DefaultableConfigParser.py

from typing import Optional
from pathlib import Path
from configparser import ConfigParser  # type: ignore

DEFAULT_CONF_PATH = Path(__file__).parent / "default_conf.cfg"

CONFIG_FILE_NAME = "config_name.cfg"


class DefaultableConfigParser(ConfigParser):
    """Custom Configparser supporting defaults"""

    def __init__(self, default_config_path: str, *args, **kwargs):
        super().__init__(*args, **kwargs)

        self.default_config = ConfigParser(*args, **kwargs)
        if default_config_path is not None:
            self.default_config.read(default_config_path)

    def get(self, section, key, **kwargs):
        section = str(section).lower()
        key = str(key).lower()

        # TODO: support get from environment variable

        option = self._get_option_from_config_file(section, key, **kwargs)
        if option is not None:
            return option

        return self._get_option_from_default_config(section, key, **kwargs)

    def _get_option_from_config_file(self, section, key, **kwargs):
        if super().has_option(section, key):
            return super().get(section, key, **kwargs)

    def _get_option_from_default_config(self, section, key, **kwargs):
        if self.default_config.has_option(section, key):
            return self.default_config.get(section, key, **kwargs)

        raise ValueError(f"section/key [{section}/{key}] not found in config")


def _config_file_lookup() -> Optional[Path]:
    """
    first check: powertrain_runtime_config.cfg under $HOME
    then check: /etc/powertrain_runtime_config.cfg
    """
    under_home = Path(f"~/{CONFIG_FILE_NAME}").expanduser()
    if under_home.is_file():
        return under_home
    under_etc = Path(f"/etc/{CONFIG_FILE_NAME}")
    if under_etc.is_file():
        return under_etc

    return None


def initialize_config():
    """Load the config files."""
    conf = DefaultableConfigParser(default_config_path=DEFAULT_CONF_PATH)
    local_config_path = _config_file_lookup()
    if local_config_path:
        conf.read(local_config_path)
    return conf