+        raw = diff.render_diff(content, content, word_diff=True)
+
+        self.assertEqual(extract_changed_from(raw), "")
+        self.assertEqual(extract_changed_to(raw),   "")
+
+
 if __name__ == '__main__':
     unittest.main()