"""The Simulation Overlay (`EpcSimulation`) — the change a single Measure
Option makes to a Property's EpcPropertyData.

An all-optional partial mirror of EpcPropertyData / SapBuildingPart, covering
the retrofit-relevant surface only (wall fields first). It is *not* an
EpcPropertyData — composition, not inheritance — and carries no scores.
Building parts are targeted by `BuildingPartIdentifier` so a measure addresses
the exact `SapBuildingPart` (the main wall vs an extension). See CONTEXT.md.
"""

from dataclasses import dataclass, field
from typing import Mapping, Optional

from datatypes.epc.domain.epc_property_data import BuildingPartIdentifier


@dataclass(frozen=True)
class BuildingPartOverlay:
    """All-optional partial of `SapBuildingPart` (wall surface first).

    A `None` field means "leave the baseline value unchanged".
    """

    wall_insulation_type: Optional[int] = None
    roof_insulation_thickness: Optional[int] = None
    floor_insulation_thickness: Optional[int] = None
    floor_insulation_type_str: Optional[str] = None


def _no_building_parts() -> dict[BuildingPartIdentifier, BuildingPartOverlay]:
    return {}


@dataclass(frozen=True)
class EpcSimulation:
    """A Simulation Overlay: the per-building-part changes a Measure Option
    makes, keyed by `BuildingPartIdentifier`."""

    building_parts: Mapping[BuildingPartIdentifier, BuildingPartOverlay] = field(
        default_factory=_no_building_parts
    )