import os
import secrets
import string
from datetime import datetime, timedelta
from pathlib import Path

from defence360agent.subsys.panels.base import InvalidTokenException
from defence360agent.contracts.config import UIRole, UserType
from defence360agent.utils import atomic_rewrite

UIRoleToUserType = {
    UIRole.ADMIN: UserType.ROOT,
    UIRole.CLIENT: UserType.NON_ROOT,
}


class JWTIssuer:
    JWT_SECRET_FILE = Path("/var/imunify360/.api-secret.key")
    JWT_SECRET_FILE_PREV = Path("/var/imunify360/.api-secret-prev.key")
    JWT_TOKEN_EXPIRATION_TTL_HOURS = os.getenv(
        "I360_JWT_TOKEN_EXPIRATION_TTL_HOURS", 6
    )
    JWT_SECRET_EXPIRATION_TTL_HOURS = os.getenv(
        "I360_JWT_SECRET_EXPIRATION_TTL_HOURS", 24
    )
    TOKEN_EXPIRATION_TTL = timedelta(hours=int(JWT_TOKEN_EXPIRATION_TTL_HOURS))
    SECRET_EXPIRATION_TTL = timedelta(
        hours=int(JWT_SECRET_EXPIRATION_TTL_HOURS)
    )

    @classmethod
    def is_secret_expired(cls):
        try:
            stat = os.stat(cls.JWT_SECRET_FILE)
        except FileNotFoundError:
            st_mtime = 0.0
        else:
            st_mtime = stat.st_mtime
        return (
            datetime.now().timestamp() - st_mtime
            > cls.SECRET_EXPIRATION_TTL.seconds
        )

    @classmethod
    def _get_secret(cls) -> str:
        if cls.is_secret_expired():
            alphabet = string.ascii_uppercase + string.digits
            new_secret = "".join(secrets.choice(alphabet) for _ in range(64))
            if not cls.JWT_SECRET_FILE.exists():
                cls.JWT_SECRET_FILE.touch()
            atomic_rewrite(
                str(cls.JWT_SECRET_FILE),
                new_secret,
                backup=str(cls.JWT_SECRET_FILE_PREV),
                uid=-1,
                permissions=0o600,
            )
            return new_secret
        else:
            return cls.JWT_SECRET_FILE.read_text()

    @classmethod
    def get_token(cls, user_name: str, user_type: UIRole) -> str:
        """
        Generates a token with several encoded fields:
            user name,
            user type,
            expiration timestamp
        """

        import jwt

        return jwt.encode(
            {
                "user_type": user_type,
                "username": user_name,
                "exp": (datetime.now() + cls.TOKEN_EXPIRATION_TTL).timestamp(),
            },
            cls._get_secret(),
        )

    @classmethod
    def _parse_token(cls, token: str, secret: str) -> dict | None:
        import jwt

        # if handle these exceptions at global level,
        # jwt shoud be imported there,
        # increasing memory consumation
        try:
            return jwt.decode(token, secret, algorithms=["HS256"])
        except jwt.PyJWTError:
            pass

    @classmethod
    def parse_token(cls, token: str):
        for secret_pth in [cls.JWT_SECRET_FILE, cls.JWT_SECRET_FILE_PREV]:
            if not secret_pth.exists():
                continue
            decoded = cls._parse_token(token, secret_pth.read_text())
            if decoded:
                return {
                    "user_name": decoded["username"],
                    "user_type": UIRoleToUserType[decoded["user_type"]],
                }
        else:
            raise InvalidTokenException("INVALID_TOKEN")
