from __future__ import annotations

import base64
import hashlib
import hmac
import os

_ALGORITHM = "pbkdf2_sha256"
_DEFAULT_ITERATIONS = 260_000
_SALT_BYTES = 16

# A valid, fixed-cost hash used when a login identity has no local password hash.
# Its plaintext value is intentionally irrelevant; the hash only keeps failed
# login attempts on the same verification path as existing local accounts.
DUMMY_PASSWORD_HASH = (
    "pbkdf2_sha256$260000$Z292b3BsYW4tZHVtbXktdjE="  # noqa: S105  # nosec B105 - non-account timing equalizer.
    "$uWgE7ht8wO6cotOqNKK2yNomPt57gstVss5ben5gTbw="
)


def hash_password(password: str, *, iterations: int = _DEFAULT_ITERATIONS) -> str:
    salt = os.urandom(_SALT_BYTES)
    digest = hashlib.pbkdf2_hmac("sha256", password.encode("utf-8"), salt, iterations)
    return "$".join(
        [
            _ALGORITHM,
            str(iterations),
            base64.b64encode(salt).decode("ascii"),
            base64.b64encode(digest).decode("ascii"),
        ]
    )


def verify_password(password: str, encoded: str | None) -> bool:
    if not encoded:
        return False
    try:
        algorithm, iterations_text, salt_b64, digest_b64 = encoded.split("$", 3)
        if algorithm != _ALGORITHM:
            return False
        iterations = int(iterations_text)
        salt = base64.b64decode(salt_b64.encode("ascii"))
        expected = base64.b64decode(digest_b64.encode("ascii"))
    except Exception:
        return False
    actual = hashlib.pbkdf2_hmac("sha256", password.encode("utf-8"), salt, iterations)
    return hmac.compare_digest(actual, expected)