import json
import pathlib
import typing


def parse_index(data_dir: pathlib.Path, db_type: str) -> typing.Dict[str, pathlib.Path]:
    try:
        index_file = data_dir / db_type / "index.json"
        with index_file.open("rt") as index:
            index_data = json.load(index)
    except Exception as e:
        raise Exception(f"Failed to read {db_type} index file: {e}")
    return {
        code: data_dir.joinpath(db_type, bfile) for code, bfile in index_data.items()
    }


class DbIndex:
    def __init__(self, data_dir: pathlib.Path, db_type: str) -> None:
        self.data_dir = data_dir
        self.db_type = db_type
        self.source_index = parse_index(self.data_dir, self.db_type)

    def validate(self) -> None:
        if not self.source_index:
            raise Exception(
                f"DB for {self.db_type} appears empty in data_dir{self.data_dir}"
            )