"""Envelope heat-loss (W/K) summed across all building parts.

Computes Sigma(U * A) + y * A_exposed over the main dwelling and every
extension on a cert.  U-values come from the cascade-defaulting helpers in
`rdsap_uvalues`; geometry is read off `sap_building_parts` + the cert's
pre-aggregated window area and door count.

Used by `transform.py` to populate the `envelope_heat_loss_w_per_k` feature
in v16.x.  See ADR-0008 for the physics-as-feature rationale.
"""

from __future__ import annotations

from typing import Any, Optional

from datatypes.epc.domain.epc_property_data import SapBuildingPart

from domain.sap10_ml.rdsap_uvalues import (
    Country,
    WALL_CAVITY,
    WALL_UNKNOWN,
    thermal_bridging_y,
    u_door,
    u_floor,
    u_party_wall,
    u_roof,
    u_wall,
    u_window,
)


# SAP10 wall_insulation_type code 4 ("None") marks no insulation declared.
_WALL_INSULATION_NONE: int = 4

# Standard SAP10 external door area (m^2) when door dimensions aren't given.
_DEFAULT_DOOR_AREA_M2: float = 1.85


def _int_or_none(value: Any) -> Optional[int]:
    return value if isinstance(value, int) else None


def _parse_thickness_mm(value: Any) -> Optional[int]:
    if value is None:
        return None
    if isinstance(value, int):
        return value
    if not isinstance(value, str):
        return None
    s = value.strip()
    if s.upper() == "NI":
        return 0
    digits = ""
    for c in s:
        if c.isdigit():
            digits += c
        else:
            break
    return int(digits) if digits else None


def _part_geometry(part: SapBuildingPart) -> dict[str, float]:
    """Sum floor area / heat-loss perimeter / party-wall length / room heights
    across the floor dimensions in a building part."""
    if not part.sap_floor_dimensions:
        return {
            "ground_floor_area_m2": 0.0,
            "ground_perimeter_m": 0.0,
            "top_floor_area_m2": 0.0,
            "total_perimeter_m": 0.0,
            "party_wall_length_m": 0.0,
            "avg_room_height_m": 2.5,
            "storey_count": 1.0,
        }
    fds = list(part.sap_floor_dimensions)
    # Ground floor = floor == 0 if present, else the first entry.
    ground = next((fd for fd in fds if fd.floor == 0), fds[0])
    # Top floor = floor with the largest non-None index, else the last entry.
    indexed = [(fd.floor if fd.floor is not None else 0, fd) for fd in fds]
    top = max(indexed, key=lambda kv: kv[0])[1]
    total_area = sum(fd.total_floor_area_m2 or 0.0 for fd in fds)
    total_perimeter = sum(fd.heat_loss_perimeter_m or 0.0 for fd in fds)
    party_length = sum(fd.party_wall_length_m or 0.0 for fd in fds)
    weighted_height = sum(
        (fd.total_floor_area_m2 or 0.0) * (fd.room_height_m or 2.5) for fd in fds
    )
    avg_height = (weighted_height / total_area) if total_area > 0 else 2.5
    return {
        "ground_floor_area_m2": ground.total_floor_area_m2 or 0.0,
        "ground_perimeter_m": ground.heat_loss_perimeter_m or 0.0,
        "top_floor_area_m2": top.total_floor_area_m2 or 0.0,
        "total_perimeter_m": total_perimeter,
        "party_wall_length_m": party_length,
        "avg_room_height_m": avg_height,
        "storey_count": float(len(fds)),
    }


def _part_heat_loss_w_per_k(
    part: SapBuildingPart,
    country: Country,
    window_area_m2: float,
    door_area_m2: float,
    window_u_value: float,
    door_u_value: float,
    roof_description: Optional[str] = None,
    wall_description: Optional[str] = None,
) -> float:
    """Heat loss coefficient (W/K) for a single building part: walls + roof +
    floor + party walls + windows + doors + thermal bridging.

    The aggregate-level caller (`envelope_heat_loss_w_per_k`) apportions windows
    and doors to whichever part it considers primary (currently the first part);
    other parts pass 0 for the window/door area.
    """
    geom = _part_geometry(part)

    age_band = part.construction_age_band
    wall_construction = _int_or_none(part.wall_construction)
    wall_ins_type = _int_or_none(part.wall_insulation_type)
    wall_ins_thickness = _parse_thickness_mm(part.wall_insulation_thickness)
    wall_ins_present = wall_ins_type is not None and wall_ins_type != _WALL_INSULATION_NONE
    party_construction = _int_or_none(part.party_wall_construction)
    roof_thickness = _parse_thickness_mm(getattr(part, "roof_insulation_thickness", None))
    floor_ins_thickness = _parse_thickness_mm(getattr(part, "floor_insulation_thickness", None))

