Need help with third person camera script!

Hello :) I am trying to create a third person shooter and I want a camera system as seen in Metal Gear Solid 5. What I have now is the camera orbiting and following the player. I want to have it so when I hold right click, the camera zooms over the character shoulder and the camera follows the mouse.

Here is my current Camera Script (attached to the main camera)

ShooterGameScript.cs:

 using UnityEngine;
 using System.Collections;
 
 // 3rd person game-like camera controller
 // keeps camera behind the player and aimed at aiming point
 public class ShooterGameCamera : MonoBehaviour {
 
     public Transform player;
     public Texture crosshair;
 
     protected Transform aimTarget; // that was public and a gameobject had to be dragged on it. - ben0bi
 
     public float smoothingTime = 10.0f; // it should follow it faster by jumping (y-axis) (previous: 0.1 or so) ben0bi
     public Vector3 pivotOffset = new Vector3(0.2f, 0.7f,  0.0f); // offset of point from player transform (?) ben0bi
     public Vector3 camOffset   = new Vector3(0.0f, 0.7f, -3.4f); // offset of camera from pivotOffset (?) ben0bi
     public Vector3 closeOffset = new Vector3(0.35f, 1.7f, 0.0f); // close offset of camera from pivotOffset (?) ben0bi
 
     public float horizontalAimingSpeed = 800f;
     public float verticalAimingSpeed = 800f;
     public float maxVerticalAngle = 80f;
     public float minVerticalAngle = -80f;
     //From the other MouseLookScript
     private float rotY = 0.0f; // rotation around the up/y axis
     private float rotX = 0.0f; // rotation around the right/x axis
 
     public float mouseSensitivity = 0.3f;
 
     public float clampAngle = 80.0f;
 
     private float angleH = 0;
     private float angleV = 0;
     private Transform cam;
     private float maxCamDist = 1;
     private LayerMask mask;
     private Vector3 smoothPlayerPos;
 
     // Use this for initialization
     void Start ()
     {
         //3 lines from mouseLook
         Vector3 rot = transform.localRotation.eulerAngles;
         rotY = rot.y;
         rotX = rot.x;
         // [edit] no aimtarget gameobject needs to be placed anymore - ben0bi
         GameObject g=new GameObject();
         aimTarget=g.transform;
         // Add player's own layer to mask
         mask = 1 << player.gameObject.layer;
         // Add Igbore Raycast layer to mask
         mask |= 1 << LayerMask.NameToLayer("Ignore Raycast");
         // Invert mask
         mask = ~mask;
 
         cam = transform;
         smoothPlayerPos = player.position;
 
         maxCamDist = 3;
     }
 
     // Update is called once per frame
     void LateUpdate () {
         if (Time.deltaTime == 0 || Time.timeScale == 0 || player == null)
             return;
    
         angleH += Mathf.Clamp(Input.GetAxis("Mouse X") /* + Input.GetAxis("Horizontal2") */ , -1, 1) * horizontalAimingSpeed * Time.deltaTime;
    
         angleV += Mathf.Clamp(Input.GetAxis("Mouse Y") /* + Input.GetAxis("Vertical2") */ , -1, 1) * verticalAimingSpeed * Time.deltaTime;
         // limit vertical angle
         angleV = Mathf.Clamp(angleV, minVerticalAngle, maxVerticalAngle);
 
         // Before changing camera, store the prev aiming distance.
         // If we're aiming at nothing (the sky), we'll keep this distance.
         float prevDist = (aimTarget.position - cam.position).magnitude;
 
         // Set aim rotation
         Quaternion aimRotation = Quaternion.Euler(-angleV, angleH, 0);
         Quaternion camYRotation = Quaternion.Euler(0, angleH, 0);
         cam.rotation = aimRotation;
 
         // Find far and close position for the camera
         smoothPlayerPos = Vector3.Lerp(smoothPlayerPos, player.position, smoothingTime * Time.deltaTime);
         smoothPlayerPos.x = player.position.x;
         smoothPlayerPos.z = player.position.z;
         Vector3 farCamPoint = smoothPlayerPos + camYRotation * pivotOffset + aimRotation * camOffset;
         Vector3 closeCamPoint = player.position + camYRotation * closeOffset;
         float farDist = Vector3.Distance(farCamPoint, closeCamPoint);
 
         // Smoothly increase maxCamDist up to the distance of farDist
         maxCamDist = Mathf.Lerp(maxCamDist, farDist, 5 * Time.deltaTime);
 
         // Make sure camera doesn't intersect geometry
         // Move camera towards closeOffset if ray back towards camera position intersects something
         RaycastHit hit;
         Vector3 closeToFarDir = (farCamPoint - closeCamPoint) / farDist;
         float padding = 0.3f;
         if (Physics.Raycast(closeCamPoint, closeToFarDir, out hit, maxCamDist + padding, mask)) {
             maxCamDist = hit.distance - padding;
         }
         cam.position = closeCamPoint + closeToFarDir * maxCamDist;
 
         // Do a raycast from the camera to find the distance to the point we're aiming at.
         float aimTargetDist;
         if (Physics.Raycast(cam.position, cam.forward, out hit, 100, mask)) {
             aimTargetDist = hit.distance + 0.05f;
         }
         else {
             // If we're aiming at nothing, keep prev dist but make it at least 5.
             aimTargetDist = Mathf.Max(5, prevDist);
         }
 
         // Set the aimTarget position according to the distance we found.
         // Make the movement slightly smooth.
         aimTarget.position = cam.position + cam.forward * aimTargetDist;
     }
 
 
     void Update()
     {
         if (Input.GetKey ("mouse 1")) {
             camOffset = new Vector3 (0.0f, 0.8f, -1.7f);
             float horizontalAimingSpeed = 0f;
             float verticalAimingSpeed = 0f;
         } else
         {
             camOffset = new Vector3(0.0f, 0.7f, -3.4f);
             float horizontalAimingSpeed = 400f;
             float verticalAimingSpeed = 400f;
         }
     }
 
 
     // so you can change the camera from a static observer (level loading) or something else
     // to your player or something else. I needed that for network init... ben0bi
     public void SetTarget(Transform t)
     {
         player=t;
     }
 
     void OnGUI ()
     {
         if (Time.time != 0 && Time.timeScale != 0)
             GUI.DrawTexture(new Rect(Screen.width/2-(crosshair.width*0.5f), Screen.height/2-(crosshair.height*0.5f), crosshair.width, crosshair.height), crosshair);
     }
 
 }

I've got the camera to zoom in over his shoulder when I hold right mouse button. I really have no idea on where to start on this?

Any help would be greatly appreciated!

Cheers.