from typing import Any, TypeVar, Callable


class ParseError(Exception):
    """An error for when parsing a config fails"""

    def __init__(self, keypath: list[str], issue: str):
        path = '.'.join(keypath)
        message = f'{path}: {issue}'
        super().__init__(message)
        self.keypath = keypath
        self.issue = issue


def assert_key_of_type(config: dict[str, Any], key: str, kind: Any):
    if key not in config:
        raise ParseError([key], 'missing')

    if not isinstance(config[key], kind):
        raise ParseError([key], f'type of "{key}" was {type(config[key])}, expected {kind}')


T = TypeVar('T')


def parse_nested_config(config: dict[str, Any], key: str, parse: Callable[[dict[str, Any]], T]) -> T:
    assert_key_of_type(config, key, dict)
    try:
        return parse(config[key])
    except ParseError as e:
        raise ParseError([key, *e.keypath], e.issue)