"""The roof Recommendation Generator.

Dispatches the MAIN roof to its single applicable insulation Measure by roof
type (ADR-0021): a sloping ceiling (rafters, 100 mm), or — the fallback — a
loft / thatched / unlodged pitched roof (joists, 300 mm); a no-access roof gets
nothing. Each emits one "Roof" Recommendation whose Option carries the
insulation Simulation Overlay (raising `roof_insulation_thickness`) and a priced
Cost (roof area x the Product's fully-loaded unit cost, with its contingency).
Flat-roof and room-in-roof branches land in later slices. No scoring, no
persistence — impact is produced later by scoring (ADR-0016).
"""

from typing import Optional

from datatypes.epc.domain.epc_property_data import (
    BuildingPartIdentifier,
    EpcPropertyData,
)
from domain.building_geometry import roof_area
from domain.modelling.measure_type import MeasureType
from domain.modelling.recommendation import Cost, MeasureOption, Recommendation
from domain.modelling.simulation import BuildingPartOverlay, EpcSimulation
from repositories.product.product_repository import ProductRepository

_LOFT_MEASURE_TYPE = MeasureType.LOFT_INSULATION
_SLOPING_CEILING_MEASURE_TYPE = MeasureType.SLOPING_CEILING_INSULATION
# RdSAP 10 Table 16: 0 mm lodged roof insulation is an uninsulated loft. The
# Elmhurst mapper resolves "As Built" to 0 for pitched/sloping/loft roofs.
_ROOF_UNINSULATED_MM = 0
# Recommended loft-insulation depth (mm). Elmhurst re-lodges a loft-insulation
# measure at 300 mm; pinning the before→after cascade (000490/001431) requires
# the overlay to match that depth exactly (see test_elmhurst_cascade_pins).
_RECOMMENDED_LOFT_THICKNESS_MM = 300
# Recommended sloping-ceiling depth (mm); Elmhurst re-lodges 100 mm (ADR-0021).
_RECOMMENDED_SLOPING_CEILING_THICKNESS_MM = 100
_FLAT_ROOF_MEASURE_TYPE = MeasureType.FLAT_ROOF_INSULATION
# Recommended flat-roof depth (mm); Elmhurst re-lodges 200 mm (ADR-0021).
_RECOMMENDED_FLAT_ROOF_THICKNESS_MM = 200


def recommend_roof_insulation(
    epc: EpcPropertyData, products: ProductRepository
) -> Optional[Recommendation]:
    """Return the single roof-insulation Recommendation for the MAIN roof,
    dispatched by roof type (ADR-0021): a sloping ceiling is insulated at the
    rafters to 100 mm. Returns None when the roof type has no applicable measure
    or the roof is already insulated."""
    main = next(
        part
        for part in epc.sap_building_parts
        if part.identifier is BuildingPartIdentifier.MAIN
    )

    # Room-in-roof safety guard (ADR-0021): a room-in-roof carries its
    # insulation on its own sloping/stud/gable surfaces (RdSAP 10 §3.10, Table
    # 17/18), which the loft/sloping overlay's flat `roof_insulation_thickness`
    # bump cannot model. Without this guard a RR with an uninsulated loft would
    # fall through to the loft fallback and mis-recommend loft insulation.
    # Defer until a dedicated RR branch lands.
    if main.sap_room_in_roof is not None:
        return None

    roof_type: str = (main.roof_construction_type or "").lower()

    # Dispatch by roof type (ADR-0021). Order matters: a sloping ceiling is
    # tested before the loft fallback, and "no access" before it too, because
    # "no access to loft" contains "loft". Loft is the fallback — it covers a
    # plain pitched loft, a thatched roof (the covering doesn't block insulating
    # the loft floor), and an unlodged roof type (the modal UK case), matching
    # the pre-dispatcher behaviour of firing on `roof_insulation_thickness == 0`.
    if "sloping ceiling" in roof_type:
        if main.roof_insulation_thickness != _ROOF_UNINSULATED_MM:
            return None
        return _roof_recommendation(
            epc,
            products,
            measure_type=_SLOPING_CEILING_MEASURE_TYPE,
            description="Sloping-ceiling insulation (insulate at the rafters)",
            thickness_mm=_RECOMMENDED_SLOPING_CEILING_THICKNESS_MM,
        )

    if "flat" in roof_type:
        # A flat roof lodges no thickness when uninsulated ("As Built" → None
        # on the Elmhurst path); a lodged thickness means it's already done.
        if main.roof_insulation_thickness is not None:
            return None
        return _roof_recommendation(
            epc,
            products,
            measure_type=_FLAT_ROOF_MEASURE_TYPE,
            description="Flat-roof insulation",
            thickness_mm=_RECOMMENDED_FLAT_ROOF_THICKNESS_MM,
        )

    if "no access" in roof_type:
        return None  # the roof void can't be reached to insulate it

    if main.roof_insulation_thickness != _ROOF_UNINSULATED_MM:
        return None
    return _roof_recommendation(
        epc,
        products,
        measure_type=_LOFT_MEASURE_TYPE,
        description="Loft insulation (top up to recommended depth)",
        thickness_mm=_RECOMMENDED_LOFT_THICKNESS_MM,
    )


def _roof_recommendation(
    epc: EpcPropertyData,
    products: ProductRepository,
    *,
    measure_type: MeasureType,
    description: str,
    thickness_mm: int,
) -> Recommendation:
    """Build a single-Option "Roof" Recommendation: the measure's insulation
    overlay (raising `roof_insulation_thickness` to the recommended depth)
    priced at the roof area."""
    product = products.get(measure_type)
    area: float = roof_area(epc, BuildingPartIdentifier.MAIN)
    cost = Cost(
        total=area * product.unit_cost_per_m2,
        contingency_rate=product.contingency_rate,
    )
    option = MeasureOption(
        measure_type=measure_type,
        description=description,
        overlay=EpcSimulation(
            building_parts={
                BuildingPartIdentifier.MAIN: BuildingPartOverlay(
                    roof_insulation_thickness=thickness_mm
                )
            }
        ),
        cost=cost,
        material_id=product.id,
    )
    return Recommendation(surface="Roof", options=(option,))