using UnityEngine;
using System.Collections;
using System.Collections.Generic;
using System.Linq;

public class Snake : MonoBehaviour
{
     // Tail Prefab
     public GameObject tailPrefab;

     // Speed
     public float speed = 0.01f;

     // Drow in next movement?
     private bool ate = false;

     // Current Movement Direction
     private Vector2 dir = Vector2.right;

     // Keep track of tail
     private List<Transform> tail = new List<Transform>();

  // Use this for initialization
  void Start ()
     {
      // Move snake every 300ms
         InvokeRepeating("Move", speed, speed);
  }
   
  // Update is called once per frame
  void Update ()
     {
         var h = Input.GetAxisRaw("Horizontal");
         var v = Input.GetAxisRaw("Vertical");

         if (v > 0)
         {
             dir = Vector2.up;
         }
         else if (v < 0)
         {
             dir = Vector2.down;
         }

         if (h < 0)
         {
             dir = Vector2.left;
         }
         else if (h > 0)
         {
             dir = Vector2.right;
         }
  }

     void Move()
     {
         // Save current position (gap will be here)
         Vector2 v = transform.position;

         // Move head into new direction (now there is a gap)
         transform.Translate(dir);

         // Ate? Then insert track into gap
         if (ate)
         {
             // Set track into grap
             var track = Instantiate(tailPrefab, v, Quaternion.identity) as GameObject;

             // Keep track into tail list
             tail.Insert(0, track.transform);

             // Reset flag
             ate = false;
         }
         else if (tail.Count > 0) // Do we have a tail?
         {
             // Move last tail element to where the head was
             tail.Last().position = v;

             // Add to front of list
             tail.Insert(0, tail.Last());

             // Remove from the back
             tail.RemoveAt(tail.Count - 1);
         }
     }

     void OnTriggerEnter2D(Collider2D coll)
     {
         // Food?
         if (coll.name.StartsWith("FoodPrefab"))
         {
             // Get longer in next Move coll
             ate = true;

             // Remove the food
             Destroy(coll.gameObject);
         }
         else // Collided with Tail or Border
         {
             // ToDo show lose scene
             Debug.Log("You lost.");
         }
     }
}

using UnityEngine;
using System.Collections;

public class SpawnFood : MonoBehaviour
{
     // Food Prefab
     public GameObject foodPrefab;

     // Borders
     public Transform borderTop;
     public Transform borderBottom;
     public Transform borderLeft;
     public Transform borderRight;

  // Use this for initialization
  void Start()
     {
         // Spawn food every 4 second, starting in 3
         InvokeRepeating("Spawn", 3, 4);
  }

     // Spawn a food
     void Spawn()
     {
         // x position between Left & Right border
         int x = (int)Random.Range(borderLeft.position.x, borderRight.position.x);

         // y position between Bottom & Top border
         int y = (int)Random.Range(borderBottom.position.y, borderTop.position.y);

         // Instantiate the food at (x, y)
         Instantiate(foodPrefab, new Vector2(x, y), Quaternion.identity);
     }
}