Model/domain/modelling/generators/heating_recommendation.py

"""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, is_heat_network_main
from domain.geospatial.planning_restrictions import PlanningRestrictions
from domain.modelling.products import (
    AshpCostInputs,
    AshpExistingSystem,
    BoilerCostInputs,
    Products,
    TuneUpCostInputs,
)
from domain.modelling.measure_type import MeasureType
from domain.modelling.product import Product
from domain.modelling.recommendation import Cost, MeasureOption, Recommendation
from domain.modelling.simulation import EpcSimulation, HeatingOverlay
from domain.sap10_calculator.tables.pcdb import gas_oil_boiler_record
from domain.sap10_calculator.tables.table_4b import (
    table_4b_seasonal_efficiencies_pct,
)
from repositories.product.product_repository import ProductRepository

_HEATING_SURFACE = "Heating & Hot Water"

_HHR_STORAGE_MEASURE_TYPE = MeasureType.HIGH_HEAT_RETENTION_STORAGE_HEATERS
_ASHP_MEASURE_TYPE = MeasureType.AIR_SOURCE_HEAT_PUMP
_GAS_BOILER_UPGRADE_MEASURE_TYPE = MeasureType.GAS_BOILER_UPGRADE
_SYSTEM_TUNE_UP_MEASURE_TYPE = MeasureType.SYSTEM_TUNE_UP
_SYSTEM_TUNE_UP_ZONED_MEASURE_TYPE = MeasureType.SYSTEM_TUNE_UP_ZONED

# 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,
    # RdSAP electric-storage-heater category (7). Set so the overlaid EPC stays
    # internally consistent: without it the pre-existing system's category (e.g.
    # 10 = electric room heaters) survives alongside the new storage code 409,
    # and the SAP 10.2 Table 12a resolver — which classifies by category —
    # misreads the off-peak storage heating as direct-acting electric and prices
    # 100% at the peak rate (verified: UPRN 100020942571 HHRSH SAP 48 vs
    # accredited Elmhurst 71; category 7 -> 73). See ADR-0024.
    main_heating_category=7,
    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",
    # Single off-peak electric immersion — drives the SAP 10.2 Table 13 HW
    # high-rate split (matches the relodged after-cert; without it the HW
    # bills 100% at the low rate, +1.26 SAP over the reference).
    immersion_heating_type=1,
    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",
    gas_connection_available=False,
)


# ASHP sizing ladder (ADR-0049): the Vaillant aroTHERM plus "& AI VIH RW" family,
# one representative PCDB Table 362 record per nominal size, ascending by rated
# max output (kW). The pump is sized to the dwelling's design heat loss so SAP
# 10.2 Appendix N reads the heat-pump efficiency near its PSR peak (~1.0), rather
# than a single fixed unit that is grossly undersized on high-heat-loss dwellings
# — where the PSR collapses and the ASHP scores at/below the resistance baseline.
# 110257 (the 5 kW rung) is the previously-fixed anchor, validated against the
# relodged after-cert.
_ASHP_SIZING_LADDER: tuple[tuple[float, int], ...] = (
    (3.76, 110249),   # aroTHERM plus 3.5 kW
    (4.37, 110257),   # aroTHERM plus 5 kW
    (6.40, 110265),   # aroTHERM plus 7 kW
    (7.93, 110273),   # aroTHERM plus 10 kW
    (11.48, 110281),  # aroTHERM plus 12 kW
)


def select_ashp_pcdb_id(design_heat_loss_kw: float) -> int:
    """The PCDB heat-pump record to install for a dwelling with
    `design_heat_loss_kw`: the smallest ladder rung whose rated output meets the
    load (PSR >= 1.0), capped at the largest rung when the load exceeds the
    domestic aroTHERM plus range (ADR-0049)."""
    raise NotImplementedError


