Fix diff not starting from last viewed snapshot (#2744)

changedetectionio/model/Watch.py

@@ -247,12 +247,9 @@ class model(watch_base):
         bump = self.history
         return self.__newest_history_key
 
-    # Given an arbitrary timestamp, find the closest next key
-    # For example, last_viewed = 1000 so it should return the next 1001 timestamp
-    #
-    # used for the [diff] button so it can preset a smarter from_version
+    # Given an arbitrary timestamp, find the best history key for the [diff] button so it can preset a smarter from_version
     @property
-    def get_next_snapshot_key_to_last_viewed(self):
+    def get_from_version_based_on_last_viewed(self):
 
         """Unfortunately for now timestamp is stored as string key"""
         keys = list(self.history.keys())
@@ -260,24 +257,23 @@ class model(watch_base):
             return None
 
         last_viewed = int(self.get('last_viewed'))
-        prev_k = keys[0]
         sorted_keys = sorted(keys, key=lambda x: int(x))
         sorted_keys.reverse()
 
-        # When the 'last viewed' timestamp is greater than the newest snapshot, return second last
-        if last_viewed > int(sorted_keys[0]):
+        # When the 'last viewed' timestamp is greater than or equal the newest snapshot, return second newest
+        if last_viewed >= int(sorted_keys[0]):
             return sorted_keys[1]
         
-        for k in sorted_keys:
-            if int(k) < last_viewed:
-                if prev_k == sorted_keys[0]:
-                    # Return the second last one so we dont recommend the same version compares itself
-                    return sorted_keys[1]
+        # When the 'last viewed' timestamp is less than or equal the oldest snapshot, return oldest
+        if last_viewed <= int(sorted_keys[-1]):
+            return sorted_keys[-1]
 
-                return prev_k
-            prev_k = k
+        for newer, older in list(zip(sorted_keys[0:], sorted_keys[1:])):
+            if last_viewed < int(newer) and last_viewed >= int(older):
+                return older
 
-        return keys[0]
+        # Unreachable, return oldest
+        return sorted_keys[-1]
 
     def get_history_snapshot(self, timestamp):
         import brotli

changedetectionio/templates/watch-overview.html

@@ -191,7 +191,7 @@
                     {% if watch.history_n >= 2 %}
 
                         {%  if is_unviewed %}
-                           <a href="{{ url_for('diff_history_page', uuid=watch.uuid, from_version=watch.get_next_snapshot_key_to_last_viewed) }}" target="{{watch.uuid}}" class="pure-button pure-button-primary diff-link">History</a>
+                           <a href="{{ url_for('diff_history_page', uuid=watch.uuid, from_version=watch.get_from_version_based_on_last_viewed) }}" target="{{watch.uuid}}" class="pure-button pure-button-primary diff-link">History</a>
                         {% else %}
                            <a href="{{ url_for('diff_history_page', uuid=watch.uuid)}}" target="{{watch.uuid}}" class="pure-button pure-button-primary diff-link">History</a>
                         {% endif %}

changedetectionio/tests/unit/test_watch_model.py

@@ -16,7 +16,6 @@ class TestDiffBuilder(unittest.TestCase):
         watch = Watch.model(datastore_path='/tmp', default={})
         watch.ensure_data_dir_exists()
 
-        watch['last_viewed'] = 110
 
         # Contents from the browser are always returned from the browser/requests/etc as str, str is basically UTF-16 in python
         watch.save_history_text(contents="hello world", timestamp=100, snapshot_id=str(uuid_builder.uuid4()))
@@ -26,30 +25,37 @@ class TestDiffBuilder(unittest.TestCase):
         watch.save_history_text(contents="hello world", timestamp=115, snapshot_id=str(uuid_builder.uuid4()))
         watch.save_history_text(contents="hello world", timestamp=117, snapshot_id=str(uuid_builder.uuid4()))
     
-        p = watch.get_next_snapshot_key_to_last_viewed
-        assert p == "112", "Correct last-viewed timestamp was detected"
+        p = watch.get_from_version_based_on_last_viewed
+        assert p == "100", "Correct 'last viewed' timestamp was detected"
+
+        watch['last_viewed'] = 110
+        p = watch.get_from_version_based_on_last_viewed
+        assert p == "109", "Correct 'last viewed' timestamp was detected"
 
-        # When there is only one step of difference from the end of the list, it should return second-last change
         watch['last_viewed'] = 116
-        p = watch.get_next_snapshot_key_to_last_viewed
-        assert p == "115", "Correct 'second last' last-viewed timestamp was detected when using the last timestamp"
+        p = watch.get_from_version_based_on_last_viewed
+        assert p == "115", "Correct 'last viewed' timestamp was detected"
 
         watch['last_viewed'] = 99
-        p = watch.get_next_snapshot_key_to_last_viewed
-        assert p == "100"
+        p = watch.get_from_version_based_on_last_viewed
+        assert p == "100", "When the 'last viewed' timestamp is less than the oldest snapshot, return oldest"
 
         watch['last_viewed'] = 200
-        p = watch.get_next_snapshot_key_to_last_viewed
-        assert p == "115", "When the 'last viewed' timestamp is greater than the newest snapshot, return second last "
+        p = watch.get_from_version_based_on_last_viewed
+        assert p == "115", "When the 'last viewed' timestamp is greater than the newest snapshot, return second newest"
 
         watch['last_viewed'] = 109
-        p = watch.get_next_snapshot_key_to_last_viewed
+        p = watch.get_from_version_based_on_last_viewed
         assert p == "109", "Correct when its the same time"
 
         # new empty one
         watch = Watch.model(datastore_path='/tmp', default={})
-        p = watch.get_next_snapshot_key_to_last_viewed
+        p = watch.get_from_version_based_on_last_viewed
         assert p == None, "None when no history available"
 
+        watch.save_history_text(contents="hello world", timestamp=100, snapshot_id=str(uuid_builder.uuid4()))
+        p = watch.get_from_version_based_on_last_viewed
+        assert p == "100", "Correct with only one history snapshot"
+
 if __name__ == '__main__':
     unittest.main()