"""backend/api/vault.py — Encrypted token vault.

GAP-VAULT-CRYPTO (fix): sostituisce XOR-stream (two-time-pad) con Fernet (AES-128-CBC + HMAC-SHA256 + nonce univoco).
GAP-VAULT-AUTH   (fix): aggiunge _require_vault_auth (Bearer VAULT_ADMIN_TOKEN) su endpoint con accesso ai valori.
Backward-compat: _vault_decrypt tenta Fernet, poi fallback XOR per segreti già salvati (migrazione trasparente).
"""
import os, base64 as _b64, hashlib as _hashlib, hmac as _hmac_mod, json as _json_v, secrets as _secrets_mod, logging, time
from pathlib import Path as _Path
from typing import Optional

from fastapi import APIRouter, HTTPException, Request, Depends, Header
from pydantic import BaseModel

try:
    from cryptography.fernet import Fernet as _Fernet, InvalidToken as _InvalidToken
    _HAS_FERNET = True
except ImportError:
    _HAS_FERNET = False

router = APIRouter()
_vault_logger = logging.getLogger('agente_ai')

# ── Vault directory resolution ─────────────────────────────────────────────────
def _resolve_vault_dir() -> _Path:
    env_path = os.getenv('VAULT_DATA_DIR', '')
    if env_path:
        return _Path(env_path)
    for candidate in [_Path('/data/.vault_data'), _Path('/tmp/.vault_data')]:
        try:
            candidate.mkdir(parents=True, exist_ok=True)
            return candidate
        except (PermissionError, OSError):
            continue
    return _Path('/tmp/.vault_data')


_VAULT_DATA_DIR = _resolve_vault_dir()
try:
    _VAULT_DATA_DIR.mkdir(parents=True, exist_ok=True)
except (PermissionError, OSError) as _exc:
    _vault_logger.debug("[vault] silenced %s", type(_exc).__name__)

_VAULT_PATH = _Path(os.getenv('VAULT_PATH', str(_VAULT_DATA_DIR / 'vault_secrets.json')))

# ── Chiave vault ───────────────────────────────────────────────────────────────
_raw_vault_key = os.getenv('VAULT_KEY', '')
_VAULT_KEY_IS_PERSISTENT = bool(_raw_vault_key)
if not _raw_vault_key:
    _raw_vault_key = _secrets_mod.token_hex(32)
    _vault_logger.critical('BOOT: VAULT_KEY not set — vault usa chiave EPHEMERAL, tutti i secret vanno persi al restart!')
    _vault_logger.critical('BOOT: Fix → imposta VAULT_KEY in HF Spaces: Settings > Repository secrets')
    _vault_logger.critical('BOOT: Genera con: python3 -c "import secrets; print(secrets.token_hex(32))"')

_VAULT_KEY_RAW = _raw_vault_key.encode()
# Per Fernet: URL-safe base64 di SHA256(VAULT_KEY)
_FERNET_KEY = _b64.urlsafe_b64encode(_hashlib.sha256(_VAULT_KEY_RAW).digest())
_fernet_instance = _Fernet(_FERNET_KEY) if _HAS_FERNET else None
# Per fallback XOR (legacy decrypt): SHA256 digest grezzo
_VAULT_KEY_BYTES = _hashlib.sha256(_VAULT_KEY_RAW).digest()

if not _HAS_FERNET:
    _vault_logger.error('BOOT: cryptography non installata — Fernet non disponibile, uso XOR legacy (meno sicuro). Aggiungi cryptography>=42 a requirements.txt')


# ── GAP-VAULT-AUTH: autenticazione Bearer ─────────────────────────────────────
_VAULT_ADMIN_TOKEN = os.getenv('VAULT_ADMIN_TOKEN', '')

async def _require_vault_auth(authorization: Optional[str] = Header(None)) -> None:
    """Richiede Authorization: Bearer VAULT_ADMIN_TOKEN se configurato.