# --- Gas boiler upgrade (Heating/HW expansion): replace an existing wet boiler
# with a modern gas condensing boiler. Validated against Elmhurst before/after
# re-lodgements (cert 001431): the upgrade always targets mains gas — gas->gas
# directly, and a non-gas wet boiler (oil/LPG/solid) ->gas ONLY where a mains-gas
# connection is present (electric boilers are left alone; electrification is the
# national target). The end-state is a Table 4b SAP code (not a PCDB index): code
# 102 for a regular boiler heating a hot-water cylinder, code 104 for a combi
# (no cylinder, a later slice). The calculator derives the condensing-boiler
# seasonal efficiency from the code, so no efficiency input is needed. ---

# Mains-gas main/water fuel code (Elmhurst -> SAP10 Table 12).
_MAINS_GAS_FUEL = 26
# Table 4a heat-emitter code for radiators (the wet-distribution end-state).
_RADIATOR_EMITTER = 1
# Table 4b SAP main-heating codes for the new gas condensing boiler: code 102
# for a regular boiler heating a cylinder, code 104 for a combi (no cylinder).
_REGULAR_GAS_BOILER_SAP_CODE = 102
_COMBI_GAS_BOILER_SAP_CODE = 104
# Water-heating code 901 — hot water from the main heating system.
_WATER_FROM_MAIN_SYSTEM_CODE = 901
# Elmhurst boiler flue type for the new condensing boiler (room-sealed/balanced);
# every relodged after lodges type 2. SAP-inert, written for end-state fidelity.
_CONDENSING_BOILER_FLUE_TYPE = 2

# Controls upgrade (SAP 10.2 Table 4e Group 1, PDF p.172): bring an inadequate
# boiler control up to full programmer + room thermostat + TRVs (code 2106).
# "Inadequate" = the Group-1 codes whose description carries NO room thermostat
# (2101 no control, 2102 programmer-only, 2107/2108/2109 programmer+TRVs without
# a room thermostat, 2111 TRVs and bypass) — these lack boiler interlock (Table
# 4c(2) / footnote c)), so adding a room thermostat is a genuine improvement.
# Controls with a room thermostat (2103/2104/2105/2106/2113) or better time-and-
# temperature zone control (2110/2112) are left unchanged — never downgraded.
_FULL_BOILER_CONTROL = 2106
_INADEQUATE_BOILER_CONTROL_CODES: frozenset[int] = frozenset(
    {2101, 2102, 2107, 2108, 2109, 2111}
)

# System tune-up control end-states (SAP 10.2 Table 4e Group 1): the two best
# competing control upgrades offered while KEEPING the existing boiler —
# "standard" (programmer + room thermostat + TRVs, code 2106) and "zone"
# (time-and-temperature zone control, code 2110, type 3). Zone gives more SAP
# uplift for more cost, so the Optimiser steps to it when its extra SAP is
# needed (ADR-0024).
_STANDARD_CONTROL = _FULL_BOILER_CONTROL  # 2106
_ZONE_CONTROL = 2110
# Controls already providing standard (2106) or better — a standard tune-up
# would be a no-op or a downgrade, so it is not offered to these.
_STANDARD_OR_BETTER_CONTROL_CODES: frozenset[int] = frozenset({2106, 2110, 2112})
# Controls already providing zone control (type 3) — a zone tune-up is not
# offered to these.
_ZONE_CONTROL_CODES: frozenset[int] = frozenset({2110, 2112})

# Wet-boiler SAP main_heating_code ranges (SAP 10.2 Table 4a + 4b): gas/oil
# boilers 101-141, solid-fuel boilers 151-161, electric boilers 191-196 (held
# locally so the generator does not depend on the calculator's internals,
# mirroring `domain/sap10_calculator/rdsap/cert_to_inputs.py`). Electric boilers
# are a wet system but are deliberately not upgraded to gas.
_WET_BOILER_SAP_CODE_RANGES: tuple[range, ...] = (
    range(101, 142),
    range(151, 162),
    range(191, 197),
)
_ELECTRIC_BOILER_SAP_CODE_RANGE = range(191, 197)

