"""An implementation of a slightly advanced key=value configuration file.
Commentary lines are started with # symbol.
Keys and values are separated by ' = ' (spaces are necessary).
Keys with . symbol are splited and right part is a nested dictionary.
Example:
    # A commentary line
    default_something = 10
    currency.RUB = ...
Above example is translated as a following dictionary:
    { "default_something": 10, "currency": { "RUB": "..." } }
"""

from os import getenv
from os.path import exists, join
from platform import system
from typing import Union

__all__ = ["Configuration", "get_configuration_path",
           "DEFAULT_CONFIGURATION_FILE"]


def get_configuration_path() -> str:
    """Returns a path to where configuration is stored."""
    if system() == "Linux":
        return getenv("XDG_CONFIG_HOME") or f"{getenv('HOME')}/.config"
    elif system() == "Windows":
        return getenv("APPDATA")


DEFAULT_CONFIGURATION_FILE_CONTENT = \
"""# A default currency's ISO code.
default-currency = SRUB

# A set of predefined currencies.
# Format is following:
# <ISO>;<CURRENCY NAME>;<COINS COUNT>;{}<FRACTION SYMBOL>,{}<CURRENCY SYMBOL>;<FACE VALUES>
# "{}" is used as a placeholder for where to put digits.
currency.RUB = RUB;Russian ruble;8;{} коп.,{}₽;1,5,10,50,100,200,500,1000
currency.SRUB = SRUB;Russian ruble;6;{} коп.,{}₽;10,50,100,200,500,1000
currency.BYN = BYN;Belarusian ruble;8;{} коп.,{}р.;1,2,5,10,20,50,100,200
currency.UAH = UAH;Ukrainian hryvnia;10;{} коп.,₴{};1,2,5,10,25,50,100,200,500,1000
currency.USD = USD;US Dollar;6;{}¢,${};1,5,10,25,50,100
currency.EUR = EUR;Euro;8;{}c,{}€;1,2,5,10,20,50,100,200
currency.GBP = GBP;Pound sterling;9;{}p,£{};1,2,5,10,20,25,50,100,200
"""

DEFAULT_CONFIGURATION_FILE = join(get_configuration_path(), "piggybank.conf")


class Configuration:
    def __init__(self, configuration_file: str = DEFAULT_CONFIGURATION_FILE) -> None:
        self._configuration_file = configuration_file
        self._configuration = dict()
        if exists(self._configuration_file):
            self.load()
        else:
            raise FileNotFoundError()

    def load(self) -> None:
        for line in open(self._configuration_file, 'r', encoding='utf8'):
            if line[0] in ['#', '\n']:
                continue
            key, value = line[:-1].split(" = ")
            if key.find(".") != -1:
                k0, k1 = key.split(".")
                if not k0 in self._configuration:
                    self._configuration[k0] = dict()
                self._configuration[k0][k1] = value
            else:
                self._configuration[key] = value

    @staticmethod
    def write_default_to_file(self, path: str = DEFAULT_CONFIGURATION_FILE) -> None:
        """Writes default configuration to a file. Overrides existing."""
        with open(path, 'w', encoding='utf8') as cf:
            cf.write(DEFAULT_CONFIGURATION_FILE_CONTENT)

    @property
    def items(self) -> dict:
        return self._configuration

    def __getitem__(self, key: str) -> Union[int, str, bool]:
        return self._configuration[key]

    def __setitem__(self, key: str, value: Union[int, str, bool]) -> None:
        self._configuration[key] = value