from __future__ import annotations

import hashlib
import hmac
import re

from cryptography.fernet import Fernet

DEVICE_UA_RE = re.compile(r"^vpnapp/v(?P<major>\d+)\.(?P<minor>\d+)/(?P<device>[0-9a-fA-F-]{36})$")


class SecretBox:
    def __init__(self, key: str) -> None:
        self._fernet = Fernet(key.encode("ascii"))

    def seal(self, value: str) -> str:
        return self._fernet.encrypt(value.encode("utf-8")).decode("ascii")

    def open(self, value: str) -> str:
        return self._fernet.decrypt(value.encode("ascii")).decode("utf-8")


def token_hash(token: str) -> str:
    return hashlib.sha256(token.encode("utf-8")).hexdigest()


def token_matches(token: str, expected_hash: str) -> bool:
    return hmac.compare_digest(token_hash(token), expected_hash)


def parse_user_agent(user_agent: str) -> str | None:
    match = DEVICE_UA_RE.fullmatch(user_agent.strip())
    return match.group("device") if match else None