"""Import util functions."""

import importlib

from dim_refresh_etl import flows


class FlowImportError(Exception):
    """Flow class import error."""

    pass


def import_workflow_class(workflow_name):
    """Import workflow class by name.

    Args:
        workflow_name (str): Name of the imported flow. Namely one of
            the `flows` package.

    Returns:
        type: Imported flow class.

    Raises:
        FlowImportError: If flow module wasn't found or the module doesn't
            contain Flow class.

    """
    try:
        module = importlib.import_module(
            '.{}.flow'.format(workflow_name), flows.__name__)
        flow_class = module.Flow
        return flow_class
    except ImportError as e:
        raise FlowImportError(
            "{} flow wasn't imported. Error: {}".format(workflow_name, str(e)))
    except AttributeError:
        raise FlowImportError(
            "Implementation of {} flow wasn't found.".format(workflow_name))