"""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 datatypes.epc.domain.field_mappings import PROPERTY_TYPE_LOOKUP
from domain.geospatial.planning_restrictions import PlanningRestrictions
from domain.modelling.products import AshpCostInputs, AshpExistingSystem, Products
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"
_ASHP_MEASURE_TYPE = "air_source_heat_pump"

# 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,
    cylinder_thermostat="Y",
    has_hot_water_cylinder=True,
    meter_type="Dual",
)

# Representative heat-pump products Domna installs (one per brand we hold
# contractor install rates for), as PCDB Table 362 indices — the catalogue we
# may simulate the ASHP bundle with. Each is a valid, currently-available,
# ~5 kW air-to-water unit providing space + water heating, chosen for high SAP
# 10.2 Appendix N efficiency (space η at the dwelling's PSR, with a healthy
# water η — many high-space records collapse on water and were rejected):
#
#   Vaillant   110257  aroTHERM plus 5 kW          space ~402% / water ~288%
#   Mitsubishi 104570  Ecodan PUZ-WM50VHA 5.0 kW   space ~368% / water ~288%
#   Daikin     105008  Altherma ERGA04DVA 5.5 kW   space ~376% / water ~288%
#   Samsung    108774  AE050CXYDEK 5 kW (R290)      space ~394% / water ~309%
#   Grant      103768  AERONA3 HPID6R32 4.8 kW      space ~395% / water ~332%
#
# We fix the Vaillant for the tracer: it is widely available for install and a
# strong all-round SAP performer. (Promoting this to a per-dwelling choice is a
# clean future change — see the sizing note below.)
_VAILLANT_AROTHERM_PLUS_5KW_PCDB = 110257

# NOTE (sizing): the bundle installs ONE fixed ~5 kW product regardless of the
# dwelling. SAP 10.2 Appendix N reads heat-pump efficiency at the dwelling's PSR
# (= pump max output / design heat loss), so a fixed output is a deliberate
# simplification: a 5 kW unit lands at a good PSR (~0.8-1.0) for modest
# dwellings but is undersized for high-heat-loss ones (low PSR → lower space
# efficiency), leaving SAP on the table. Sizing the pump to the dwelling (and
# selecting the matching PCDB record) is future work — it also feeds the
# size-banded ASHP costing.

# The ASHP bundle's absolute end-state (ADR-0024): the fixed, representative,
# contractor-installable heat pump above (RdSAP category 4) with time-and-
# temperature-zone control (2210), a heat-pump hot-water cylinder, a single
# (non off-peak) meter, and the dwelling switched off mains gas. The index is
# the efficiency anchor — the applicator clears any stale `sap_main_heating_code`
# when an index is set, so the calculator resolves the heat pump's SCOP from the
# PCDB record. Pinned against the relodged after-cert.
_ASHP_OVERLAY = HeatingOverlay(
    main_fuel_type=_ELECTRICITY_FUEL,
    main_heating_control=2210,
    main_heating_index_number=_VAILLANT_AROTHERM_PLUS_5KW_PCDB,
    main_heating_category=_HEAT_PUMP_CATEGORY,
    # Hot water from the main heat-pump system via the new cylinder (code 901,
    # "from main system"). Set absolutely so a combi (909/611) or electric
    # (903/908) before is reset to the fixed HP end-state, not just the case
    # where the before already lodged 901.
    water_heating_code=901,
    water_heating_fuel=_ELECTRICITY_FUEL,
    cylinder_size=4,
    cylinder_insulation_type=1,
    cylinder_insulation_thickness_mm=50,
    cylinder_thermostat="Y",
    has_hot_water_cylinder=True,
    meter_type="Single",
    mains_gas=False,
)


# --- ASHP cost interpretation (ADR-0025): read the dwelling into the typed
# inputs the catalogue math needs. The modelling-layer half of the split; the
# pricing itself lives on `Products`. ---

# A dwelling at or below this floor area is treated as a 1-2 bed property (only
# affects the electric-storage decommission line — a £270 swing).
_SMALL_PROPERTY_MAX_M2 = 75.0
# Design heat loss proxy: industry rule of thumb ~50 W per m2 of floor area.
# The cost pump-size band is a minor lever, so this floor-area proxy is used in
# preference to the calculator's HLC (ADR-0025).
_KW_PER_M2 = 0.05
# Radiators ~= habitable rooms + kitchen + hall + bathroom (RdSAP excludes the
# latter three from habitable rooms); fallback ~1 radiator per 13 m2.
_RADIATOR_ROOM_OFFSET = 3
_RADIATOR_M2_PER_RADIATOR = 13.0
# main_fuel_type codes (gov API enum and/or Table 12) by fuel. Classification
# keys on the heating *fuel*, NOT the `mains_gas` flag — that flag means gas is
# available at the property, which is True even for electrically-heated dwellings
# on a gas street (every 001431 electric fixture lodges mains_gas=True).
_GAS_FUEL_CODES = frozenset({26, 1})
_OIL_FUEL_CODES = frozenset({28, 4, 71, 73, 75, 76})
_LPG_FUEL_CODES = frozenset({27, 2, 3, 5, 9})