# RdSAP main_heating_category values that denote a wet central-heating boiler:
# 1 ("central heating with separate HW") and 2 ("boiler and radiators"). Both
# imply a wet primary loop — the fuel (not the category) says gas/oil/electric.
# Used only for the fallback classification of a lodgement that carries a
# category but no `sap_main_heating_code` (mirrors the calculator's
# `cert_to_inputs._is_wet_boiler_main`).
_WET_BOILER_CATEGORIES: frozenset[int] = frozenset({1, 2})
# Electricity main-fuel codes: the SAP Table 12 code (30, Elmhurst/cascade) and
# the raw gov-API enum (29). An electric-fuelled boiler is the electrification
# path, not a gas swap, so it is excluded from the gas-boiler upgrade even when
# the SAP code is absent (the code range can't identify it).
_ELECTRICITY_FUEL_CODES: frozenset[int] = frozenset({29, 30})

# Cylinder jacket end-state (from the after-cert): an 80 mm jacket
# (`cylinder_insulation_type=2`). The jacket is added only when the existing
# cylinder is below this thickness — bringing every cylinder up to 80 mm and
# never downgrading a better-insulated one.
_CYLINDER_JACKET_INSULATION_TYPE = 2
_MIN_CYLINDER_INSULATION_MM = 80

# The new condensing boiler's winter efficiency: SAP 10.2 Table 4b codes 102
# (regular condensing) and 104 (condensing combi) both lodge 84% winter. A
# like-for-like gas swap onto an existing gas boiler that already meets this
# gains nothing, so it is not offered (the dwelling gets a tune-up instead). The
# gate is gas-only: a non-gas boiler → gas is a fuel switch whose value is not
# captured by winter efficiency alone, so it is never suppressed on efficiency.
_NEW_BOILER_WINTER_EFFICIENCY_PCT = 84.0


# --- 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(),
    considered_measures: Optional[frozenset[MeasureType]] = None,
) -> 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)

    boiler_option = _boiler_upgrade_option(epc, products)
    if boiler_option is not None:
        options.append(boiler_option)

    options.extend(_system_tune_up_options(epc, products, considered_measures))

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


def _system_tune_up_options(
    epc: EpcPropertyData,
    products: ProductRepository,
    considered_measures: Optional[frozenset[MeasureType]] = None,
) -> list[MeasureOption]:
    """The system tune-up options: keep the existing wet boiler but install
    better heating controls (standard 2106 and/or zone 2110, as competing
    options) and fix the cylinder (jacket when under-insulated, thermostat when
    absent). Each control option is offered only when it genuinely improves the
    existing controls — never a downgrade or a no-op (ADR-0024)."""
    main: MainHeatingDetail = epc.sap_heating.main_heating_details[0]
    if not _is_wet_boiler(main):
        return []
    control = main.main_heating_control
    control_code: Optional[int] = control if isinstance(control, int) else None

    options: list[MeasureOption] = []
    if control_code not in _STANDARD_OR_BETTER_CONTROL_CODES:
        options.append(
            _tune_up_option(
                epc,
                products,
                measure_type=_SYSTEM_TUNE_UP_MEASURE_TYPE,
                control=_STANDARD_CONTROL,
                description=(
                    "Tune up the heating: install a programmer, room thermostat "
                    "and TRVs and insulate and thermostat the hot-water cylinder"
                ),
            )
        )
    if control_code not in _ZONE_CONTROL_CODES and (
        considered_measures is None
        or _SYSTEM_TUNE_UP_ZONED_MEASURE_TYPE in considered_measures
    ):
        options.append(
            _tune_up_option(
                epc,
                products,
                measure_type=_SYSTEM_TUNE_UP_ZONED_MEASURE_TYPE,
                control=_ZONE_CONTROL,
                description=(
                    "Tune up the heating: install time-and-temperature zone "
                    "control and insulate and thermostat the hot-water cylinder"
                ),
            )
        )
    return options


def _tune_up_option(
    epc: EpcPropertyData,
    products: ProductRepository,
    *,
    measure_type: MeasureType,
    control: int,
    description: str,
) -> MeasureOption:
    """One tune-up Option: the existing boiler is kept; only the heating control
    and the conditional cylinder fixes change. Cost is composed per dwelling from
    those components (ADR-0027); the catalogue row is read for its id."""
    product = products.get(measure_type)
    cost: Cost = Products().tune_up_cost(
        tune_up_cost_inputs(epc, is_zoned=control == _ZONE_CONTROL)
    )
    return MeasureOption(
        measure_type=measure_type,
        description=description,
        overlay=EpcSimulation(heating=_tune_up_overlay(epc, control)),
        cost=cost,
        material_id=product.id,
    )


