from __future__ import annotations

import base64
import hashlib
import hmac
import secrets


PBKDF2_ROUNDS = 210_000


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


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


def hash_secret(secret: str) -> str:
    salt = secrets.token_bytes(16)
    digest = hashlib.pbkdf2_hmac("sha256", secret.encode("utf-8"), salt, PBKDF2_ROUNDS)
    return f"pbkdf2_sha256${PBKDF2_ROUNDS}${_b64(salt)}${_b64(digest)}"


def verify_secret(secret: str, stored_hash: str) -> bool:
    try:
        algorithm, rounds_text, salt_text, digest_text = stored_hash.split("$", 3)
        if algorithm != "pbkdf2_sha256":
            return False
        rounds = int(rounds_text)
        salt = _unb64(salt_text)
        expected = _unb64(digest_text)
    except (ValueError, TypeError):
        return False
    actual = hashlib.pbkdf2_hmac("sha256", secret.encode("utf-8"), salt, rounds)
    return hmac.compare_digest(actual, expected)


def generate_api_key() -> str:
    return "rcg_" + secrets.token_urlsafe(32)


def key_prefix(secret: str) -> str:
    return secret[:12]


def generate_csrf_token() -> str:
    return secrets.token_urlsafe(24)