"""Restricting a modelling run to a chosen set of measure types.

The allowlist a run "considers" — mirroring the legacy engine's `inclusions`
(`backend/app/plan/schemas.py`). It filters the candidate Recommendations at the
Option level so a multi-option Recommendation (e.g. Heating & Hot Water competing
HHRSH against an ASHP bundle) is kept with only its allowed Options; a
Recommendation left with no allowed Option is dropped. The Optimiser still
freely chooses among what survives — including choosing nothing.

A `None` allowlist means "consider every modelled measure" (the unrestricted
default).
"""

from __future__ import annotations

from collections.abc import Iterable
from typing import Optional

from domain.modelling.measure_type import MeasureType
from domain.modelling.recommendation import Recommendation


def combine_considered_measures(
    a: Optional[frozenset[MeasureType]],
    b: Optional[frozenset[MeasureType]],
) -> Optional[frozenset[MeasureType]]:
    """Intersect two allowlists, treating ``None`` as "all measures". Used to
    layer an explicit override over the allowlist a Scenario's exclusions imply:
    None ∧ x = x, and both present narrows to their intersection."""
    if a is None:
        return b
    if b is None:
        return a
    return a & b


def restrict_to_considered_measures(
    recommendations: Iterable[Recommendation],
    considered_measures: Optional[frozenset[MeasureType]],
) -> list[Recommendation]:
    """Keep only the Options whose measure type is in ``considered_measures``,
    dropping any Recommendation left with none. ``None`` keeps everything."""
    if considered_measures is None:
        return list(recommendations)
    restricted: list[Recommendation] = []
    for recommendation in recommendations:
        kept = tuple(
            option
            for option in recommendation.options
            if option.measure_type in considered_measures
        )
        if kept:
            restricted.append(
                Recommendation(surface=recommendation.surface, options=kept)
            )
    return restricted