Translate full-SAP electricity tariff into the RdSAP meter type 🟩

Full-SAP energy_tariff (1=standard/2=7hr/3=10hr/4=24hr) and RdSAP meter_type
(1=dual/2=single/3=unknown/4=24hr) are different code spaces; the mapper passed
the code through untranslated, reading standard-tariff full-SAP certs as Economy 7
(over-rated) and Economy-7 certs as single (under-rated). Map onto the RdSAP word
aliases so the resolved Table 12a tariff is correct; absent/ND -> unknown.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

datatypes/epc/domain/mapper.py

@@ -866,7 +866,9 @@ class EpcPropertyDataMapper:
             # explicit flag); tariff → meter_type; wind turbines pass through.
             sap_energy_source=SapEnergySource(
                 mains_gas=_sap_dwelling_on_mains_gas(schema),
-                meter_type=str(schema.sap_energy_source.electricity_tariff or ""),
+                meter_type=_sap_17_1_meter_type(
+                    schema.sap_energy_source.electricity_tariff
+                ),
                 pv_battery_count=0,
                 wind_turbines_count=schema.sap_energy_source.wind_turbines_count or 0,
                 gas_smart_meter_present=False,
@@ -2943,7 +2945,21 @@ def _sap_17_1_meter_type(electricity_tariff: Optional[int]) -> str:
     standard-tariff cert as Economy 7 (over-rated) and an Economy-7 cert as
     single (under-rated). Map onto the RdSAP word aliases so the resolved tariff
     is correct; absent/ND → "" (the unknown→standard sentinel)."""
-    raise NotImplementedError(electricity_tariff)
+    if electricity_tariff is None:
+        return ""
+    return _SAP_TARIFF_TO_RDSAP_METER_TYPE.get(electricity_tariff, "")
+
+
+# full-SAP `energy_tariff` code → RdSAP `meter_type` word alias (consumed by
+# `tariff_from_meter_type` / `_METER_STR_TO_INT`). 10-hour (3) has no dedicated
+# RdSAP meter code — it maps to "dual", and the §12 dispatch resolves 7-/10-hour
+# from the heating system.
+_SAP_TARIFF_TO_RDSAP_METER_TYPE: dict[int, str] = {
+    1: "single",          # standard tariff
+    2: "dual",            # off-peak 7 hour (Economy 7)
+    3: "dual",            # off-peak 10 hour (§12 dispatch resolves 7/10hr)
+    4: "dual (24 hour)",  # 24-hour tariff
+}
 
 
 def _sap_17_1_heating(schema: SapSchema17_1) -> SapHeating:

datatypes/epc/domain/tests/test_from_sap_schema.py

@@ -156,6 +156,29 @@ class TestFullSapElectricityTariffTranslation:
 
         assert tariff_from_meter_type(meter_type) is Tariff.SEVEN_HOUR
 
+    @pytest.mark.parametrize(
+        ("energy_tariff", "expected"),
+        [
+            (1, "STANDARD"),         # standard tariff → single-rate (was over-rated as E7)
+            (2, "SEVEN_HOUR"),       # off-peak 7-hour → Economy 7
+            (3, "SEVEN_HOUR"),       # off-peak 10-hour → dual (§12 resolves 7/10hr)
+            (4, "TWENTY_FOUR_HOUR"),  # 24-hour tariff (e.g. property 709874 — unchanged)
+            (None, "STANDARD"),      # absent/ND → unknown → standard
+        ],
+    )
+    def test_energy_tariff_resolves_to_the_correct_calculator_tariff(
+        self, energy_tariff: Any, expected: str
+    ) -> None:
+        from domain.sap10_calculator.tables.table_12a import (
+            tariff_from_meter_type,
+        )
+
+        from datatypes.epc.domain.mapper import _sap_17_1_meter_type
+
+        resolved = tariff_from_meter_type(_sap_17_1_meter_type(energy_tariff))
+
+        assert resolved.name == expected
+
 
 class TestFromSapSchema17_1DisplayElements:
     """Display EnergyElements the WIP mapper dropped, leaving the FE