"""Functions to get the parameters from the YAML files during the importing."""

import logging
import os
from os import path
import re

import yaml

logger = logging.getLogger(__name__)

YAML_ENVVAR_RGX = re.compile(r'^ENV\[(.*)\]$')


def _parse_envvar(token):
    """Parse a string containing an ENV variable.

    Args:
        token (str): String from the config file.
    Returns:
        str: Name of an environment variable.
    """
    return YAML_ENVVAR_RGX.match(token).groups()[0]


def _yaml_envvar_constructor(loader, node):
    """Get the variable value from the environment.

    Args:
        loader (Loader): An instance of a yaml.Loader class.
        node (ScalarNode): An instance of a node of a config.
    Returns:
        str: The value of an environment variable.
    """
    token = loader.construct_scalar(node)
    env_var = _parse_envvar(token)
    if env_var in os.environ:
        return os.environ[env_var]
    logger.warning('Undefined env var: {}'.format(env_var))
    return None


yaml.add_implicit_resolver('!env_var', YAML_ENVVAR_RGX)
yaml.add_constructor('!env_var', _yaml_envvar_constructor)


def getconf(name, ext='yml'):
    """Get the configuration parameters from the YAML stream.

    Args:
        name (str): A name of a file.
        ext (str): An extension of the file.
    Returns:
        dict: The values of a config.
    """
    filename = '.'.join((name, ext))
    logger.debug('loading config file %s', filename)
    basepath = path.dirname(__file__)
    with open(f'{basepath}/{filename}', 'r') as f:
        data = f.read()
    return yaml.full_load(data)