CameraRotator

using UnityEngine;
using System.Collections;

public enum Orientation
{
    up,down,left,right,forward,back
}


public class CameraRotator : MonoBehaviour
{
    public float speed = 90f;
    public bool gravityOn = true;
    public float gravScale = -100f;
    public bool debugOn = false;
    public float minSqrDist = 10f;

    public Orientation orientation = Orientation.forward;

    public bool isActive
    { get; set; }

    private static CameraRotator _instance;
    public static CameraRotator instance
    {
        get
        {
            if (_instance == null)
            {
                _instance = GameObject.FindObjectOfType<CameraRotator>();
                DontDestroyOnLoad(_instance.gameObject);
            }

            return _instance;
        }
    }

    void Awake()
    {
        if (_instance == null)
        {
            _instance = this;
            DontDestroyOnLoad(this);
        }
        else
        {
            if (this != _instance)
                Destroy(this.gameObject);
        }

        isActive = false;
    }


    public Vector3 oV()
    {
        switch (orientation)
        {
            case Orientation.up:
                return Vector3.up;
            case Orientation.down:
                return Vector3.down;
            case Orientation.left:
                return Vector3.left;
            case Orientation.right:
                return Vector3.right;
            case Orientation.forward:
                return Vector3.forward;
            case Orientation.back:
                return Vector3.back;
            default:
                return Vector3.forward;
        }
    }
    float angle;
    bool isDragging;
    Vector3 mouseStart, mousePos, worldPos, vectorToTarget;
    Quaternion q;
    void Update()
    {
        if (gravityOn)
            Physics.gravity = gravScale * gameObject.transform.up;

        if (!isActive)
        {
            mouseStart = Vector3.zero;
            angle = 0f;
            return;
        }

        if (Input.GetMouseButtonDown(0))
            mouseStart = Input.mousePosition;

        mousePos = Input.mousePosition;


        if (Input.GetMouseButton(0) && (mousePos - mouseStart).sqrMagnitude > minSqrDist)
        {
            isDragging = true;

            mousePos.z = 100;
            worldPos = Camera.main.ScreenToWorldPoint(mousePos);
            vectorToTarget = worldPos - gameObject.transform.position;
            angle = Mathf.Atan2(vectorToTarget.y, vectorToTarget.x) * Mathf.Rad2Deg;
            q = Quaternion.AngleAxis(angle, oV());
            gameObject.transform.rotation = Quaternion.Slerp(gameObject.transform.rotation, q, Time.deltaTime * speed);

        }
    }

    void OnMouseUp()
    {
        isDragging = false;
    }

    void OnGUI()
    {
        if (!debugOn)
            return;

        GUI.Label(new Rect(0, 0, 500, 500),
            angle.ToString() + "\ndragging: " + isDragging.ToString()
            + "\nmouse: " + mousePos.ToString()
            + "\nworld: " + worldPos.ToString()
            + "\nvtt: " + vectorToTarget.ToString()
            + "\nq: " + q.ToString()
            + "\ndown: " + gameObject.transform.up);
    }
}