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

//Usage:
//void Awake() {
//  StaticPool staticPool = new StaticPool(); //This could be cleaned up for better singleton creation
//  ...
//}
//
//...
//
//void Shoot() {
//  GameObject bullet = StaticPool.GetObj(bulletPrefab); //Will grab or create a new bullet and return it
//  ...
//}

public class StaticPool {

    static StaticPool s_instance;

    public Dictionary<GameObject, List<GameObject>> objLists;

    const int DEFAULT_SIZE = 10;
    const int SIZE_INCREMENT = 5;

    [System.NonSerialized]
    public GameObject parent;

    public StaticPool () {
        s_instance = this;
        objLists = new Dictionary<GameObject, List<GameObject>>();
        parent = new GameObject("StaticPool");
        GameObject.DontDestroyOnLoad(parent);
    }

    /// <summary>
    /// Not necessary. Can be used to preload prefab for the pool for loading screens.
    /// </summary>
    /// <param name="prefab">Prefab.</param>
    public static void InitObj(GameObject prefab) {
        if(s_instance.objLists.ContainsKey(prefab) == false) {
            GameObject holder = new GameObject(prefab.name);
            holder.transform.parent = s_instance.parent.transform;

            s_instance.objLists.Add (prefab, new List<GameObject>());
            AddToList(prefab, DEFAULT_SIZE, holder.transform);
        }
    }

    /// <summary>
    /// Gets the object of type prefab.
    /// </summary>
    /// <returns>The object.</returns>
    /// <param name="prefab">Prefab.</param>
    public static GameObject GetObj(GameObject prefab) {
        InitObj(prefab);

        // Find inactive
        for(int i = 0, n = s_instance.objLists[prefab].Count; i < n; i++) {
            if(s_instance.objLists[prefab][i].activeSelf == false) {
                s_instance.objLists[prefab][i].SetActive(true);
                return s_instance.objLists[prefab][i];
            }
        }

        // None found
        AddToList(prefab, SIZE_INCREMENT, s_instance.parent.transform.FindChild(prefab.name));

//      Debug.Log(s_instance.objLists[prefab].Count - SIZE_INCREMENT);

        // Zero indexed and minus what we just added
        s_instance.objLists[prefab][s_instance.objLists[prefab].Count - SIZE_INCREMENT].SetActive(true);
        return s_instance.objLists[prefab][s_instance.objLists[prefab].Count - SIZE_INCREMENT];

    }

    static void AddToList(GameObject prefab, int count, Transform holder) {
        for(int i = 0; i < count; i++) {
            GameObject obj = (GameObject)GameObject.Instantiate(prefab, Vector3.one * 1000f, Quaternion.identity);
            s_instance.objLists[prefab].Add(obj);
            obj.transform.parent = holder;
            obj.SetActive(false);
        }
    }
}