"""Password hashing helpers for lab users."""

from __future__ import annotations

import base64
import hashlib
import hmac
import secrets


def _b64(value: bytes) -> str:
    return base64.urlsafe_b64encode(value).rstrip(b"=").decode()


def _unb64(value: str) -> bytes:
    return base64.urlsafe_b64decode(value + "=" * (-len(value) % 4))


def hash_secret(secret: str, *, salt: bytes | None = None) -> str:
    actual_salt = salt or secrets.token_bytes(16)
    digest = hashlib.scrypt(secret.encode(), salt=actual_salt, n=2**14, r=8, p=1, dklen=32)
    return f"scrypt$16384$8$1${_b64(actual_salt)}${_b64(digest)}"


def verify_secret(secret: str, encoded: str) -> bool:
    try:
        algorithm, n, r, p, salt, expected = encoded.split("$")
        if algorithm != "scrypt":
            return False
        actual = hashlib.scrypt(
            secret.encode(), salt=_unb64(salt), n=int(n), r=int(r), p=int(p), dklen=32
        )
        return hmac.compare_digest(actual, _unb64(expected))
    except (ValueError, TypeError):
        return False