def _tune_up_overlay(epc: EpcPropertyData, control: int) -> HeatingOverlay:
    """Build a tune-up end-state: set the heating control to ``control`` and
    apply the conditional cylinder fixes (an 80 mm jacket when under-insulated, a
    thermostat when absent) — only when the dwelling has a cylinder. The boiler,
    fuel and meter are left unchanged (the boiler is kept)."""
    sap_heating = epc.sap_heating
    jacket_type: Optional[int] = None
    jacket_thickness_mm: Optional[int] = None
    thermostat: Optional[str] = None
    if epc.has_hot_water_cylinder:
        if _cylinder_under_insulated(sap_heating.cylinder_insulation_thickness_mm):
            jacket_type = _CYLINDER_JACKET_INSULATION_TYPE
            jacket_thickness_mm = _MIN_CYLINDER_INSULATION_MM
        if sap_heating.cylinder_thermostat != "Y":
            thermostat = "Y"
    return HeatingOverlay(
        main_heating_control=control,
        cylinder_insulation_type=jacket_type,
        cylinder_insulation_thickness_mm=jacket_thickness_mm,
        cylinder_thermostat=thermostat,
    )


def _boiler_upgrade_option(
    epc: EpcPropertyData, products: ProductRepository
) -> Optional[MeasureOption]:
    """The gas-condensing-boiler upgrade for a dwelling with an existing wet
    boiler: a combi (Table 4b code 104) where there is no cylinder, or a regular
    boiler (code 102) heating the existing cylinder where there is one. Both
    upgrade inadequate controls and the cylinder variant adds the conditional
    cylinder fixes (a jacket when under-insulated, a thermostat when absent). One
    Option per dwelling — a dwelling has a cylinder or it does not — offered only
    where a mains-gas connection makes the gas end-state installable (ADR-0024
    revised)."""
    if not _boiler_upgrade_eligible(epc):
        return None
    has_cylinder: bool = epc.has_hot_water_cylinder
    overlay: HeatingOverlay = (
        _boiler_cylinder_overlay(epc) if has_cylinder else _boiler_combi_overlay(epc)
    )
    description: str = (
        "Replace the boiler with a gas condensing boiler and insulate and "
        "thermostat the hot-water cylinder"
        if has_cylinder
        else "Replace the boiler with a gas condensing combi boiler"
    )
    # Cost is composed per dwelling from the boiler + the controls/cylinder
    # fixes the overlay installs (ADR-0027), not the flat catalogue scalar; the
    # catalogue row is still read for its id.
    product = products.get(_GAS_BOILER_UPGRADE_MEASURE_TYPE)
    cost: Cost = Products().boiler_bundle_cost(boiler_cost_inputs(epc))
    return MeasureOption(
        measure_type=_GAS_BOILER_UPGRADE_MEASURE_TYPE,
        description=description,
        overlay=EpcSimulation(heating=overlay),
        cost=cost,
        material_id=product.id,
    )


def _boiler_upgrade_eligible(epc: EpcPropertyData) -> bool:
    """Whether a dwelling's existing wet boiler can be upgraded to a gas
    condensing boiler. The gas end-state is installable only with a mains-gas
    connection, so gas dwellings always qualify and a non-gas wet boiler
    (oil/LPG/solid) qualifies only where mains gas is present. Electric boilers
    are left alone — electrification, not a gas swap, is their upgrade path. A
    gas boiler that already meets the new condensing efficiency is not re-offered
    a like-for-like swap (it gains nothing — the dwelling gets a tune-up
    instead); a non-gas boiler is a fuel switch, so it is never gated on
    efficiency."""
    main: MainHeatingDetail = epc.sap_heating.main_heating_details[0]
    if not _is_wet_boiler(main):
        return False
    if _is_electric_boiler(main):
        return False
    if not epc.sap_energy_source.gas_connection_available:
        return False
    if main.main_fuel_type in _GAS_FUEL_CODES and _already_condensing(main):
        return False
    return True


