How to raycast camera 3rd Person?

Guys, help me plz how go I creat a raycast to the cameraHolder, to Camera... So when camera touch on some place goes foward and get back in place if is not....

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 namespace SA
 {
     public class CameraManager : MonoBehaviour
     {
 
 
         public bool lockOn;
         public float followSpeed = 9;
         public float mouseSpeed = 2;
 
         public Transform target;
         public EnemyTargget lockonTarget;
         public Transform lockonTransfrom;
 
         [HideInInspector]
         public Transform pivot;
         [HideInInspector]
         public Transform camTrans;
         StateManager states;
 
         float turnSmothing = 0.1f;
         public float minAngle = -35;
         public float maxAngle = 85;
 
         float SmoothX;
         float SmoothY;
         float SmoothXvelocity;
         float SmoothYvelocity;
 
         public float lookAngle;
         public float tiltAngle;
 
         void Start ()
         {
             Cursor.lockState = CursorLockMode.Locked;
             Cursor.visible = false;
         }
 
         public void Init (StateManager st)
         {
             states = st;
             target = st.transform;
             camTrans = Camera.main.transform;
             pivot = camTrans.parent;
         }
 
         public void Tick (float d)
         {
             float h = Input.GetAxis ("Mouse X");
             float v = Input.GetAxis ("Mouse Y");
             float targetSpeed = mouseSpeed;
             if (lockonTransfrom != null) {
                 if (lockonTransfrom == null) {
                     lockonTransfrom = lockonTarget.GetTarget ();
                     states.lockonTransform = lockonTransfrom;
                 }    
             }
             FollowTarget (d);
             HandleRotations (d, h, v, targetSpeed);
 
         }
 
         void FollowTarget (float d)
         {
             float speed = followSpeed * d;
             Vector3 targgetPosition = Vector3.Lerp (transform.position, target.position, speed);
             transform.position = target.position;
         }
 
         void HandleRotations (float d, float h, float v, float targetSpeed)
         {
             if (turnSmothing > 0) {
                 SmoothX = Mathf.SmoothDamp (SmoothX, h, ref SmoothXvelocity, turnSmothing);
                 SmoothY = Mathf.SmoothDamp (SmoothY, v, ref SmoothYvelocity, turnSmothing);
 
             } else {
                 SmoothX = h;
                 SmoothY = v;
             }
 
             tiltAngle -= SmoothY * targetSpeed;
             tiltAngle = Mathf.Clamp (tiltAngle, minAngle, maxAngle);
             pivot.localRotation = Quaternion.Euler (tiltAngle, 0, 0);
 
             if (lockOn && lockonTarget != null) {
                 Vector3 targetDir = lockonTransfrom.position - transform.position;
                 targetDir.Normalize ();
 
                 if (targetDir == Vector3.zero) {
                     targetDir = transform.forward;
                 }
                 Quaternion targetRot = Quaternion.LookRotation (targetDir);
                 transform.rotation = Quaternion.Slerp (transform.rotation, targetRot, d * 9);
                 lookAngle = transform.eulerAngles.y;
                 return;
             }
             lookAngle += SmoothX * targetSpeed;
             transform.rotation = Quaternion.Euler (0, lookAngle, 0);
         }
 
         public static CameraManager Singleton;
 
         void Awake ()
         {
             Singleton = this;
         }
     }
 }

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