    Se VAULT_ADMIN_TOKEN non è impostato: nessuna protezione aggiuntiva (backward compat).
    Configura VAULT_ADMIN_TOKEN in HF Spaces secrets per abilitare l'autenticazione.
    Genera con: python3 -c "import secrets; print(secrets.token_hex(32))"
    """
    if not _VAULT_ADMIN_TOKEN:
        return  # Auth disabilitata — imposta VAULT_ADMIN_TOKEN per proteggere il vault
    if authorization != f'Bearer {_VAULT_ADMIN_TOKEN}':
        _vault_logger.warning('vault: unauthorized access attempt')
        raise HTTPException(status_code=401, detail='Vault: non autorizzato — Bearer token non valido o mancante')


# ── Crittografia: Fernet (AES-128-CBC + HMAC-SHA256 + nonce univoco) ───────────

def _vault_encrypt(plaintext: str) -> str:
    """GAP-VAULT-CRYPTO fix: Fernet con nonce casuale per ogni cifratura (niente two-time-pad)."""
    if _fernet_instance:
        return _fernet_instance.encrypt(plaintext.encode('utf-8')).decode('ascii')
    # Fallback XOR legacy se cryptography non installata
    return _vault_encrypt_xor(plaintext)


def _vault_decrypt(ciphertext: str) -> str:
    """Decrittografia con migrazione trasparente: tenta Fernet, poi XOR legacy."""
    if _fernet_instance:
        try:
            return _fernet_instance.decrypt(ciphertext.encode('ascii')).decode('utf-8')
        except Exception:
            pass  # Potrebbe essere un vecchio ciphertext XOR — prova fallback
    return _vault_decrypt_xor(ciphertext)


# ── XOR legacy (usato solo come fallback per migrazione segreti esistenti) ────

def _vault_encrypt_xor(plaintext: str) -> str:
    pt = plaintext.encode('utf-8')
    key_stream = b''
    i = 0
    while len(key_stream) < len(pt):
        key_stream += _hashlib.sha256(_VAULT_KEY_BYTES + i.to_bytes(4, 'big')).digest()
        i += 1
    ct = bytes(a ^ b for a, b in zip(pt, key_stream[:len(pt)]))
    sig = _hmac_mod.new(_VAULT_KEY_BYTES, ct, _hashlib.sha256).digest()
    return _b64.b64encode(sig + ct).decode()


def _vault_decrypt_xor(ciphertext: str) -> str:
    raw = _b64.b64decode(ciphertext)
    sig, ct = raw[:32], raw[32:]
    expected_sig = _hmac_mod.new(_VAULT_KEY_BYTES, ct, _hashlib.sha256).digest()
    if not _hmac_mod.compare_digest(sig, expected_sig):
        raise ValueError('VAULT: firma non valida — chiave errata o dati corrotti')
    key_stream = b''
    i = 0
    while len(key_stream) < len(ct):
        key_stream += _hashlib.sha256(_VAULT_KEY_BYTES + i.to_bytes(4, 'big')).digest()
        i += 1
    return bytes(a ^ b for a, b in zip(ct, key_stream[:len(ct)])).decode('utf-8')


# ── I/O ────────────────────────────────────────────────────────────────────────

def _vault_load() -> dict:
    try:
        return _json_v.loads(_VAULT_PATH.read_text()) if _VAULT_PATH.exists() else {}
    except Exception:
        return {}


def _vault_save_data(data: dict) -> None:
    _VAULT_PATH.write_text(_json_v.dumps(data, indent=2))


