Change script to make the object only movable in one direction and add collision

I have a script that makes an object drag-able with the mouse. How do I change t$$anonymous$$s script to make the object only be movable in one direction (for example only the X value can be changed), and also adding collision so the object I'm moving can't phase through walls.

Here's the script

  using UnityEngine;
  using System.Collections;
  
  [RequireComponent(typeof(MeshCollider))]
  
  public class GizmosController : MonoBehaviour 
  {
  
  private Vector3 screenPoint;
  private Vector3 offset;
  
  void OnMouseDown()
  {
      screenPoint = Camera.main.WorldToScreenPoint(gameObject.transform.position);
  
      offset = gameObject.transform.position - Camera.main.ScreenToWorldPoint(new Vector3(Input.mousePosition.x, Input.mousePosition.y, screenPoint.z));
  
  }
  
  void OnMouseDrag()
  {
      Vector3 curScreenPoint = new Vector3(Input.mousePosition.x, Input.mousePosition.y, screenPoint.z);
  
  Vector3 curPosition = Camera.main.ScreenToWorldPoint(curScreenPoint) + offset;
  transform.position = curPosition;
  
  }
  
  }