"""Product — a catalogue entry a Measure Option installs.

Carries the data needed to price an Option: a fully-loaded unit cost and the
per-Measure-Type contingency rate carried alongside it (CONTEXT.md). The
catalogue is equipment-dominated (heat pumps, glazing, PV) — hence "Product",
not "material". Read via a `ProductRepository`.
"""

from dataclasses import dataclass
from typing import Optional


@dataclass(frozen=True)
class Product:
    measure_type: str
    unit_cost_per_m2: float
    contingency_rate: float
    # The catalogue row id, threaded onto the persisted Plan Measure as
    # ``recommendation.material_id`` (the single-material reference that replaces
    # the retired ``recommendation_materials`` BOM). Optional: the JSON
    # stopgap catalogue carries no ids.
    id: Optional[int] = None