# ── Rate limiting ──────────────────────────────────────────────────────────────
_vault_rl: dict[str, list[float]] = {}
_VAULT_RL_LIMIT  = 30
_VAULT_RL_WINDOW = 60.0


def _vault_rate_check(request: Request) -> None:
    ip  = (request.client.host if request.client else None) or 'unknown'
    now = time.monotonic()
    hits = [t for t in _vault_rl.get(ip, []) if now - t < _VAULT_RL_WINDOW]
    if len(hits) >= _VAULT_RL_LIMIT:
        _vault_logger.warning('vault rate limit hit: ip=%s hits=%d', ip, len(hits))
        raise HTTPException(status_code=429, detail='Vault rate limit exceeded - max 30 req/min per IP')
    hits.append(now)
    _vault_rl[ip] = hits
    if len(_vault_rl) > 200:
        cutoff = now - _VAULT_RL_WINDOW
        stale = [k for k, v in list(_vault_rl.items()) if not v or v[-1] < cutoff]
        for k in stale:
            _vault_rl.pop(k, None)


class _VaultSaveRequest(BaseModel):
    key: str
    value: str
    description: str = ''


# ── Endpoints ──────────────────────────────────────────────────────────────────

@router.get('/api/vault/health')
async def vault_health():
    """Stato vault: chiave persistente o effimera, path, count. Pubblico (nessun valore esposto)."""
    data = _vault_load()
    warning = None if _VAULT_KEY_IS_PERSISTENT else (
        'VAULT_KEY non configurata: chiave effimera in uso. '
        'Tutti i segreti andranno PERSI al prossimo restart del container. '
        'Imposta VAULT_KEY nei secrets HF Spaces (Settings > Repository secrets).'
    )
    auth_warning = None if _VAULT_ADMIN_TOKEN else (
        'VAULT_ADMIN_TOKEN non configurato: endpoint vault accessibili senza autenticazione. '
        'Imposta VAULT_ADMIN_TOKEN nei secrets HF Spaces per proteggere i token.'
    )
    return {
        'persistent':    _VAULT_KEY_IS_PERSISTENT,
        'encryption':    'fernet' if _HAS_FERNET else 'xor-legacy',
        'vault_path':    str(_VAULT_PATH),
        'secrets_count': len(data),
        'warning':       warning,
        'auth_warning':  auth_warning,
    }


@router.get('/api/vault/status')
async def vault_status():
    """Lista chiavi (non valori). Pubblico: espone solo nomi, non segreti."""
    data = _vault_load()
    return {'keys': list(data.keys()), 'count': len(data)}


@router.post('/api/vault')
async def vault_save(
    req: _VaultSaveRequest,
    request: Request,
    _auth: None = Depends(_require_vault_auth),
):
    """Salva un segreto cifrato con Fernet. Richiede Bearer VAULT_ADMIN_TOKEN se configurato."""
    _vault_rate_check(request)
    key = req.key.lower().strip().replace(' ', '_')
    if not key or not req.value.strip():
        raise HTTPException(status_code=400, detail='key e value sono obbligatori')
    data = _vault_load()
    data[key] = _vault_encrypt(req.value.strip())
    _vault_save_data(data)
    _vault_logger.info('vault: saved key=%s enc=fernet', key)
    return {'ok': True, 'key': key, 'encrypted': True, 'encryption': 'fernet' if _HAS_FERNET else 'xor-legacy'}


@router.get('/api/vault/token/{key}')
async def vault_get_token(
    key: str,
    request: Request,
    _auth: None = Depends(_require_vault_auth),
):
    """Restituisce il valore decifrato. Richiede Bearer VAULT_ADMIN_TOKEN se configurato."""
    _vault_rate_check(request)
    data = _vault_load()
    if key not in data:
        raise HTTPException(status_code=404, detail=f"Chiave '{key}' non trovata nel vault")
    try:
        return {'key': key, 'value': _vault_decrypt(data[key])}
    except Exception as e:
        raise HTTPException(status_code=500, detail=f'Decryption error: {e}')


@router.delete('/api/vault/{key}')
async def vault_delete(
    key: str,
    request: Request,
    _auth: None = Depends(_require_vault_auth),
):
    """Elimina un segreto. Richiede Bearer VAULT_ADMIN_TOKEN se configurato."""
    _vault_rate_check(request)
    data = _vault_load()
    if key not in data:
        raise HTTPException(status_code=404, detail=f"Chiave '{key}' non trovata")
    del data[key]
    _vault_save_data(data)
    return {'ok': True, 'key': key, 'deleted': True}