https://medium.com/@J.3/unity-game-debut-part-0-of-10-bc37729ef7fe

GameController.cs

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

public class GameController : Singleton<GameController>
{

    protected GameController() { } // guarantee this will be always a singleton only - can't use the constructor!

    private int mHealth = 100;

    private int mTime = 30;

    private bool mGameOver = false;

    public event EventHandler GameOverEvent;


    private void OnGameOver()
    {
        if (GameOverEvent != null)
        {
            GameOverEvent(this, EventArgs.Empty);
        }
    }


    void Start()
    {
        InvokeRepeating("Count", 0.0f, 1.0f);
    }


    void Count()
    {
        if (mTime == 0)
        {

            mGameOver = true;
            CancelInvoke("Count");
            OnGameOver();
        }
        else
        {
            mTime--;
        }
    }


    public void SetDamage(int damage)
    {
        if (mGameOver)
            return;

        mHealth -= damage;
        if (mHealth <= 0)
        {
            mHealth = 0;

            //TODO: Add player  dead logic
            mGameOver = true;
            CancelInvoke("Count");
            OnGameOver();
        }
    }


    public bool IsGameOver
    {
        get
        {
            return mGameOver;
        }
    }


    public bool IsWon
    {
        get
        {
            if (Health <= 0)
                return false;
            return true;
        }
    }


    /* public int GetHealth()
     {
         return mHealth;
     }*/

    public int Health
    {
        get
        {
            return mHealth;
        }
    }


    public int Time
    {
        get
        {
            return mTime;
        }
    }



}