Unity AR Foundation: Plane Detection & Object Placement

using System.Collections.Generic;
using UnityEngine;
using UnityEngine.XR.ARFoundation;
using UnityEngine.XR.ARSubsystems;
using UnityEngine.EventSystems;

[RequireComponent(typeof(ARRaycastManager))]
public class ARPlacementManager : MonoBehaviour {
    public GameObject prefabToPlace;
    private GameObject _spawnedObject;
    private ARRaycastManager _raycastManager;
    private List<ARRaycastHit> _hits = new List<ARRaycastHit>();

    void Awake() {
        _raycastManager = GetComponent<ARRaycastManager>();
    }

    void Update() {
        if (Input.touchCount == 0) return;
        
        Touch touch = Input.GetTouch(0);
        if (touch.phase != TouchPhase.Began) return;

        // Sensible UI guard: don't place objects if tapping a UI button
        if (EventSystem.current.IsPointerOverGameObject(touch.fingerId)) return;

        if (_raycastManager.Raycast(touch.position, _hits, TrackableType.PlaneWithinPolygon)) {
            Pose hitPose = _hits[0].pose;

            if (_spawnedObject == null) {
                _spawnedObject = Instantiate(prefabToPlace, hitPose.position, hitPose.rotation);
            } else {
                // Reposition the existing object instead of instantiating endlessly
                _spawnedObject.transform.position = hitPose.position;
                _spawnedObject.transform.rotation = hitPose.rotation;
            }
        }
    }
}