from datetime import datetime, timedelta, timezone
from sqlalchemy.orm import Session
from sqlalchemy.exc import SQLAlchemyError
from backend.app.db.models.epc import EpcStore


class EpcStoreService:
    """
    Service layer for EPC data lookup and persistence.
    """

    FRESHNESS_DAYS = 30

    # status labels
    FRESH = "fresh"
    EXPIRED = "expired"
    MISSING = "missing"

    @classmethod
    def get_epc_for_uprn(cls, session: Session, uprn: int):
        """
        Query EPC data for a given UPRN and return a dict describing:
        - epc_api: only if within last 30 days
        - epc_page: only if epc_api exists
        - status: 'fresh', 'expired', or 'missing'
        """

        record = session.query(EpcStore).filter(EpcStore.uprn == uprn).first()

        if not record:
            return {"status": cls.MISSING, "epc_api": None, "epc_page": None}

        if not record.epc_api_created_at:
            # API data missing → treat as missing even if page data exists
            return {"status": cls.MISSING, "epc_api": None, "epc_page": None}

        # check freshness
        cutoff = datetime.now(timezone.utc) - timedelta(days=EpcStoreService.FRESHNESS_DAYS)

        if record.epc_api_created_at.date() < cutoff.date():
            return {"status": cls.EXPIRED, "epc_api": None, "epc_page": None}

        # Fresh API → include page only if present
        return {
            "status": cls.FRESH,
            "epc_api": record.epc_api,
            "epc_page": record.epc_page if record.epc_page else None,
            "epc_page_rrn": record.epc_page_rrn,
            "epc_api_created_at": record.epc_api_created_at,
            "epc_page_created_at": record.epc_page_created_at,
        }

    @classmethod
    def check_insert_needed(cls, epc_cache, epc_estimated, uprn):
        """
        Check if an insert is needed based on existing data.
        :return:
        """
        no_existing_epc_cache = epc_cache.get("epc_api") is None
        existing_cache_expired = (
            epc_cache.get("status") == cls.EXPIRED
        )

        needs_insert = bool((no_existing_epc_cache or existing_cache_expired) and not epc_estimated and uprn)

        return needs_insert

    @staticmethod
    def upsert_epc_data(
        session: Session,
        uprn: int,
        epc_api: dict | None,
        epc_page: str | None,
        epc_page_rrn: str | None,
        epc_api_created_at: datetime | None = None,
        epc_page_created_at: datetime | None = None,
    ):
        """
        Insert or update EPC data for a UPRN.

        Rules:
        - If record exists → update it
        - If record does not exist → create new
        """

        try:
            record = session.query(EpcStore).filter(EpcStore.uprn == uprn).first()

            if record:
                # update path
                if epc_api is not None:
                    record.epc_api = epc_api
                    if epc_api_created_at is None:
                        epc_api_created_at = datetime.now(timezone.utc)
                    record.epc_api_created_at = epc_api_created_at

                # update page data only if BOTH:
                # 1) the caller passed page data
                # 2) epc_api is not None (page only allowed when API exists)
                if epc_page is not None and epc_api is not None:
                    record.epc_page = epc_page
                    record.epc_page_rrn = epc_page_rrn
                    if epc_page_created_at is None:
                        epc_page_created_at = datetime.now(timezone.utc)
                    record.epc_page_created_at = epc_page_created_at
            else:
                # insert path
                record = EpcStore(
                    uprn=uprn,
                    epc_api=epc_api,
                    epc_api_created_at=epc_api_created_at,
                    epc_page=epc_page if epc_api is not None else None,
                    epc_page_rrn=epc_page_rrn if epc_api is not None else None,
                    epc_page_created_at=epc_page_created_at if epc_api is not None else None,
                )
                session.add(record)

            session.flush()
            session.commit()

            return record

        except SQLAlchemyError as e:
            session.rollback()
            raise e