feat(modelling): recommend_lighting upgrades all non-LED bulbs to LED

Slice 2 of the lighting generator (ADR-0023): detect non-LED bulbs
(incandescent + CFL + low-energy-unknown > 0) and emit one "Lighting"
Recommendation whose single low_energy_lighting Option converts every bulb to
LED — the overlay sets led = total, the other three counts 0. Priced as a flat
per-bulb average x the non-LED count, contingency 0.26; the description names
"LED" while the measure_type stays MEASURE_MAP-aligned. None when already
all-LED or no bulb counts are lodged.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

domain/modelling/generators/lighting_recommendation.py

@@ -0,0 +1,63 @@
+"""The lighting Recommendation Generator (LED upgrade).
+
+Detects a dwelling's non-LED fixed-lighting bulbs and emits one "Lighting"
+Recommendation whose single Option converts **every** bulb to LED (ADR-0023).
+SAP 10.2 RdSAP §12-1 rates lamp efficacy LED > low-energy-unknown > CFL >
+incandescent, so converting every non-LED type — incandescent, CFL, and the
+"low energy, type unknown" (LEL) bulbs alike — strictly improves the Appendix L
+lighting energy (worksheet line (232)).
+
+Unlike the fabric generators this is a **whole-dwelling** Measure: its overlay
+writes the four top-level bulb counts directly (`led = total`, the rest 0). It
+is a free Optimiser candidate — an LED upgrade improves SAP at low cost, so the
+Optimiser keeps or leaves it for least-cost-to-target (contrast ventilation's
+forced dependency). Detection + pricing only; impact is produced later by
+scoring (ADR-0016).
+"""
+
+from typing import Final, Optional
+
+from datatypes.epc.domain.epc_property_data import EpcPropertyData
+from domain.modelling.recommendation import Cost, MeasureOption, Recommendation
+from domain.modelling.simulation import EpcSimulation, LightingOverlay
+from repositories.product.product_repository import ProductRepository
+
+_LIGHTING_MEASURE_TYPE: Final[str] = "low_energy_lighting"
+
+
+def recommend_lighting(
+    epc: EpcPropertyData, products: ProductRepository
+) -> Optional[Recommendation]:
+    """Return a lighting Recommendation upgrading every non-LED bulb to LED — its
+    single Option — else None when the dwelling has no non-LED bulbs (already
+    all-LED, or no bulb counts lodged)."""
+    led: int = epc.led_fixed_lighting_bulbs_count or 0
+    cfl: int = epc.cfl_fixed_lighting_bulbs_count or 0
+    incandescent: int = epc.incandescent_fixed_lighting_bulbs_count or 0
+    low_energy: int = epc.low_energy_fixed_lighting_bulbs_count or 0
+
+    non_led: int = cfl + incandescent + low_energy
+    if non_led == 0:
+        return None
+
+    product = products.get(_LIGHTING_MEASURE_TYPE)
+    overlay = EpcSimulation(
+        lighting=LightingOverlay(
+            led_fixed_lighting_bulbs_count=led + non_led,
+            cfl_fixed_lighting_bulbs_count=0,
+            incandescent_fixed_lighting_bulbs_count=0,
+            low_energy_fixed_lighting_bulbs_count=0,
+        )
+    )
+    cost = Cost(
+        total=non_led * product.unit_cost_per_m2,
+        contingency_rate=product.contingency_rate,
+    )
+    option = MeasureOption(
+        measure_type=_LIGHTING_MEASURE_TYPE,
+        description="Replace all non-LED bulbs with LED",
+        overlay=overlay,
+        cost=cost,
+        material_id=product.id,
+    )
+    return Recommendation(surface="Lighting", options=(option,))

