CollisionDirections2D

using UnityEngine;
using System.Collections;

// But in unity you cant mix 2D and 3D so if you want to mix it than rays are your best bet

[RequireComponent(typeof(Rigidbody2D))]
public class CollisionDirections : MonoBehaviour {

    public bool right=false, left=false, up=true, down=false;

    // Use this for initialization
    void Start () {

    }

    // Update is called once per frame
    void Update () {

    }

    void OnCollisionEnter2D(Collision2D coll){
        //for every collision coll saves 2 points of contact test begining of collision and end of collision
        if(coll.contacts.Length==2){
            //chack are two points on x axis the same
            if( coll.contacts[0].point.x == coll.contacts[1].point.x ){
                // chack where they are in regards to game object origin
                if( coll.contacts[0].point.x > transform.position.x ){
                    right=true;
                }else{
                    left=true;
                }
            }else if(coll.contacts[0].point.y == coll.contacts[1].point.y){
                if(coll.contacts[0].point.y > transform.position.y){
                    up=true;
                }else{
                    down=true;
                }
            }
        }else{
            Debug.LogError("This script is defined only for 2D collisions");
        }
    }

    void OnCollisionExit2D(Collision2D coll){
        if(coll.contacts.Length==2){
            if( coll.contacts[0].point.x == coll.contacts[1].point.x ){
                if( coll.contacts[0].point.x > transform.position.x ){
                    right=false;
                }else{
                    left=false;
                }
            }else if(coll.contacts[0].point.y == coll.contacts[1].point.y){
                if(coll.contacts[0].point.y > transform.position.y){
                    up=false;
                }else{
                    down=false;
                }
            }
        }
    }
}