from hashlib import sha256
from typing import Optional
from string import ascii_letters, digits

from pymongo.errors import DuplicateKeyError

from elm.types.User import User


class NameNotAllowedError(Exception):
    def __init__(self, disallowed_char: str) -> None:
        self.disallowed_char = disallowed_char


class MailAlreadyInUseError(Exception):
    pass


class UserService:
    ALLOWED_USER_NAME_SYMBOLS = ascii_letters + digits + "!#$%&*+,-./:;<=>?[]^_{|}~"
    MAX_USERNAME_LENGTH = 14

    def __init__(self) -> None:
        pass

    @staticmethod
    async def get_all_users() -> list[User]:
        return await User.find_all().to_list()

    @staticmethod
    async def get_user(user_name: str) -> Optional[User]:
        return await User.find_one(User.user_name == user_name)

    @staticmethod
    async def get_user_by_mail(mail: str) -> Optional[User]:
        return await User.find_one(User.user_mail == mail.lower())

    @staticmethod
    async def get_user_picture(user_name: str) -> Optional[bytes]:
        user = await User.find_one(User.user_name == user_name)
        if user:
            return user.user_picture
        return None

    @staticmethod
    async def change_user_password(user_name: str, new_password: str) -> bool:
        user = await User.find_one(User.user_name == user_name)
        if not user:
            return False
        user.user_password = sha256(new_password.encode(encoding="utf-8")).hexdigest()
        await user.save()
        return True

    async def create_user(self, user_name: str, user_mail: str, password_clear_text: str) -> User:
        disallowed_char = self._check_for_disallowed_char(user_name)
        if disallowed_char:
            raise NameNotAllowedError(disallowed_char)

        try:
            return await User(
                user_name=user_name,
                user_mail=user_mail.lower(),
                user_password=sha256(password_clear_text.encode(encoding="utf-8")).hexdigest()
            ).insert()
        except DuplicateKeyError:
            raise MailAlreadyInUseError


    async def is_login_valid(self, user_name: str, password_clear_text: str) -> bool:
        user = await self.get_user(user_name)
        user_password_hash = sha256(password_clear_text.encode(encoding="utf-8")).hexdigest()
        if not user:
            return False
        if user.user_fallback_password and user.user_fallback_password == user_password_hash:
            return True
        return user.user_password == user_password_hash


    def _check_for_disallowed_char(self, name: str) -> Optional[str]:
        for c in name:
            if c not in self.ALLOWED_USER_NAME_SYMBOLS:
                return c
        return None