def ashp_cost_inputs(epc: EpcPropertyData) -> AshpCostInputs:
    """Read an `EpcPropertyData` into the typed inputs `Products.ashp_bundle_cost`
    needs: the existing system, property-size band, design heat loss (floor-area
    proxy), radiator count, and whether a wet system can be reused (ADR-0025)."""
    system: AshpExistingSystem = _existing_system(epc)
    floor_area: float = epc.total_floor_area_m2
    return AshpCostInputs(
        existing_system=system,
        is_small_property=floor_area <= _SMALL_PROPERTY_MAX_M2,
        design_heat_loss_kw=floor_area * _KW_PER_M2,
        radiator_count=_radiator_count(epc),
        has_reusable_wet_system=system
        in (AshpExistingSystem.GAS, AshpExistingSystem.OIL, AshpExistingSystem.LPG),
    )


def _existing_system(epc: EpcPropertyData) -> AshpExistingSystem:
    """Classify the dwelling's pre-retrofit system for decommission + reuse,
    keyed on the heating *fuel code* (not the misleading `mains_gas` flag).
    Electricity, gas, oil and LPG map to their categories; a dwelling with no
    lodged main system to NONE; anything unrecognised to OTHER (which prices the
    gas-line decommission fallback). The storage-vs-other-electric split is
    deliberately not made — both price the same decommission line (ADR-0025)."""
    details: list[MainHeatingDetail] = epc.sap_heating.main_heating_details
    if not details:
        return AshpExistingSystem.NONE
    fuel = details[0].main_fuel_type
    if fuel == _ELECTRICITY_FUEL:
        return AshpExistingSystem.ELECTRIC_STORAGE
    if fuel in _GAS_FUEL_CODES:
        return AshpExistingSystem.GAS
    if fuel in _OIL_FUEL_CODES:
        return AshpExistingSystem.OIL
    if fuel in _LPG_FUEL_CODES:
        return AshpExistingSystem.LPG
    return AshpExistingSystem.OTHER


def _radiator_count(epc: EpcPropertyData) -> int:
    """Estimate radiators from habitable rooms (+ kitchen/hall/bathroom), or
    from floor area when the room count is missing (ADR-0025). Products clamps
    to its distribution table bounds."""
    habitable: int = epc.habitable_rooms_count
    if habitable > 0:
        return habitable + _RADIATOR_ROOM_OFFSET
    return round(epc.total_floor_area_m2 / _RADIATOR_M2_PER_RADIATOR)


def recommend_heating(
    epc: EpcPropertyData,
    products: ProductRepository,
    restrictions: PlanningRestrictions = PlanningRestrictions(),
) -> Optional[Recommendation]:
    """Return a "Heating & Hot Water" Recommendation of competing whole-system
    bundles for the dwelling, else None when no bundle is eligible. ASHP is
    additionally gated by the Property's planning protections (ADR-0024)."""
    options: list[MeasureOption] = []

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

    ashp_option = _ashp_option(epc, products, restrictions)
    if ashp_option is not None:
        options.append(ashp_option)

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


def _ashp_option(
    epc: EpcPropertyData,
    products: ProductRepository,
    restrictions: PlanningRestrictions,
) -> Optional[MeasureOption]:
    """The air-source heat-pump bundle, offered for any non-flat house/bungalow
    that is not listed/heritage and not already a heat pump."""
    if not _ashp_eligible(epc, restrictions):
        return None
    # Cost is composed per-dwelling from the rate sheet (ADR-0025), not the
    # single catalogue scalar; the catalogue row is still read for its id.
    product = products.get(_ASHP_MEASURE_TYPE)
    cost: Cost = Products().ashp_bundle_cost(ashp_cost_inputs(epc))
    return MeasureOption(
        measure_type=_ASHP_MEASURE_TYPE,
        description=(
            "Replace the heating with an air-source heat pump, time-and-"
            "temperature-zone controls and a heat-pump hot-water cylinder"
        ),
        overlay=EpcSimulation(heating=_ASHP_OVERLAY),
        cost=cost,
        material_id=product.id,
    )


def _ashp_eligible(epc: EpcPropertyData, restrictions: PlanningRestrictions) -> bool:
    """ASHP suits any non-flat house/bungalow that is not already a heat pump and
    is not fabric-protected. Eligibility encodes only physical/planning
    installability — the Optimiser owns the economics (ADR-0024), so floor area,
    built form, fuel, and fabric are deliberately not gates. A conservation area
    does not exclude ASHP (offered with a planning caveat); a listed/heritage
    protection (`blocks_internal`) does."""
    main: MainHeatingDetail = epc.sap_heating.main_heating_details[0]
    if main.main_heating_category == _HEAT_PUMP_CATEGORY:
        return False
    if restrictions.blocks_internal:
        return False
    return _is_house_or_bungalow(epc)


def _is_house_or_bungalow(epc: EpcPropertyData) -> bool:
    """Whether the dwelling is a house or bungalow (not a flat/maisonette). The
    Elmhurst path lodges the name; the API path a stringified RdSAP code
    (`PROPERTY_TYPE_LOOKUP`: 0 House, 1 Bungalow, 2 Flat, 3 Maisonette)."""
    raw: str = (epc.property_type or "").strip()
    if raw.lower() in ("house", "bungalow"):
        return True
    if raw.isdigit():
        return PROPERTY_TYPE_LOOKUP.get(int(raw)) in ("House", "Bungalow")
    return False


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 = not epc.sap_energy_source.mains_gas
    electric_main: bool = main.main_fuel_type == _ELECTRICITY_FUEL
    return electric_main or off_gas