Animate current value += something in React Spring

Is there a way to animate the current value += something ?
I'm trying to do a half rotation on each click.

// Toggling rotating somewhere else
const [rotating, setRotating] = useState(false);

// Rotate
const rotation = useSpring({
  rotation: rotating ? CURRENT += Math.PI : CURRENT
});

I ended up using useRef and manually updating the value on each iteration.

https://codesandbox.io/s/interesting-haslett-emreol?file=/src/App.js

import { useRef } from 'react'
import { Canvas } from '@react-three/fiber'
import { useSpring, a, config } from '@react-spring/three'

function Box(props) {
  return (
    <mesh {...props}>
      <tetrahedronGeometry args={[2, 2]} />
      <meshStandardMaterial color="orange" flatShading={true} />
    </mesh>
  )
}

export default function App() {
  const currentRotation = useRef(0)
  const { rotation } = useSpring({
    from: {
      rotation: 0
    },
    config: config.gentle
  })
  return (
    <Canvas>
      <directionalLight position={[3, 2, 2]} intensity={1.5} />
      <spotLight position={[-1, 0, 5]} intensity={0.5} />
      <a.group
        rotation-y={rotation}
        onClick={() => {
          rotation.start({
            to: currentRotation.current - Math.PI / 4
          })
          currentRotation.current -= Math.PI / 4
        }}>
        <Box position={[0, 0, 0]} />
      </a.group>
    </Canvas>
  )
}