using UnityEngine;

//-----------------------------------------------------------------------------
// Copyright 2014-2020 RenderHeads Ltd.  All rights reserved.
//-----------------------------------------------------------------------------

namespace RenderHeads.Media.AVProDeckLink
{
	public class Singleton<T> : MonoBehaviour where T : MonoBehaviour
	{
		private static T _instance;

		private static object _lock = new object();

		private static bool _manuallyCreated = true;

		public static T Instance
		{
			get
			{
				if (applicationIsQuitting)
				{
					return null;
				}

				lock (_lock)
				{
					if (_instance == null)
					{
						
						_instance = (T)FindObjectOfType(typeof(T));

						if (FindObjectsOfType(typeof(T)).Length > 1)
						{
							Debug.LogError("[Singleton] Something went really wrong " +
								" - there should never be more than 1 singleton!" +
								" Reopenning the scene might fix it.");
							return _instance;
						}

						if (_instance == null)
						{
							_manuallyCreated = false;
							GameObject singleton = new GameObject();
							_instance = singleton.AddComponent<T>();
							singleton.name = "(singleton) " + typeof(T).ToString();

							Debug.Log("constructing " + singleton.name);

							DontDestroyOnLoad(singleton);
						}
					}

					return _instance;
				}
			}
		}

		private static bool applicationIsQuitting = false;

		public void Awake()
		{
			if (_manuallyCreated)
			{
				applicationIsQuitting = false;
			}
		}

		public void OnDestroy()
		{
			applicationIsQuitting = true;
		}
	}
}