def _is_wet_boiler(main: MainHeatingDetail) -> bool:
    """Whether the main system is a wet boiler the tune-up / boiler-upgrade
    generators can evaluate. Identifies by the Table 4a/4b `sap_main_heating_code`
    when lodged; when it is absent, falls back to the gov-EPC-API lodgement shape
    (a PCDB Table 105 gas/oil boiler index, or an RdSAP `main_heating_category`
    of 1/2 "central heating") — the same fallback the calculator's
    `cert_to_inputs._is_wet_boiler_main` uses, so the generators evaluate the
    same population the calculator already models as wet boilers (#1388 A#2).
    Heat pumps (category 4) are never wet boilers."""
    if main.main_heating_category == _HEAT_PUMP_CATEGORY:
        return False
    code: Optional[int] = main.sap_main_heating_code
    if code is not None:
        return any(code in r for r in _WET_BOILER_SAP_CODE_RANGES)
    index: Optional[int] = main.main_heating_index_number
    if index is not None and gas_oil_boiler_record(index) is not None:
        return True
    return main.main_heating_category in _WET_BOILER_CATEGORIES


def _is_electric_boiler(main: MainHeatingDetail) -> bool:
    """Whether the wet boiler runs on electricity — the electrification path, not
    a gas swap, so it is excluded from the gas-boiler upgrade. Identified by the
    Table 4a electric-boiler code range when lodged, else by an electricity main
    fuel (the code range can't identify an electric boiler lodged with no SAP
    code)."""
    code: Optional[int] = main.sap_main_heating_code
    if code is not None:
        return code in _ELECTRIC_BOILER_SAP_CODE_RANGE
    return main.main_fuel_type in _ELECTRICITY_FUEL_CODES


def _already_condensing(main: MainHeatingDetail) -> bool:
    """Whether an existing gas boiler already meets the new condensing boiler's
    winter efficiency. Uses the SAP 10.2 Table 4b figure for the lodged
    `sap_main_heating_code`; when no code is lodged (the gov-EPC-API PCDB cohort),
    reads the boiler's declared winter efficiency from its PCDB Table 105 record
    instead. A boiler whose efficiency cannot be resolved (no Table 4b entry, no
    PCDB record) is not treated as already-condensing — the upgrade is offered."""
    code: Optional[int] = main.sap_main_heating_code
    if code is not None:
        efficiencies: Optional[tuple[float, float]] = (
            table_4b_seasonal_efficiencies_pct(code)
        )
        if efficiencies is None:
            return False
        return efficiencies[0] >= _NEW_BOILER_WINTER_EFFICIENCY_PCT
    index: Optional[int] = main.main_heating_index_number
    if index is not None:
        record = gas_oil_boiler_record(index)
        if record is not None and record.winter_efficiency_pct is not None:
            return record.winter_efficiency_pct >= _NEW_BOILER_WINTER_EFFICIENCY_PCT
    return False


def _boiler_combi_overlay(epc: EpcPropertyData) -> HeatingOverlay:
    """Build the per-dwelling combi end-state: a gas condensing combi (Table 4b
    code 104, fanned flue) on radiators with hot water from the boiler, plus a
    controls upgrade when the existing controls are inadequate. No cylinder, so
    no cylinder fields are touched."""
    main: MainHeatingDetail = epc.sap_heating.main_heating_details[0]
    return HeatingOverlay(
        main_fuel_type=_MAINS_GAS_FUEL,
        heat_emitter_type=_RADIATOR_EMITTER,
        sap_main_heating_code=_COMBI_GAS_BOILER_SAP_CODE,
        fan_flue_present=True,
        boiler_flue_type=_CONDENSING_BOILER_FLUE_TYPE,
        main_heating_control=_upgraded_boiler_control(main),
        water_heating_code=_WATER_FROM_MAIN_SYSTEM_CODE,
        water_heating_fuel=_MAINS_GAS_FUEL,
    )


