C# snake

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.SceneManagement;
using UnityEngine.UI;

public class Snake : MonoBehaviour
{
    public int xSize, ySize; //velikos grida v igri
    public GameObject block;
    GameObject head;
    public Material headMaterial, tailMaterial;
    List<GameObject> tail;

    Vector2 dir; //notr damo movment od kače
    public Text points;
    void Start()
    {
        timeBetweenMovements = 0.5f;
        dir = Vector2.right;
        // rob
        createGrid();
        createPlayer();
        spawnFood();
        block.SetActive(false);
        isAlive = true;
    }

    private Vector2 getRandomPos() {
        return new Vector2(Random.Range(-xSize/2+1, xSize/2), Random.Range(-ySize/2+1, ySize/2));
    }

    private bool containedInSnake(Vector2 spawnPos) {
        bool isInHead = spawnPos.x == head.transform.position.x && spawnPos.y == head.transform.position.y;
        bool isInTail = false;
        foreach(var item in tail) {
            if(item.transform.position.x == spawnPos.x && item.transform.position.y == spawnPos.y) {
                isInTail = true;
            }
        }
        return isInHead || isInTail;
    }

    GameObject food;
    bool isAlive;

    private void spawnFood() {
        Vector2 spawnPos = getRandomPos();
        while(containedInSnake(spawnPos)) {
            spawnPos = getRandomPos();
        }
        food = Instantiate(block);
        food.transform.position = new Vector3(spawnPos.x, spawnPos.y, 0);
        food.SetActive(true);
    }

    private void createPlayer() {
        head = Instantiate(block) as GameObject;
        head.GetComponent<MeshRenderer>().material = headMaterial;
        tail = new List<GameObject>();
    }
    private void createGrid() {
        for(int x = 0; x <= xSize; x++) {
            //The Instantiate method returns a reference to the Rigidbody component on the new instance.
            // This is useful because it makes it simple to set the velocity of the Rigidbody immediately after instantiating it.
            GameObject borderBottom = Instantiate(block) as GameObject;
            //definiramo pozicijo tega roba
            borderBottom.GetComponent<Transform>().position = new Vector3(x-xSize/2, -ySize/2, 0);

             GameObject borderTop = Instantiate(block) as GameObject;
             borderTop.GetComponent<Transform>().position = new Vector3(x-xSize/2, ySize-ySize/2, 0);
        }

        for(int y = 0; y <= ySize; y++) {
            GameObject borderRight = Instantiate(block) as GameObject;
            borderRight.GetComponent<Transform>().position = new Vector3(-xSize/2, y-ySize/2, 0);
            GameObject borderLeft = Instantiate(block) as GameObject;
            borderLeft.GetComponent<Transform>().position = new Vector3(xSize-xSize/2, y-ySize/2, 0);
        }
    }

    float passedTime, timeBetweenMovements;

    public GameObject gameOverUI;
    private void gameOver() {
        isAlive = false;
        gameOverUI.SetActive(true);
    }

    public void restart() {
        SceneManager.LoadScene(0);
    }
    void Update()
    {
        if(Input.GetKey(KeyCode.DownArrow)) {
            dir = Vector2.down;
        } else if(Input.GetKey(KeyCode.UpArrow)) {
            dir = Vector2.up;
        } else if(Input.GetKey(KeyCode.RightArrow)) {
            dir = Vector2.right;
        } else if(Input.GetKey(KeyCode.LeftArrow)) {
            dir = Vector2.left;
        } 

        passedTime += Time.deltaTime;
        if(timeBetweenMovements < passedTime && isAlive) {
            passedTime = 0;
            //move
            Vector3 newPosition = head.GetComponent<Transform>().position + new Vector3(dir.x, dir.y, 0);
            //ali se je zaletela
            if(newPosition.x >= xSize/2
            || newPosition.x <= -xSize/2
            || newPosition.y >= ySize/2
            || newPosition.y <= -ySize/2) {
                gameOver();
            }

            foreach(var item in tail) {
                if(item.transform.position == newPosition) {
                     gameOver();
                }
            }

            if(newPosition.x == food.transform.position.x && newPosition.y == food.transform.position.y) {
                GameObject newTile = Instantiate(block);
                newTile.SetActive(true);
                newTile.transform.position = food.transform.position;
                DestroyImmediate(food);
                head.GetComponent<MeshRenderer>().material = tailMaterial;
                tail.Add(head);
                head = newTile;
                head.GetComponent<MeshRenderer>().material = headMaterial;
                spawnFood();
                points.text = "Points: " + tail.Count;
            } else {

            }

            if(tail.Count == 0) {
                head.transform.position = newPosition;
            } else {
                head.GetComponent<MeshRenderer>().material = tailMaterial;
                tail.Add(head);
                head = tail[0];
                head.GetComponent<MeshRenderer>().material = headMaterial;
                tail.RemoveAt(0);
                head.transform.position = newPosition;
            }
        }
    }
}