"""FastAPI dependencies for authentication."""
from fastapi import Depends, HTTPException, status
from fastapi.security import HTTPBearer, HTTPAuthorizationCredentials

from .service import decode_access_token

security = HTTPBearer()


async def get_current_user(
    credentials: HTTPAuthorizationCredentials = Depends(security),
) -> str:
    """Extract and validate the current user from the Authorization header."""
    payload = decode_access_token(credentials.credentials)
    if payload is None:
        raise HTTPException(
            status_code=status.HTTP_401_UNAUTHORIZED,
            detail="Invalid or expired token",
            headers={"WWW-Authenticate": "Bearer"},
        )
    username: str | None = payload.get("sub")
    if not username:
        raise HTTPException(
            status_code=status.HTTP_401_UNAUTHORIZED,
            detail="Token missing subject",
        )
    return username