evcc breaking changes in forecast api

[MaStr]

evcc-io/evcc#32391

[MaStr]

Investigation

evcc-io/evcc#32391 ("API: publish forecast as arrays with unix timestamps (BC)") changes the site state wire format for forecast data — co2, feedin, grid, planner, solar.timeseries, temperature — from RFC3339 objects ({"start": "...", "end": "...", "value": ...}) to compact [start_unix, end_unix, value] / [ts, val] arrays. This lives in core/site_tariffs.go (forecastRates()) and core/solar.go (timeseries.MarshalJSON()), and feeds the site state published over MQTT/WS//api/state (consumed by evcc's own UI, iOS app, Garmin integration, HA integration, openHAB).

I traced this against the actual endpoints batcontrol calls:

• src/batcontrol/dynamictariff/evcc.py -> GET <url> where url is typically .../api/tariff/grid
• src/batcontrol/forecastsolar/evcc_solar.py -> .../api/tariff/solar

Both hit the dedicated GET /api/tariff/{usage} route (server/http_site_handler.go: tariffHandler), which builds {"rates": api.Rates} directly from t.Rates() and is untouched by PR #32391 (verified by diffing that function between main and the PR branch — no changes). So batcontrol is not broken by this PR today.

Proposed plan (proactive compatibility, not a hotfix)

Given evcc's stated motivation ("the forecast is the largest payload evcc sends and RFC3339 timestamps are two thirds of it") and the pattern already established in evcc.py/evcc_solar.py of tolerating older evcc response shapes, I'd rather add forward compatibility now than wait for /api/tariff/{usage} to possibly get the same treatment later:

1. src/batcontrol/dynamictariff/evcc.py (_get_prices_native): branch per rate item on isinstance(item, (list, tuple)):
   • New shape: item = [start_unix, end_unix, value], parsed via datetime.datetime.fromtimestamp(item[0], tz=self.timezone) etc.
   • else: keep the current RFC3339 dict parsing (item['start'], item.get('end'), item.get('value', item.get('price'))) as the fallback branch, with a comment such as # evcc < X.Y.Z (pre evcc-io/evcc#32391) sends {start,end,value|price} objects so the version context isn't lost.
2. src/batcontrol/forecastsolar/evcc_solar.py (get_forecast_from_raw_data): same isinstance(item, (list, tuple)) branch, dict-parsing kept as else fallback, same style of version comment.
3. Both branches funnel into the existing downstream logic (15-min interval indexing / Wh conversion) unchanged.
4. Tests: add array-shaped rates fixtures to tests/batcontrol/dynamictariff/test_evcc.py and tests/batcontrol/forecastsolar/test_evcc_solar.py, asserting identical results to the existing object-shaped fixtures.
5. No config changes — URL-based config is unaffected, so no updates needed in config/batcontrol_config_dummy.yaml or the HA add-on config.yaml.
6. Docs: docs/configuration/dynamic-tariff-provider.md / docs/configuration/solar-forecast.md don't show raw JSON payloads, so no changes expected there; will double-check while implementing.

Note on the version comment: PR #32391 is unreleased as of 2026-08-16 (no tag yet), so I'll use a placeholder (evcc >= dev, evcc-io/evcc#32391) and swap in the concrete release tag once it ships, matching this repo's existing convention of citing specific evcc versions in comments.

Let me know if you'd like me to implement this now, or hold until /api/tariff/{usage} actually changes.

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