"""Field priority rules for canonical record merging.

When multiple sources provide conflicting values for the same field,
these dicts define which source to prefer (highest-priority first).

Algorithm reference: decisions/Cross_Source_Matching_Strategy.md sec 4.5
"""

from __future__ import annotations

from sqlalchemy.orm import Session

# Higher-priority source listed first.
# For each column, prefer the first source in the list that has a non-NULL value.

HOUSE_FIELD_PRIORITY: dict[str, list[str]] = {
    'year_built':     ['cian', 'avito_houses', 'rosreestr'],
    'address':        ['avito', 'cian', 'rosreestr'],
    'cadastral_number': ['rosreestr', 'cian', 'avito'],
    'building_class': ['cian', 'avito_houses'],
    'floors_count':   ['cian', 'avito_houses'],
    'series_name':    ['cian'],
    'entrances':      ['cian'],
    'flat_count':     ['cian'],
}

LISTING_FIELD_PRIORITY: dict[str, list[str]] = {
    # Price: always from latest-seen source wins among equal-priority sources.
    'price_rub':      ['avito', 'cian', 'yandex'],
    'area_m2':        ['rosreestr', 'cian', 'avito'],
    'living_area_m2': ['cian', 'avito'],
    'kitchen_area_m2': ['cian', 'avito'],
    'floor':          ['rosreestr', 'cian', 'avito'],
    'rooms':          ['rosreestr', 'cian', 'avito'],
    'ceiling_height': ['cian', 'avito'],
    'description':    ['avito', 'cian'],
    'phones':         ['avito', 'cian'],
    'photos':         ['avito', 'cian'],
    'cadastral_number': ['rosreestr', 'cian', 'avito'],
}


def update_canonical_fields(
    db: Session,
    listing_id: int,
    ext_source: str,
    lot_data: object,
) -> None:
    """Merge source fields into the canonical listings row.

    Stage 8 v1: populate-NULL strategy only — write source value only when
    the canonical column is currently NULL. Full priority arbitration with
    conflict logging is planned for Stage 8.x when ≥2 sources are live.

    Args:
        db:         Active SQLAlchemy session.
        listing_id: Canonical listings.id.
        ext_source: Source identifier (e.g. 'cian', 'avito').
        lot_data:   ScrapedLot or similar object with attribute access.
                    Unknown attributes are silently skipped.
    """
    raise NotImplementedError("Stage 8.x — full priority arbitration not yet implemented")