PecHub/backend/app/core/security.py

"""
Modulo sicurezza – cifratura AES-256-GCM, hashing password, JWT utilities.

ADR-002: Le credenziali IMAP/SMTP vengono cifrate con AES-256-GCM prima di
essere scritte in DB. La chiave è in variabile d'ambiente (ENCRYPTION_KEY).
Formato storage: base64(nonce_12byte || ciphertext || tag_16byte)
"""

import base64
import os
from datetime import UTC, datetime, timedelta
from typing import Any
from uuid import UUID

import bcrypt as _bcrypt
from cryptography.hazmat.primitives.ciphers.aead import AESGCM
from jose import JWTError, jwt

from app.config import get_settings

settings = get_settings()

# ─── Password hashing (bcrypt diretto, compatibile con bcrypt 4.x/5.x) ───────
_BCRYPT_ROUNDS = 12


def hash_password(password: str) -> str:
    """Genera hash bcrypt della password (work factor 12)."""
    pwd_bytes = password.encode("utf-8")
    salt = _bcrypt.gensalt(rounds=_BCRYPT_ROUNDS)
    return _bcrypt.hashpw(pwd_bytes, salt).decode("utf-8")


def verify_password(plain_password: str, hashed_password: str) -> bool:
    """Verifica password contro il suo hash."""
    try:
        return _bcrypt.checkpw(
            plain_password.encode("utf-8"),
            hashed_password.encode("utf-8"),
        )
    except Exception:
        return False


# ─── JWT ──────────────────────────────────────────────────────────────────────
def create_access_token(
    subject: str | UUID,
    tenant_id: str | UUID,
    role: str,
    extra_claims: dict[str, Any] | None = None,
) -> str:
    """
    Crea un JWT access token con scadenza configurabile.

    Claims standard:
      - sub: user_id (string)
      - tid: tenant_id
      - role: ruolo utente
      - exp: scadenza
      - iat: emesso a
    """
    now = datetime.now(UTC)
    expire = now + timedelta(minutes=settings.access_token_expire_minutes)

    payload: dict[str, Any] = {
        "sub": str(subject),
        "tid": str(tenant_id),
        "role": role,
        "iat": now,
        "exp": expire,
        "type": "access",
    }
    if extra_claims:
        payload.update(extra_claims)

    return jwt.encode(payload, settings.secret_key, algorithm=settings.algorithm)


def create_refresh_token(subject: str | UUID, tenant_id: str | UUID) -> str:
    """
    Crea un JWT refresh token con scadenza lunga (30 giorni default).
    Non contiene il ruolo – viene rivalutato a ogni refresh.
    """
    now = datetime.now(UTC)
    expire = now + timedelta(days=settings.refresh_token_expire_days)

    payload: dict[str, Any] = {
        "sub": str(subject),
        "tid": str(tenant_id),
        "iat": now,
        "exp": expire,
        "type": "refresh",
    }
    return jwt.encode(payload, settings.secret_key, algorithm=settings.algorithm)


def decode_token(token: str) -> dict[str, Any]:
    """
    Decodifica e valida un JWT token.
    Solleva JWTError se il token è invalido o scaduto.
    """
    return jwt.decode(token, settings.secret_key, algorithms=[settings.algorithm])


def is_token_valid(token: str, expected_type: str = "access") -> bool:
    """Verifica rapidamente la validità del token senza sollevare eccezioni."""
    try:
        payload = decode_token(token)
        return payload.get("type") == expected_type
    except JWTError:
        return False


# ─── AES-256-GCM cifratura credenziali (ADR-002) ─────────────────────────────
def encrypt_credential(plaintext: str) -> str:
    """
    Cifra una stringa con AES-256-GCM usando la chiave applicativa.

    Formato output: base64(nonce_12byte || ciphertext || tag_16byte)
    Il tag GCM (16 byte) è automaticamente concatenato al ciphertext da AESGCM.
    """
    key = settings.encryption_key_bytes
    aesgcm = AESGCM(key)
    nonce = os.urandom(12)  # 12 byte nonce raccomandato per GCM

    # AESGCM.encrypt() restituisce ciphertext + tag concatenati
    ciphertext_with_tag = aesgcm.encrypt(nonce, plaintext.encode("utf-8"), None)

    # Concatena nonce + ciphertext_with_tag e codifica in base64
    raw = nonce + ciphertext_with_tag
    return base64.b64encode(raw).decode("ascii")


def decrypt_credential(encrypted: str) -> str:
    """
    Decifra una stringa cifrata con encrypt_credential().
    Solleva ValueError se la decifratura fallisce (chiave errata o dati corrotti).
    """
    key = settings.encryption_key_bytes
    aesgcm = AESGCM(key)

    try:
        raw = base64.b64decode(encrypted.encode("ascii"))
        nonce = raw[:12]
        ciphertext_with_tag = raw[12:]
        plaintext_bytes = aesgcm.decrypt(nonce, ciphertext_with_tag, None)
        return plaintext_bytes.decode("utf-8")
    except Exception as e:
        raise ValueError(f"Decifratura fallita: {e}") from e


# ─── Hash sicuro per refresh token storage ────────────────────────────────────
import hashlib


def hash_token(token: str) -> str:
    """SHA-256 del token raw per storage sicuro in DB."""
    return hashlib.sha256(token.encode("utf-8")).hexdigest()