def _boiler_cylinder_overlay(epc: EpcPropertyData) -> HeatingOverlay:
    """Build the per-dwelling boiler-with-cylinder end-state: a regular gas
    condensing boiler on radiators, hot water from the main system, a controls
    upgrade when the existing controls are inadequate, and the conditional
    cylinder fixes — an 80 mm jacket only when the cylinder is under-insulated, a
    thermostat only when one is absent. The existing cylinder size and meter are
    left unchanged."""
    sap_heating = epc.sap_heating
    main: MainHeatingDetail = sap_heating.main_heating_details[0]
    jacket_type: Optional[int] = None
    jacket_thickness_mm: Optional[int] = None
    if _cylinder_under_insulated(sap_heating.cylinder_insulation_thickness_mm):
        jacket_type = _CYLINDER_JACKET_INSULATION_TYPE
        jacket_thickness_mm = _MIN_CYLINDER_INSULATION_MM
    thermostat: Optional[str] = "Y" if sap_heating.cylinder_thermostat != "Y" else None
    return HeatingOverlay(
        main_fuel_type=_MAINS_GAS_FUEL,
        heat_emitter_type=_RADIATOR_EMITTER,
        sap_main_heating_code=_REGULAR_GAS_BOILER_SAP_CODE,
        fan_flue_present=True,
        boiler_flue_type=_CONDENSING_BOILER_FLUE_TYPE,
        main_heating_control=_upgraded_boiler_control(main),
        water_heating_code=_WATER_FROM_MAIN_SYSTEM_CODE,
        water_heating_fuel=_MAINS_GAS_FUEL,
        cylinder_insulation_type=jacket_type,
        cylinder_insulation_thickness_mm=jacket_thickness_mm,
        cylinder_thermostat=thermostat,
        has_hot_water_cylinder=True,
    )


def _cylinder_under_insulated(thickness_mm: Optional[int]) -> bool:
    """Whether a hot-water cylinder is below the 80 mm jacket end-state (an
    un-jacketed cylinder lodges no thickness)."""
    return thickness_mm is None or thickness_mm < _MIN_CYLINDER_INSULATION_MM


def _upgraded_boiler_control(main: MainHeatingDetail) -> Optional[int]:
    """The full-controls code (2106) when the existing boiler control is
    inadequate (lacks a room thermostat — SAP 10.2 Table 4e Group 1), else
    ``None`` to leave a room-thermostatted or better control unchanged. So the
    overlay only ever moves controls where it genuinely improves them."""
    control = main.main_heating_control
    code: Optional[int] = control if isinstance(control, int) else None
    if code is None and isinstance(control, str) and control.isdigit():
        code = int(control)
    if code in _INADEQUATE_BOILER_CONTROL_CODES:
        return _FULL_BOILER_CONTROL
    return None


# --- Boiler / tune-up cost interpretation (ADR-0027): read the dwelling into the
# typed inputs the catalogue math needs. The pricing itself lives on `Products`;
# this is the modelling-layer half that the catalogue stays free of. ---

# SAP 10.2 Table 4e Group 1 (PDF p.172) — which standard-control parts each
# boiler control code already provides: (has_programmer, has_room_thermostat,
# has_TRVs). Lets the standard-controls cost charge only the missing parts to
# reach 2106 (programmer + room thermostat + TRVs). Zone codes (2110/2112) are
# omitted — a standard upgrade is never offered to them.
_CONTROL_FEATURES_BY_CODE: dict[int, tuple[bool, bool, bool]] = {
    2101: (False, False, False),  # No time or thermostatic control
    2102: (True, False, False),  # Programmer, no room thermostat
    2103: (False, True, False),  # Room thermostat only
    2104: (True, True, False),  # Programmer and room thermostat
    2105: (True, True, False),  # Programmer and at least two room thermostats
    2106: (True, True, True),  # Programmer, room thermostat and TRVs
    2107: (True, False, True),  # Programmer, TRVs and bypass
    2108: (True, False, True),  # Programmer, TRVs and flow switch
    2109: (True, False, True),  # Programmer, TRVs and boiler energy manager
    2111: (False, False, True),  # TRVs and bypass
    2113: (False, True, True),  # Room thermostat and TRVs
}


