Smooth rotation to child object

Questions & Answers
1

I have car model which is build from different parts (separate 3d meshes such as mirrors, bumpers, wheels etc) all contained in Unity GameObject’s hierarchy. The car itself stands on a cylindrical platform. Based on a part of user choice I would like it to have positioned/rotated towards the camera. For example if a mirror has been selected I would like the platform to rotate so that the mirror would become aligned with camera view. I’m attaching the code I’ve been working on, which of course has some errors. Help highly appreciated.

public class PlatformBase : MonoBehaviour {

    private Transform selection;  // selected part
    private Quaternion q;

    void Update ()
    {    
        transform.rotation = Quaternion.Lerp(transform.rotation, q, Time.deltaTime);    
    }

    public Transform Selection
    {
        set
        {
                selection = value;
                angle = Vector3.Angle(
                    -Camera.main.transform.forward, 
                    new Vector3(selection.forward.x, 0.0f, selection.forward.z).normalized);
                q = Quaternion.AngleAxis(angle, Vector3.up);         
        }
2

The problem with the above code was in returned value of Vector3.Angle function as it returns an angle of a positive value (0, 360) whereas in the method I came up above I needed a value from (-180, 180) scope. Below I’m attaching working snipped of code

    // class ...
    void Update ()
    {   
        transform.rotation = Quaternion.Lerp(transform.rotation, q, Time.deltaTime);
    }

    public PartUpgrade Selection
    {
        set
        {
             selection = value.transform;

              Vector3 camFwd = -Camera.main.transform.forward; // camera fwd always (0, 0, -1)
              Vector3 selFwd = new Vector3(selection.forward.x, 0, selection.forward.z).normalized;

              angle = Vector3.Angle(camFwd, selFwd) * 
                 Mathf.Sign(Vector3.Dot(-Vector3.up, Vector3.Cross(camFwd, selFwd)));
                    
               q = transform.rotation * Quaternion.AngleAxis(angle, Vector3.up);
        }
    }