import hashlib
import os
import uuid
from datetime import datetime, timedelta, timezone
from typing import Optional

from fastapi import Depends, Header, HTTPException, status
from fastapi.security import OAuth2PasswordBearer
from jose import JWTError, jwt
from passlib.context import CryptContext

from bd import make_engine

SECRET_KEY: str = os.getenv("SECRET_KEY", "")
if not SECRET_KEY:
    import secrets
    SECRET_KEY = secrets.token_hex(32)
    print("WARNING: SECRET_KEY not set in environment. Using a random key — tokens will be invalidated on restart!")

ALGORITHM = "HS256"
ACCESS_TOKEN_EXPIRE_MINUTES = int(os.getenv("ACCESS_TOKEN_EXPIRE_MINUTES", "60"))

pwd_context = CryptContext(schemes=["bcrypt"], deprecated="auto")
oauth2_scheme = OAuth2PasswordBearer(tokenUrl="/auth/login")


def _prehash(password: str) -> str:
    """SHA-256 пред-хеш чтобы обойти 72-байтовый лимит bcrypt."""
    return hashlib.sha256(password.encode()).hexdigest()


def hash_password(password: str) -> str:
    return pwd_context.hash(_prehash(password))


def verify_password(plain: str, hashed: str) -> bool:
    return pwd_context.verify(_prehash(plain), hashed)


def create_access_token(data: dict, expires_delta: Optional[timedelta] = None) -> str:
    to_encode = data.copy()
    expire = datetime.now(timezone.utc) + (expires_delta or timedelta(minutes=ACCESS_TOKEN_EXPIRE_MINUTES))
    to_encode["exp"] = expire
    return jwt.encode(to_encode, SECRET_KEY, algorithm=ALGORITHM)


def get_session():
    from sqlalchemy.orm import sessionmaker
    return sessionmaker(bind=make_engine(), future=True)


def get_current_user(token: str = Depends(oauth2_scheme)):
    """FastAPI dependency: валидирует Bearer-токен и возвращает объект User."""
    credentials_exc = HTTPException(
        status_code=status.HTTP_401_UNAUTHORIZED,
        detail="Could not validate credentials",
        headers={"WWW-Authenticate": "Bearer"},
    )
    try:
        payload = jwt.decode(token, SECRET_KEY, algorithms=[ALGORITHM])
        user_id: str = payload.get("sub")
        if user_id is None:
            raise credentials_exc
    except JWTError:
        raise credentials_exc

    from bd.tables.users import User

    try:
        uid = uuid.UUID(user_id)
    except Exception:
        raise credentials_exc

    Session = get_session()
    with Session() as session:
        user = session.get(User, uid)
        if user is None:
            raise credentials_exc
        # detach from session so object can be used outside
        session.expunge(user)
        return user


def require_admin_key(x_admin_key: Optional[str] = Header(default=None)):
    """FastAPI dependency: проверяет секретный ключ администратора (заголовок X-Admin-Key)."""
    admin_key = os.getenv("ADMIN_KEY", "")
    if not admin_key:
        raise HTTPException(
            status_code=status.HTTP_503_SERVICE_UNAVAILABLE,
            detail="Admin access is disabled: ADMIN_KEY not configured",
        )
    if x_admin_key != admin_key:
        raise HTTPException(
            status_code=status.HTTP_403_FORBIDDEN,
            detail="Invalid admin key",
        )