"""Copy data from a legacy combined data.db into the split databases.

The legacy database contained users, sensors and readouts in one file. Run the
new migrations first, then import the old rows:

    alembic upgrade head
    alembic -c alembic_users.ini upgrade head
    python migrate_legacy_db.py

The legacy file is only read; nothing is deleted from it.
"""

import argparse
from pathlib import Path

from sqlalchemy import MetaData, Table, create_engine, inspect, select
from sqlalchemy.dialects.sqlite import insert

from models import Sensor, SensorReadout
from user_models import User


def _sqlite_engine(path: Path):
    if not path.exists():
        raise SystemExit(f"database not found: {path}")
    return create_engine(f"sqlite:///{path}")


def _copy_table(source, destination, table) -> int:
    if table.name not in inspect(source).get_table_names():
        return 0

    source_table = Table(table.name, MetaData(), autoload_with=source)
    with source.connect() as conn:
        rows = [dict(row._mapping) for row in conn.execute(select(source_table))]
    if not rows:
        return 0

    with destination.begin() as conn:
        conn.execute(insert(table).on_conflict_do_nothing(), rows)
    return len(rows)


def main() -> None:
    parser = argparse.ArgumentParser(description=__doc__)
    parser.add_argument("--legacy", default="data.db", type=Path)
    parser.add_argument("--sensors", default="sensors.db", type=Path)
    parser.add_argument("--main-app", default="main_app.db", type=Path)
    args = parser.parse_args()

    legacy = _sqlite_engine(args.legacy)
    sensors = _sqlite_engine(args.sensors)
    main_app = _sqlite_engine(args.main_app)

    if not inspect(sensors).has_table(Sensor.__tablename__):
        raise SystemExit(f"{args.sensors} has no schema; run alembic upgrade head first")
    if not inspect(main_app).has_table(User.__tablename__):
        raise SystemExit(
            f"{args.main_app} has no schema; run alembic -c alembic_users.ini upgrade head first"
        )

    sensor_count = _copy_table(legacy, sensors, Sensor.__table__)
    readout_count = _copy_table(legacy, sensors, SensorReadout.__table__)
    user_count = _copy_table(legacy, main_app, User.__table__)

    print(
        f"Copied {sensor_count} sensors, {readout_count} readouts and "
        f"{user_count} users. The legacy database was not modified."
    )


if __name__ == "__main__":
    main()