def _control_features(main: MainHeatingDetail) -> tuple[bool, bool, bool]:
    """The standard-control parts a dwelling already has, from its SAP control
    code. An unrecognised/absent code defaults to none present (charge the full
    standard kit) — conservative, and the standard option is only offered when
    the control is improvable anyway."""
    control = main.main_heating_control
    code: Optional[int] = control if isinstance(control, int) else None
    return (
        _CONTROL_FEATURES_BY_CODE.get(code, (False, False, False))
        if (code is not None)
        else (False, False, False)
    )


def _cylinder_fix_needs(epc: EpcPropertyData) -> tuple[bool, bool]:
    """Whether the dwelling needs a cylinder jacket and/or a thermostat — the
    same predicates the overlay uses (only when a cylinder exists)."""
    if not epc.has_hot_water_cylinder:
        return (False, False)
    sap_heating = epc.sap_heating
    needs_jacket: bool = _cylinder_under_insulated(
        sap_heating.cylinder_insulation_thickness_mm
    )
    needs_thermostat: bool = sap_heating.cylinder_thermostat != "Y"
    return (needs_jacket, needs_thermostat)


def tune_up_cost_inputs(epc: EpcPropertyData, *, is_zoned: bool) -> TuneUpCostInputs:
    """Read a dwelling into the inputs `Products.tune_up_cost` needs: the control
    level, the radiator count (per-radiator items), the standard-control parts
    already fitted, and the cylinder fixes that apply (ADR-0027)."""
    main: MainHeatingDetail = epc.sap_heating.main_heating_details[0]
    has_programmer, has_room_thermostat, has_trvs = _control_features(main)
    needs_jacket, needs_thermostat = _cylinder_fix_needs(epc)
    return TuneUpCostInputs(
        is_zoned=is_zoned,
        radiator_count=_radiator_count(epc),
        has_programmer=has_programmer,
        has_room_thermostat=has_room_thermostat,
        has_trvs=has_trvs,
        needs_cylinder_jacket=needs_jacket,
        needs_cylinder_thermostat=needs_thermostat,
    )


def boiler_cost_inputs(epc: EpcPropertyData) -> BoilerCostInputs:
    """Read a dwelling into the inputs `Products.boiler_bundle_cost` needs: the
    boiler is always priced; controls are added only when the upgrade fires a
    controls change, and the cylinder fixes when applicable (ADR-0027)."""
    main: MainHeatingDetail = epc.sap_heating.main_heating_details[0]
    has_programmer, has_room_thermostat, has_trvs = _control_features(main)
    needs_jacket, needs_thermostat = _cylinder_fix_needs(epc)
    return BoilerCostInputs(
        upgrades_controls=_upgraded_boiler_control(main) is not None,
        radiator_count=_radiator_count(epc),
        has_programmer=has_programmer,
        has_room_thermostat=has_room_thermostat,
        has_trvs=has_trvs,
        needs_cylinder_jacket=needs_jacket,
        needs_cylinder_thermostat=needs_thermostat,
    )


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 read only for its id, so an
    # absent ASHP row must not suppress the bundle — it just carries no id.
    product: Optional[Product] = products.get_optional(_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 if product is not None else None,
    )


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. Community heating (SAP Table 4a codes
    301–304 or category 6) is excluded by topology: replacing a shared heat
    network with an individual ASHP is never appropriate."""
    main: MainHeatingDetail = epc.sap_heating.main_heating_details[0]
    if main.main_heating_category == _HEAT_PUMP_CATEGORY:
        return False
    if is_heat_network_main(main):
        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 a non-gas-fuel dwelling, unless it is already HHR or a
    heat pump.  Eligibility keys on the heating *fuel* (main_fuel_type not in
    _GAS_FUEL_CODES), not the gas-connection flag — a dwelling on a gas street
    with electric or oil heating has gas_connection_available=True but still
    qualifies. Community heating (SAP Table 4a codes 301–304 or category 6) is
    excluded by topology regardless of fuel: ripping out a shared heat network
    to install storage heaters is never appropriate."""
    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
    if is_heat_network_main(main):
        return False
    return main.main_fuel_type not in _GAS_FUEL_CODES