from backend.app.db.connection import get_db_session
from backend.app.db.models.whlg import Whlg


def upsert_whlg_postcode(postcode: str):
    """
    Manually upsert a postcode into the WHLG table.
    No unique constraint is required.
    """

    cleaned = postcode.lower().replace(" ", "")

    with get_db_session() as session:
        # Check if record exists
        existing = session.query(Whlg).filter(Whlg.postcode == cleaned).first()

        if existing:
            return existing  # nothing to update, just return it

        # Insert a new row
        record = Whlg(postcode=cleaned)
        session.add(record)
        session.commit()
        session.refresh(record)

        return record


# One time script to upload 400,000 records in one go with the pay 
# of pandas and one insert 
from backend.app.db.connection import get_db_session
from backend.app.db.models.whlg import Whlg
from sqlalchemy import select
from sqlalchemy.orm import Session


def upload_whlg_from_dataframe(df):
    """
    FAST bulk insert of WHLG postcodes (400k+ rows).
    No unique constraint needed.
    """

    if "Postcode" not in df.columns:
        raise ValueError("DataFrame must contain a 'Postcode' column")

    # 1. Clean incoming postcodes
    cleaned_postcodes = (
        df["Postcode"]
        .astype(str)
        .str.lower()
        .str.replace(" ", "", regex=False)
        .dropna()
        .unique()
        .tolist()
    )

    with get_db_session() as session:
        # 2. Fetch existing postcodes once (VERY FAST)
        existing = session.exec(select(Whlg.postcode)).all()
        existing_set = set(existing)

        # 3. Determine which are new
        new_postcodes = [
            pc for pc in cleaned_postcodes if pc not in existing_set
        ]

        if not new_postcodes:
            return {"inserted": 0, "skipped_existing": len(cleaned_postcodes)}

        # 4. Bulk insert new postcodes in one shot
        objects = [Whlg(postcode=pc) for pc in new_postcodes]

        session.bulk_save_objects(objects)
        session.commit()

        return {
            "inserted": len(new_postcodes),
            "skipped_existing": len(cleaned_postcodes) - len(new_postcodes),
            "total_provided": len(cleaned_postcodes)
        }