    # Floor — pick the ground-floor's floor_dimension for the BS EN ISO 13370
    # area/perimeter inputs.
    ground_fd = next(
        (fd for fd in part.sap_floor_dimensions if fd.floor == 0),
        part.sap_floor_dimensions[0] if part.sap_floor_dimensions else None,
    )
    floor_area = ground_fd.total_floor_area_m2 if ground_fd is not None else None
    floor_perimeter = ground_fd.heat_loss_perimeter_m if ground_fd is not None else None
    floor_construction = (
        _int_or_none(ground_fd.floor_construction) if ground_fd is not None else None
    )

    uw = u_wall(
        country=country,
        age_band=age_band,
        construction=wall_construction if wall_construction != WALL_UNKNOWN else None,
        insulation_thickness_mm=wall_ins_thickness,
        insulation_present=wall_ins_present,
        description=wall_description,
    )
    ur = u_roof(
        country=country,
        age_band=age_band,
        insulation_thickness_mm=roof_thickness,
        description=roof_description,
    )
    uf = u_floor(
        country=country,
        age_band=age_band,
        construction=floor_construction,
        insulation_thickness_mm=floor_ins_thickness,
        area_m2=floor_area,
        perimeter_m=floor_perimeter,
        wall_thickness_mm=part.wall_thickness_mm,
    )
    upw = u_party_wall(party_wall_construction=party_construction)
    y = thermal_bridging_y(age_band=age_band)

    # Areas.
    storey_count = geom["storey_count"]
    storey_height = geom["avg_room_height_m"]
    # SAP10.2 wall area: gross exposed perimeter * storey height * storey count
    # minus openings.  Heat-loss perimeter (heat_loss_perimeter_m on each floor
    # dimension) already excludes party walls.
    gross_wall_area = geom["ground_perimeter_m"] * storey_height * storey_count
    net_wall_area = max(0.0, gross_wall_area - window_area_m2 - door_area_m2)
    party_area = geom["party_wall_length_m"] * storey_height * storey_count
    roof_area = geom["top_floor_area_m2"]
    floor_area_total = geom["ground_floor_area_m2"]

    conduction = (
        uw * net_wall_area
        + upw * party_area
        + ur * roof_area
        + uf * floor_area_total
        + window_u_value * window_area_m2
        + door_u_value * door_area_m2
    )
    bridging_area = net_wall_area + party_area + roof_area + floor_area_total + window_area_m2 + door_area_m2
    return conduction + y * bridging_area


def envelope_heat_loss_w_per_k(
    sap_building_parts: list[SapBuildingPart],
    *,
    country_code: Optional[str],
    window_total_area_m2: float,
    window_avg_u_value: Optional[float],
    door_count: int,
    insulated_door_count: int,
    insulated_door_u_value: Optional[float],
    age_band_for_door: Optional[str] = None,
    roof_description: Optional[str] = None,
    wall_description: Optional[str] = None,
) -> float:
    """Total envelope heat-loss coefficient (W/K) summed over all building parts.

    Windows and doors are apportioned entirely to the first part (the main
    dwelling) per RdSAP10 convention -- the cert's window list is not split
    across extensions.  All U-values cascade through `rdsap_uvalues` defaults,
    so the return is never null.

    `roof_description` carries the worst-case surveyor description across the
    top-level `roofs[i]` list (e.g. "Pitched, no insulation"). When the cert
    flags a roof as uninsulated, u_roof returns Table 16 0mm/12mm values
    instead of the optimistic Table 18 age-band default -- catastrophic
    heritage roofs need that correction.
    """
    if not sap_building_parts:
        return 0.0
    country = Country.from_code(country_code)
    door_area = max(0, door_count) * _DEFAULT_DOOR_AREA_M2
    if window_avg_u_value is None or window_avg_u_value <= 0:
        window_u = u_window(installed_year=None, glazing_type=None, frame_type=None)
    else:
        window_u = window_avg_u_value
    # Door U: blend insulated/uninsulated by share.
    door_uninsulated = u_door(
        country=country,
        age_band=age_band_for_door or sap_building_parts[0].construction_age_band,
        insulated=False,
        insulated_u_value=None,
    )
    door_insulated = (
        insulated_door_u_value
        if insulated_door_u_value is not None
        else u_door(country=country, age_band="M", insulated=True, insulated_u_value=None)
    )
    insulated_share = (insulated_door_count or 0) / door_count if door_count > 0 else 0.0
    door_u = (1.0 - insulated_share) * door_uninsulated + insulated_share * door_insulated

    total = 0.0
    for i, part in enumerate(sap_building_parts):
        # Windows and doors only on the first (main) part.
        w_area = window_total_area_m2 if i == 0 else 0.0
        d_area = door_area if i == 0 else 0.0
        total += _part_heat_loss_w_per_k(
            part=part,
            country=country,
            window_area_m2=w_area,
            door_area_m2=d_area,
            window_u_value=window_u,
            door_u_value=door_u,
            roof_description=roof_description,
            wall_description=wall_description,
        )
    return total