"""Helper-e utilizatori web (email + parola scrypt). US-001 PRD 3.3.

Parola NICIODATA stocata in clar. Fiecare user are un salt per-user generat cu
secrets.token_bytes(16). Parametrii scrypt stocati ca eticheta de versiune pentru
migrare cost viitoare (C9).
"""

from __future__ import annotations

import hashlib
import hmac
import secrets
import sqlite3

SCRYPT_PARAMS = "n16384_r8_p1"
_N = 2**14
_R = 8
_P = 1
_DKLEN = 32
_MAXMEM = 64 * 1024 * 1024

_PASSWORD_MIN = 10
_PASSWORD_MAX = 128


def _parse_scrypt_params(label: str) -> tuple[int, int, int] | None:
    """Parseaza 'nN_rR_pP' -> (N, R, P). Returneaza None la format necunoscut/corupt."""
    try:
        parts = label.split("_")
        if len(parts) != 3 or parts[0][0] != "n" or parts[1][0] != "r" or parts[2][0] != "p":
            return None
        return (int(parts[0][1:]), int(parts[1][1:]), int(parts[2][1:]))
    except (ValueError, IndexError):
        return None


def _scrypt_hash(password: str, salt: bytes, n: int = _N, r: int = _R, p: int = _P) -> bytes:
    return hashlib.scrypt(
        password.encode("utf-8"),
        salt=salt,
        n=n,
        r=r,
        p=p,
        maxmem=_MAXMEM,
        dklen=_DKLEN,
    )


def create_user(conn: sqlite3.Connection, account_id: int, email: str, password: str) -> int:
    """Creeaza un user nou si intoarce id-ul.

    Valideaza ca: contul exista, parola intre 10 si 128 caractere, emailul nu e duplicat.
    Stocheaza DOAR hash scrypt + salt (hex), niciodata parola in clar.
    Email duplicat (case-insensitive, via UNIQUE COLLATE NOCASE) -> ValueError.
    """
    email = email.strip()

    acct = conn.execute("SELECT 1 FROM accounts WHERE id=?", (account_id,)).fetchone()
    if not acct:
        raise ValueError(f"cont inexistent: {account_id}")

    if len(password) < _PASSWORD_MIN:
        raise ValueError(f"parola prea scurta (minim {_PASSWORD_MIN} caractere)")
    if len(password) > _PASSWORD_MAX:
        raise ValueError(f"parola prea lunga (maxim {_PASSWORD_MAX} caractere, anti-DoS)")

    salt = secrets.token_bytes(16)
    pw_hash = _scrypt_hash(password, salt)

    try:
        cur = conn.execute(
            "INSERT INTO users (account_id, email, password_hash, salt, scrypt_params) "
            "VALUES (?, ?, ?, ?, ?)",
            (account_id, email, pw_hash.hex(), salt.hex(), SCRYPT_PARAMS),
        )
    except sqlite3.IntegrityError:
        raise ValueError("email deja folosit")

    return int(cur.lastrowid or 0)


def verify_password(conn: sqlite3.Connection, email: str, password: str) -> int | None:
    """Verifica parola pentru email. Intoarce account_id la potrivire, None altfel.

    Nu distinge intre email inexistent si parola gresita (evita enumerare useri).
    Comparatie constant-time cu hmac.compare_digest.
    """
    row = conn.execute(
        "SELECT account_id, password_hash, salt, scrypt_params FROM users "
        "WHERE email=? COLLATE NOCASE",
        (email.strip(),),
    ).fetchone()

    if row is None:
        # Executa un hash dummy pentru a evita timing oracle pe email inexistent
        _scrypt_hash(password, b"\x00" * 16)
        return None

    salt = bytes.fromhex(row["salt"])
    expected = bytes.fromhex(row["password_hash"])

    params = _parse_scrypt_params(row["scrypt_params"] or "")
    if params is None:
        return None
    n, r, p = params
    actual = _scrypt_hash(password, salt, n=n, r=r, p=p)

    if hmac.compare_digest(actual, expected):
        return int(row["account_id"])
    return None


def get_user_by_email(conn: sqlite3.Connection, email: str) -> dict | None:
    """Metadate user dupa email (FARA password_hash si salt)."""
    row = conn.execute(
        "SELECT id, account_id, email, is_admin, email_verified, created_at "
        "FROM users WHERE email=? COLLATE NOCASE",
        (email.strip(),),
    ).fetchone()
    return dict(row) if row else None