from abc import ABCMeta, abstractmethod
from typing import Type, Optional

import yaml

from kissconfig.config import ConfigClass


class EmptyConfig (ValueError):
    pass


class Loader (metaclass=ABCMeta):
    def __init__(self, namespace: Optional[str] = None):
        self.namespace = namespace

    @abstractmethod
    def parse_file(self, path: str) -> dict:
        pass

    def from_file(self, config_class: Type[ConfigClass], path: str) -> ConfigClass:
        data = self.parse_file(path)
        if not data:
            raise EmptyConfig("Configuration file seems to be empty")
        if self.namespace is not None:
            data = data.get(self.namespace, {})
        return config_class.from_dict(data)


class YamlLoader (Loader):
    def parse_file(self, path: str) -> dict:
        with open(path) as f:
            return yaml.safe_load(f)