Refactor forecast metrics into dedicated ForecastMetrics module

[MaStr]

Motivation

The original _compute_night_surplus() method tried to answer one question
("how much battery is left at dawn?") but the answer depended on whether solar
was currently active or not, making the single value ambiguous for automation
decisions. After working through the four relevant scenarios (solar active now /
surplus or not, nighttime / surplus tomorrow or not), the metric was replaced by
a more expressive triplet:

Metric	Meaning
solar_surplus_wh	PV overflow that cannot be stored — safe to run flexible loads now
pv_start_battery_wh	Battery level when PV first exceeds consumption — how depleted will the battery be at dawn?
forecast_min_battery_wh	Minimum battery over the entire forecast horizon — will the battery ever run out?

These three values form a 2-D decision matrix for flexible load control (heat
pump, EV charging). See docs/WIKI_forecast_metrics.md for the full decision
guide.

Key Changes

New module: src/batcontrol/forecast_metrics.py

All three metrics extracted into a dedicated ForecastMetrics class with
static methods. Pure computation, no inverter or MQTT dependencies.

• solar_active_and_surplus() — moved from Batcontrol._compute_solar_active_and_surplus()
• pv_start_battery() — new: slot-by-slot simulation until net-charging crossover (net_consumption < 0)
• forecast_min_battery() — new: deepest trough over full forecast horizon with floor/ceiling clamping

Both new metrics use proper slot-by-slot simulation instead of a net-sum, because the battery floor (MIN_SOC) and ceiling (MAX_SOC) make a naive sum incorrect across multi-day cycles.

Removed from Batcontrol (core.py)

• _compute_solar_active_and_surplus() instance method (~30 lines)
• _compute_night_surplus() instance method (~60 lines)

MQTT API changes

Topic	Change
/night_surplus_wh	Removed — replaced by the two metrics below
/pv_start_battery_wh	Added — battery level (Wh above MIN_SOC) at next net-charging point
/forecast_min_battery_wh	Added — minimum battery level (Wh above MIN_SOC) over forecast horizon
/solar_surplus_wh, /solar_active	Unchanged

Home Assistant auto-discovery updated accordingly. A tombstone (empty retained
payload) is published to the legacy batcontrol_night_surplus_wh discovery
topic on connect so existing brokers remove the stale HA entity automatically.
The tombstone is marked # TODO(0.9.1) for removal once brokers have been cleaned up.

Bug fixes included in this PR

• Stale net_consumption in core.py: net_consumption was computed
  before production[0] / consumption[0] were factorized for elapsed time
  (lines 606-607). The array was not updated after the in-place mutation.
  pv_start_battery and forecast_min_battery now receive the correct
  time-adjusted slot-0 value.

Tests

• Removed: tests/batcontrol/test_night_surplus.py
• Updated: tests/batcontrol/test_solar_surplus.py — calls ForecastMetrics directly, no Batcontrol mock needed
• Added: tests/batcontrol/test_pv_battery_metrics.py — 13 tests for pv_start_battery and forecast_min_battery covering edge cases (depletion before sunrise, multi-day troughs, 15-min resolution, floor clamp)

Documentation

• Added: docs/WIKI_forecast_metrics.md — explains each metric, the 2-D decision
  matrix, MQTT topics, HA auto-discovery entities, and implementation notes

Test plan

• All CI tests green
• solar_surplus_wh, pv_start_battery_wh, forecast_min_battery_wh appear in HA after upgrade
• night_surplus_wh HA entity disappears automatically (tombstone cleanup)
• Verify slot-0 time-adjustment reflected in pv_start_battery_wh (check near interval boundary)

https://claude.ai/code/session_01AbZuZ73iEQMiwTkwy3Mt1h

[Copilot]

Pull request overview

This PR refactors forecast-derived battery metrics out of Batcontrol into a dedicated ForecastMetrics module, and replaces the prior “night surplus” signal with two more granular forecast metrics that are published via MQTT (including Home Assistant discovery updates).

Changes:

• Added ForecastMetrics pure-style helpers for solar surplus plus two new battery forecast metrics (pv_start_battery, forecast_min_battery).
• Updated Batcontrol.run() to use ForecastMetrics and publish the new MQTT metrics instead of night_surplus_wh.
• Refactored tests to target ForecastMetrics directly; removed the legacy night_surplus tests and added new coverage for the new metrics.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/batcontrol/forecast_metrics.py	New module implementing forecast-derived metrics used by Batcontrol and tested directly.
src/batcontrol/core.py	Switches runtime metric computation from instance methods to ForecastMetrics and publishes new metrics.
src/batcontrol/mqtt_api.py	Replaces night_surplus_wh publishing/discovery with new topics and adds a retained tombstone cleanup for HA discovery.
tests/batcontrol/test_solar_surplus.py	Updates surplus tests to call ForecastMetrics directly (no Batcontrol mocking).
tests/batcontrol/test_pv_battery_metrics.py	Adds tests for pv_start_battery and forecast_min_battery.
tests/batcontrol/test_night_surplus.py	Removes legacy test suite for the deleted night-surplus metric.

[Copilot]

Pull request overview

Copilot reviewed 7 out of 7 changed files in this pull request and generated no new comments.