tests/domain/modelling/test_lighting_recommendation.py

@@ -0,0 +1,121 @@
+"""Behaviour of the lighting Recommendation Generator: detecting non-LED bulbs
+and emitting one "Lighting" Recommendation whose single Option upgrades every
+bulb to LED (ADR-0023). A free Optimiser candidate (it improves SAP), unlike
+ventilation's forced dependency. Detection + pricing only, no scores (ADR-0016).
+"""
+
+import copy
+
+from datatypes.epc.domain.epc_property_data import EpcPropertyData
+from domain.modelling.generators.lighting_recommendation import recommend_lighting
+from domain.modelling.product import Product
+from domain.modelling.recommendation import Recommendation
+from domain.modelling.simulation import LightingOverlay
+from repositories.product.product_repository import ProductRepository
+from tests.domain.sap10_calculator.worksheet._elmhurst_worksheet_000490 import (
+    build_epc,
+)
+
+
+class _StubProducts(ProductRepository):
+    """In-memory ProductRepository returning a fixed per-bulb lighting price.
+
+    `unit_cost_per_m2` carries the catalogue row's fully-loaded total, reused as
+    a flat average price per bulb (ADR-0023)."""
+
+    def get(self, measure_type: str) -> Product:
+        return Product(
+            measure_type=measure_type,
+            unit_cost_per_m2=5.0,
+            contingency_rate=0.26,
+            id=7,
+        )
+
+
+def _with_bulbs(
+    epc: EpcPropertyData, *, led: int, cfl: int, incandescent: int, low_energy: int
+) -> EpcPropertyData:
+    """Return a copy of `epc` with the four fixed-lighting bulb counts set."""
+    clone: EpcPropertyData = copy.deepcopy(epc)
+    clone.led_fixed_lighting_bulbs_count = led
+    clone.cfl_fixed_lighting_bulbs_count = cfl
+    clone.incandescent_fixed_lighting_bulbs_count = incandescent
+    clone.low_energy_fixed_lighting_bulbs_count = low_energy
+    return clone
+
+
+def test_dwelling_with_non_led_bulbs_yields_a_lighting_recommendation() -> None:
+    # Arrange — a mixed inventory: 2 LED + 3 CFL + 4 incandescent + 1 LEL.
+    baseline: EpcPropertyData = _with_bulbs(
+        build_epc(), led=2, cfl=3, incandescent=4, low_energy=1
+    )
+
+    # Act
+    recommendation: Recommendation | None = recommend_lighting(
+        baseline, _StubProducts()
+    )
+
+    # Assert — one all-LED Option: led = total (10), every other count zeroed.
+    assert recommendation is not None
+    assert recommendation.surface == "Lighting"
+    assert len(recommendation.options) == 1
+    option = recommendation.options[0]
+    assert option.measure_type == "low_energy_lighting"
+    assert option.overlay.lighting == LightingOverlay(
+        led_fixed_lighting_bulbs_count=10,
+        cfl_fixed_lighting_bulbs_count=0,
+        incandescent_fixed_lighting_bulbs_count=0,
+        low_energy_fixed_lighting_bulbs_count=0,
+    )
+
+
+def test_already_all_led_dwelling_yields_no_recommendation() -> None:
+    # Arrange — every bulb is already LED; nothing to upgrade.
+    baseline: EpcPropertyData = _with_bulbs(
+        build_epc(), led=9, cfl=0, incandescent=0, low_energy=0
+    )
+
+    # Act
+    recommendation: Recommendation | None = recommend_lighting(
+        baseline, _StubProducts()
+    )
+
+    # Assert
+    assert recommendation is None
+
+
+def test_dwelling_with_no_lodged_bulbs_yields_no_recommendation() -> None:
+    # Arrange — no bulb counts lodged (the calculator's L5b fallback case): with
+    # no inventory to size against, no Recommendation is offered (ADR-0023).
+    baseline: EpcPropertyData = _with_bulbs(
+        build_epc(), led=0, cfl=0, incandescent=0, low_energy=0
+    )
+
+    # Act
+    recommendation: Recommendation | None = recommend_lighting(
+        baseline, _StubProducts()
+    )
+
+    # Assert
+    assert recommendation is None
+
+
+def test_recommendation_prices_a_flat_average_per_non_led_bulb() -> None:
+    # Arrange — 8 non-LED bulbs (3 CFL + 4 incandescent + 1 LEL) at £5 each; the
+    # 2 existing LEDs are not priced (not replaced).
+    baseline: EpcPropertyData = _with_bulbs(
+        build_epc(), led=2, cfl=3, incandescent=4, low_energy=1
+    )
+
+    # Act
+    recommendation: Recommendation | None = recommend_lighting(
+        baseline, _StubProducts()
+    )
+
+    # Assert
+    assert recommendation is not None
+    cost = recommendation.options[0].cost
+    assert cost is not None
+    assert cost.total == 8 * 5.0
+    assert cost.contingency_rate == 0.26
+    assert recommendation.options[0].material_id == 7