Backport PR #1699: fix: convert charge point sensors values to timestamp on client side (#1699)

* fix: convert to datetime if the sensor's unit is second

* fix: send event_values for CP sensors as epoch timestamps(miliseconds)

* fix: define value var

* refactor to make it more JS friendly

Signed-off-by: Ahmad Wahid <ahmedwahid16101@gmail.com>

* add a comment to explain the conversion

* docs: changelog entry

Signed-off-by: F.N. Claessen <felix@seita.nl>

---------

Signed-off-by: Ahmad Wahid <ahmedwahid16101@gmail.com>
Signed-off-by: F.N. Claessen <felix@seita.nl>
Co-authored-by: F.N. Claessen <felix@seita.nl>
(cherry picked from commit bbd29f8)

Author: Ahmad-Wahid

documentation/changelog.rst

@@ -10,6 +10,7 @@ v0.28.2 | October 3, 2025
 Bugfixes
 -----------
 * Fix horizons in UI chart tooltips [see `PR #1730 <https://www.github.com/FlexMeasures/flexmeasures/pull/1730>`_]
+* Fix UI chart for Charge Point sessions [see `PR #1699 <https://www.github.com/FlexMeasures/flexmeasures/pull/1699>`_]
 * Fix two audit logs in the sensor API, which were not committed to db [see `PR #1721 <https://github.com/FlexMeasures/flexmeasures/pull/1721>`_]
 
 

flexmeasures/data/models/generic_assets.py

@@ -820,19 +820,6 @@ def search_beliefs(  # noqa C901
                         ),
                     ).reset_index()
 
-                    # Handle datetime conversion for seconds unit
-                    if sensor.unit == "s":
-                        time_mask = df["event_value"].notna()
-                        time_values = df.loc[time_mask, "event_value"]
-                        df["event_value"] = df["event_value"].astype(
-                            f"datetime64[ns, {self.timezone}]"
-                        )
-                        df.loc[time_mask, "event_value"] = (
-                            pd.to_datetime(time_values, unit="s", origin="unix")
-                            .dt.tz_localize("UTC")
-                            .dt.tz_convert(self.timezone)
-                        )
-
                     # VECTORIZED PROCESSING instead of for loops for speed
                     # Convert timestamps to milliseconds vectorized
                     event_start_ms = (

flexmeasures/ui/templates/base.html

@@ -372,10 +372,12 @@
                 const sensor = responseData.sensors[belief.sid] || {};
                 const source = responseData.sources[belief.src] || {};
 
+                // Special case: for sensors with seconds unit, convert to datetime here
+                const value = (sensor.unit === 's' && typeof belief.val === 'number') ? new Date(belief.val * 1000) : belief.val;
                 return {
                     // Map shortened field names back to original names
                     event_start: belief.ts,
-                    event_value: belief.val,
+                    event_value: value,
                     belief_horizon: belief.bh,
                     scale_factor: belief.sf,
                     belief_time: belief.bt,