"""The heating Recommendation Generator.

Detects a dwelling whose heating system should be replaced and emits one
"Heating & Hot Water" Recommendation of competing whole-system bundles — the
Optimiser picks at most one (ADR-0024). Each bundle is a whole-system change:
main heating + controls + fuel + meter + the implied hot water, folded into one
Measure Option's `HeatingOverlay`. Hot water is never a separate competing
measure; the legacy heating-vs-HW split double-counted.

This slice covers the high-heat-retention storage (HHRSH) bundle; the ASHP and
boiler bundles land in later slices. Detection + pricing only — impact is
produced by scoring (ADR-0016).
"""

from typing import Optional

from datatypes.epc.domain.epc_property_data import EpcPropertyData, MainHeatingDetail
from domain.modelling.recommendation import Cost, MeasureOption, Recommendation
from domain.modelling.simulation import EpcSimulation, HeatingOverlay
from repositories.product.product_repository import ProductRepository

_HEATING_SURFACE = "Heating & Hot Water"

_HHR_STORAGE_MEASURE_TYPE = "high_heat_retention_storage_heaters"

# Electricity main-fuel code (Elmhurst → SAP10 Table 12).
_ELECTRICITY_FUEL = 30
# Table 4a SAP main-heating code for high-heat-retention storage heaters; an
# existing HHR system lodges this already, so it is not re-recommended.
_HHR_STORAGE_SAP_CODE = 409
# RdSAP main_heating_category for a heat pump (Table 4a) — an existing heat pump
# is never downgraded to storage heaters.
_HEAT_PUMP_CATEGORY = 4

# The HHRSH bundle's absolute end-state (ADR-0024): high-heat-retention storage
# heaters (Table 4a code 409) on a dual off-peak meter, with an off-peak
# electric immersion hot-water cylinder. Pinned against the relodged after-cert
# in the cascade tests; `mains_gas` and the heat emitter are unchanged by this
# measure, so they are not written.
_HHR_STORAGE_OVERLAY = HeatingOverlay(
    main_fuel_type=_ELECTRICITY_FUEL,
    sap_main_heating_code=_HHR_STORAGE_SAP_CODE,
    main_heating_control=2404,
    water_heating_code=903,
    water_heating_fuel=_ELECTRICITY_FUEL,
    cylinder_size=2,
    cylinder_insulation_type=1,
    cylinder_insulation_thickness_mm=120,
    has_hot_water_cylinder=True,
    meter_type="Dual",
)


def recommend_heating(
    epc: EpcPropertyData, products: ProductRepository
) -> Optional[Recommendation]:
    """Return a "Heating & Hot Water" Recommendation of competing whole-system
    bundles for the dwelling, else None when no bundle is eligible."""
    options: list[MeasureOption] = []

    hhr_option = _hhr_storage_option(epc, products)
    if hhr_option is not None:
        options.append(hhr_option)

    if not options:
        return None
    return Recommendation(surface=_HEATING_SURFACE, options=tuple(options))


def _hhr_storage_option(
    epc: EpcPropertyData, products: ProductRepository
) -> Optional[MeasureOption]:
    """The high-heat-retention storage bundle, offered for an electrically-heated
    (or off-gas) dwelling that is not already HHR or a heat pump."""
    if not _hhr_storage_eligible(epc):
        return None
    product = products.get(_HHR_STORAGE_MEASURE_TYPE)
    return MeasureOption(
        measure_type=_HHR_STORAGE_MEASURE_TYPE,
        description=(
            "Replace the heating with high heat retention storage heaters on an "
            "off-peak tariff, with an off-peak electric hot-water cylinder"
        ),
        overlay=EpcSimulation(heating=_HHR_STORAGE_OVERLAY),
        cost=Cost(
            total=product.unit_cost_per_m2, contingency_rate=product.contingency_rate
        ),
        material_id=product.id,
    )


def _hhr_storage_eligible(epc: EpcPropertyData) -> bool:
    """HHR storage suits an electrically-heated or off-gas dwelling, unless it is
    already HHR or a heat pump (translated from legacy `HeatingRecommender.
    is_high_heat_retention_valid`, which keyed on description strings)."""
    main: MainHeatingDetail = epc.sap_heating.main_heating_details[0]
    if main.sap_main_heating_code == _HHR_STORAGE_SAP_CODE:
        return False
    if main.main_heating_category == _HEAT_PUMP_CATEGORY:
        return False
    off_gas: bool = epc.sap_energy_source is None or not epc.sap_energy_source.mains_gas
    electric_main: bool = main.main_fuel_type == _ELECTRICITY_FUEL
    return electric_main or off_gas