using UnityEngine;
using System;

#if UNITY_EDITOR
using UnityEditor;
#endif

// This call is the type used by any other code to hold a reference to an object by GUID
// If the target object is loaded, it will be returned, otherwise, NULL will be returned
// This always works in Game Objects, so calling code will need to use GetComponent<>
// or other methods to track down the specific objects need by any given system

// Ideally this would be a struct, but we need the ISerializationCallbackReciever
[System.Serializable]
public class GuidReference : ISerializationCallbackReceiver
{
    // cache the referenced Game Object if we find one for performance
    private GameObject cachedReference;
    private bool isCacheSet;
    
    // store our GUID in a form that Unity can save
    [SerializeField]
    private byte[] serializedGuid;
    private System.Guid guid;

#if UNITY_EDITOR
    // decorate with some extra info in Editor so we can inform a user of what that GUID means
    [SerializeField]
    private string cachedName;
    [SerializeField]
    private SceneAsset cachedScene;
#endif

    // Set up events to let users register to cleanup their own cached references on destroy or to cache off values
    public event Action<GameObject> OnGuidAdded = delegate (GameObject go) { };
    public event Action OnGuidRemoved = delegate() { };

    // create concrete delegates to avoid boxing. 
    // When called 10,000 times, boxing would allocate ~1MB of GC Memory
    private Action<GameObject> addDelegate;
    private Action removeDelegate;
    
    // optimized accessor, and ideally the only code you ever call on this class
    public GameObject gameObject
    {
        get
        {
            if( isCacheSet )
            {
                return cachedReference;
            }

            cachedReference = GuidManager.ResolveGuid( guid, addDelegate, removeDelegate );
            isCacheSet = true;
            return cachedReference;
        }

        private set {}
    }

    public GuidReference() { }

    public GuidReference(GuidComponent target)
    {
        guid = target.GetGuid();
    }

    private void GuidAdded(GameObject go)
    {
        cachedReference = go;
        OnGuidAdded(go);
    }

    private void GuidRemoved()
    {
        cachedReference = null;
        isCacheSet = false;
        OnGuidRemoved();
    }

    //convert system guid to a format unity likes to work with
    public void OnBeforeSerialize()
    {
        serializedGuid = guid.ToByteArray();
    }

    // convert from byte array to system guid and reset state
    public void OnAfterDeserialize()
    {
        cachedReference = null;
        isCacheSet = false;
        if (serializedGuid == null || serializedGuid.Length != 16)
        {
            serializedGuid = new byte[16];
        }
        guid = new System.Guid(serializedGuid);
        addDelegate = GuidAdded;
        removeDelegate = GuidRemoved;

    }
}