using UnityEngine;

/// <summary>
/// Be aware this will not prevent a non singleton constructor
///   such as `T myT = new T();`
/// To prevent that, add `protected T () {}` to your singleton class.
/// 
/// As a note, this is made as MonoBehaviour because we need Coroutines.
/// </summary>
	
	public class Singleton<T> : MonoBehaviour where T : MonoBehaviour
	{
		private static T _instance;

		private static object _lock = new object();

		public static T Instance
		{
			get
			{
//				if (applicationIsQuitting) {
//					Debug.LogWarning("[Singleton] Instance '"+ typeof(T) +
//						"' already destroyed on application quit." +
//						" Won't create again - returning null.");
//					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) {
							GameObject singleton = new GameObject ();
							_instance = singleton.AddComponent<T> ();
							singleton.name = "(singleton) " + typeof(T).ToString ();

							DontDestroyOnLoad (singleton);

							Debug.Log ("[Singleton] An instance of " + typeof(T) +
							" is needed in the scene, so '" + singleton +
							"' was created with DontDestroyOnLoad.");
						} else {
							Debug.Log ("[Singleton] Using instance already created: " +
							_instance.gameObject.name);
						}
					}

					return _instance;
				}
			}
		}

		//private static bool applicationIsQuitting = false;
		/// <summary>
		/// When Unity quits, it destroys objects in a random order.
		/// In principle, a Singleton is only destroyed when application quits.
		/// If any script calls Instance after it have been destroyed, 
		///   it will create a buggy ghost object that will stay on the Editor scene
		///   even after stopping playing the Application. Really bad!
		/// So, this was made to be sure we're not creating that buggy ghost object.
		/// </summary>
//		public void OnDestroy () {
//			applicationIsQuitting = true;
//		}
	
}