feat: classify offline charges using newly geofence charge_type hint

[finikwashere]

Problem

Closes #4401

When a car charges in a location with no internet (underground garage, gym, etc.), TeslaMate synthesises the charging session from the last known state before going offline and the first state after reconnecting. All charges rows for that session have NULL charger_phases and fast_charger_present, so every Grafana dashboard query that uses:

CASE WHEN NULLIF(mode() within group (order by charger_phases),0) IS NULL
  THEN 'DC' ELSE 'AC' END

incorrectly labels the session as DC — even for a plain home AC wallbox.

Affected dashboards: Charges, Charging Stats, Battery Health, Trip (9 SQL queries total).

Solution

Introduce an optional Default charge type hint on Geofences (AC / DC / auto-detect). The Grafana SQL falls back to it only when it cannot determine the type from live telemetry.

Priority order in the new CASE expression

1. charger_phases IS NOT NULL → AC (normal online session)
2. fast_charger_present = true → DC (online DC session without phase data)
3. geofence.charge_type IS NOT NULL → use configured hint (offline sessions at known locations)
4. Fallback → DC

Changes

File	What changed
priv/repo/migrations/20260510111557_add_charge_type_to_geofences.exs	Add nullable charge_type varchar column to geofences
lib/teslamate/locations/geo_fence.ex	Add charge_type Ecto.Enum field and include in changeset
lib/teslamate_web/live/geofence_live/form.html.heex	Add "Default charge type" dropdown to geofence edit form
grafana/dashboards/charges.json	Fix charge_type CASE expression
grafana/dashboards/charging-stats.json	Fix 4 CASE expressions + add geofences JOIN
grafana/dashboards/battery-health.json	Fix CASE expression + add geofences JOIN
grafana/dashboards/trip.json	Fix 3 CASE expression variants + add geofences JOIN

Why this fixes existing data retroactively

The fix is applied at query time in Grafana. No UPDATE to historical rows is needed — setting charge_type = 'AC' on a geofence immediately corrects all past charging sessions at that location.

Testing

Tested on a live TeslaMate instance with an underground home garage (no cell reception during charging). Before the fix every Home charge showed as DC. After setting charge_type = 'AC' on the Home geofence, all historical home charges immediately show as AC while Supercharger and public DC fast-charger sessions remain correctly classified as DC.

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[CLAassistant]

All committers have signed the CLA.

[JakobLichterfeld]

Thanks for your contribution.

immediately corrects all past charging sessions at that location.

This is not the best practice for changing historical charging types. It is okay to change them if they were offline, but otherwise, the correct data may become corrupted.

[finikwashere]

This is not the best practice for changing historical charging types. It is okay to change them if they were offline, but otherwise, the correct data may become corrupted.

Should it be optional, triggered by the user after upgrade?

[brianmay]

immediately corrects all past charging sessions at that location.

Not sure, there might be some confusion here in how this was documented.

The wording implies that we change (correct) the database at query time. "correct" would mean we write new values to the database.

That would be bad, queries have to remain read only. My grafana only has read only access to the database.

But my reading of the queries seems to indicate that they are read only and do not change any data.

Or am I totally confused here?

[brianmay]

I strongly suspect the tests will need fixing...

[finikwashere]

Apologies for the confusion.
The tests are updated.
I've also updated the translations.

On "corrects all past charging sessions"** (@brianmay): Grafana queries are read-only, and this is what the SQL here also does. The wording in the PR description was misleading. What I meant is:

Setting charge_type = 'AC' on a geofence causes all future queries to return 'AC' for historical sessions at that location — no data is written or modified. The SQL purely reads geofences.charge_type as an additional input to the CASE expression at query time.

The new CASE expression uses the geofence hint only as step 3 of 4, after the live telemetry signals have already been checked:

CASE
  WHEN NULLIF(mode() within group (order by charger_phases), 0) IS NOT NULL THEN 'AC'  -- online AC session
  WHEN bool_or(fast_charger_present) = true THEN 'DC'                                  -- online DC session
  WHEN MAX(g.charge_type::text) IS NOT NULL THEN MAX(g.charge_type::text)              -- offline fallback
  ELSE 'DC'
END

So for any session that was online during charging (i.e. charger_phases or fast_charger_present has real data), the geofence hint is never reached. It only kicks in for sessions where the car had no connectivity and both signals are NULL — which is exactly the scenario described in #4401.