"""Restore from the most recent 'pre_migration'-tagged backup."""
from __future__ import annotations

from pathlib import Path

from . import backup as backup_mod


class NoBackupFoundError(Exception):
    """Raised when rollback() is called with no pre_migration backup on disk."""


def rollback_to_pre_migration(*, db_url: str, images_root: Path) -> dict:
    manifest = backup_mod.find_latest_backup(images_root, tag="pre_migration")
    if manifest is None:
        raise NoBackupFoundError(
            "no pre_migration-tagged backup found under <images_root>/_backups/"
        )
    return backup_mod.restore_backup(
        manifest=manifest, db_url=db_url, images_root=images_root,
    )