import os
from pathlib import Path
from typing import Dict, ItemsView, Iterator, KeysView, Mapping, Union, ValuesView

from ..logger import get_logger
from .parse_error import ParseError
from .pattern import pattern

ENVIRONMENT_VARIABLE_KEY_PREFIX = "ENV"

logger = get_logger("ConfigFile")


class ConfigFile(Mapping[str, str]):
    def __init__(self, path: Union[Path, str]) -> None:
        if not isinstance(path, Path):
            path = Path(path)

        if not path.exists():
            raise FileNotFoundError(path.absolute())

        self._path = path
        self._key_values: Dict[str, str] = {}

        self._parse()

    def _parse(self) -> None:
        with open(self._path, encoding="utf-8") as f:
            lines: str = f.read()

        matches = pattern.findall(lines)
        for key, *values in matches:
            try:
                value = next(v for v in values if v)
            except StopIteration:
                raise ParseError(
                    f"Cannot parse config file ({self._path.absolute()}), error at key `{key}`"
                )

            already_exists = key in self._key_values
            if already_exists and not value.startswith(
                f"{ENVIRONMENT_VARIABLE_KEY_PREFIX}:"
            ):
                raise KeyError(
                    f"Key `{key}` has been already defined and its value is `{self._key_values[key]}`"
                )

            if value.startswith(f"{ENVIRONMENT_VARIABLE_KEY_PREFIX}:"):
                _, value = value.split(":")
                if value not in os.environ:
                    issue = f'The value of `{key}` contains the "{ENVIRONMENT_VARIABLE_KEY_PREFIX}` prefix but `{value}` is not defined as an environment variable'
                    if already_exists:
                        logger.warning(
                            f"{issue}, using the default value defined above (`{self._key_values[key]}`)"
                        )
                        continue
                    else:
                        raise KeyError(
                            f"{issue} and no default value has been provided"
                        )
                else:
                    value = os.environ[value]

            self._key_values[key] = value

    def __getattr__(self, key: str) -> str:
        if key in self._key_values:
            return self._key_values[key]
        raise KeyError(
            f"Key `{key}` is not found in configuration file ({self._path.absolute()})"
        )

    __getitem__ = __getattr__

    def __iter__(self) -> Iterator[str]:
        return iter(self._key_values)

    def __len__(self) -> int:
        return len(self._key_values)

    def keys(self) -> KeysView[str]:
        return self._key_values.keys()

    def values(self) -> ValuesView[str]:
        return self._key_values.values()

    def items(self) -> ItemsView[str, str]:
        return self._key_values.items()

    def __repr__(self) -> str:
        return f"{type(self).__name__}(path={self._path}) {self._key_values}"