"""Password hashing and opaque token helpers."""

from __future__ import annotations

import base64
import hashlib
import hmac
import secrets


def hash_password(password: str) -> str:
    salt = secrets.token_bytes(16)
    derived = hashlib.scrypt(password.encode("utf-8"), salt=salt, n=16384, r=8, p=1)
    return "scrypt$16384$8$1${}${}".format(
        base64.b64encode(salt).decode("ascii"),
        base64.b64encode(derived).decode("ascii"),
    )


def verify_password(password: str, encoded: str | None) -> bool:
    if not encoded:
        return False
    try:
        algorithm, n_value, r_value, p_value, salt_encoded, digest_encoded = encoded.split("$", maxsplit=5)
    except ValueError:
        return False
    if algorithm != "scrypt":
        return False
    salt = base64.b64decode(salt_encoded.encode("ascii"))
    expected = base64.b64decode(digest_encoded.encode("ascii"))
    actual = hashlib.scrypt(
        password.encode("utf-8"),
        salt=salt,
        n=int(n_value),
        r=int(r_value),
        p=int(p_value),
    )
    return hmac.compare_digest(actual, expected)


def generate_token() -> str:
    return secrets.token_urlsafe(32)


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


def token_prefix(token: str) -> str:
    return token[:8]


def mask_secret(value: str, *, prefix: int = 6, suffix: int = 4, mask_char: str = "*") -> str:
    text = (value or "").strip()
    if not text:
        return ""
    if len(text) <= prefix + suffix:
        return mask_char * len(text)
    hidden = len(text) - prefix - suffix
    return f"{text[:prefix]}{mask_char * hidden}{text[-suffix:]}"