from typing import Generator, Optional
from fastapi import Depends, HTTPException, status
from fastapi.security import HTTPBearer, HTTPAuthorizationCredentials
from sqlalchemy.orm import Session
from app.core.database import SessionLocal
from app.core.security import decode_access_token

security = HTTPBearer(auto_error=False)

def get_db() -> Generator:
    """Dependency that yields a database session and ensures closure."""
    db = SessionLocal()
    try:
        yield db
    finally:
        db.close()

def get_current_user_token(credentials: Optional[HTTPAuthorizationCredentials] = Depends(security)) -> Optional[dict]:
    """Extracts and verifies JWT token payload from Authorization header."""
    if not credentials:
        return None
    token = credentials.credentials
    payload = decode_access_token(token)
    return payload

def require_current_user(payload: Optional[dict] = Depends(get_current_user_token)) -> dict:
    """Ensures request is authenticated with a valid token."""
    if not payload:
        raise HTTPException(
            status_code=status.HTTP_401_UNAUTHORIZED,
            detail="Could not validate credentials or token expired",
            headers={"WWW-Authenticate": "Bearer"},
        )
    return payload