import os
from datetime import datetime, timedelta, timezone
from typing import Optional, Callable, Iterable

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

from . import models
from .database import get_db


SECRET_KEY = os.getenv("SECRET_KEY", "dev-secret-change-me")
ALGORITHM = "HS256"
ACCESS_TOKEN_EXPIRE_MINUTES = int(os.getenv("ACCESS_TOKEN_EXPIRE_MINUTES", "60"))

# Use pbkdf2_sha256 to avoid external bcrypt backend issues
pwd_context = CryptContext(schemes=["pbkdf2_sha256"], deprecated="auto")
oauth2_scheme = OAuth2PasswordBearer(tokenUrl="/auth/token")


def verify_password(plain_password: str, password_hash: str) -> bool:
    return pwd_context.verify(plain_password, password_hash)


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


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.update({"exp": expire})
    return jwt.encode(to_encode, SECRET_KEY, algorithm=ALGORITHM)


def get_user_by_username(db: Session, username: str) -> Optional[models.User]:
    return db.query(models.User).filter(models.User.username == username).first()


def authenticate_user(db: Session, username: str, password: str) -> Optional[models.User]:
    user = get_user_by_username(db, username)
    if not user:
        return None
    if not verify_password(password, user.password_hash):
        return None
    return user


async def get_current_user(token: str = Depends(oauth2_scheme), db: Session = Depends(get_db)) -> models.User:
    credentials_exception = 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])
        username: str = payload.get("sub")
        if username is None:
            raise credentials_exception
    except JWTError:
        raise credentials_exception
    user = get_user_by_username(db, username=username)
    if user is None:
        raise credentials_exception
    return user


def require_roles(allowed_roles: Iterable[str]) -> Callable[[models.User], models.User]:
    allowed = set(allowed_roles)

    def _dependency(user: models.User = Depends(get_current_user)) -> models.User:
        if user.role not in allowed:
            raise HTTPException(status_code=status.HTTP_403_FORBIDDEN, detail="Insufficient permissions")
        return user

    return _dependency