from typing import Generator

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

from app.core.config import settings
from app.db.session import SessionLocal
from app.models.user import User
from app.schemas.token import TokenPayload

oauth2_scheme = OAuth2PasswordBearer(tokenUrl=f"{settings.API_V1_STR}/auth/login")


def get_db() -> Generator:
    """
    Get a database session as a dependency for routes.
    """
    db = SessionLocal()
    try:
        yield db
    finally:
        db.close()


def get_current_user(
    db: Session = Depends(get_db), token: str = Depends(oauth2_scheme)
) -> User:
    """
    Get the current user based on the JWT token.
    """
    credentials_exception = HTTPException(
        status_code=status.HTTP_401_UNAUTHORIZED,
        detail="Could not validate credentials",
        headers={"WWW-Authenticate": "Bearer"},
    )
    try:
        payload = jwt.decode(
            token, settings.SECRET_KEY, algorithms=[settings.ALGORITHM]
        )
        username: str = payload.get("sub")
        if username is None:
            raise credentials_exception
        token_data = TokenPayload(username=username)
    except JWTError:
        raise credentials_exception
    
    user = db.query(User).filter(User.username == token_data.username).first()
    if user is None:
        raise credentials_exception
    return user