using UnityEngine;
using System.Collections.Generic;

/*
This PoolingManager class aims to manage and recycle instancied prefabs.
When in need of a new instance, ask this PoolingManager to provide it.
It will check if a disabled instance of your specified prefab is avalaible and if not, it will create a new instance.
Just make sure that instead of destroying prefabs, they are disabled once they have achieved their purpose.
*/
public class PoolingManager : MonoBehaviour {

	static PoolingManager instance;
	public static PoolingManager Instance { get { if (instance == null) { instance = FindObjectOfType<PoolingManager>(); } return instance; } }

	// A dictionnary is used to keep references of all instancied objects in the scene.
	// The key is the name of a prefab and is associated with a list of all created instances of that prefab
	Dictionary<string, List<GameObject>> _instanciedObjects;

	void Start()
	{
		_instanciedObjects = new Dictionary<string, List<GameObject>>();
	}

	public GameObject Provide(GameObject pPrefab)
	{
		GameObject result = null;

		if (_instanciedObjects.ContainsKey(pPrefab.name))
		{
			List<GameObject> existingObjects = _instanciedObjects[pPrefab.name];

			// Check if there's an available(disabled) object to reuse before creating a new one :
			foreach(GameObject obj in existingObjects)
			{
				if(obj.gameObject.activeInHierarchy == false)
				{
					result = obj;
					break;
				}
			}

			// No available object so create one :
			if(result == null)
			{
				result = CeateNewObject(pPrefab);
				existingObjects.Add(result);
			}
		}
		else
		{
			// No object of this prefab was instancied before so create a new object and a new list to store the future objects of its kind
			result = CeateNewObject(pPrefab);
			List<GameObject> newList = new List<GameObject>();
			newList.Add(result);
			_instanciedObjects.Add(pPrefab.name, newList);
		}

		result.gameObject.SetActive(true);
		return result;
	}

	GameObject CeateNewObject(GameObject pPrefab)
	{
		var newObject = Instantiate(pPrefab);

		return newObject;
	}

	// Useful to call when the game has to be reset, for example.
	public void DeactivateAllObjects()
	{
		foreach (KeyValuePair<string, List<GameObject>> keyValue in _instanciedObjects)
		{
			List<GameObject> list = keyValue.Value;
			foreach (GameObject obj in list)
			{
				obj.gameObject.SetActive(false);
			}
		}
	}
}