"""The ventilation Measure Dependency — a data-declared "fabric insulation
requires adequate ventilation" edge (CONTEXT.md: Measure Dependency; ADR-0016).

Wall insulation tightens the envelope, so SAP10.2 (and good practice) require
adequate ventilation alongside it. The optimiser must never *choose* ventilation
(it only ever costs SAP), so it is excluded from the candidate pool and instead
injected into the Optimised Package before the whole-package re-score, where its
real — negative — SAP contribution lands in the truthful figure and the repair
decision. The trigger set is held as data (mirroring the legacy
`assumptions.measures_needing_ventilation`), so extending it (e.g. to roof
insulation) is a data edit, not control flow.

This module owns only the **selection semantics** (the trigger set + the
forced-edge wrapping). **Production** — detecting that the dwelling needs
ventilation and pricing the work — is the ventilation Recommendation Generator's
job (`generators.ventilation_recommendation`), exactly like wall/roof/floor.
`ventilation_dependency` delegates to it and wraps its Recommendation into the
forced edge; the Recommendation is consumed here, never offered to the pool.
"""

from typing import Optional

from datatypes.epc.domain.epc_property_data import EpcPropertyData
from domain.modelling.generators.ventilation_recommendation import (
    recommend_ventilation,
)
from domain.modelling.optimisation.optimiser import MeasureDependency, ScoredOption
from domain.modelling.recommendation import MeasureOption, Recommendation
from repositories.product.product_repository import ProductRepository

# The measure types that force a ventilation dependency (cf. legacy
# `assumptions.measures_needing_ventilation`).
MEASURES_NEEDING_VENTILATION: frozenset[str] = frozenset(
    {
        "cavity_wall_insulation",
        "internal_wall_insulation",
        "external_wall_insulation",
    }
)


def ventilation_dependency(
    epc: EpcPropertyData, products: ProductRepository
) -> Optional[MeasureDependency]:
    """The ventilation Measure Dependency for a dwelling, or None when it needs
    no ventilation (already mechanically ventilated). Delegates production —
    detection + pricing — to the ventilation Recommendation Generator, then
    wraps its Recommendation into the forced "fabric requires ventilation"
    edge."""
    recommendation: Optional[Recommendation] = recommend_ventilation(epc, products)
    if recommendation is None:
        return None
    return MeasureDependency(
        triggers=MEASURES_NEEDING_VENTILATION,
        # Forced, never freely scored — the role-1 signal is irrelevant (0.0).
        required=ScoredOption(option=_required_option(recommendation), sap_gain=0.0),
    )


def _required_option(recommendation: Recommendation) -> MeasureOption:
    """Pick the Option the dependency forces in — the cheapest, mirroring the
    legacy "default to the cheapest ventilation unit". There is one MEV Option
    today; this readies the seam for MEV-c / MVHR alternatives."""
    return min(recommendation.options, key=_option_total)


def _option_total(option: MeasureOption) -> float:
    if option.cost is None:
        raise ValueError(
            f"ventilation option {option.measure_type!r} has no cost; cannot force in"
        )
    return option.cost.total