CameraController.cs

using System.Collections;
using UnityEngine;

public class CameraController : MonoBehaviour
{
    private Quaternion rotation = Quaternion.identity;  //Creates a quaternion with only zeros (x=0, y=0, z=0, w=0)
    public Transform target; //the player the camera should follow
    public float height; //how heigh the camera should be away from player
    private float speedX; //mouse X
    private float speedY; //mouse Y
    public float horizontalSpeed = 200;//basically some kind of sensitivity (200 worked best for me)
    public float verticalSpeed = 200; //basically some kind of sensitivity (200 worked best for me)
    private float finalDistance;
    public float maxDistance = 5; //maximum distance camera should be away from player
    public float minDistance = 0.5;  //minimum distance camera should be away from player
    private void Start()
    {
    }
    private void Update()
    {
        GetInput(); // update speedX and speedY
        NormalRotation(); //set rotation based off mouse
        CalculateFinalPosition(); //calculate camera position
    }

    private void CalculateFinalPosition()
    {
        //Setup temporary variables
        RaycastHit hit;
        Vector3 targetPosition = target.position + target.up * height;
        Vector3 direction = (transform.position - targetPosition).normalized;
        finalDistance = maxDistance;

        //Check collision
        if (Physics.Raycast(targetPosition, direction, out hit, Mathf.Infinity)) { finalDistance = hit.distance - 0.1f; }

        //Apply position
        finalDistance = Mathf.Clamp(finalDistance, minDistance, maxDistance);
        transform.position = (target.position + target.up * height) - transform.forward * finalDistance;
    }

    public void GetInput()
    {
        speedX = Input.GetAxis("Mouse X");
        speedY = Input.GetAxis("Mouse Y");
        print(speedX);
        print(speedY);
    }

    private void NormalRotation()
    {
        //Set rotation values
        rotation.x += speedX * horizontalSpeed * Time.deltaTime;
        rotation.y += speedY * verticalSpeed * Time.deltaTime;
        rotation.y = Mathf.Clamp(rotation.y, -50, 90);

        //Apply rotation
        transform.rotation = Quaternion.Euler(rotation.y, rotation.x, rotation.z);
    }
}